Application; Signals - ABB RELION 620 Series Technical Manual

Section 4
Protection functions
4.4.4.5
4.4.4.6
364
be used to block the TRIP signal. The operation timer counting can be frozen on the
prevailing value by activation of the FR_TIMER input.

Application

The task of a generator in a power plant is to convert mechanical energy into electrical
energy. Sometimes the mechanical power from the prime mover may decrease so much
that it does not cover the internal losses. The task of an underpower protection is to protect
the generator from very low power output conditions.
Steam turbines become easily overheated if the steam flow becomes too low or if the
steam ceases to flow through the turbine. Hydro turbine of the Kaplan type may be
damaged due to the fact that the turbine blade surfs on the water and sets up axial pressure
on the bearing. Diesel engines may be damaged due to insufficient lubrication.
If the generator size is very large, it is uneconomical to continue running it with low
generated power. In the reverse power condition, large generators draw a considerable
amount of power from the rest of the system to feed their internal losses. Hence, it is
desirable to disconnect the generator in such situations.
In case of the parallel-connected generators, for example, the load of one generator may
be so low that it is better to disconnect it and let the remaining generators feed the network.
Where a low value of power setting is required, for example less than 2%,
the correction parameters should be used to compensate for the measuring
errors. The manufacturer of the measuring devices is to be contacted for
information on the measuring errors.
If the measuring errors are not compensated for, the underpower setting
should not be lower than the sum of the current-measuring and voltage-
measuring errors.
For example, if the error of the current-measuring device is 2% and that of
the voltage-measuring device is 1%, the minimum setting is (2 + 1)% =
3%.

Signals

Table 300: 32U Input signals
Name Type
I3P GROUP
SIGNAL
U3P GROUP
SIGNAL
BLOCK BOOLEAN
Table continues on next page
Default Description
0.0 Group signal for current inputs
0.0 Group signal for voltage inputs
FALSE Block signal for activating the blocking mode
1MAC504801-IB E
620 series ANSI
Technical Manual