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Join Date: Sep 2008
Posts: 1

Reverse power to Generator

09/03/2008 10:13 AM

If a generator gets reverse power, will it move in opposite direction to prime mover? What other effects can be? Can it burn the winding as well? Thanks.

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United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
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Re: Reverse power to Generator

09/03/2008 10:49 AM

<...a generator gets reverse power...>

Does this mean,

  1. "a spinning generator is inadvertently connected to a supply where the phase rotation is the reverse of that coming out of this one", or
  2. "A stationary generator is inadvertently connected to an energised supply that might be used to turn it"?

If the equipment is correctly protected, item 1 will cause the circuit protective devices to operate.

"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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Engineering Fields - Marine Engineering - New Member

Join Date: May 2007
Location: Australia.
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Re: Reverse power to Generator

09/03/2008 8:43 PM

The normal way of of disconnecting a generator from the system is by the use of the reverse power protection relay, this is to prevent over speeding, the governing valves are controlling at a speed below normal operating speed. As to what will happen with regard to the generator, it will be driven by the system and act as a synchronous capacitor affecting the system voltage, the amount depending on excitation, Also as the steam flow has dropped to zero, there is what they call windage in the LP blading that can cause damage if it persists. Getting rusty on the subject but I think this answers your question.

Regards JD.

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Active Contributor

Join Date: Sep 2008
Location: Lusaka, Zambia
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Re: Reverse power to Generator

09/05/2008 5:11 AM

A generator will experience reverse power ( drawing ACTIVE power from the grid) in the event of failure of the prime mover. It will continue in same direction of normal operation and protection is mainly employed to prevent damage to machanical plant items associated with the prime mover. Specifically, a diesel engine is at risk of fire or explosion because of un-burnt fuel in the engine as it continues rotating, gas turbines risk gearbox damage, and hydro plants risk cavitation of the runner and blades when rotating in little or no water. Electrically, the winding is not at risk of burning because the current due to reverse power is a fraction of the nominal current of the unit (which can draw large magnitudes of reactive current in some modes of operation).

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Join Date: Jul 2008
Location: Anywhere I may be at the time
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Re: Reverse power to Generator

09/07/2008 9:00 AM

To sum it up in laymens terms, your generator is a motor driving your prime mover (engine). This is no good for anything engine, generator, control circut, etc.

"Reverse Power" has the entire generator skid running in REVERSE. I have seen some small units (Detroit Diesel) actualy be running in reverse power, smoke comming from the air cleaner becouse of there 2 cycle design. Believe it or not, the engine was stopped, re started and just put back on line with no damage.

This is not the norm, especialy when dealing with a larger unit.

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Anonymous Poster

Re: Reverse power to Generator

09/12/2008 11:18 PM

No the prime movr will not turn in reverse direction. The reverse power protection device (reverse power relay) is a current detection device. Instead of "generating" or pushing power out from the generator the current is absorbed toward the alternator, just like turning an electric motor....a very expensive way of turning an engine oro the like.

Sum: A current DIRETION alternator protection device.

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Anonymous Poster

Re: Reverse power to Generator

03/01/2010 5:22 PM

reverse power will occur for the generator due to the decreasing of the fuel required for the gas turbine to build up the required mechanical torque to maintain the generator on grid which cause the active power to be deleiverd from grid to the generator.

the effect of the reverse power is the motorizing the genewator which may affect the mechanical parts of the turbine.

on other hand if the generator excitation system is not ok this will cause damaging for the gen and overheating for rotor.

so this must be protected via the turbine protection and generator protection and the coordination should be done between the both protections.


Eng.Abd Elaziz Taman

Egfypt,Nubaria Power Station

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