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High Voltage Transformers

Transformer types and Applications
MV Transformer Nameplate
  1. GSU
  2. Principal of operation

    3. Long-term resistance to ageing A GSU transformer is loaded at 100 percent rating 24/7, throughout the year. It must be built to withstand the thermal load of high currents being fed into its windings from the generator without overheating, which would shorten its lifetime due to accelerated ageing. Standards organizations such as American National Standards Institute/Institute of Electrical and Electronic Engineers (ANSI/IEEE) consider average GSU transformer life to be 20 to 25 years. This estimate is based on continuous operation at rated load and service conditions with an average ambient temperature of 40 ºC (104 degrees Fahrenheit [ºF]) and a temperature rise of 65 ºC. This estimate is also based on the assumption that transformers receive adequate maintenance over their service life [26].

    They are suitable for nuclear, thermal and hydraulic applications from small to high voltages with power ratings from 5 MVA to 1000 MVA. The step-up transformers have delta-connected LV windings energized by the generator voltage, while star connected HV windings are connected to the transmission lines.

    Large GSUs may be rated in hundreds of MVAs. A GSU transformer can cost well over a million dollars and take 18 months to 2 years or longer to obtain. Each one is designed for a specific application. If one fails, this may mean a unit or whole plant could be down for as long 2 years, costing multiple millions of dollars in lost generation, in addition to the replacement cost of the transformer itself. This is one reason that proper maintenance is critical.

    Transformers play an important role in our electrical generation transmission and distribution systems. Transformers make it possible to transmit large amounts of power over long distances.

    Transformer function is based on the principle that electrical energy is transferred efficiently by magnetic induction from one circuit to another. When one winding of a transformer is energized from an alternating current (AC) source, an alternating magnetic field is established in the transformer core. Alternating magnetic lines of force, called “flux,” circulate through the core. With a second winding around the same core, a voltage is induced by the alternating flux lines. A circuit, connected to the terminals of the second winding, results in current flow.

KVA

Medium Voltage Dry Type transformer.

Medium Voltage Transformers
Principal of
Operation

Transformer function is based on the principle that electrical energy is transferred efficiently by magnetic induction from one circuit to another. When one winding of a transformer is energized from an alternating current (AC) source, an alternating magnetic field is established in the transformer core. Alternating magnetic lines of force, called “flux,” circulate through the core. With a second winding around the same core, a voltage is induced by the alternating flux lines. A circuit, connected to the terminals of the second winding, results in current flow.

Three Phase
Pad Mounted
  1. Pad Mounted Transformer (liquid-filled and dry-type)

    2. Three-phase, pad-mounted transformers,are best suited for commercial applications in public access areas and where underground service is required. Construction allows installation in locations accessible to the general public without the need for protective fencing or vaults. These units are ideally suited for apartment buildings, schools, hospitals, shopping centers, commercial buildings, or industrial sites

  2. Distribution Transformers 500KVA or Smaller

    3. Transformers smaller than 500 kVA are generally called distribution transformers. Pole-top and small, pad-mounted transformers that serve residences and small businesses are typically distribution transformers. Generator step-up transformers, used in Reclamation powerplants, receive electrical energy at generator voltage and increase it to a higher voltage for transmission lines. Conversely, a step-down transformer receives energy at a higher voltage and delivers it at a lower voltage for distribution to various loads.

  3. Power Transformers 500KVA or Larger

    4. Power transformers are defined as transformers rated 500 kVA and larger. Larger transformers are oil-filled for insulation and cooling; a typical GSU transformer may contain several thousand gallons of oil. One must always be aware of the possibility of spills, leaks, fires, and environmental risks this oil poses.

centrifugal treatment

Substation
  1. SUBSTATION liquid-filled transformers are ideal for use in light to medium industrial applications.

    2. The substation transformer is the heart of the electrical substation. This transformer changes the relationship between the incoming voltage and current and the outgoing voltage and current. Substation transformers are rated by their primary and secondary voltage relationship and their power carrying capability. For example, a typical substation transformer would be rated 15 kV, 25 kV, 35 kV or 46 kV on the primary at a power rating of about 5-20 MVA. The secondary or low voltage can be 15 kV down to 5 kV or even less than 600 V. Substation-style transformer design and functionality is dictated by IEEE standards C57.12.00 and C57.12.36. These type transformers consist of a core and coils immersed in oil or dielectric fluid in a steel tank. The oil or fluid serves both as an insulator and as a coolant to keep the core at reliable operating temperatures. Substation units are easily identified by their exposed bushings, gauges, panels or monitoring equipment and are typically located behind a fence or with a restricted area.

The substation transformer is the heart of the electrical substation.

Auto Transformers
  • Auto transformers usually consist of a single coil with a tap connection at a designated location on the winding.

    • INFO

    Overhead
    Transformers

    Single-phase pole-mounted transformers are frequently installed in residential areas but can also be common for small businesses requiring three-phase power from a bank. These transformers can vary in size from as small as 5 kVA to as large as 500 kVA, with voltages up to 35 kV line-to-line. Pole-mounted transformer banks allow three single phase units to be connected to a three-phase system to distribute through overhead lines. Winding connection styles, mounting standards, and overall layout and functionality is held to IEEE standard C57.12.20.

    INFO

    Power Transformer Nameplate Data
    MV Transformer Nameplate

    Manufactures:

    1. Eaton
    2. General Electric
    3. Square D
    4. Siemens
    5. ABB
    6. Cooper Power
    7. Federal Pacific

    Dry Type:

    "Dry-type" is a reference to the type of insulation medium, which means that the core and coil is cooled and insulated by air, as opposed to "liquid immersed" transformers that use oil as the coolant/insulant.

    MCCB-internal-view

    Medium Voltage Dry Type transformer.

    Dry Type:

    "Dry-type" is a reference to the type of insulation medium, which means that the core and coil is cooled and insulated by air, as opposed to "liquid immersed" transformers that use oil as the coolant/insulant.

    MCCB-internal-view

    Medium Voltage Dry Type transformer.

    Oil Filled:

    Increasing the cooling rate of a transformer increases its capacity. Cooling methods must not only maintain a sufficiently low average temperature but must prevent an excessive temperature rise in any portion of the transformer (i.e., it must prevent hot spots). For this reason, working parts of large transformers are usually submerged in high-grade insulating oil. This oil must be kept as free as possible from moisture and oxygen, dissolved combustible gases, and particulates.

    MCCB-internal-view

    Medium Voltage Dry Type transformer

    Oil Filled:

    Increasing the cooling rate of a transformer increases its capacity. Cooling methods must not only maintain a sufficiently low average temperature but must prevent an excessive temperature rise in any portion of the transformer (i.e., it must prevent hot spots). For this reason, working parts of large transformers are usually submerged in high-grade insulating oil. This oil must be kept as free as possible from moisture and oxygen, dissolved combustible gases, and particulates.

    MCCB-internal-view

    Medium Voltage Dry Type transformer

    CORE:

    1. Construction

      2. A simple transformer is composed of two coils wound around a soft iron core. The core creates a path for magnetic lines of flux, coupling the magnetic flux produced by the primary source winding, to the secondary load windings.

    2. Magnetic Coupling.

      3. Magnetic field coupling, also called inductive coupling, occurs when energy is coupled from one circuit to another through a magnetic field.

    3. Primary Winding Coil

      4. The primary winding currents are the sources of magnetic fields, producing lines of flux, which induce voltage and current in the secondary winding.

    4. Secondary Winding Coil

      5. The voltage and current induced in secondary winding coil produces the output current and voltage of the transformer. Thus, the load is connected to it.

    KVA

    Basic Transformer Model

    KVA

    Magnetic Core

    KVA

    Magnetic Core

    Turns Ratio:

    1. Definition

      2. This is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding. The voltage times the amperage on the primary winding is equal to the voltage times the amperage on the secondary winding. The ratio between the primary voltage and the secondary voltage is the same as the ratio between the number of turns on the primary windings and the number of turns on the secondary winding. The current ratio is the inverse of the turns ration. Thus, by knowing the turns ratio and the volt-amps of one winding, the volt-amps of the other winding can be determined. Knowing the amount of current that runs through each is important when planning a new service installation, troubleshooting, or balancing loads

    2. Voltage, current, and turns relationship

      3. \( Turns Ratio = \frac{ N_{1}}{N_{2}} = \frac{ V_{1}}{V_{2}} = \frac{ I_{2}}{I_{1}} \)

    KVA

    Basic Transformer Model

    1. N1: Primary Turns
    2. N2: Secondary Turns
    1. V1: Primary Voltage
    2. V2: Secondary Voltage
    1. I1: Primary Current
    2. I2: Secondary Current

    A transformer rated for 2,400 volts on its primary side, and 240 volts on its secondary side has a turns ratio of 10:1. The implication here is that a transformer with a 10:1 turns ratio could have 2,400 turns on the primary and 240 turns on the secondary, or 8,000 turns on the primary and 800 turns on the secondary, etc.

    KVA:

    1. Transformers are rated in kilo-volt-amperes (kVA).

      2. kVA is used to express a transformer rating because not all transformer loads are purely resistive. The resistive component consumes power that is measured in watts, whereas the reactive component consumes power measured in VARs. The vector sum of these two loads is the total load, VA or kVA

    2. Transformer Capacity

      3. Capacity (or rating) of a transformer is limited by the temperature that the insulation can tolerate. Ratings can be increased by reducing core and copper losses, by increasing the rate of heat dissipation (better cooling), or by improving transformer insulation so it will withstand higher temperatures.

    KVA

    Medium Voltage Dry Type transformer.

    Voltage:

    Voltage & Current Relationship

    The total induced voltage in each winding is proportional to the number of turns in that winding. If E1 is the primary voltage and I1 the primary current, E2 the secondary voltage and I2 the secondary current, N1 the primary turns and N2 the secondary turns, then:

    \( \frac{ E_{1}}{E_{2}} = \frac{ N_{1}}{N_{2}} = \frac{ I_{2}}{I_{1}} \)

    MCCB-internal-view

    Medium Voltage Dry Type transformer.

    Current:

    Single Phase Current

    \(I_{FLA}=\frac{KVA \cdot 1000}{V_{Phase}} \)

    Three Phase Current

    \(I_{FLA}=\frac{KVA \cdot 1000}{\sqrt{3}\cdot V_{Phase}} \)

    Polarity

    1. Description

      2. Polarity is the relative direction of induced voltages between the high-voltage terminals and the low-voltage terminals. With standard markings, the voltage from H1 to H2 is always in the same direction or in phase with the voltage from X1 to X2. Polarity is a property of single-phase transformers having to do with the identification and location of terminals. For individual use of single-phase transformers, polarity is unimportant, but for parallel connection or connection in a three-phase bank, polarity is very important

    2. Terminal markigs

      3. Polarity is the relative direction of induced voltages between the high-voltage terminals and the low-voltage terminals. With standard markings, the voltage from H1 to H2 is always in the same direction or in phase with the voltage from X1 to X2.

    3. AC WAVE

      4. Because a 60-cycle sine wave (AC) reverses its direction 120 times a second, it is hard to determine the direction at any particular time. In designating polarity, we pick an instant, any instant, and assume the current is flowing in one direction. Polarity is the relative instantaneous direction of current in the leads of a transformer. At a given instant, the primary and secondary leads have the same polarity when the current enters the primary lead and leaves the secondary lead in the same direction as through the two leads form a continuous circuit.

    KVA

    Medium Voltage Dry Type transformer.

    KVA

    Medium Voltage Dry Type transformer.

    Frequency:

    1. Hertz(Hz) is also termed “Cycles per Second” or “Frequency”. With relation to sine waves, it’s the time it takes for one complete cycle.
    2. The three common frequencies available are 50Hz, 60Hz and 400Hz.

      3. European power is typically 50Hz while North American power is usually 60hz.
      The 400 Hz is reserved for high-powered applications such as aerospace and some special-purpose computer power supplies and hand-held machine tools. Such high frequencies cannot be economically transmitted long distances, so 400 Hz power systems are usually confined to the building or vehicle.

    3. Transformer frequency is fixed

      4. Transformers cannot change the frequency of the source kva (voltage & current). If the source frequency is 60 Hz, the output will also be 60 Hz. In most parts of the Americas, it is typically 60Hz, and in the rest of the world it is typically 50Hz. Places that use the 50 Hz frequency tend to use 230 V RMS, and those that use 60Hz tend to use 117 V RMS.

    ***

    MCCB-internal-view

    Medium Voltage Dry Type transformer

    Impedance:

    What is Meant by "Impedance" in Transformers?

    Impedance is the current limiting characteristic of a transformer and is expressed in percentage.

    The percentage impedance of a transformer (Z%) is the voltage drop on full load due to the winding resistance and leakage reactance expressed as a percentage of the rated voltage.
    Electrical impedance of the load is expressed in ohms, and the relationship between the current and the voltage in the circuit is controlled by the impedance in the circuit.

    In general, impedance has a complex value, which means that loads generally have a resistance to the source that is in phase with a sinusoidal source signal and reactance that is out of phase with a sinusoidal source signal.
    The total impedance is the vector sum of the resistance and the reactance. The impedance is measured by shorting the low voltage terminals.

    Why is Impedance Important?

    It is used for determining the interrupting capacity of a circuit breaker or fuse employed to protect the primary of a transformer. Example: Determine a minimum circuit breaker trip rating and nterrupting capacity for a 10 KVA single phase transformer with 4% impedance, to be operated from a 480 volt  50 Hz source.

    Maximum Short Circuit Secondary Current

    The maximum short circuit current that can be obtained from the output of the transformer is limited by the impedance of the transformer and is determined by multiplying the reciprocal of the impedance times the full load current.

    1. Hertz(Hz) is also termed “Cycles per Second” or “Frequency”. With relation to sine waves, it’s the time it takes for one complete cycle.
    2. Transformer percent impedance voltages shall not be less than the following:

      1. 75 kVA 2.7%
      2. 150 kVA 3.1%
      3. 300 kVA 3.1%
      4. 750 kVA 4.4%

    3. Units with impedance values less than the listed values may be rejected by the City. All other impedance requirements, per IEEE C57.12.34 and IEEE C5712.00, shall be met. Identically rated transformers shall be suitable for parallel operation and shall be built to industry tolerance for impedance of ±7.5% per IEEE C57.12.00.

    ***

    MCCB-internal-view

    Medium Voltage Dry Type transformer

    Transformer Construction:

    1. Transformer tanks

      2. Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    MCCB-internal-view

    Free Breathing:

    1. Transformer tanks

      2. Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    MCCB-internal-view

    Sealed:

    1. Transformer tanks

      2. Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    MCCB-internal-view

    Breathing Regulator:

    1. Transformer tanks

      2. Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    MCCB-internal-view

    Cloride Regulator :

    1. Transformer tanks

      2. Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    MCCB-internal-view

    Breathing Regulator:

    1. Transformer tanks

      2. Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    MCCB-internal-view

    Expansion Tank:

    1. Transformer tanks

      2. Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    MCCB-internal-view

    Gas Seealed (Nitrogen):

    1. Transformer tanks

      2. Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    MCCB-internal-view
    Transfomer Tank

    Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    Free Breathing

    The insulating ability of transformer oil is dependent particularly on its being completely free of water and oxygen. Unless prevented, a transformer will draw in atmospheric water and oxygen during normal operation. As the oil heats, due to incident sunlight and/or the flow of load

    current, the oil will expand. This will force the air over the oil out of the transformer. When, later, the oil cools, it decreases in volume, drawing ambient air into the tank. In this way, water vapor and oxygen obtain access to the transformer oil. This process is known as “breathing.’

    Sealed

    In smaller distribution level power transformers, the tank will simply be sealed to prevent movement of air out and back. The gaskets and seals must be able to withstand the internal pressures caused by sun loading and the name plate load heating.

    Breathing Regulator

    To control internal pressures in larger transformers, without hazarding the oil, some transformers are designed to breathe through a regulator. The regulator prevents the free movement of air into and out of the transformer but allows air to flow at preset levels of differential pressure between the tank and atmosphere.

    When the oil expands due to heating, transformers with a breathing regulator will allow internal gas to escape when the internal pressure in the tank rises to 5 pounds per square inch (PSI). When the internal pressure drops to 1  PSI or less, the regulator will admit atmosphere into the gas space above the oil level. Figure 3.4-7 shows a sealed tank with a breathing regulator.

    Chloride Breathing

    To control internal tank pressures, without hazarding the oil, some transformers are designed to breathe through a desiccant (moisture absorber). This system, while generally not in use in the SCE system, is a simple improvement to the breathing regulator explained above. The desiccant removes the water vapor from the air that is being allowed to enter the tank. This chloride breather system, as it is called, is shown in Figure 3.4-8.

    Conservator

    atmosphere into the space above the oil. The regulator allows both water vapor and oxygen in, while the chloride unit only allows in oxygen. A system that provides improved control of the oil in the tank is the conservator tank type, illustrated in Figure 3.4-9, and pictured as it looks in the field in Figure 3.4-10.

    As with the other methods described, the oil will rise and fall as load and temperature rise and fall. The conservator tank allows the tank to be completely filled. Note in Figure 3.4-9 that the free surface of the oil that rises and falls is in the conservator tank. The surface area exposed to the atmosphere is much smaller than in the previous methods. This reduction of surface area limits the ability of oxygen and water vapor to contaminate the insulating oil.

    To provide additional pressure protection for the tank, a relief diaphragm is used (also shown in Figure 3.4-9). It backs up the conservator tank and breather in case of sudden internal pressures that exceed their capabilities. Relief diaphragms on a real transformer are shown in Figure 3.4-11.

    Expansion Tank

    To control internal tank pressures, without hazarding the oil, some transformers are designed to breathe through a desiccant (moisture absorber). This system, while generally not in use in the SCE system, is a simple improvement to the breathing regulator explained above. The desiccant removes the water vapor from the air that is being allowed to enter the tank. This chloride breather system, as it is called, is shown in Figure 3.4-8.

    Gas Sealed
    (Nitrogen)

    Figure 3.4-13 shows an improvement on the breathing regulator. The gas in the space above the oil is nitrogen. An automatic pressure relief valve is connected to the gas space so that when the internal pressure reaches 5 psi, gas will be vented to reduce the pressure within the tank. A source of pressurized nitrogen is also connected to the gas space. This keeps a positive pressure in the gas space, which prevents entry of air through leaks. If the gas space pressure falls to   psi or less, the positive pressure is restored from the nitrogen bottle.

    There are gauges to allow the Operator to monitor the pressures in the system. There is a low-pressure gauge, which is used to monitor the pressure in the gas space above the oil. The range of the low-pressure gauge is typically -5 to +10 psi. A high-pressure gauge is used to monitor the nitrogen supply to the pressure regulator. The range of the high-pressure gauge is typically from 0 to 4000 psi. In some systems, the low-pressure gauge is equipped with high and low-pressure activated switches so an alarm can be sounded when the transformer gas pressure reaches an abnormal value. The high-pressure gauge may be equipped with a pressure switch to sound an alarm when the cylinder pressure reaches a minimum value.

    Winding Insulation:

    Transformer windings are made of aluminum or copper. The windings are insulated by:

    1. Enamel
    2. Varnish
    3. Paper

    Insulating oils, fluids in liquid-filled transformers performs two functions:

    Insulating oils, fluids in liquid-filled transformers performs two functions:

    1. Acts as a dielectric; better insulator than air

      2. It penetrates all parts of the winding insulation and replacing the weaker air insulation.

    2. Cooling Medium

      3. Cooling Medium which remove the heat, generated in the windings and in the core, to the tank wall where it can be dissipated to the surrounding air

      The core loss and the copper loss in the transformer are converted to heat. Unless some means is provided for continuously removing the heat from the core and windings, they would get progressively hotter and eventually result in the failure of the transformer from overheating. In the oil filled transformer the oil is used, in addition to its insulating qualities, as a medium for carrying heat in the core and coils to the tank wall. The tank wall then dissipates this _hear to the surrounding air and maintains a heat balance.

    MCCB-internal-view
    Terminology
    Fire Point:

    The fire point of a liquid is the temperature at which it will continue to burn after ignition for at least 5 seconds. NEC 450-23 requires “less flammable liquids” to have Fire point more than 300 C. Conventional mineral oil does not meet this requirement. See table 1 for comparative data.
    Flash Point:

    The flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture in air. At this temperature the vapor may cease to burn when the source of ignition is removed.
    viscosity:

    Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. In everyday terms, viscosity is "thickness". Thus, water is "thin"; having a lower viscosity, while honey is "thick" having a higher viscosity. The efficiency of cooling depends on fluid flow within the transformer and also through the cooling equipments like radiators. Therefore, a liquid with low viscosity is better for improved cooling (heat and mass transfer).

    Dielectric Strength:

    of an insulating material, the maximum electric field strength that it can withstand intrinsically without breaking down. This is an important electrical property for the insulating liquid. The solid insulation (like paper or pressboard) when impregnated with the liquid offers a better dielectric property than the original material. A higher dielectric strength of the liquid makes the overall insulation system better.

    Dissipation Factor
    "Power Factor"

    An “ideal” insulating material would not dissipate any power within itself. But all practical insulating materials do dissipate a small amount of energy as heat. Thus the dissipation factor measures the “inefficiency” of an insulating material; a lower factor means a better insulator. Dissipation factor is a significant indicator of contamination or deterioration. Dissipation factor is temperature dependent. Dissipation factor is sometimes popularly called “power factor”.

    Insulating Fluids:

    Insulating oils, fluids in liquid-filled transformers performs two functions:

    Insulating oils, fluids in liquid-filled transformers performs two functions:

    1. Acts as a dielectric; better insulator than air

      2. It penetrates all parts of the winding insulation and replacing the weaker air insulation.

    2. Cooling Medium

      3. Cooling Medium which remove the heat, generated in the windings and in the core, to the tank wall where it can be dissipated to the surrounding air

      The core loss and the copper loss in the transformer are converted to heat. Unless some means is provided for continuously removing the heat from the core and windings, they would get progressively hotter and eventually result in the failure of the transformer from overheating. In the oil filled transformer the oil is used, in addition to its insulating qualities, as a medium for carrying heat in the core and coils to the tank wall. The tank wall then dissipates this _hear to the surrounding air and maintains a heat balance.

    MCCB-internal-view
    Terminology
    Fire Point:

    The fire point of a liquid is the temperature at which it will continue to burn after ignition for at least 5 seconds. NEC 450-23 requires “less flammable liquids” to have Fire point more than 300 C. Conventional mineral oil does not meet this requirement. See table 1 for comparative data.
    Flash Point:

    The flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture in air. At this temperature the vapor may cease to burn when the source of ignition is removed.
    viscosity:

    Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. In everyday terms, viscosity is "thickness". Thus, water is "thin"; having a lower viscosity, while honey is "thick" having a higher viscosity. The efficiency of cooling depends on fluid flow within the transformer and also through the cooling equipments like radiators. Therefore, a liquid with low viscosity is better for improved cooling (heat and mass transfer).

    Dielectric Strength:

    of an insulating material, the maximum electric field strength that it can withstand intrinsically without breaking down. This is an important electrical property for the insulating liquid. The solid insulation (like paper or pressboard) when impregnated with the liquid offers a better dielectric property than the original material. A higher dielectric strength of the liquid makes the overall insulation system better.

    Dissipation Factor
    "Power Factor"

    An “ideal” insulating material would not dissipate any power within itself. But all practical insulating materials do dissipate a small amount of energy as heat. Thus the dissipation factor measures the “inefficiency” of an insulating material; a lower factor means a better insulator. Dissipation factor is a significant indicator of contamination or deterioration. Dissipation factor is temperature dependent. Dissipation factor is sometimes popularly called “power factor”.

    Mineral Oil:

    1. Commonly used

      2. It has been used as the dielectric fluid for several generations of transformers. It has a longstanding record of good performance and low costs. It is considered a top choice for transformers for outdoor installations. It has very good dielectric and thermal performance. In fact, most of the norms for liquid filled transformers have been based on mineral oil. However, mineral oil is considered to be a flammable liquid and therefore, suffers from certain restrictions on its use and containment

    MCCB-internal-view

    Silicone:

    For several decades this was the preferred fluid when a “lessflammable” liquid was required. It has a relatively high fire point and is generally self extinguishing when the source of ignition is removed. Silicone has been used for many years in indoor applications, generally in vaulted areas. However, at high temperatures silicone can produce some chemicals which can be a health hazard. Also, it is the most expensive insulating fluid

    Beta:

    It is a blend of petrochemical oils and is 100% hydrocarbon. It has a fire point which is higher than mineral oil, thus qualifying as “less-flammable” liquid. However, its fire point is lower than either silicone or Envirotemp (FR3). Also, it is more expensive than mineral oil.

    MCCB-internal-view

    FR3:

    It is a soy-based natural ester dielectric fluid which meets the requirements of “less-flammable” liquid. It is bio-degradable and is environment friendly. Cooper Power system claims that FR3 can extend the insulation life by drawing out moisture from paper insulation. The heat transfer properties are inferior to that of mineral oil and transformers have to be suitably designed for that, adding to cost. Also, certain precautions are needed during manufacture when using this liquid. It is much costlier than mineral oil and makes the initial cost of the transformer higher. The inherent dissipation factor of FR3 is higher than mineral oil and as a result the power factor of the whole transformer with FR3 is higher than one with mineral oil. The existing norms for acceptance for power factor of a new transformer are based on mineral oil and cannot be met with FR3. This fluid is still more expensive than Beta Fluid.

    MCCB-internal-view
    Liquid-Immersed, Air-Cooled

    OA

    Oil-immersed, self-cooled. Transformer windings and core are immersed in some type of oil and are self-cooled by natural circulation of air around the outside enclosure. Finsor radiators may be attached to the enclosure to aid in cooling.

    OA/FA

    Liquid-immersed, self-cooled/forced air-cooled. Same as OA, with the addition of fans. Fans are usually mounted on radiators. The transformer typically has two load ratings: one with the fans off (OA) and a larger rating with fans operating (FA). Fans may be wired to start automatically at a pre-set temperature.

    OA/FA/FA

    Liquid-immersed, self-cooled/forced air-cooled/forced air-cooled. Same as OA/FA, with an additional set of fans. There typically will be three load ratings corresponding to each increment of cooling. Increased ratings are obtained by increasing cooling air over portions of the cooling surfaces. Typically, there are radiators attached to the tank to aid in cooling. The two groups of fans may be wired to start automatically at pre-set levels as temperature increases. There are no oil pumps. Oil flows through the transformer windings by the natural principle of convection (heat rising).

    Liquid-Immersed, Air-Cooled/Forced Liquid-Cooled

    OA/FA/FOA

    Liquid-immersed, self-cooled/forced aircooled/forced liquid, and forced air-cooled. Windings and core are immersed in some type of oil. This transformer typically has radiators attached to the enclosure. The transformer has self-cooling (OA) natural ventilation, forced air-cooling FA (fans), and forced oil-cooling (pumps) with additional forced air-cooling (FOA) (more fans). The transformer has three load ratings corresponding to each cooling step. Fans and pumps may be wired to start automatically at pre-set levels as temperature increases

    OA/FOA/FOA

    Liquid-immersed, self-cooled/forced oil, and forced air-cooled/forced oil, and forced air-cooled. Cooling controls are arranged to start only part of the oil pumps and part of the fans for the first load rating/temperature increase, and the remaining pumps and fans for the second load rating increase. The nameplate will show at least three load ratings.

    Neta Table 100.5
    Liquid-Immersed, Water-Cooled

    OW

    Transformer coil and core are immersed in oil.Typically, an oil/water heat exchanger (radiator) is attached to the outside of the tank. Cooling water is pumped through the heat exchanger, but the oil flows only by natural circulation. As oil is heated by the windings, it rises to the top and exits through piping to the radiator. As oil is cooled, it descends through the radiator and re-enters the transformer tank at the bottom.

    Class OW/A

    Transformer coil and core are immersed in oil. This transformer has two ratings. Cooling for one rating (OW) is obtained as in item 1. above. The self-cooled rating (A) is obtained by natural circulation of air over the tank and cooling surfaces.

    Liquid-Immersed, Forced Liquid-Cooled

    FOA

    Liquid-immersed, forced liquid-cooled withforced air-cooled. This transformer normally has only one rating. The transformer is cooled by pumping oil (forced oil) through a radiator normally attached to the outside of the tank. Also, air is forced by fans over the cooling surface.

    FOW

    Liquid-immersed, forced liquid-cooled, water cooled. This transformer is cooled by an oil/water heat exchanger normally mounted separately from the tank. Both the transformer oil and the cooling water are pumped (forced) through the heat exchanger to accomplish cooling

    1. What are voltage taps:

      2. Voltage taps allow an operator to change the wiring configuration of a transformer winding. Physically they are either a bolted connection between different winding positions or a switch; each switch position corresponds too a different winding configuration and voltage.

    1. Why Change our Voltage Tap:

      2. Most power transformers have taps on either primary or secondary windings to vary the number of turns and, thus, the output voltage. The percentage of voltage change, above or below normal, between different tap positions varies in different transformers.

    KVA

    Medium Voltage Dry Type transformer.

    1. Why Change our Voltage Tap:

      2. Voltage supplied to a Transformer may vary from nominal voltage due to the distance from the substation or source. Higher or lower input voltage will result in higher or lower output voltage if there are no voltage adjustment taps present.

      In order to compensate for this voltage difference, transformers secondary voltage can be adjusted to nominal levels by adjusting the transformer's primary winding's voltage Tap.

      Transformer voltage taps change the voltage ratio of a transformer so that its secondary voltage stays at nominal. On large power transformers, taps on the primary are used to offset any higher or lower input voltages. These tap connections are usually set at the factory for nominal line voltage. If the voltage at the site is different, the taps are changed accordingly.

      Changing Voltage Taps
      1. decreasing the primary voltage Tap will increase secondary voltage
      2. Increasing the primary voltage Tap will decrease secondary voltage

        3. Standard tap arrangements are at two and one-half and five percent of the rated primary voltage for both high and low voltage conditions. For example, if the transformer has a 480 volt primary and the available line voltage is running at 504 volts, the primary should be connected to the 5% tap above normal in order that the secondary voltage be maintained at the proper rating. The standard ASA and NEMA designation for taps are "ANFC" (above normal full capacity) and "BNFC" (below normal full capacity).

    MCCB-internal-view

    No Load Tap Changer:

    Tap changers on power transformers are either load tap changers or no-load tap changers. They may be installed in either or both the high or low side windings. The load tap changer permits the changing of taps while the transformer continues to carry load. The no-load tap changer requires the transformer be removed from service to permit the tap to be changed. Most no-load tap changers are installed on the high side winding and their movement has an inverse effect on the low side voltage. When the high side tap is ra winding. All three phases of the transformer change at the same time. However, each phase can be operated independently either electrically or manually. Lights or a calibrated dial are installed on each phase to show the tap position.

    MCCB-internal-view

    LTC:

    Tap changers on power transformers are either load tap changers or no-load tap changers. They may be installed in either or both the high or low side windings. The load tap changer permits the changing of taps while the transformer continues to carry load. The no-load tap changer requires the transformer be removed from service to permit the tap to be changed. Most no-load tap changers are installed on the high side winding and their movement has an inverse effect on the low side voltage. When the high side tap is ra winding. All three phases of the transformer change at the same time. However, each phase can be operated independently either electrically or manually. Lights or a calibrated dial are installed on each phase to show the tap position.

    MCCB-internal-view
    TANK:
    1. Transformer tanks

      2. Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    MCCB-internal-view

    Free Breathing:

    1. Free Breathing:

      2. This type is open to the atmosphere (i.e., the airspace above the liquid is at atmospheric pressure). The transformer breathes as the air pressure and temperature change outside the tank. Some of these transformers can be equipped with dehydrating compounds in the breather.

    MCCB-internal-view

    Sealed:

    1. Sealed:

      2. These transformers are equipped with an inert gas, such as nitrogen that is under pressure above the liquid in the transformer tank. Generally, the pressure range for this type of transformer is −8 to +8 lb/in.2

    MCCB-internal-view

    Breathing Regulator:

    1. Transformer tanks

      2. Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    MCCB-internal-view

    Cloride Regulator :

    1. Transformer tanks

      2. Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    MCCB-internal-view

    Breathing Regulator:

    1. Transformer tanks

      2. Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    MCCB-internal-view

    Expansion Tank:

    1. Transformer tanks

      2. Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    MCCB-internal-view

    Gas Seealed (Nitrogen):

    1. Transformer tanks

      2. Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    MCCB-internal-view
    Transfomer Tank

    Transformer tanks are ruggedly made of high quality steel. Welds are leak-proof and bolted covers are equipped with gaskets. The tank provides the means to hold the core and windings in an oil bath so that the insulation and the cooling properties of the materials used in the construction of the core and windings are optimized. Oil that is outside of the transformer on the tank or on the ground indicates a problem that the Substation Operator should investigate.

    Free Breathing

    The insulating ability of transformer oil is dependent particularly on its being completely free of water and oxygen. Unless prevented, a transformer will draw in atmospheric water and oxygen during normal operation. As the oil heats, due to incident sunlight and/or the flow of load

    current, the oil will expand. This will force the air over the oil out of the transformer. When, later, the oil cools, it decreases in volume, drawing ambient air into the tank. In this way, water vapor and oxygen obtain access to the transformer oil. This process is known as “breathing.’

    Sealed

    In smaller distribution level power transformers, the tank will simply be sealed to prevent movement of air out and back. The gaskets and seals must be able to withstand the internal pressures caused by sun loading and the name plate load heating.

    Breathing Regulator

    To control internal pressures in larger transformers, without hazarding the oil, some transformers are designed to breathe through a regulator. The regulator prevents the free movement of air into and out of the transformer but allows air to flow at preset levels of differential pressure between the tank and atmosphere.

    When the oil expands due to heating, transformers with a breathing regulator will allow internal gas to escape when the internal pressure in the tank rises to 5 pounds per square inch (PSI). When the internal pressure drops to 1  PSI or less, the regulator will admit atmosphere into the gas space above the oil level. Figure 3.4-7 shows a sealed tank with a breathing regulator.

    Chloride Breathing

    To control internal tank pressures, without hazarding the oil, some transformers are designed to breathe through a desiccant (moisture absorber). This system, while generally not in use in the SCE system, is a simple improvement to the breathing regulator explained above. The desiccant removes the water vapor from the air that is being allowed to enter the tank. This chloride breather system, as it is called, is shown in Figure 3.4-8.

    Conservator

    atmosphere into the space above the oil. The regulator allows both water vapor and oxygen in, while the chloride unit only allows in oxygen. A system that provides improved control of the oil in the tank is the conservator tank type, illustrated in Figure 3.4-9, and pictured as it looks in the field in Figure 3.4-10.

    As with the other methods described, the oil will rise and fall as load and temperature rise and fall. The conservator tank allows the tank to be completely filled. Note in Figure 3.4-9 that the free surface of the oil that rises and falls is in the conservator tank. The surface area exposed to the atmosphere is much smaller than in the previous methods. This reduction of surface area limits the ability of oxygen and water vapor to contaminate the insulating oil.

    To provide additional pressure protection for the tank, a relief diaphragm is used (also shown in Figure 3.4-9). It backs up the conservator tank and breather in case of sudden internal pressures that exceed their capabilities. Relief diaphragms on a real transformer are shown in Figure 3.4-11.

    Expansion Tank

    To control internal tank pressures, without hazarding the oil, some transformers are designed to breathe through a desiccant (moisture absorber). This system, while generally not in use in the SCE system, is a simple improvement to the breathing regulator explained above. The desiccant removes the water vapor from the air that is being allowed to enter the tank. This chloride breather system, as it is called, is shown in Figure 3.4-8.

    Gas Sealed
    (Nitrogen)

    Figure 3.4-13 shows an improvement on the breathing regulator. The gas in the space above the oil is nitrogen. An automatic pressure relief valve is connected to the gas space so that when the internal pressure reaches 5 psi, gas will be vented to reduce the pressure within the tank. A source of pressurized nitrogen is also connected to the gas space. This keeps a positive pressure in the gas space, which prevents entry of air through leaks. If the gas space pressure falls to   psi or less, the positive pressure is restored from the nitrogen bottle.

    There are gauges to allow the Operator to monitor the pressures in the system. There is a low-pressure gauge, which is used to monitor the pressure in the gas space above the oil. The range of the low-pressure gauge is typically -5 to +10 psi. A high-pressure gauge is used to monitor the nitrogen supply to the pressure regulator. The range of the high-pressure gauge is typically from 0 to 4000 psi. In some systems, the low-pressure gauge is equipped with high and low-pressure activated switches so an alarm can be sounded when the transformer gas pressure reaches an abnormal value. The high-pressure gauge may be equipped with a pressure switch to sound an alarm when the cylinder pressure reaches a minimum value.

    Temperature Rise:

    Transformer temperature rise is defined as the average temperature rise of the windings above the ambient (surrounding) temperature, when the transformer is loaded at its nameplate rating.

    Liquid-filled transformers come in the following standard rises:

    • 55C
    • 65C

    These values are based on a maximum ambient temperature of 40C. That means, for example, that an 80C rise dry transformer will operate at an average winding temperature of 120C when at full-rated load, in a 40C ambient environment.

    What is BIL and How Does it Apply to Transformers Listed

    BIL is an abbreviation for Basic Impulse Level. Impulse tests are dielectric tests that consist of the application of a high frequency steep wave front voltage between windings, and between windings and ground. The Basic Impulse Level of a transformer is a method of expressing the voltage surge (lightning, switching surges, etc.) that a transformer will tolerate without breakdown. All transformers manufactured in this catalog, 600 volts and below, will withstand the NEMA standard BIL rating, which is 10 KV. This assures the user that he will not experience breakdowns when his system is properly protected with lightning arrestors or similar surge protection devices.

    Basic impulse insulation level (BIL): BIL is the crest value of the impulse voltage that the transformer is required to withstand without failure. The transformer BIL impulse duration is 1.2   50 μs. That is, the impulse reaches its peak value in 1.2 μs and then decays to 50% of its peak value in 50 μs. In addition to full BIL value, transformers are tested for chopped-wave withstand (115% of BIL) and front-of-the-wave withstand (160% of BIL). These tests are intended to simulate conditions that can occur when transformers are subjected to lightning surges.

    Liquid-Immersed, Air-Cooled

    OA

    Oil-immersed, self-cooled. Transformer windings and core are immersed in some type of oil and are self-cooled by natural circulation of air around the outside enclosure. Finsor radiators may be attached to the enclosure to aid in cooling.

    OA/FA

    Liquid-immersed, self-cooled/forced air-cooled. Same as OA, with the addition of fans. Fans are usually mounted on radiators. The transformer typically has two load ratings: one with the fans off (OA) and a larger rating with fans operating (FA). Fans may be wired to start automatically at a pre-set temperature.

    OA/FA/FA

    Liquid-immersed, self-cooled/forced air-cooled/forced air-cooled. Same as OA/FA, with an additional set of fans. There typically will be three load ratings corresponding to each increment of cooling. Increased ratings are obtained by increasing cooling air over portions of the cooling surfaces. Typically, there are radiators attached to the tank to aid in cooling. The two groups of fans may be wired to start automatically at pre-set levels as temperature increases. There are no oil pumps. Oil flows through the transformer windings by the natural principle of convection (heat rising).

    Liquid-Immersed, Air-Cooled/Forced Liquid-Cooled

    OA/FA/FOA

    Liquid-immersed, self-cooled/forced aircooled/forced liquid, and forced air-cooled. Windings and core are immersed in some type of oil. This transformer typically has radiators attached to the enclosure. The transformer has self-cooling (OA) natural ventilation, forced air-cooling FA (fans), and forced oil-cooling (pumps) with additional forced air-cooling (FOA) (more fans). The transformer has three load ratings corresponding to each cooling step. Fans and pumps may be wired to start automatically at pre-set levels as temperature increases

    OA/FOA/FOA

    Liquid-immersed, self-cooled/forced oil, and forced air-cooled/forced oil, and forced air-cooled. Cooling controls are arranged to start only part of the oil pumps and part of the fans for the first load rating/temperature increase, and the remaining pumps and fans for the second load rating increase. The nameplate will show at least three load ratings.

    Neta Table 100.5
    Liquid-Immersed, Water-Cooled

    OW

    Transformer coil and core are immersed in oil.Typically, an oil/water heat exchanger (radiator) is attached to the outside of the tank. Cooling water is pumped through the heat exchanger, but the oil flows only by natural circulation. As oil is heated by the windings, it rises to the top and exits through piping to the radiator. As oil is cooled, it descends through the radiator and re-enters the transformer tank at the bottom.

    Class OW/A

    Transformer coil and core are immersed in oil. This transformer has two ratings. Cooling for one rating (OW) is obtained as in item 1. above. The self-cooled rating (A) is obtained by natural circulation of air over the tank and cooling surfaces.

    Liquid-Immersed, Forced Liquid-Cooled

    FOA

    Liquid-immersed, forced liquid-cooled withforced air-cooled. This transformer normally has only one rating. The transformer is cooled by pumping oil (forced oil) through a radiator normally attached to the outside of the tank. Also, air is forced by fans over the cooling surface.

    FOW

    Liquid-immersed, forced liquid-cooled, water cooled. This transformer is cooled by an oil/water heat exchanger normally mounted separately from the tank. Both the transformer oil and the cooling water are pumped (forced) through the heat exchanger to accomplish cooling

    :

    1. Transformers are rated in kilo-volt-amperes (kVA).

      2. kVA is used to express a transformer rating because not all transformer loads are purely resistive. The resistive component consumes power that is measured in watts, whereas the reactive component consumes power measured in VARs. The vector sum of these two loads is the total load, VA or kVA

    2. Transformer Capacity

      3. Capacity (or rating) of a transformer is limited by the temperature that the insulation can tolerate. Ratings can be increased by reducing core and copper losses, by increasing the rate of heat dissipation (better cooling), or by improving transformer insulation so it will withstand higher temperatures.

    MCCB-internal-view

    Voltage:

    The voltage designation defines both the way a transformer may be applied to a system and the transformer design. IEEE Std C57.12.00 defines the designation of voltage ratings of single and three-phase transformers.

    MCCB-internal-view
    Voltage & Current Relationship

    The total induced voltage in each winding is proportional to the number of turns in that winding. If E1 is the primary voltage and I1 the primary current, E2 the secondary voltage and I2 the secondary current, N1 the primary turns and N2 the secondary turns, then:

    \( \frac{ E_{1}}{E_{2}} = \frac{ N_{1}}{N_{2}} = \frac{ I_{2}}{I_{1}} \)

    Where:

    Voltage:

    The voltage designation defines both the way a transformer may be applied to a system and the transformer design. IEEE Std C57.12.00 defines the designation of voltage ratings of single and three-phase transformers.

    MCCB-internal-view
    Voltage & Current Relationship

    The total induced voltage in each winding is proportional to the number of turns in that winding. If E1 is the primary voltage and I1 the primary current, E2 the secondary voltage and I2 the secondary current, N1 the primary turns and N2 the secondary turns, then:

    \( \frac{ E_{1}}{E_{2}} = \frac{ N_{1}}{N_{2}} = \frac{ I_{2}}{I_{1}} \)

    Where:

    Voltage:

    The voltage designation defines both the way a transformer may be applied to a system and the transformer design. IEEE Std C57.12.00 defines the designation of voltage ratings of single and three-phase transformers.

    MCCB-internal-view
    Voltage & Current Relationship

    The total induced voltage in each winding is proportional to the number of turns in that winding. If E1 is the primary voltage and I1 the primary current, E2 the secondary voltage and I2 the secondary current, N1 the primary turns and N2 the secondary turns, then:

    \( \frac{ E_{1}}{E_{2}} = \frac{ N_{1}}{N_{2}} = \frac{ I_{2}}{I_{1}} \)

    Where:
    Transformer Test Procedures
    Dry Type, Low Voltage 600 volts or Greater
    1. Maintenance

      2. Transformers do not require as much attention as most other equipment; however, the care and maintenance they do require is absolutely critical. Because of their reliability, maintenance is sometimes ignored, causing reduced service life and, at times, outright failure.

    2. Visual and Mechanical Inspection
    3. Transformer Turns Ratio (TTR)
    4. Winding Resistance
    5. Insulation Resistance
    6. Power Factor
    7. Oil Sample
    NETA Test Procedure

    NETA ATS

    7.2.2 Transformers, Liquid-Filled

    A. Visual and Mechanical Inspection:
    1. Compare equipment nameplate data with drawings and specifications.
    2. Inspect physical and mechanical condition..
    3. Inspect impact recorder prior to unloading.
    4. *Test dew point of tank gases
    5. Inspect anchorage, alignment, and grounding.
    6. Verify the presence of PCB content labeling.
    7. Verify removal of any shipping bracing after placement.
    8. Verify the bushings are clean.
    9. Verify that alarm, control, and trip settings on temperature and level indicators are as specified.
    10. Verify operation of alarm, control, and trip circuits from temperature and level indicators, pressure relief device, gas accumulator, and fault pressure relay.
    11. Verify that cooling fans and pumps operate correctly and have appropriate overcurrent protection.
    12. Inspect bolted electrical connections for high resistance using one or more of the following methods:
      1. Use of a low-resistance ohmmeter in accordance with Section 7.2.1.1.B.1.
      2. Verify tightness of accessible bolted electrical connections by calibrated torque-wrench method in accordance with manufacturer’s published data or Table 100.12.
      3. Perform thermographic survey in accordance with Section 9.
    13. Verify correct liquid level in tanks and bushings.
    14. Verify valves are in the correct operating position.
    15. Verify that positive pressure is maintained on gas-blanketed transformers.
    16. Perform inspections and mechanical tests as recommended by the manufacturer.
    17. Test load tap-changer in accordance with Section 7.12.3.
    18. Verify presence of transformer surge arresters.
    19. Verify de-energized tap-changer position is left as specified.
    B. Electrical Tests:
    1. Perform resistance measurements through bolted connections with a low-resistance ohmmeter if applicable, in accordance with Section 7.2.2.A.12.1.
    2. Perform insulation-resistance tests winding-to-winding and each winding-to-ground. Apply voltage in accordance with manufacturer’s published data or in the absence of manufacturer’s published data, use Table 100.5. Calculate polarization index.
    3. Perform turns-ratio tests at all tap positions.
    4. Perform insulation power-factor or dissipation-factor tests on all windings in accordance with test equipment manufacturer’s published data.
    5. Perform power-factor or dissipation-factor tests on each bushing equipped with a powerfactor/ capacitance tap. In the absence of a power-factor/ capacitance tap, perform hot-collar tests. These tests shall be in accordance with the test equipment manufacturer’s published data.
    6. Perform excitation-current tests in accordance with test equipment manufacturer’s published data.
    7. Perform sweep frequency response analysis tests.
    8. Measure the resistance of each high-voltage winding in each de-energized tap-changer position. Measure the resistance of each low-voltage winding in each de-energized tapchanger position
    9. *Perform leakage reactance three phase equivalent and per phase tests.
    10. *If core ground strap is accessible, remove and measure core insulation resistance at 500 volts dc.
    11. *Measure the percentage of oxygen in the gas blanket.
    12. Remove a sample of insulating liquid in accordance with ASTM D 923. Sample shall be tested for the following:
      1. Dielectric breakdown voltage: ASTM D 877 and/or ASTM D 1816
      2. Acid neutralization number: ANSI/ASTM D 974
      3. *Specific gravity: ANSI/ASTM D 1298
      4. Interfacial tension: ANSI/ASTM D 971
      5. Color: ANSI/ASTM D 1500
      6. Visual Condition: ASTM D 1524Visual Condition: ASTM D 1524
      7. Water in insulating liquids: ASTM D 1533.
      8. *Power factor or dissipation factor in accordance with ASTM D 924.
    13. Remove a sample of insulating liquid in accordance with ASTM D923 and perform dissolved-gas analysis (DGA) in accordance with ANSI/IEEE C57.104 or ASTM D3612.
    14. Test instrument transformers in accordance with Section 7.10.
    15. Test surge arresters in accordance with Section 7.19, if present.
    16. Test transformer neutral grounding impedance device, if present.
    17. Verify operation of cubicle or air terminal compartment space heaters.
    C. Test Values – Visual and Mechanical
    1. Alarm, control, and trip circuits from temperature and level indicators as well as pressure relief device and fault pressure relay shall operate within manufacturer’s recommendations for their specified settings. (7.2.2.A.10)
    2. Cooling fans and pumps shall operate. (7.2.2.A.11)
    3. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value. (7.2.2.A.12.1)
    4. Bolt-torque levels shall be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.12. (7.2.2.A.12.2)
    5. Results of the thermographic survey shall be in accordance with Section 9. (7.2.2.A.12.3)
    6. Liquid levels in the transformer tanks and bushings shall be within indicated tolerances. (7.2.2.A.13
    7. Positive pressure shall be indicated on pressure gauge for gas-blanketed transformers. (7.2.2.A.15)
    D. Test Values – Electrical
    1. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value.
    2. Minimum insulation-resistance values of transformer insulation shall be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.5. Values of insulation resistance less than this table or manufacturer’s recommendations should be investigated. The polarization index shall not be less than 1.0.
    3. Turns-ratio test results shall not deviate by more than one-half percent from either the adjacent coils or the calculated ratio.
    4. Maximum winding insulation power-factor/dissipation-factor values of liquid-filled transformers shall be in accordance with the manufacturer’s published data. In the absence of manufacturer’s published data use Table 100.3. Distribution transformer power factor results shall compare to previously obtained results.
    5. Investigate bushing power-factor values that vary from nameplate values by more than 150 percent. Investigate bushing capacitance values that vary from nameplate values by more than five percent. Investigate bushing hot-collar test values that exceed 0.1 Watts.
    6. Typical excitation-current test data pattern for a three-legged core transformer is two similar current readings and one lower current reading.
    7. Sweep frequency response analysis test results should compare to factory and previous test results.
    8. Consult the manufacturer if winding-resistance test values vary by more than two percent from factory test values or between adjacent phases.
    9. Investigate leakage reactance per phase test results that deviate from the average of the three readings by more than 3%. The three phase equivalent test results serve as a benchmark for future tests.
    10. Core insulation values shall be compared to the factory test value but not less than one megohm at 500 volts dc.
    11. Investigate the presence of oxygen in the nitrogen gas blanket.
    12. Insulating liquid values shall be in accordance with Table 100.4.
    13. Evaluate results of dissolved-gas analysis in accordance with ANSI/IEEE Standard C57.104.
    14. Results of electrical tests on instrument transformers shall be in accordance with Section 7.10.
    15. Results of surge arrester tests shall be in accordance with Section 7.19.
    16. Compare grounding impedance device values to manufacturer’s published data.
    17. Heaters shall be operational.

    NETA ATS

    7.2.1.2 Transformers, Dry Type, Air-Cooled, Large

    NOTE: This category consists of power transformers with windings rated higher than 600 volts and low-voltage transformers larger than 167 kVA single-phase or 500 kVA three-phase.
    A. Visual and Mechanical Inspection:
    1. Compare equipment nameplate data with drawings and specifications.
    2. Inspect physical and mechanical condition..
    3. Inspect anchorage, alignment, and grounding.
    4. Verify that resilient mounts are free and that any shipping brackets have been removed..
    5. Verify the unit is clean.
    6. *Verify that control and alarm settings on temperature indicators are as specified.
    7. Verify that cooling fans operate and that fan motors have correct overcurrent protection.
    8. Inspect bolted electrical connections for high resistance using one or more of the following methods:
      1. Use of a low-resistance ohmmeter in accordance with Section 7.2.1.2.B.1.
      2. Verify tightness of accessible bolted electrical connections by calibrated torque-wrench method in accordance with manufacturer’s published data or Table 100.12.
      3. Perform thermographic survey in accordance with Section 9.
    9. Perform specific inspections and mechanical tests as recommended by the manufacturer.
    10. Verify that as-left tap connections are as specified.
    11. Verify the presence of surge arresters.
    B. Electrical Tests:
    1. Perform resistance measurements through bolted connections with a low-resistance ohmmeter, if applicable, in accordance with Section 7.2.1.2.A.8.1.
    2. Perform insulation-resistance tests winding-to-winding and each winding-to-ground. Apply voltage in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.5. Calculate polarization index.
    3. Perform power-factor or dissipation-factor tests on all windings in accordance with the test equipment manufacturer’s published data.
    4. *Perform a power-factor or dissipation-factor tip-up test on windings greater than 2.5 kV.
    5. Perform turns-ratio tests at all tap positions.
    6. *Perform an excitation-current test on each phase.
    7. *Measure the resistance of each winding at each tap connection.
    8. Measure core insulation resistance at 500 volts dc if the core is insulated and the core ground strap is removable.
    9. *Perform an applied voltage test on all high- and low-voltage windings-to-ground. See ANSI/IEEE C57.12.91, Sections 10.2 and 10.9.
    10. Verify correct secondary voltage, phase-to-phase and phase-to-neutral, after energization and prior to loading.
    11. Test surge arresters in accordance with Section 7.19.
    C. Test Values – Visual and Mechanical
    1. Control and alarm settings on temperature indicators shall operate within manufacturer’s recommendations for specified settings. (7.2.1.2.A.6)
    2. Cooling fans shall operate. (7.2.1.2.A.7)
    3. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value. (7.2.1.2.A.8.1)
    4. Bolt-torque levels shall be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.12. (7.2.1.2.A.8.2)
    5. Results of the thermographic survey shall be in accordance with Section 9. (7.2.1.2.A.8.3)
    6. Tap connections shall be left as found unless otherwise specified. (7.2.1.2.A.10)
    D. Test Values – Electrical
    1. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value.
    2. Minimum insulation-resistance values of transformer insulation shall be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.5. Values of insulation resistance less than this table or manufacturer’s recommendations should be investigated. The polarization index shall not be less than 1.0.
    3. The following values are typical for insulation power factor tests:
      1. CHL Power transformers: 2.0 percent or less
      2. CHL Distribution transformers: 5.0 percent or less
      3. CH and CL power-factor or dissipation-factor values will vary due to support insulators and bus work utilized on dry transformers. Consult transformer manufacturer’s or test equipment manufacturer’s data for additional information.
    4. Power-factor or dissipation-factor tip-up exceeding 1.0 percent shall be investigated.
    5. Turns-ratio test results shall not deviate more than one-half percent from either the adjacent coils or the calculated ratio.
    6. The typical excitation current test data pattern for a three-legged core transformer is two similar current readings and one lower current reading.
    7. Temperature-corrected winding-resistance values shall compare within one percent of previously-obtained results.
    8. Core insulation-resistance values shall not be less than one megohm at 500 volts dc.
    9. AC dielectric withstand test voltage shall not exceed 75 percent of factory test voltage for one minute duration. DC dielectric withstand test voltage shall not exceed 100 percent of the ac rms test voltage specified in ANSI C57.12.91, Section 10.2 for one minute duration. If no evidence of distress or insulation failure is observed by the end of the total time of voltage application during the dielectric withstand test, the test specimen is considered to have passed the test.
    10. Phase-to-phase and phase-to-neutral secondary voltages shall be in agreement with nameplate data.
    11. Test results for surge arresters shall be in accordance with Section 7.19.

    NETA MTS

    7.2.1.1 Transformers, Dry Type, Air-Cooled, Low-Voltage, Small

    NOTE: This category consists of power transformers with windings rated 600 volts or less and sizes equal to or less than 167 kVA single-phase or 500 kVA three-phase.
    A. Visual and Mechanical Inspection:
    1. Inspect physical and mechanical condition.
    2. Inspect anchorage, alignment, and grounding.
    3. Prior to cleaning the unit, perform as-found tests, if required.
    4. VClean the unit.
    5. Inspect bolted electrical connections for high resistance using one or more of the following methods:
      1. Use of a low-resistance ohmmeter in accordance with Section 7.2.1.1.B.1.
      2. Verify tightness of accessible bolted electrical connections by calibrated torque-wrench method in accordance with manufacturer’s published data or Table 100.12.
      3. Perform thermographic survey in accordance with Section 9.
    6. Perform as-left tests..
    7. Verify that as-left tap connections are as specified.
    B. Electrical Tests:
    1. Perform resistance measurements through bolted connections with a low-resistance ohmmeter, if applicable, in accordance with Section 7.2.1.1.A.5.1.
    2. Perform insulation-resistance tests winding-to-winding and each winding-to-ground. Apply voltage in accordance with manufacturer’s published data or in the absence of manufacturer’s published data, use Table 100.5. Calculate polarization index.
    3. *Perform turns-ratio tests at all tap positions.
    C. Test Values – Visual and Mechanical
    1. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value. (7.2.1.1.A.5.1)
    2. Bolt-torque levels shall be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.12. (7.2.1.1.A.5.2)
    3. Results of the thermographic survey shall be in accordance with Section 9. (7.2.1.1.A.5.3)
    4. Tap connections are left as found unless otherwise specified. (7.2.1.1.A.7)
    D. Test Values – Electrical
    1. Compare bolted electrical connection resistances to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value.
    2. Minimum insulation-resistance values of transformer insulation shall be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.5. Values of insulation resistance less than this table or manufacturer’s recommendations should be investigated. The polarization index shall not be less than 1.0.
    3. Turns-ratio test results shall not deviate by more than one-half percent from either the adjacent coils or the calculated ratio.

    NETA MTS

    7.2.1.2 Transformers, Dry Type, Air-Cooled, Large

    NOTE: This category consists of power transformers with windings rated higher than 600 volts and low-voltage transformers larger than 167 kVA single-phase or 500 kVA three-phase.
    A. Visual and Mechanical Inspection:
    1. Inspect physical and mechanical condition..
    2. Inspect anchorage, alignment, and grounding.
    3. Prior to cleaning the unit, perform as-found tests, if required.
    4. Clean the unit.
    5. *Verify that control and alarm settings on temperature indicators are as specified.
    6. Verify that cooling fans operate correctly.
    7. Inspect bolted electrical connections for high resistance using one or more of the following methods:
      1. Use of a low-resistance ohmmeter in accordance with Section 7.2.1.2.B.1.
      2. Verify tightness of accessible bolted electrical connections by calibrated torque-wrench method in accordance with manufacturer’s published data or Table 100.12.
      3. Perform thermographic survey in accordance with Section 9.
    8. Perform specific inspections and mechanical tests as recommended by the manufacturer.
    9. Perform as-left tests.
    10. Verify that as-left tap connections are as specified.
    11. Verify the presence of surge arresters.
    B. Electrical Tests:
    1. Perform resistance measurements through bolted connections with a low-resistance ohmmeter, if applicable, in accordance with Section 7.2.1.2.A.7.1.
    2. Perform insulation-resistance tests winding-to-winding and each winding-to-ground. Apply voltage in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.5. Calculate polarization index.
    3. Perform insulation power-factor or dissipation-factor tests on all windings in accordance with the test equipment manufacturer’s published data.
    4. *Perform a power-factor or dissipation-factor tip-up test on windings rated greater than 2.5 kV.
    5. Perform turns-ratio tests at the designated tap position.
    6. *Perform an excitation-current test on each phase.
    7. *Measure the resistance of each winding at the designated tap position.
    8. Measure core insulation resistance at 500 volts dc if the core is insulated and if the core ground strap is removable.
    9. *Perform an applied voltage test on all high- and low-voltage windings-to-ground. See IEEE C57.12.91-2001, Sections 103.
    10. Verify correct secondary voltage phase-to-phase and phase-to-neutral after energization and prior to loading.
    11. Test surge arresters in accordance with Section 7.19.
    12. *Perform online partial-discharge survey on winding rated higher than 600 volts in accordance with Section 11.
    C. Test Values – Visual and Mechanical
    1. Control and alarm settings on temperature indicators shall operate within manufacturer’s recommendations for specified settings. (7.2.1.2.A.5)
    2. Cooling fans shall operate. (7.2.1.2.A.6)
    3. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value. (7.2.1.2.A.7.1)
    4. Bolt-torque levels shall be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.12. (7.2.1.2.A.7.2)
    5. Results of the thermographic survey shall be in accordance with Section 9. (7.2.1.2.A.7.3)
    6. Tap connections shall be left as found unless otherwise specified. (7.2.1.2.A.10)
    D. Test Values – Electrical
    1. Compare bolted connection resistance values to values of similar connections. Investigate values which deviate from those of similar bolted connections by more than 50 percent of the lowest value.
    2. Minimum insulation-resistance values of transformer insulation shall be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, use Table 100.5. Values of insulation resistance less than this table or manufacturer’s recommendations should be investigated. The polarization index shall not be less than 1.0.
    3. The following values are typical for insulation power factor tests:
      1. CHL Power transformers: 2.0 percent or less
      2. CHL Distribution transformers: 5.0 percent or less
      3. CH and CL power-factor or dissipation-factor values will vary due to support insulators and bus work utilized on dry transformers. Consult transformer manufacturer’s or test equipment manufacturer’s data for additional information.
    4. Power-factor or dissipation-factor tip-up exceeding 1.0 percent shall be investigated.
    5. Turns-ratio test results shall not deviate more than one-half percent from either the adjacent coils or the calculated ratio.
    6. The typical excitation current test data pattern for a three-legged core transformer is two similar current readings and one lower current reading.
    7. Temperature-corrected winding-resistance values shall compare within one percent of previously-obtained results.
    8. Core insulation-resistance values shall not be less than one megohm at 500 volts dc.
    9. AC dielectric withstand test voltage shall not exceed 65 percent of factory test voltage for one minute duration. DC dielectric withstand test voltage shall not exceed 100 percent of the ac rms test voltage specified in IEEE C57.12.91, Section 10.2 for one minute duration. If no evidence of distress or insulation failure is observed by the end of the total time of voltage application during the dielectric withstand voltage test, the test specimen is considered to have passed the test.
    10. Phase-to-phase and phase-to-neutral secondary voltages shall be in agreement with nameplate data.
    11. Test results for surge arresters shall be in accordance with Section 7.19.
    12. Results of online partial-discharge survey should be in accordance with manufacturer’s published data. In the absence of manufacturer’s published data, refer to Table 100.23.
    NETA ATS / MTS
    TABLE 100.5
    Neta Table 100.5
    NETA ATS / MTS
    Neta Table 100.12.1
    Neta Table 100.12.2
    NETA ATS / MTS
    Neta Table 100.4.1
    Neta Table 100.4.2
    Neta Table 100.4.3
    Mineral Oil
    Low Info
    Moisture

    The ability of insulating oils, fluids, and gases to serve as effective dielectric and coolant is adversely affected by their deterioration.

    The deterioration of insulating oil, fluids, and gases is due to contamination, overheating, electrical stress, and oxidation.

    Moisture is the most common contaminant which adversely affects the insulating properties of these liquids and gases. High temperatures from increased load and/or environmental conditions accelerate the deterioration process.

    To assure service, safety, and maintenance, a condition monitoring program, consisting of electrical and chemical testing, is necessary for these dielectrics.

    Moisture

    Moisture contamination is the most common cause of deterioration in the insulating quality of oil. Water can be present in oil in a dissolved form, as tiny droplets mixed with the oil (emulsion), or in a free state at the bottom of the container holding the oil.

    Demulsifi cation occurs when the tiny droplets unite to form larger drops, which sink to the bottom and form a pool of free water. Water in the free state may be readily removed by fi ltering or centrifugal treatment. However, dissolved water is not removed by centrifugal treatment

    Oxidation

    Atmospheric oxygen and oxygen contained in water are the sources available for the oxidation of insulating oils. When water is present in insulating oils, oxidation of the oil will take place

    Transformer Types
    Low Voltage, Greater than 600V
    Askerels

    There has been a great increase in the use of less flammable liquids as an insulating and cooling medium in transformers. As these liquids are chemically different from mineral oils, they cannot be substituted in equipment designed for the use of mineral-oil type liquid. The NEC has officially designated these synthetic liquids as less flammable.

    There has been a great increase in the use of less flammable

    Askerels

    Moisture contamination is the most common cause of deterioration in the insulating quality of oil. Water can be present in oil in a dissolved form, as tiny droplets mixed with the oil (emulsion), or in a free state at the bottom of the container holding the oil.

    Demulsifi cation occurs when the tiny droplets

    Silicone

    Atmospheric oxygen and oxygen contained in water are the sources available for the oxidation of insulating oils. When water is present in insulating oils, oxidation of the oil will take place

    RTemp

    Atmospheric oxygen and oxygen contained in water are the sources available for the oxidation of insulating oils. When water is present in insulating oils, oxidation of the oil will take place

    Wecosol R113

    Atmospheric oxygen and oxygen contained in water are the sources available for the oxidation of insulating oils. When water is present in insulating oils, oxidation of the oil will take place

    envirotemp (FR-3)

    Atmospheric oxygen and oxygen contained in water are the sources available for the oxidation of insulating oils. When water is present in insulating oils, oxidation of the oil will take place

    Oil Sample Test

    Dielectric Breakdown Voltage:
    ASTM D 877 and/or ASTM D 1816

    Dielectric Breakdown Voltage Test (Cup Tests)

    AC overvoltage test applied to the insulating liquids to detect their breakdown strength.

    The dielectric test simply consists of placing a liquid sample from the transformer or (circuit breaker) in a cup containing two electrodes of specifi ed gap. High voltage is then applied to the sample. The test is repeated for a least fi ve different samples to determine the average dielectric strength.

    Fluid Range Result
    Mineral Oil Less Than 23KV
    Greater Than 23KV

    Acid Neutralization Number:
    ANSI/ASTM D 974

    The acid number of the neutralization number is the milligrams (mg) of potassium hydroxide (KOH) required to neutralize the acid contained in 1 g of transformer liquid. Test data indicate that the acidity is proportional to the amount of oxygen absorbed by the liquid.

    The acidity test measures the content of acids formed by oxidation. The acids are directly responsible for sludge formation. These acids precipitate out, as their concentration increases, and become sludge. They also react with metals to form another form of sludge in the transformer. The ASTM D974 and D664 are laboratory tests whereas D1534 is a field test which determines the approximate total acid value of the oil.

    ASTM D974 and D664 The ASTM D974 and D664 are laboratory tests whereas D1534 is a fi eld test which determines the approximate total acid value of the oil.

    Fluid Range Result
    Mineral Oil Less Than 0.4
    0.4 - 1.0
    Askerel Less Than 0.05
    Greater Than 0.5
    Silicone Less Than 0.01
    Greater Than 0.01
    RTemp Less Than 0.5
    Greater Than 0.5
    R113
    GE     		Less Than or equal 0.2
    Greater Than 0.2
    Wescol Less Than or equal 0.25
    Greater Than 0.25

    Specific Gravity:
    ANSI/ASTM D 1298

    Specific gravity of oil is defined as the ratio of the mass of a given volume of oil to the mass of an equal volume of oil of water at a specifi ed temperature. This test is conducted by fl oating a hydrometer in oil and taking the reading at the meniscus. For oil free of contaminants, such as water, askarel, or silicone, the reading should be less than 0.84.

    Fluid Range Result
    Mineral Oil Less Than 0.84
    Greater Than 0.84

    Interfacial Tension:
    ANSI/ASTM D 971

    1. The IFT test is employed as an indication of the sludging characteristics of power transformer insulating liquid

    2. determines conditions under which sludge may form, but does not necessarily indicate that actual sludging conditions exist.

    Fluid Range Result
    Mineral Oil Greater Than 40 dyn/cm
    less than 40 dyn/cm
    Askerel Greater Than 40 dyn/cm
    less than 40 dyn/cm
    Silicon Greater Than 28 dyn/cm
    less than 28 dyn/cm
    Envirotemp
    FR3     		Greater Than 30 dyn/cm
    less than 30 dyn/cm

    Color:
    ANSI/ASTM D1500

    1. The color chart ranges from 0.5 to 8

    2. Color number 1 represent new oil

    Fluid Range Result
    Mineral Oil Less than 3.5
    Greater than 3.5
    Fluid Range Result
    Askerel Less than 2
    Greater than 2
    Fluid Range Result
    Silicone Less than 15
    Greater than 15

    Visual Condition: ASTM D 1524Visual Condition: ASTM D 1524

    Water in Insulating Liquids:
    ASTM D 1533.

    Moisture (Karl Fischer method)

    Water content: The ASTM D1533 method can be used for the FR3 fl uid without modifi cation. If erratic or unusual results are observed while conducting this test, then use the Karl Fisher reagents for aldehydes and ketones instead of those used for mineral oil.

    Power Factor (Dissipation Factor) ASTM D 924
    ANSI/IEEE C57.104
    ASTM D3612.

    The power factor indicates the dielectric loss of the liquid and thus its dielectric heating. The power factor test is widely used as an acceptance and preventive maintenance test for insulating liquid.

    Liquid power factor testing in the field is usually done with portable, direct-reading power factor measuring test equipment, which is available from several companies, who provide this service. Power factor tests on oil and transformer liquids are commonly made with ASTM D-924 test cell.

    • Good new oil has a power factor of 0.05% or less at 20 C.
    • Higher power factors indicate deterioration and/or contamination with moisture, carbon or other conducting matter, varnish, glyptal, sodium soaps asphalt compounds, or deterioration products. Carbon or asphalt in oil can cause discoloration. Carbon in oil will not necessarily increase the power factor of the oil unless moisture is also present.
    Mineral Oil Less Than 0.5%
    Greater Than 0.5%

    Dissolved-Gas Analysis (DGA)
    ANSI/IEEE C57.104
    ASTM D3612.

    The DGA is the most informative method of detecting combustible gases. Although this is a laboratory method, it provides the earliest possible detection of any abnormal conditions in the transformer.