, where the lowering function is an example. The delay T1
remains active as long as the measured voltage is outside the hysteresis limits of
half the value of
Band width voltage. The factory setting for the hysteresis is 10
percent of the set
Band width voltage.
Band
width
voltage
U
ΔU
step
t
bandwidth limit
hysteresis limit
U
m
, measured voltage
U
p
, control voltage
T1
s
ta
rt
T1
re
se
t
T1
s
ta
rt
Lowe
r
T1
Figure 559: Voltage-regulating function. A control pulse to lower the voltage is
issued after the elapsed T1.
If the measured voltage is outside the hysteresis when the delay counter T1 reaches
its setting value, the raising or lowering output relay is activated. This activates
either output pulse
RAISE_OWN
or
LOWER_OWN
, and the motor drive of the tap
changer operates. The status of these outputs can be read from the output data
RAISE_OWN
or
LOWER_OWN
.
If the measured voltage falls or rises within the hysteresis limits during the
operating time, the delay counter is reset.
The pulse length can be defined with the
LTC pulse time setting. The default value is
1.5 seconds.
A short delay same as the typical tap changer operating time is active before the
start of the next operating timer is possible. For OLATCC, the delay is set to 6
seconds. If one tap changer operation is not enough to regulate the transformer
voltage within the hysteresis limits, a second adjustable delay T2 (
Control delay
time 2), usually with a shorter time setting than T1, starts. This delay is used for
the control commands within the same sequence until the recovery of voltage
occurs. The delays T1 and T2 can be selected either with definite or inverse time
characteristics. In the inverse time mode operation, the operating time depends on
the difference between the control voltage and the measured voltage as shown in
. The bigger the difference in the voltage, the shorter the operating
time. More information on the inverse time operation can be found in
Regulation equation
The simple regulating principle is often complemented by additional features to
take the voltage drop of lines into account (line drop compensation), coordinate the
regulation of parallel transformers and change the voltage level according to the
loading state of the network. The control voltage U
p
is calculated according to the
equation
1MRS757644 H
Control functions
620 series
Technical Manual
1051
