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Protective Relays

NEC Requirements and UL Standards

The National Electric Code 225.56 Inspections and Tests.

  1. Article 225.56(A) Pre-Energization and Operating Tests

    2. The complete electrical system design, including settings for protective, switching, and control circuits, shall be prepared in advance and made available on request to the authority having jurisdiction and shall be performance tested when first installed on-site. Each protective, switching, and control circuit shall be adjusted in accordance with the system design and tested by actual operation using current injection or equivalent methods as necessary to ensure that each and every such circuit operates correctly to the satisfaction of the authority having jurisdiction.

  2. Article 225.56(A)(2) Protective Relays.

    3. Each protective relay shall be demonstrated to operate by injecting current or voltage, or both, at the associated instrument transformer output terminal and observing that the associated switching and signaling functions occur correctly and in proper time and sequence to accomplish the protective function intended.

NETA Test Procedure

NETA ATS

7.9.1 Protective Relays, Electromechanical and Solid-State

A. Visual and Mechanical Inspection:
  1. Compare equipment nameplate data with drawings and specifications.
  2. Inspect relays and cases for physical damage. Remove shipping restraint material.
  3. Verify the unit is clean.
  4. Inspect the unit.
    1. Relay Case
      1. Tighten case connections.
      2. Inspect cover for correct gasket seal.
      3. Inspect shorting hardware, connection paddles, and knife switches.
      4. Remove any foreign material from the case.
      5. Verify target reset.
      6. Clean cover glass.
    2. Relay
      1. Inspect relay for foreign material, particularly in disk slots of the damping and electromagnets.
      2. Verify disk clearance. Verify contact clearance and spring bias.
      3. Inspect spiral spring convolutions.
      4. Inspect disk and contacts for freedom of movement and correct travel.
      5. Verify tightness of mounting hardware and connections.
      6. Burnish contacts.
      7. Inspect bearings and pivots.
  5. Verify that all settings are in accordance with coordination study or setting sheet supplied by owner.
B. Electrical Tests:
  1. Perform an insulation-resistance test on each circuit-to-frame. Procedures for performing insulation-resistance tests on solid-state relays shall be determined from the relay manufacturer’s published data.
  2. Test targets and indicators.
      1. Determine pickup and dropout of electromechanical targets.
      2. Verify operation of all light-emitting diode indicators.
      3. Set contrast for liquid-crystal display readouts.
  3. Protection Elements
    1. 2/62 Timing Relay
      1. Determine time delay.
      2. Verify operation of instantaneous contacts.
    2. 21 Distance Relay
      1. Determine maximum reach.
      2. Determine maximum torque angle and directional characteristic.
      3. Determine offset.
      4. Plot impedance circle.
    3. 24 Volts/Hertz Relay
      1. Determine pickup frequency at rated voltage.
      2. Determine pickup frequency at a second voltage level.
      3. Determine time delay.
    4. 25 Sync Check Relay
      1. Determine closing zone at rated voltage.
      2. Determine maximum voltage differential that permits closing at zero degrees.
      3. Determine live line, live bus, dead line, and dead bus set points.
      4. Determine time delay.
      5. Determine advanced closing angle.
      6. Verify dead bus/live line, dead line/live bus and dead bus/dead line control functions.
    5. 27 Undervoltage Relay
      1. Determine dropout voltage.
      2. Determine time delay.
      3. Determine time delay at a second point on the timing curve for inverse time relays.
    6. 32 Directional Power Relay
      1. Determine minimum pickup at maximum torque angle.
      2. Determine tripping zone.
      3. Determine maximum torque angle.
      4. Determine time delay.
      5. Verify time delay at a second point on the timing curve for inverse time relays.
      6. Plot the operating characteristic.
    7. 40 Loss of Field (Impedance) Relay
      1. Determine maximum reach.
      2. Determine maximum torque angle.
      3. Determine offset.
      4. Plot impedance circle.
    8. 46 Current Balance Relay
      1. Determine pickup of each unit.
      2. Determine percent slope.
      3. Determine time delay.
    9. 46N Negative Sequence Current Relay
      1. Determine negative sequence alarm level.
      2. Determine negative sequence minimum trip level.
      3. Determine maximum time delay.
      4. Verify two points on the (I2)2t curve.
    10. 47 Phase Sequence or Phase Balance Voltage Relay
      1. Determine positive sequence voltage to close the normally open contact.
      2. Determine positive sequence voltage to open the normally closed contact (undervoltage trip).
      3. Verify negative sequence trip.
      4. Determine time delay to close the normally open contact with sudden application of 120 percent of pickup.
      5. Determine time delay to close the normally closed contact upon removal of voltage when previously set to rated system voltage.
    11. 49R Thermal Replica Relay
      1. Determine time delay at 300 percent of setting.
      2. Determine a second point on the operating curve.
      3. Determine pickup.
    12. 49T Temperature (RTD) Relay
      1. Determine trip resistance.
      2. Determine reset resistance.
    13. 50 Instantaneous Overcurrent Relay
      1. Determine pickup.
      2. Determine dropout.
      3. Determine time delay.
    14. 50BF Breaker Failure
      1. Determine current supervision pickup.
      2. Determine time delays.
      3. Test all inputs and outputs.
    15. 55 Power Factor Relay
      1. Determine tripping angle.
      2. Determine time delay.
    16. 59 Overvoltage Relay
      1. Determine overvoltage pickup.
      2. Determine time delay to close the contact with sudden application of 120 percent of pickup.
    17. 63 Transformer Sudden Pressure Relay
      1. Determine rate-of-rise or the pickup level of suddenly applied pressure in accordance with manufacturer’s published data.
      2. Verify operation of the 63 FPX seal-in circuit.
      3. Verify trip circuit to remote operating device.
    18. 64 Ground Detector Relay
      1. Determine maximum impedance to ground causing relay pickup.
    19. 67 Directional Overcurrent Relay
      1. Determine directional unit minimum pickup at maximum torque angle.
      2. Determine tripping zone.
      3. Determine maximum torque angle.
      4. Plot operating characteristics.
      5. Determine overcurrent unit pickup.
      6. Determine overcurrent unit time delay at two points on the time current curve.
    20. 79 Reclosing Relay
      1. Determine time delay for each programmed reclosing interval.
      2. Verify lockout for unsuccessful reclosing.
      3. Determine reset time.
      4. Determine close pulse duration.
      5. Verify instantaneous overcurrent lockout.
    21. 81 Frequency Relay
      1. Verify frequency set points.
      2. Determine time delay.
      3. Determine undervoltage cutoff.
    22. 85 Pilot Wire Monitor
      1. Determine overcurrent pickup.
      2. Determine undercurrent pickup.
      3. Determine pilot wire ground pickup level.
    23. 87 Differential
      1. Determine operating unit pickup.
      2. Determine the operation of each restraint unit.
      3. Determine slope.
      4. Determine harmonic restraint.
      5. Determine instantaneous pickup.
      6. Plot operating characteristics for each restraint.
    24. Control Verification/Functional Tests

      25. Verify that each of the relay contacts performs its intended function in the control scheme including breaker trip tests, close inhibit tests, 86 lockout tests, and alarm functions. Refer to Section 8.

C. Test Values – Visual and Mechanical
  1. Relay Case
    1. Case connections shall be torqued in accordance with manufacturer’s published data. (7.9.1.A.4.1.1
    2. Cover gasket shall be intact and able to prevent foreign matter from entering the case. (7.9.1.A.4.1.2)
    3. Cover glass, connection paddles, and/or knife switches shall be clean. (7.9.1.A.4.1.3)
    4. Case shall be free of foreign material. (7.9.1.A.4.1.4)
    5. The target reset shall be operational. (7.9.1.A.4.1.5)
  2. Relay
    1. Relay shall be free of foreign material. (7.9.1.A.4.2.1)
    2. Relay disc clearance, contact clearance, and spring bias shall operate in accordance with manufacturer’s published data. (7.9.1.A.4.2.2)
    3. Relay spiral spring shall be concentric. (7.9.1.A.4.2.3)
    4. Relay discs and contacts shall have freedom of movement and correct travel distance in accordance with manufacturer’s published data. (7.9.1.A.4.2.4)
    5. Mounting hardware and connections shall be tightened to the manufacturer’s recommended torque values. (7.9.1.A.4.2.5)
    6. Contacts shall be clean and make good contact with each other. (7.9.1.A.4.2.6)
    7. Bearings and pivots shall have clean and fluid movement. (7.9.1.A.4.2.7)
  3. Relay settings shall match the coordination study or setting sheet supplied by owner. (7.9.1.A.5)
D. Test Values – Electrical
  1. Relay Case
    1. Insulation-resistance values shall be in accordance with manufacturer’s published data. Values of insulation resistance less than the manufacturer’s recommendations shall be investigated.
    2. Targets and Indicators
      1. Pickup and dropout of electromechanical targets shall be in accordance with manufacturer’s published data.
      2. Light-emitting diodes shall illuminate.
    3. Operation of protection elements for devices listed in Section 7.9.1.B, one through 25, shall be calibrated using manufacturer’s recommended tolerances unless critical test points are specified by the setting engineer.
    4. Control Verification
      1. Control verification outputs and protection schemes, as listed in Section 7.9.1.B.4, shall operate as per the design. Results shall be within the manufacturer’s published tolerances.
      2. When critical test points are specified, the relay shall be calibrated to those points even though other test points may be out of tolerance.

NETA MTS

7.9.2 Protective Relays, Microprocessor-Based

A. Visual and Mechanical Inspection:
  1. Record model number, style number, serial number, firmware revision, software revision, and rated control voltage.
  2. Verify operation of light-emitting diodes, display, and targets.
  3. Record passwords for all access levels.
  4. Clean the front panel and remove foreign material from the case.
  5. Check tightness of connections.
  6. Verify that the frame is grounded in accordance with manufacturer’s instructions.
  7. Set the relay in accordance with the engineered setting file and coordination study.
  8. Download settings and logic from the relay and compare the settings to those specified in the coordination study or setting sheet supplied by owner.
  9. Connect backup battery.
  10. Set clock if not controlled externally and verify relay displays the correct date and time.
  11. Check with setting engineer for applicable firmware updates and product recalls.
  12. Inspect, clean, and verify operation of shorting devices.
B. Electrical Tests
  1. Perform insulation-resistance tests from each circuit to the grounded frame in accordance with manufacturer’s published data.
  2. Apply voltage or current to all analog inputs and verify correct registration of the relay meter functions.
  3. Verify SCADA metering values at remote terminals.
  4. Protection Elements

    5. Check functional operation of each element used in the protection scheme as described for electromechanical and solid-state relays in 7.9.1.B.3. When not otherwise specified, use manufacturer’s recommended tolerances.

  5. Control Verification
    1. Check operation of all active digital inputs.
    2. Check all output contacts or SCRs, preferably by operating the controlled device such as circuit breaker, auxiliary relay, or alarm.
    3. Check all internal logic functions used in the protection scheme.
    4. For pilot schemes, perform a loop-back test to check the receive and transmit communication circuits.
    5. Upon completion of testing, reset all min/max records and fault counters. Delete sequence-of-events records and all event records.
    6. Verify trip and close coil monitoring functions.
    7. Verify setting change alarm to SCADA.
    8. Verify relay SCADA communication and indications such as protection operate, protection fail, communication fail, fault recorder trigger.
    9. Verify all communication links are operational.
C. Test Values – Visual and Mechanical
  1. Light-emitting diodes, displays, and targets should illuminate. (7.9.2.A.2)
  2. Relay should be clean and operational. (7.9.2.A.4)
  3. Settings and logic should agree with the most recent engineered setting files. (7.9.2.A.8)
  4. Verify relay displays the correct date and time. (7.9.2.A.10)
D. Test Values – Electrical
  1. Insulation-resistance values should be in accordance with manufacturer’s published data. Values of insulation resistance less than manufacturer’s recommendations should be investigated.
  2. Voltage and current analog readings should be in accordance with manufacturer’s published tolerances.
  3. SCADA readings should be within the manufacturer’s published tolerances.
  4. Operation of protection elements for devices as listed in 7.9.1.B, items 1 through 25, should be operational and within manufacturer’s recommended tolerances.
  5. Control verification inputs, outputs, and protection schemes, as listed in 7.9.2.B.5, items 1 through 9, should operate as per the design. Results should be within the manufacturer’s published tolerances.
NETA ATS / MTS
Neta Table 100.1
NETA ATS / MTS
Neta Table 100.12
Neta Table 100.12
Protection Functions
apple watch
Basics:
Buff Boof IEEE
15.2.1 Short-circuit currents:

When performing a coordination study, some or all of the following information on shortcircuit currents for each local bus may be necessary:

  1. Maximum and minimum momentary (first cycle) single- and three-phase short-circuit current

    2. The momentary currents are used to determine the maximum and minimum currents to which instantaneous and direct-acting trip devices respond.

  2. Maximum and minimum interrupting duty (1.5 cycles to 8 cycles) three-phase shortcircuit current

    3. The maximum interrupting current is the value at which the circuit protection device coordination time interval (CTI) is most often established. This practice results in conservative CTis for all values of short-circuit current. The minimum interrupting current is needed to determine whether the circuit protection sensitivity is adequate.

  3. Maximum and minimum 30-cycle three-phase short-circuit current

    4. The 30-cycle fault currents (no motor contribution) may be used to set the CTI for timeovercurrent protective devices in the system. By the time these protective devices operate, the motor contribution to the fault current will have decayed to zero or to minimal levels. Many short-circuit calculation programs also have the capability of calculating the current flow to and from a bus. The actual fault current flowing through the protective device should be used for coordination. In addition, it may be necessary to obtain the XIR ratios applicable to singleand three-phase short-circuit currents.

  4. Maximum and minimum ground-fault current

    5. Maximum and minimum Ground fault current Maximum short-circuit currents are important because they are the upper current limits for the protective device characteristic curve to be plotted. the protective device should never have to operate above this current level.

6.3.2 Phase instantaneous overcurrent

Primary-side instantaneous phase overcurrent elements (50) provide high-speed primary protection for internal phase faults. These elements should trip the transformer high-side breaker and/or the transformer lockout relay.

Fast clearing of severe internal faults may be obtained through the use of instantaneous overcurrent units. When used, instantaneous overcurrent units should be set to pick up at a value higher than the maximum asymmetrical through-fault current. This is usually the fault current through the transformer for a low-side three-phase fault.

For instantaneous units subject to transient overreach, a pickup of 175% (variations in settings of 125–200% are common) of the calculated maximum low-side three-phase symmetrical fault current generally provides sufficient margin to avoid false tripping for a low-side bus fault, while still providing protection for severe internal faults. For instantaneous units with negligible transient overreach, a lesser margin can be used. The settings in either case should also be above the transformer inrush current to prevent nuisance tripping.

In some cases, instantaneous trip relays cannot be used because the necessary settings are greater than the available fault currents. In these cases, a harmonic restraint instantaneous relay may be considered to provide the desired protection.

The pickup current IPU for a phase overcurrent device must be set at a value larger than the maximum load current IML and lower than the minimum phase-to-phase fault current IFpp.

Ground Fault Overcurrent Protection (50/51)

Relay Ground Fault setting A ground relay must ‘see’ all phase-to-ground faults within its zone of protection, and under conditions which give a minimum fault current. Note that in calculating ground current it is the zero-sequence current that is of interest. (Ground current = 3I0.) There is no concern for load current, but normal phase and load unbalance and CT errors must be considered and the relays set above these values. Again, setting between twice the ‘normal’ ground current and a third of the minimum fault value is desirable. In the absence of any other information, the normal ground current may be taken to be 10% of the load current. 2x normal ground current < Igf (PU) < 1/3x I fault (min)

Maximum and minimum Ground fault current Maximum short-circuit currents are important because they are the upper current limits for the protective device characteristic curve to be plotted. the protective device should never have to operate above this current level.