10.2.2 Functionality
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
10.2.3 Function block
IEC06000280_2_en.vsd
SAPTOF
U3P*
BLOCK
BLKTRIP
TRIP
START
BLKDMAGN
FREQ
IEC06000280 V2 EN
Figure 265: SAPTOF function block
10.2.4 Signals
Table 309: SAPTOF Input signals
Name
Type Default Description
U3P GROUP
SIGNAL
- Three phase group signal for voltage inputs
BLOCK BOOLEAN 0 Block of function
BLKTRIP BOOLEAN 0 Blocking operate output
Table 310: SAPTOF Output signals
Name
Type Description
TRIP BOOLEAN General trip signal
START BOOLEAN General start signal
BLKDMAGN BOOLEAN Measurement blocked due to low amplitude
FREQ REAL Measured frequency
1MRK502052-UEN B Section 10
Frequency protection
549
Technical manual
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