ABB RELION REX640 Technical Manual page 1060

Protection functions
the whole function is blocked and the timers are reset. In the "Block OPERATE
output" mode, the function operates normally but the OPERATE output is not
activated.
4.8.1.6 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.
4.8.1.7 Signals
DUPPDPR Input signals
Table 992: DUPPDPR Input signals
Name
I3P
U3P
BLOCK
DISABLE
1060
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%.
Type
SIGNAL
SIGNAL
BOOLEAN
BOOLEAN
Default Description
- Three-phase currents
- Three-phase voltages
0=False Block signal for acti-
vating the blocking
mode
0=False Signal to block the
function during gen-
erator startup
1MRS759142 F
REX640
Technical Manual