The magnitude of the injected voltage signal is measured on
the secondary side of the neutral point voltage transformer or
grounding transformer. In addition, the resulting injected
current is measured through a resistive shunt located within
the injection box. These two measured values are fed to the
IED. Based on these two measured quantities, the IED
determines the stator winding resistance to ground. The
resistance value is then compared with the preset fault
resistance alarm and trip levels.
The protection function can not only detect the earth fault at
the generator star point, but also along the stator windings
and at the generator terminals, including the connected
components such as voltage transformers, circuit breakers,
excitation transformer and so on. The measuring principle
used is not influenced by the generator operating mode and
is fully functional even with the generator at standstill. It is still
required to have a standard 95% stator earth-fault protection,
based on the neutral point fundamental frequency
displacement voltage, operating in parallel with the 100%
stator earth-fault protection function.
Requires injection unit REX060 and optional shunt resistor
unit REX062 for correct operation.
Underimpedance protection for generators and transformers
ZGVPDIS
GUID-5D0E6F04-8B60-4F12-8DA6-7043BE09A3CC v5
The under impedance protection is a three zone full scheme
impedance protection using offset mho characteristics for
detecting faults in the generator, generator-transformer and
transmission system. The three zones have fully independent
measuring loops and settings. The functionality also
comprises an under voltage seal-in feature to ensure issuing
of a trip even if the current transformer goes into saturation
and, in addition, the positive-sequence-based load
encroachment feature for the second and the third
impedance zone. Built-in compensation for the step-up
transformer vector group connection is available.
5. Current protection
Instantaneous phase overcurrent protection PHPIOC
M12910-3 v12
The instantaneous three phase overcurrent function has a low
transient overreach and short tripping time to allow use as a
high set short-circuit protection function.
Four-step phase overcurrent protection OC4PTOC
M12846-3 v16
The four step three-phase overcurrent protection function
OC4PTOC has an inverse or definite time delay independent
for step 1 to 4 separately.
All IEC and ANSI inverse time characteristics are available
together with an optional user defined time characteristic.
The directional function needs voltage as it is voltage
polarized with memory. The function can be set to be
directional or non-directional independently for each of the
steps.
A second harmonic blocking level can be set for the function
and can be used to block each step individually.
Instantaneous residual overcurrent protection EFPIOC
M12701-3 v14
The Instantaneous residual overcurrent protection EFPIOC
has a low transient overreach and short tripping times to
allow the use for instantaneous earth-fault protection, with the
reach limited to less than the typical eighty percent of the line
at minimum source impedance. EFPIOC is configured to
measure the residual current from the three-phase current
inputs and can be configured to measure the current from a
separate current input.
Four step residual overcurrent protection, zero sequence and
negative sequence direction EF4PTOC
M13667-3 v18
The four step residual overcurrent protection EF4PTOC has
an inverse or definite time delay independent for each step.
All IEC and ANSI time-delayed characteristics are available
together with an optional user defined characteristic.
EF4PTOC can be set directional or non-directional
independently for each of the steps.
IDir, UPol and IPol can be independently selected to be either
zero sequence or negative sequence.
Second harmonic blocking can be set individually for each
step.
EF4PTOC can be used as main protection for phase-to-earth
faults.
EF4PTOC can also be used to provide a system back-up for
example, in the case of the primary protection being out of
service due to communication or voltage transformer circuit
failure.
Directional operation can be combined together with
corresponding communication logic in permissive or blocking
teleprotection scheme. Current reversal and weak-end infeed
functionality are available as well.
Residual current can be calculated by summing the three
phase currents or taking the input from neutral CT
Four step negative sequence overcurrent protection
NS4PTOC
GUID-485E9D36-0032-4559-9204-101539A32F47 v5
Four step negative sequence overcurrent protection
(NS4PTOC) has an inverse or definite time delay independent
for each step separately.
All IEC and ANSI time delayed characteristics are available
together with an optional user defined characteristic.
The directional function is voltage polarized.
NS4PTOC can be set directional or non-directional
independently for each of the steps.
1MRK 502 068-BEN D
Generator protection REG670 2.1 IEC
Product version: 2.1
ABB
21
