ABB Relion 670 Series Applications Manual page 162

Section 8
Current protection
IMagComp5, IMagComp30, IMagComp100
VMagComp5, VMagComp30, VMagComp100
IMagComp5, IMagComp30, IMagComp100
The angle compensation is given as difference between current and voltage angle errors.
The values are given for operating points 5, 30 and 100% of rated current/voltage. The values
should be available from instrument transformer test protocols.
8.7 Directional overpower protection GOPPDOP (32)
8.7.1 Identification
Function description
Directional overpower protection
8.7.2 Application
The task of a generator in a power plant is to convert mechanical energy available as a torque on a
rotating shaft to electric energy.
Sometimes, the mechanical power from a prime mover may decrease so much that it does not
cover bearing losses and ventilation losses. Then, the synchronous generator becomes a
synchronous motor and starts to take electric power from the rest of the power system. This
operating state, where individual synchronous machines operate as motors, implies no risk for the
machine itself. If the generator under consideration is very large and if it consumes lots of electric
power, it may be desirable to disconnect it to ease the task for the rest of the power system.
Often, the motoring condition may imply that the turbine is in a very dangerous state. The task of
the reverse power protection is to protect the turbine and not to protect the generator itself.
Steam turbines easily become overheated if the steam flow becomes too low or if the steam
ceases to flow through the turbine. Therefore, turbo-generators should have reverse power
protection. There are several contingencies that may cause reverse power: break of a main steam
pipe, damage to one or more blades in the steam turbine or inadvertent closing of the main stop
valves. In the last case, it is highly desirable to have a reliable reverse power protection. It may
prevent damage to an otherwise undamaged plant.
During the routine shutdown of many thermal power units, the reverse power protection gives the
tripping impulse to the generator breaker (the unit breaker). By doing so, one prevents the
disconnection of the unit before the mechanical power has become zero. Earlier disconnection
would cause an acceleration of the turbine generator at all routine shutdowns. This should have
caused overspeed and high centrifugal stresses.
156
IEC 61850
identification
GOPPDOP
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IEC 60617 ANSI/IEEE C37.2
identification device number
32
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