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Section 8
Voltage protection
8.2.7.3
8.2.7.4
138
Voltage
UL1
UL2
UL3
IEC05000016 V2 EN
Figure 58:
Voltage used for the inverse time characteristic integration
A TRIP requires that the overvoltage 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 selected voltage level dependent time curves for the inverse time mode (IDMT). If
the START condition, with respect to the measured voltage ceases during the delay
time, the corresponding START output is reset.
Blocking
It is possible to block two step overvoltage protection (OV2PTOV) partially or
completely, by binary input signals where:
BLOCK:
BLKST1:
BLKST2:
Design
The voltage measuring elements continuously measure the three phase-to-earth
voltages or the three phase-to-phase voltages. Recursive Fourier filters or true RMS
filters of input voltage signals are used. The phase voltages are individually compared
to the set value, and the highest voltage is used for the inverse time characteristic
integration. A special logic is included to achieve the 1 out of 3, 2 out of 3 or 3 out of 3
criteria to fulfill the START condition. The design of Two step overvoltage protection
(OV2PTOV) is schematically described in
blocks all outputs
blocks all start and trip outputs related to step 1
blocks all start and trip outputs related to step 2
Figure
1MRK 505 288-UEN A
IDMT Voltage
IEC05000016-2-en.vsd
59.
Technical manual
Time
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