P&B protection relays tested and repaired. 48V versions converted to 24V

EPS recently converted some P&B protection relays from 48V to 24V on behalf of our customer. This allowed them to use some of their other spare/redundant equipment to keep other items up and running.

The OEM no longer repair or support this model of P&B protection relays however we were able to test and repair a number different types.

EPS can repair & test many types of control boards. Get in touch to see if we can help you

P&B protection relays

P&B protection relays are crucial for safeguarding generators from faults and abnormal conditions. It continuously monitors the generator’s operating conditions and disconnects it from the system in case of any harmful issues. Thhe key protection functions typically provided by P&B protection relays are:

1. Overcurrent Protection (50/51)

  • 50 (Instantaneous Overcurrent): Protects against short-circuits or high-magnitude faults that occur instantaneously.
  • 51 (Time-Delayed Overcurrent): Protects against longer-duration overcurrent conditions, such as overloads.

2. Differential Protection (87G)

  • Detects internal faults (like short circuits) in the stator winding by comparing current entering and leaving the generator. If there’s a significant mismatch, it trips the generator.

3. Overvoltage Protection (59)

  • Protects against excessive voltage, which can damage insulation or lead to instability. It trips the generator if voltage exceeds the safe limit.

4. Under/Overfrequency Protection (81U/81O)

  • Underfrequency (81U): Protects the generator from operating at a frequency lower than the system frequency (which can be caused by a load surge or generation shortage).
  • Overfrequency (81O): Protects against frequencies higher than the rated frequency, which can occur due to load shedding.

5. Reverse Power Protection (32)

  • Protects the generator from motoring, which occurs when the prime mover fails, and the generator draws power instead of supplying it. This is essential in avoiding mechanical damage to the turbine or prime mover.

6. Loss of Excitation Protection (40)

  • Detects the loss of excitation in the generator. Without proper excitation, a generator can fall out of synchronism with the grid, leading to system instability.

7. Overload Protection (49)

  • Protects the generator from prolonged overload conditions by monitoring the temperature of the stator windings and initiating a trip if overheating occurs.

8. Negative Sequence Protection (46)

  • Detects unbalanced load conditions, which can lead to rotor heating. Negative sequence currents can cause severe damage to the generator rotor, so this function trips the generator if these currents exceed safe levels.

9. Overexcitation Protection (24)

  • Protects against high levels of excitation that cause the voltage to rise above the permissible limit, leading to core saturation and overheating.

10. Out-of-Step (Pole Slipping) Protection (78)

  • Protects the generator from falling out of step (losing synchronism with the grid), which can occur due to power swings or disturbances.

11. Stator Earth Fault Protection (64G)

  • Detects ground faults in the stator winding of the generator, protecting it from damage due to insulation failure or short circuits to ground.

12. Over/Under Voltage Protection (27/59)

  • Undervoltage (27): Protects against voltages below a certain threshold, which could indicate a system disturbance or failure.
  • Overvoltage (59): Prevents high voltages that may occur due to sudden disconnection of large loads or regulator malfunction.

13. Rotor Earth Fault Protection (64R)

  • Protects against ground faults in the rotor winding. This is essential to detect insulation breakdowns in the rotor, which could otherwise lead to significant generator damage.

14. Rate of Change of Frequency (ROCOF, 81R)

  • Protects against sudden changes in system frequency, which could indicate a major disturbance, islanding, or load shedding event.

15. Voltage-Reactive Power (V/Hz) Protection (24)

  • Protects the generator from overexcitation by monitoring the ratio of voltage to frequency (V/Hz). If it exceeds the permissible limit, the relay trips the generator.

Ensuring your P&B protection relays are checked frequently is important in maintaining the integrity of your system.

Having spare P&B protection relays helps you maintain your operation uptime.

  • P&B protection relays