ABB RELION 670 Series Product Manual page 27

Bay control REC670 2.1 IEC
triggers the individual event timer, which is the
continuous time spent within the given frequency band,
and the accumulation timer, which is the cumulative
time spent within the given frequency band. Once the
timers reach their limit, an alarm or trip signal is
activated to protect the turbine against the abnormal
frequency operation. This function is blocked during
generator start-up or shut down conditions by
monitoring the circuit breaker position and current
threshold value. The function is also blocked when the
system positive sequence voltage magnitude deviates
from the given voltage band limit which can be enabled
by EnaVoltCheck setting.
It is possible to create functionality with more than one
frequency band limit by using multiple instances of the
function. This can be achieved by a proper configuration
based on the turbine manufacturer specification.
8. Multipurpose protection
General current and voltage protection CVGAPC
The General current and voltage protection (CVGAPC)
can be utilized as a negative sequence current
protection detecting unsymmetrical conditions such as
open phase or unsymmetrical faults.
CVGAPC can also be used to improve phase selection for
high resistive earth faults, outside the distance
protection reach, for the transmission line. Three
functions are used, which measures the neutral current
and each of the three phase voltages. This will give an
independence from load currents and this phase
selection will be used in conjunction with the detection
of the earth fault from the directional earth fault
protection function.
Voltage-restrained time overcurrent protection
VRPVOC
Voltage-restrained time overcurrent protection
(VRPVOC) function can be used as generator backup
protection against short-circuits.
The overcurrent protection feature has a settable
current level that can be used either with definite time
or inverse time characteristic. Additionally, it can be
voltage controlled/restrained.
One undervoltage step with definite time characteristic
is also available within the function in order to provide
functionality for overcurrent protection with
undervoltage seal-in.
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9. Secondary system supervision
Current circuit supervision CCSSPVC
Open or short circuited current transformer cores can
cause unwanted operation of many protection functions
such as differential, earth-fault current and negative-
sequence current functions.
Current circuit supervision (CCSSPVC) compares the
residual current from a three phase set of current
transformer cores with the neutral point current on a
separate input taken from another set of cores on the
current transformer.
A detection of a difference indicates a fault in the circuit
and is used as alarm or to block protection functions
expected to give inadvertent tripping.
Fuse failure supervision FUFSPVC
The aim of the fuse failure supervision function
FUFSPVC is to block voltage measuring functions at
failures in the secondary circuits between the voltage
transformer and the IED in order to avoid inadvertent
operations that otherwise might occur.
The fuse failure supervision function basically has three
different detection methods, negative sequence and
zero sequence based detection and an additional delta
voltage and delta current detection.
The negative sequence detection algorithm is
recommended for IEDs used in isolated or high-
impedance earthed networks. It is based on the
negative-sequence quantities.
The zero sequence detection is recommended for IEDs
used in directly or low impedance earthed networks. It is
based on the zero sequence measuring quantities.
The selection of different operation modes is possible
by a setting parameter in order to take into account the
particular earthing of the network.
A criterion based on delta current and delta voltage
measurements can be added to the fuse failure
supervision function in order to detect a three phase
fuse failure, which in practice is more associated with
voltage transformer switching during station
operations.
Fuse failure supervision VDSPVC
Different protection functions within the protection IED
operates on the basis of measured voltage at the relay
point. Some example of protection functions are:
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