Overfrequency Protection Saptof (81); Identification; Application; Setting Guidelines - Hitachi Relion 670 Series Applications Manual

Section 10
Frequency protection
Equipment protection, such as for motors and generators
The setting has to be well below the lowest occurring "normal" frequency and well above the lowest
acceptable frequency for the equipment.
Power system protection, by load shedding
The setting has to be below the lowest occurring "normal" frequency and well above the lowest
acceptable frequency for power stations, or sensitive loads. The setting level, the number of levels and
the distance between two levels (in time and/or in frequency) depends very much on the characteristics
of the power system under consideration. The size of the "largest loss of production" compared to "the
size of the power system" is a critical parameter. In large systems, the load shedding can be set at a
fairly high frequency level, and the time delay is normally not critical. In smaller systems the frequency
pickup level has to be set at a lower value, and the time delay must be rather short.
The voltage related time delay is used for load shedding. The settings of SAPTUF (81) could be the
same all over the power system. The load shedding is then performed firstly in areas with low voltage
magnitude, which normally are the most problematic areas, where the load shedding also is most
efficient.
10.2

Overfrequency protection SAPTOF (81)

10.2.1

Identification

Function description
Overfrequency protection
10.2.2

Application

Overfrequency protection function SAPTOF (81) is applicable in all situations, where reliable detection of
high fundamental power system frequency is needed. The power system frequency, and rate of change
of frequency, is a measure of the unbalance between the actual generation and the load demand. High
fundamental frequency in a power system indicates that the available generation is too large compared
to the power demanded by the load connected to the power grid. SAPTOF (81) detects such situations
and provides an output signal, suitable for generator shedding, HVDC-set-point change and so on.
SAPTOF (81) is very sensitive and accurate and can also be used to alert operators that frequency has
slightly deviated from the set-point, and that manual actions might be enough.
10.2.3

Setting guidelines

All the frequency and voltage magnitude conditions in the system where SAPTOF (81) performs its
functions must be considered. The same also applies to the associated equipment, its frequency and
time characteristic.
There are two application areas for SAPTOF (81):
162
IEC 61850
identification
SAPTOF
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IEC 60617 ANSI/IEEE C37.2
identification device number
81
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Phasor measurement unit RES670
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IP15747-1 v3
M14866-1 v4
M14952-3 v4
M14959-3 v7
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