ABB RELION REX640 Technical Manual page 1553

1MRS759142 C
REX640
Technical Manual
regulator. The control voltage is compared to the measured voltage and the difference
between the two forms the regulating process error.
Since the tap changer changes the voltage in steps, a certain error has to be allowed.
The error, called Band width voltage, is also set by the user. A recommended setting
for Band width voltage is close to twice the step voltage of the transformer ΔU
never below it as a minimum. For example, Band width voltage is twice the value of
ΔU in Figure 812.
step
If the measured voltage fluctuates within the control voltage ± half the Band width
voltage setting, the regulator is inactive. If the measured voltage is outside the half-
bandwidth voltage limits, an adjustable delay T1 (Control delay time 1 ) starts, as
shown in Figure 812, 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.
U
ΔU
step
Band
width
voltage
GUID-EECE177A-F216-45AF-A01B-27359AF6BF53 V1 EN
Figure 812: 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. For OL5ATCC, the delay is set to 6 seconds. If one tap
changer operation is not enough to regulate the transformer voltage within the
Section 9
Control functions
T1
bandwidth limit
hysteresis limit
U , measured voltage
m
U , control voltage
p
t
and
step
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