What is inverted running of an alternator? Whether any protection is required to prevent this condition?

Inverted Running of Generator - This condition can occur when there is a failure in the prime mover such as an engine or a turbine which drives the generator i.e. no fuel to gas turbine or diesel engine, no steam to steam turbine etc. and generator is still connected to the Power system. This leads to generator operating as MOTOR - motoring action. During the Motoring action of the generator the power flows from the busbars to the machine and this condition is called as REVERSE POWER.

This is prevented by the DIRECTIONAL protection called Reverse Power protection provided with Generators. A reverse power relay is a directional power relay that is used to monitor the power from a generator running in parallel with another generator or the utility. The function of the reverse power relay is to prevent a reverse power condition in which power flows from the bus bar into the generator. .

 

 

I agree with Ranvir. When the Prime mover steam is cut off the alternator starts to draw Power from the Grid and Starts to behave as a Motor. The speed of rotor can be controlled by varying amounts of steam input normally but in this case the rotor speed cannot be controlled and may lead to extensive damages in various parts of the Rotor (Bearings, Blades etc).

ANSI 32 – Directional Power Relay or Reverse Power Relay (also called anti-motoring protection) should be applied in this case.

If the input of prime mover is gradually restored the alternator will pick up the load without disturbing the system if the input failures likely to be prolonged machine can be safely isolated by the control room attendant When input to the prime mover fails the prime over most stops conservation of mechanical energy into electrical energy if the alternator work in parallel with other alternators then it will start working as a synchronous motor running at a synchronous speed this motoring conditions is known as inverting running

When Input supplies to Alternator fails the Alternator Start Running as Motor or Rather Synchronous Motor so Instead delivering Power to the System it will Draw the Power/Current from the System Supply but keeps on rotating.This rotating Effect of Alternator is known as INVERTED RUNNING.Differential Protections can be used in such Conditions.