Sel 751A, Инструкция по эксплуатации

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4.6
SEL-751A Relay Instruction Manual Date Code 20100129
Protection and Logic Functions
Basic Protection
NOTE:
The cosine filter provides
excellent performance in removing dc
offset and harmonics. However, the
bipolar peak detector has the best
performance in situations of severe
CT saturation when the cosine filter
magnitude estimation is significantly
degraded. Combining the two
methods provides an elegant solution
for ensuring dependable short circuit
overcurrent element operation.
The phase instantaneous overcurrent elements (50P1 through 50P4; see
Figure 4.1 ) normally operate using the output of the one cycle cosine filtered
phase current. During severe CT saturation, the cosine filtered phase current
magnitude may be substantially reduced because of the high harmonic content
and reduced magnitude of the distorted secondary waveform. If the
overcurrent element relied only on the output of the cosine filtered secondary
current, this may severely delay and may even jeopardize the operation of any
high-set instantaneous overcurrent element. For any phase instantaneous
overcurrent element in the SEL-751A relay set above eight times the relay
current input rating (40 A in a 5 A relay), the overcurrent element also
operates on the output of a bipolar peak detector if the current waveform is
highly distorted, as is the case with severe CT saturation. This ensures fast
operation of the 50P
n phase overcurrent elements even with severe CT
saturation.
When the harmonic distortion index exceeds the fixed threshold, which
indicates severe CT saturation, the phase overcurrent elements operate on the
output of the peak detector. When the harmonic distortion index is below the
fixed threshold, the phase overcurrent elements operate on the output of the
cosine filter.
Table 4.5 Neutral Overcurrent Settings
Setting Prompt Setting Range
Setting Name :=
Factory Default
NEUT OC TRIP LVL OFF, 0.50–100.00 A
a
,
0.10–20.00 A
b
,
0.13–12.50 mA
c
5.0–1000.0 mA
d
a
For I
NOM
= 5 A.
b
For I
NOM
= 1 A.
c
For I
NOM
= 2.5 mA.
d
For I
NOM
= 50 mA.
50N1P := OFF
NEUT OC TRIP DLY 0.00–5.00 sec 50N1D := 0.50
NEUT OC TRQ CON SEL
OGIC
50N1TC := 1
NEUT OC TRIP LVL OFF, 0.50–100.00 A
a
,
0.10–20.00 A
b
,
0.13–12.50 mA
c
5.0–1000.0 mA
d
50N2P := OFF
NEUT OC TRIP DLY 0.00–5.00 sec 50N2D := 0.50
NEUT OC TRQ CON SEL
OGIC
50N2TC := 1
NEUT OC TRIP LVL OFF, 0.50–100.00 A
a
,
0.10–20.00 A
b
,
0.13–12.50 mA
c
5.0–1000.0 mA
d
50N3P := OFF
NEUT OC TRIP DLY 0.00–5.00 sec 50N3D := 0.50
NEUT OC TRQ CON SEL
OGIC
50N3TC := 1
NEUT OC TRIP LVL OFF, 0.50–100.00 A
a
,
0.10–20.00 A
b
,
0.13–12.50 mA
c
5.0–1000.0 mA
d
50N4P := OFF
NEUT OC TRIP DLY 0.00–5.00 sec 50N4D := 0.50
NEUT OC TRQ CON SEL
OGIC
50N4TC := 1