Directional Underpower Protection Guppdup; Identification; Application - ABB Relion REC670 Applications Manual

1MRK 511 358-UEN A
CurrSel : Operation of the current based pole discordance protection. Can be set: Off / CB oper
monitor / Continuous monitor . In the alternative CB oper monitor the function is activated only
directly in connection to breaker open or close command (during 200 ms). In the alternative
Continuous monitor function is continuously activated.
CurrUnsymLevel : Unsymmetrical magnitude of lowest phase current compared to the highest,
set in % of the highest phase current. Natural difference between phase currents in 1 1/2
breaker installations must be considered. For circuit breakers in 1 1/2 breaker configured
switch yards there might be natural unbalance currents through the breaker. This is due to the
existence of low impedance current paths in the switch yard. This phenomenon must be
considered in the setting of the parameter.
CurrRelLevel : Current magnitude for release of the function in % of IBase .
7.12

Directional underpower protection GUPPDUP

7.12.1

Identification

Function description
Directional underpower protection
7.12.2

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.
Application manual
IEC 61850 IEC 60617
identification identification
GUPPDUP
P <
2
SYMBOL-LL V2 EN-US
Section 7
Current protection
SEMOD156693-1 v4
SEMOD158941-2 v4
ANSI/IEEE C37.2
device number
37
SEMOD151283-4 v5
153