Directional Underpower Protection Guppdup (37); Identification; Application - ABB REB670 Applications Manual

1MRK 505 337-UUS -
7.8
7.8.1
7.8.2
Application manual

Directional underpower protection GUPPDUP (37)

Identification

Function description
Directional underpower protection

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.
IEC 61850 IEC 60617
identification identification
GUPPDUP
P <
2
SYMBOL-LL V2 EN
Section 7
Current protection
ANSI/IEEE C37.2
device number
37
209