ABB REB670 Series Applications Manual page 228

Section 9
Frequency protection
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.
The voltage related time delay is used for load shedding. The settings of SAPTUF 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.
9.2 Overfrequency protection SAPTOF
9.2.1 Identification
Function description
Overfrequency protection
9.2.2 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 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 detects such situations and provides an output signal,
suitable for generator shedding, HVDC-set-point change and so on. SAPTOF 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.
222
IEC 61850 IEC 60617
identification identification
SAPTOF
f >
SYMBOL-O V1 EN-US
1MRK 505 370-UEN D
ANSI/IEEE C37.2
device number
81
Busbar protection REB670
Application manual
IP15747-1 v3
M14866-1 v4
M14952-3 v4