ABB Switzerland Ltd REG 316*4 1MRB520049-Uen / Rev. F
3-194
E. Setting instructions
There are often several stages of frequency protection using
several single-stage relays.
Settings:
Frequency Frequency
Delay Delay
Undervoltage blocking BlockVoltage
Under or over frequency MaxMin
Frequency protection is used either to protect synchronous
machines and prime-movers against the effects of operating at
under or overfrequency or for load-shedding in the event of an
overload.
The adverse effects in the former case prevented by the fre-
quency protection are:
· excessive temperature rise and additional iron losses in the
generator
· damage to the generator and the prime-mover by vibration.
Some synchronous machines are subject to severe vibration if
they are operated at speeds other than their rated speed.
Vibration occurs more usual at speeds below rated frequency,
but can occur both above and below. A complete scheme often
comprises therefore 4 stages, two for alarm and tripping for
overfrequency and two for alarm and tripping for underfre-
quency. Tripping is delayed to avoid the risk of maloperation
during transients.
Typical settings:
1. Protection of machines
1st. stage 2nd. stage 3rd. stage 4th. stage
Alarm Tripping Alarm Tripping
Frequency (Hz)
51.0 52.0 49.0 48.0
Delay (s)
1.5 3 1.5 3
BlockVoltage
0.6 0.6 0.6 0.6
MaxMin
MAX MAX MIN MIN
Table 3.5.18.1 Typical settings for alarm and tripping stages
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