Low foreword power protection

TSURESH,

Since you put this question in the Power Generation community, I'm going to presume you are referring to a protective relay on a generator set.

Low <b>forward</b> power relay is quite often used to describe what is more commonly referred to as 'reverse power' relay.

The primary purpose of the reverse power relay is to prevent motoring or motorizing a generator when the energy flow-rate into the generator's prime mover (turbine; reciprocating engine; etc.) is less than required to keep the generator rotor spinning at synchronous speed.

Motoring or motorizing a generator doesn't really hurt the generator--but when the generator becomes a motor (which is what happens when "reverse" current flows in the generator stator windings) can be very destructive to the prime mover (a turbine or reciprocating engine). The generator, when motoring with current from the grid, is spinning the prime mover--and some prime movers do NOT handle being spun very well!

Some prime mover/generator sets have the reverse power relay set at a slight "positive" power so prevent any reverse power or motoring of the generator and to protect the prime mover against being spun by a motorized generator.

Remember: there is virtually no difference between a motor and a generator. A motor is a device for converting amperes into torque, and a generator is a device for converting torque into amperes. If there is insufficient torque being provided by a prime mover to a generator to keep it spinning at least at synchronous speed (zero power) then current will flow into the generator from the grid to keep the generator rotor spinning at synchronous speed--and will spin the prime mover, too.

Some motors, like elevator motors in tall buildings, can become generators--such as when the elevator car is being lowered. The motor drive actually converts the amperes generated by the motor as it's trying to control the speed of the elevator car as it's "falling" down the elevator shaft. This is called "dynamic braking" but what's really happening is that the motor is being used as a generator and that limits the speed of the elevator car as it's "falling" (being lowered). Electric automobiles also employ dynamic braking to convert the drive motors to generators during braking to help charge the drive battery.

Hope this helps! If this isn't what you were looking for, please clarify your post by telling us about the application of the low forward power relay you are trying to learn more about.
 
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