Overfrequency Protection Saptof (81) - ABB RET670 Applications Manual

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1MRK504116-UUS C

Application manual

Overfrequency protection SAPTOF (81)

Function description

Overfrequency protection

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.

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 especially two application areas for SAPTOF (81):

to protect equipment against damage due to high frequency, such as generators,

to protect a power system, or a part of a power system, against breakdown, by

shedding generation, in over production situations.

The overfrequency PICKUP value is set in Hz. All voltage magnitude related settings

are made as a percentage of a settable base voltage, which normally is set to the

nominal voltage level (phase-to-phase) of the power system or the high voltage

equipment under consideration.

Some applications and related setting guidelines for the frequency level are given below:

identification

SYMBOL-O V1 EN

IED application

ANSI/IEEE C37.2

device number

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