P
TD A
t D
Vpickup V
B C
Vpickup
×
= +
< -
× -
é ù
ê ú
ê ú
ê ú
æ ö
ê ú
ç ÷
è ø
ë û
EQUATION1609 V1 EN-US (Equation 172)
When the denominator in the expression is equal to zero the time delay will be infinity. There will
be an undesired discontinuity. Therefore a tuning parameter
CrvSatn
is set to compensate for this
phenomenon. In the voltage interval
Vpickup<
down to
Vpickup<
· (1.0 –
CrvSatn/
100) the used
voltage will be:
Vpickup<
· (1.0 –
CrvSatn
/100). If the programmable curve is used this parameter
must be calculated so that:
EQUATION1435 V1 EN-US (Equation 173)
The lowest voltage is always used for the inverse time delay integration. The details of the
different inverse time characteristics are shown in section
"Inverse characteristics".
Voltage
IDMT Voltage
Time
VA
VB
VC
ANSI12000186-1-en.vsd
ANSI12000186 V2 EN-US
Figure 323: 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
tIReset2
pickup for the inverse time) the corresponding pickup output is reset. 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. 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: the timer is reset instantaneously, the timer value is frozen
during the reset time, or the timer value is linearly decreased during the reset time. See figure
324
and figure
325.
1MRK 502 066-UUS B Section 9
Voltage protection
605
Technical manual
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