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
Figure 5.
Protection principles for STEFPHIZ function
8. Frequency protection
Underfrequency protection SAPTUF
Underfrequency occurs as a result of a lack of sufficient
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.
Overfrequency protection SAPTOF
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.
Rate-of-change frequency protection SAPFRC
The rate-of-change 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.
9. Secondary system supervision
Fuse failure supervision SDDRFUF
The aim of the fuse failure supervision function SDDRFUF 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.
Generator protection REG650
1MRK 502 050-BEN B
Product version: 1.3
18
ABB
