ABB Relion 670 Series Technical Reference Manual page 500

Section 8
Voltage protection
Voltage
VL1
VL2
VL3
494
The lowest voltage is always used for the inverse time delay integration. The details of
the different inverse time characteristics are shown in section
characteristics".
Figure 248: Voltage used for the inverse time characteristic integration
Trip signal issuing requires that the undervoltage condition continues for at least the
user set time delay. This time delay is set by the parameter t1 and t2 for definite time
mode (DT) and by some special voltage level dependent time curves for the inverse
time mode (TUV). If the pickup condition, with respect to the measured voltage ceases
during the delay time, and is not fulfilled again within a user defined reset time
(tReset1 and tReset2 for the definite time and tIReset1 and tIReset2pickup for the
inverse time) the corresponding pickup output is reset. Here it should be noted that
after leaving the hysteresis area, the pickup condition must be fulfilled again and it is
not sufficient for the signal to only return back to the hysteresis area. Note that for the
undervoltage function the TUV reset time is constant and does not depend on the
voltage fluctuations during the drop-off period. However, there are three ways to reset
the timer, either the timer is reset instantaneously, or the timer value is frozen during
the reset time, or the timer value is linearly decreased during the reset time. See
figure 249 and figure 250.
1MRK505222-UUS C
22.3 "Inverse
IDMT Voltage
Time
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Technical reference manual