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7.5 Basic time delay
The Basic Time Delay setting is required to inhibit the tapchanger from unnecessary
operations on temporary voltage excursions and is commonly set at 30 to 60 seconds. The
timer includes two selectable elements "Definite/Inverse" and "Integrating/Instant
Reset".
The control will only respond to an out-of-band voltage excursion after the Basic Time
Delay has timed out. The Basic Time Delay can be set as an integrating timer or an
instantaneous reset timer upon the voltage return to an in-band condition. As an
integrating timer, it increments during time out-of-band and decrements during time in-
band, but not below zero.
The Basic Time Delay can be set to either a Definite or Inverse delay. Both types of delay
will work in Forward or Reverse Power Flow. The inverse time delay will follow the curve
in
Figure 416 .
Inverse Time Example
• Bandcenter 120 V
• Bandwidth 3 V
• Inverse Time Delay Setting 120 s
• ΔV = (Bandwidth/2) = 1.5 V
• V
in
= 123 V
Voltage deviation in multiples of ΔV
= [V
in
– Bandcenter]/ΔV
= (123 – 120)/1.5
= 2
Time delay from Figure 416
= 50% of Inverse Time Delay setting
= 60 sec
1VAC388793-MB A
Section 7
Setpoints
TCC300 521
User Manual