In this example situation the set voltage window is still too tight compared to the tap effect. This time
the AVR reaches the target window with one tap change, but afterwards the voltage is very close to the
limit. If the voltage goes back to the original value, another tap change is needed. This may cause an
excessive number of tap operations, and the quality of the network voltage is not significantly
improved.
Figure. 5.4.4 - 175. Voltage window according to the recommendation.
In this example the voltage window limits are set according to the recommendation: the set window is
20 % bigger than the tap step effect. This ensures that after tap changing the voltage it's not too near
the opposite voltage window limit. If the user wants more sensitivity, the voltage window can be set
lower; however, it is not recommended that the set window is less than 5 % bigger than the tap step
effect.
In automatic voltage regulator applications the first window (U>/<
window
) is usually used for slower
operation with a definite set operating time and small deviations. Typically this operating time is
30…120 seconds. The function starts counting the operating time when the measured voltage
exceeds either of the set window limits. If the voltage remains beyond the limits until the set operating
time has passed, a tap change operation is applied. If the measured voltage returns to within the target
voltage window, the operating time counter is reset. A 3 % hysteresis is applied for the U> and U< pick-
up resets in the voltage window.
When defining the setting limits for the second (fast operation) voltage window, it must be ensured that
one tap change cannot bring the voltage within the first voltage window. See the image below, where
the first window is 20 % bigger than the tap step effect and the second window is increased by two tap
steps from the first window. When the voltage exceeds the higher limit of the second voltage window,
one tap change operation is applied and it brings the voltage down. However, the voltage stays within
the second window limits. Only when a second tap change is applied does the voltage drop within the
limits of the first voltage window.
A
AQ
Q-T215
-T215
Instruction manual
Version: 2.04
272
