changer alarm is activated if the tap changer does not move downwards in Cmd
error delay time after the pulse activation, resulting that ALARM_REAS in the
monitored data contains a command error value.
The lowering control works in a similar way, as shown in
Figure 397. In the output
data, the LOWER_OWN output value is TRUE. An alarm is generated if the tap
changer does not move upwards in Cmd error delay time after the pulse activation,
assuming that the own tap changer position is connected.
9.5.9 Automatic voltage regulation of single transformer
OLATCC is intended to control the power transformers with a motor-driven on-
load tap changer. The function is designed to regulate the voltage at the secondary
side of the power transformer. The control method is based on a step-by-step
principle, which means that one control pulse at a time is issued to the tap changer
mechanism to move it exactly one position upwards or downwards. However,
when intermediate steps are not indicated for the tap changer, it does not cause
alarm if more than one step change is met.
The purpose of the regulator is to maintain a stable secondary voltage of the power
transformer. The basis for this operation is the Band center voltage setting. By
increasing or decreasing various compensation factors, the regulator calculates a
control voltage from the band center voltage as shown in
Equation 89. Hence, the
control voltage is the desired transformer secondary voltage to be maintained by
the 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 should be close to twice the step
voltage of the transformer ΔU
step
and never below it as a minimum. For example,
Band width voltage is twice the value of ΔU
step
in
Figure 397.
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 397, 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.
Section 9 1YHT530004D05 D
Control functions
732 615 series
Technical Manual
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