Table of Contents
Advertisement
2.12
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 with a mal-
functioning residual steam pass (defective stop valves) after the switching off of the
circuit breaker the turbine generator unit is accelerated to overspeed. For this reason,
the system isolation should only be performed after the detection of active power input
into the machine.
2.12.1 Function Description
Reverse Power De-
The reverse power protection of the 7UM61 precisely calculates the active power from
termination
the symmetrical components 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 cal-
culated 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
commissioning of the protection device in the system. The correction angle is set
under Power System Data 1 (see Section 2.3).
Pickup Seal-In Time
To ensure that frequently occurring short pickups can cause tripping, it is possible to
perform a selectable prolongation 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 adds up and become longer than the time delay.
Trip Signal
For bridging a perhaps short power input during synchronisation 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 trip-
ping 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.
7UM61 Manual
C53000-G1176-C127-3
2.12 Reverse Power Protection (ANSI 32R)
85
Advertisement
Table of Contents
