phase(s) in which the phase selection function has
operated.
For delayed tripping, single pole and three pole delays
are separately and independently settable. Furthermore,
it is possible to enable or disable single pole and three
pole delayed tripping. For single phase faults, it is
possible to include a residual current check in the
tripping logic. Three pole tripping is always selected for
phase selection on more than one phase. Three pole
tripping will also occur if the residual current exceeds
the set level during fuse failure for a time longer than
the three pole trip delay time.
9. Frequency protection
Underfrequency protection SAPTUF
M13349-3 v13
Underfrequency occurs as a result of a lack of
generation in the network.
Underfrequency protection (SAPTUF) measures
frequency with high accuracy, and is used for load
shedding systems, remedial action schemes, gas turbine
startup and so on. Separate definite time delays are
provided for operate and restore.
SAPTUF is provided with undervoltage blocking.
The operation is based on positive sequence voltage
measurement and requires two phase-phase or three
phase-neutral voltages to be connected.
Overfrequency protection SAPTOF
M14953-3 v12
Overfrequency protection function (SAPTOF) is
applicable in all situations, where reliable detection of
high fundamental power system frequency is needed.
Overfrequency occurs because of sudden load drops or
shunt faults in the power network. Close to the
generating plant, generator governor problems can also
cause over frequency.
SAPTOF measures frequency with high accuracy, and is
used mainly for generation shedding and remedial
action schemes. It is also used as a frequency stage
initiating load restoring. A definite time delay is
provided for operate.
SAPTOF 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.
Rate-of-change of frequency protection SAPFRC
M14965-3 v14
The rate-of-change of frequency protection function
(SAPFRC) gives an early indication of a main disturbance
in the system. SAPFRC measures frequency with high
accuracy, and can be used for generation shedding, load
shedding and remedial action schemes. SAPFRC can
discriminate between a positive or negative change of
frequency. A definite time delay is provided for operate.
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
M13083-11 v9
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
GUID-EB0B11C3-FF79-4B8D-A335-649623E832F9 v3
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
M12444-3 v10
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.
Line differential protection RED670
1MRK 505 379-BEN N
42 Hitachi Power Grids
© Copyright 2017 Hitachi Power Grids. All rights reserved
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