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Line distance protection REL670
Version 2.2
SAPFRC is provided with an undervoltage blocking. The
operation is based on positive sequence voltage
measurement and requires two phase-phase or three
phase-neutral voltages to be connected.
10. 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.
11. General calculation
Multipurpose filter SMAIHPAC
The multi-purpose filter function block (SMAIHPAC) is
arranged as a three-phase filter. It has very much the same
user interface (e.g. inputs and outputs) as the standard pre-
processing function block SMAI. However the main
difference is that it can be used to extract any frequency
component from the input signal. Thus it can, for example,
be used to build sub-synchronous resonance protection for
synchronous generator.
12. 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
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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:
• Distance protection function.
• Undervoltage function.
• Energisation function and voltage check for the weak
infeed logic.
These functions can operate unintentionally, if a fault occurs
in the secondary circuits between voltage instrument
transformers and the IED. These unintentional operations
can be prevented by fuse failure supervision (VDSPVC).
VDSPVC is designed to detect fuse failures or faults in
voltage measurement circuit, based on phase wise
comparison of voltages of main and pilot fused circuits.
VDSPVC blocking output can be configured to block
functions that need to be blocked in case of faults in the
voltage circuit.
Voltage based delta supervision DELVSPVC
Delta supervision function is used to quickly detect (sudden)
changes in the network. This can, for example, be used to
detect faults in the power system networks and islanding in
grid networks. Voltage based delta supervision
(DELVSPVC) is needed at the grid interconnection point.
Current based delta supervision DELISPVC
Delta supervision function is used to quickly detect (sudden)
changes in the network. This can, for example, be used to
detect disturbances in the power system network. Current
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