10
Line drop
compensation
The line drop compensation feature is used for
compensating the voltage drop along a line or
network fed by the transformer. The compen-
sation setting parameters can be calculated theo-
retically, if the resistance and reactance of the
line are known, or practically by measuring the
line drop. If the transformer is feeding two or
more lines, the regulator can be given an aver-
age of the line parameters, thus providing a more
stable voltage supply in the line ends, than would
be possible without compensation.
The line drop compensation also operates in
"reverse direction". At reversed power flow, the
compensation reduces the secondary voltage of
the transformer according to the line drop, in-
stead of raising it.
Line drop compensation is possible in single
transformer applications and in applications
with parallel transformers. Please refer to the
manual of module SPCU 1D50 for further in-
formation.
Blockings
The operation of the voltage regulator may be
blocked for several reasons. Undervoltage and
overcurrent blockings are caused internally in
the regulator if the values measured exceed the
user settable limits. External blocking is acti-
vated by the external control input. Further-
more, there is an overvoltage detection feature,
which blocks operation of the regulator except
for the "fast lower control". Selector switches
in the module SPCU 1D50 are used for ena-
bling or disabling the internal blockings and the
overvoltage detection feature. If the manual
voltage regulating module SPCN 1D56 is in-
cluded in the regulator, the blocking situations
and overvoltage detection are indicated by red
alarm LEDs. Manual voltage regulation is ena-
bled in undervoltage and overvoltage situations.
In overcurrent and external blocking situations,
however, manual voltage regulation is disabled.
Exceptions to the operation explained above if
SGF2/2 is in position 1:
- an overvoltage situation U> will activate the
I> output relay, disable manual voltage regu-
lation and lit both I> and U> alarm LEDs.
- an overcurrent blocking I> will disable auto-
matic voltage regulation and not block manual
voltage regulation.
Undervoltage blocking:
The undervoltage blocking feature blocks the
regulator if, for some reason, the measured volt-
age, is too low to be corrected by operating the
tap-changer. Such a situation may be due to a
faulty measuring circuit, an earth-fault or and
overcurrent situation.
Overcurrent blocking:
Overcurrent blocking is mainly used for pre-
venting the tap-changer from operating in an
overcurrent situation, for example, if the cur-
rent is not high enough to activate the protec-
tive relay of the substation but still fatal for the
diverter switch of the tap-changer.
External blocking:
The operation of the voltage regulator can be
entirely blocked via the external blocking con-
trol input. This input can also be configured as
remote/local control input using the software
switch SGF1/3 in the module SPCU 1D50.
Overvoltage detection:
If the voltage measured exceeds the setting value
for "overvoltage detection" and this feature is
enabled, the regulator will provide fast lower
control until the voltage falls below the speci-
fied limit. Fast lower control means that the tap-
changer is operated faster than normal by lower
control pulses.
