point 3rd harmonic undervoltage principle or the terminal side
3rd harmonic overvoltage principle can be applied. However,
differential principle is strongly recommended. Combination of
these two measuring principles provides coverage for entire
stator winding against earth faults.
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
N
N
CB 1
stator winding
uT
uN
1 - x
1 - 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
7. Frequency protection
Underfrequency protection SAPTUF
M13349-3 v12
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. For information about how
to connect analog inputs, refer to Application manual/IED
application/Analog inputs/Setting guidelines
Overfrequency protection SAPTOF
M14953-3 v11
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. For information about how
to connect analog inputs, refer to Application manual/IED
application/Analog inputs/Setting guidelines
1MRK 502 068-BEN D
Generator protection REG670 2.1 IEC
Product version: 2.1
ABB
25
