x E3
Rf
T
CB 2
(1- x) E3
over- voltage protection 10% – 100%
Differential
0% – 30%
CB 1 may not exist
RN
N
CB 1
stator winding
uT
uN
x E3
Rf
Transformer
T
CB 2
(1- x) E3
x
Neutral point fundamental frequency
over-voltage protection 5% - 100%
3rd harmonic
differential
0% - 30%
CB 1 may not exist
1 or 100 %
RN
NN
CB 1
stator winding
uT
uN
1 - x1 - x
Samples of the
neutral voltage
from which the
fundamental and
3rd harmonic
voltages are
filtered out
Samples of the
terminal voltage
from which the
3rd harmonic
voltage is filtered
out
IEC10000202-1-en.vsd
IEC10000202 V1 EN-US
Figure 6. Protection principles for STEFPHIZ function
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.
Frequency time accumulation protection FTAQFVR
GUID-020CE8CF-9BEA-455D-ACBD-13023B93B4D1 v5
Frequency time accumulation protection (FTAQFVR) is
based on measured system frequency and time
Generator protection REG670
1MRK 502 074-BEN M
34 Hitachi Power Grids
© Copyright 2017 Hitachi Power Grids. All rights reserved
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