ABB REQ650 User Manual

1. to protect equipment against damage due to low frequency, such as generators,
transformers, and motors. Overexcitation is also related to low frequency
2. to protect a power system, or a part of a power system, against breakdown, by
shedding load, in generation deficit situations.
The under frequency START value is set in Hz. All voltage magnitude related settings
are made as a percentage of a global base voltage parameter. The UBase value should
be set as a primary phase-to-phase value.
Some applications and related setting guidelines for the frequency level are given
below:
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 START level has to be set at a lower value, and the time delay
must be rather short.
8.2 Overfrequency protection SAPTOF
8.2.1 Identification
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Overfrequency protection SAPTOF
f >
SYMBOL-O V1 EN
81
8.2.2 Application
Overfrequency protection function SAPTOF 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
Section 8 1MRK 505 291-UEN A
Frequency protection
168
Application manual

ABB REQ650 Specifications

General

Brand	ABB
Model	REQ650
Category	Protection Device
Language	English