4-4
Close Logic
Date Code 20010731
SEL-352-1, -2 Instruction Manual
SYNCTD
SYNCdo
0
CLSdo
SCT
SCTD
RCLS
MCLOSE
CLOSE
25C
25M
Y59L3
X59L3
M3520009
MCTD
MCT
(CYCLES)
0
2
0
(CYCLES)
TRIPA
TRIPB
TRIPC
SYNCT
Figure 4.5: Synchronism Controlled Close Logic
Point-On-Wave
Point-on-wave closing reduces transients on the system during closing. Many factors cause
transients. Closing a breaker at a certain point on the voltage waveform can reduce transients.
Four conditions may exist when closing into de-energized equipment: the equipment has a
standing positive voltage charge remaining (called trapped charge), the equipment has a standing
negative voltage charge remaining, the equipment is completely de-energized (no trapped
charge), or the equipment has a standing ac voltage on it from coupling or equipment resonance.
The accuracy of the point-on-wave closing depends greatly on breaker closing consistency.
Breakers vary in tolerance depending on breaker type and manufacturer. Consult the breaker
manufacturer for close time tolerances. Breaker closing times vary according to ambient
temperature changes, control voltage level, age of the breaker, and time since last operation. The
SEL-352 controls none of these factors, but calculates the instant to issue the close pulse to the
breaker based on the above information. The location of this point can cause close time
variation.
If a breaker closes into a dead line with the system voltage at a peak, the breaker will pre-strike
(conduct before poles physically contact). If the voltage is at a zero crossing, the breaker will
not conduct until the heads actually contact. This time difference between the pre-strike and the
actual contact of the heads can account for breaker close time variation.
Trapped Charge Detection
The logic shown in Figure 4.6 monitors the voltage input channels for A-phase. B-phase logic
and C-phase logic are similar.
Содержание SEL-352-1
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