- 319 -
As for an intermittent fault (the former in the figure), the time counter will not reach the
trip level. In the other words, the operation of the OVG1 element is paralyzed in the reset time
set by [TOVG1R].
If a series of fault occurs repeatedly (the latter in the figure), and if the value of the time
counter reaches at trip level, the OVG1 element will issue a trip command after a certain delay.
After issuing the trip command, if a series of fault completely disappears after issuing the trip
command, the value of the time counter will be expired after the reset time [TOVG1R].
When the user requires resetting the operation of the OVG1 element immediately, setting
zero for the settings [TOVG1R] is needed. Consequently, when a voltage falls below the reset
threshold (drop-off), the operation of the OVG1 element is reset promptly.
Figure 2.23-3 Faults occurrences and reset operation when IDMT being applied
2.23.4 Miscellaneous functions
(i) OVG operation blocked by the occurrence of VT failure
Blocking the OVG function may be required when a failure in the voltage transformer occurs.
The user shall set Block for scheme switch [OVG1-VTFBlk]. Non (as a default) is set for scheme
switch [OVG1-VTFBlk] in order that the OVG function is not blocked by the failure.
(ii) Switch of OVG trip command
The OVG function issues a trip command for the TRC† when Trip is set for scheme switch
[OVG1-UseFor] as the normal trip operation. However, when an alarm signal in place of the
trip command is required, the user can set Alarm for the scheme switch [OVG1-UseFor].
Condition fault occurrence
Fault observation by the relay
Incrimination of time counter
corresponding to the fault
duration.
T
1
: Resetting time set by the user
T
2
: Actual resetting time in the relay operation
T
3
: Time gap between fault occurrence and relay start time
Increment process in time
counter
Value maintenance of time counter
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