Reverse Power Protection Working Principle -32R

Reverse Power Protection Working Principle 32R:

Reverse power protection is the most Predominate protection in generator/alternator protection. It is used to protect the alternator/generator from motoring action when the turbine failed to give mechanical power. It is a backup protection to the low forward protection.

Why Reverse Power protection is Important?

When the current entering into the generator winding from the grid, the generator act as an induction motor. The generator stars rotating in the direction of the turbine. Here the generator takes high input current as to rotate his heavy rotor. Therefore, the rotor current starts flowing in the rotor coils. But the rotor coils end with the RRA (Rotating Rectifier assembly). Due to the diode property, the diode blocks the reverse current which generated in the rotor. This current is larger than the diode reverse breaking current. Hence the diode might be damaged. To avoid this, the reverse power protection time delay should be carefully set.

Reverse Power protection working principle:

Upon the reduced turbine output, typically, the generator is not able to produce the output power less than no-load losses while the generator is still on-line, the generator will operate as a motor and driving the turbine. This current reversal detected by the reverse power relay. The relay trips the generator circuit breaker.

reverse power protection
reverse power protection

Reason for Reverse Power:

  • Turbine output is lesser than the generator no load losses.
  • CT connection reversal.

ANSI code for Reverse power protection: 32R

Relays acted:

  • 32R Flag operation at Protection panel.
  • 86M Gen Master Trip Relay Opted

Restart the machine and increase the input power to the turbine as quickly as possible within low forward power time setting. Even after two to three attempts, the machine is tripping on the same protection; probably the governor of turbine is faulty. Inform to maintenance staff for rectification of the same.

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