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2.1.2.5 Directional Negative Sequence Overcurrent Protection
GRD150 provides the directional negative sequence overcurrent protection with inverse time and
definite time characteristics.
Two independent elements DNOC1 and DNOC2 are provided for tripping and alarming. The
DNOC1 has selective inverse time and definite time characteristics. The DNOC2 has definite time
characteristic only. These elements can be directionalised by polarising against the negative
sequence voltage.
The DNOC protection is enabled when three-phase current is introduced and the scheme switch
[APPL-CT] is set to "3P".
Scheme Logic
Figure 2.1.47 shows the scheme logic of inverse time or definite time selective directional
negative sequence inverse time overcurrent protection and definite time overcurrent protection.
In Figure 2.1.47, the definite time protection is selected by setting [MDNC1] to "DT". The definite
time element is enabled for directional negative sequence overcurrent protection and trip signal
DNOC1 TRIP is given through the delayed pick-up timer TDNC1.
The inverse time protection is selected by setting [MDNC1] to either "IEC", "IEEE", "US" or
"CON" according to the inverse time characteristic to employ. The element DNOCI1 is enabled
and trip signal DNOC1 TRIP is given.
The forward operate zone or reverse operate zone is selectable by the scheme switch [DNC1-DIR].
ICD is the inrush current detector ICD, which detects second harmonic inrush current during
transformer energisation, and can block the DNOC1 protection by the scheme switch [DNC1-2F].
See Section 2.1.7.
The DNOC1 protection can be disabled by the scheme switch [DNC1EN] or PLC logic signal
DNOC1 BLOCK.
Figure 2.1.48 shows the scheme logic of DNOC2 protection with definite time delayed operation.
The DNOC2 gives an alarm signal DNOC2 ALARM through delayed pick-up timer TDNC2.
The forward operate zone or reverse operate zone is selectable by the scheme switch [DNC2-DIR].
The DNOC2 protection can be disabled by the scheme switch [DNC2EN] or PLC logic signal
DNOC2 BLOCK. The DNOC2 can also be blocked by the ICD.
140, 1832
DNOC1F
&
156, 1848
DNOC1R
&
"FWD"
[DNC1-DIR]
"REV"
+
[DNC1-2F]
+
"BLK"
&
ICD
[DNC1EN]
+
"ON"
1
1564
DNOC1 BLOCK
Figure 2.1.47
Directional Negative Sequence Overcurrent Protection Scheme Logic
92, 1784
DNOC1I
≥1
[MDNC1]
+
"IEC"
"IEEE"
"US"
"CON"
"DT"
⎯
⎯
53
437
≥1
&
TDNC1
0
t
&
0.00 - 300.00s
6 F 2 S 0 8 4 2
DNOC1 TRIP
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