Setting Guidelines - ABB REL650 Applications Manual

Section 9
Frequency protection
9.1.3
9.2
270

Setting guidelines

All the frequency and voltage magnitude conditions in the system where SAPTUF (81)
performs its functions should be considered. The same also applies to the associated
equipment, its frequency and time characteristic.
There are two specific application areas for SAPTUF (81):
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 PICKUP 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
PICKUP level has to be set at a lower value, and the time delay must be rather short.
Overfrequency protection SAPTOF (81)
1MRK 506 334-UUS A
Application manual