Functions
2.17 Reverse Power Protection (ANSI 32R)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
145
2.17 Reverse Power Protection (ANSI 32R)
Reverse power protection is used to protect a turbo-generator unit on failure of energy to the prime mover when
the synchronous generator runs as a motor and drives the turbine taking motoring energy from the network.
This condition leads to overheating of the turbine blades and must be interrupted within a short time by tripping
the network circuit-breaker. For the generator, there is the additional risk that, in case of a malfunctioning re-
sidual steam pass (defective stop valves) after the switching off of the circuit breakers, the turbine-generator-
unit is speeded up, thus reaching an overspeed. For this reason, the system should only be disconnected after
active power input into the machine has been detected.
2.17.1 Functional Description
Reverse Power Determination
The reverse power protection of the 7UM62 precisely calculates the active power from the symmetrical com-
ponents of the fundamental waves of voltages and currents by averaging the values of the last 16 cycles. The
evaluation of only the positive phase-sequence systems makes the reverse power determination independent
of current and voltage asymmetries and corresponds to actual loading of the drive end. The calculated active
power value corresponds to the overall active power. By taking the error angles of the instrument transformers
into account, the active power component is exactly calculated even with very high apparent powers and low
power factor cos ϕ. The correction is performed by a W0 constant correction angle determined during commis-
sioning of the protection device in the system. The correction angle is set under Power System Data 1 (see
Section 2.5).
Pickup Seal-In Time
To ensure that frequently occurring short pickups can cause tripping, it is possible to perform a selectable pro-
longation of these pickup pulses at parameter 3105 T-HOLD. Each positive edge of the pickup pulses triggers
this time stage again. For a sufficient number of pulses, the pickup signals add up and become longer than the
time delay.
Trip Signal
For bridging a perhaps short power input during synchronization or during power swings caused by system
faults, the trip command is delayed by a selectable time T-SV-OPEN. In case of a closed emergency tripping
valve, a short delay is, however, sufficient. By means of entering the emergency tripping valve position via a
binary input, the short time delay T-SV-CLOSED becomes effective under an emergency tripping condition.
The time T-SV-OPEN is still effective as back-up stage.
It is also possible to block tripping via an external signal.
The following figure shows the logic diagram for the reverse power protection.
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