Schweitzer Engineering Laboratories SEL-352-1, Instruction Manual

Page: 138 / 444

4-14 Close Logic Date Code 20010731
SEL-352-1, -2 Instruction Manual
X = [1 – fraction of (Nominal Breaker Close Timer / 16.67)]
•
16.67
Y = Adjustment for centering error band =
2
Error Pos Error Neg
+
If the negative error is greater than the positive error, Y is positive.
If the positive error is greater than the negative error, Y is negative.
Setting of the B-phase timer is similar to that for the A-phase timer. The relay performs the
adjustment for the 120° phase shift between A-phase and B-phase. Refer to the A-phase
calculations. If all three phases are to close at the same point on their corresponding voltage
waveform, and within the same cycle interval, set all three timers to the same value. This will
result in A-phase closing first, B-phase second, and C-phase third. If you want a different order,
add a 1-cycle offset to the phase that needs to be delayed.
Setting of the C-phase timer is similar to that for the A-phase timer. The relay performs the
adjustment for the 240° shift between A-phase and C-phase. Refer to the A-phase calculations.
If all three phases are to close at the same point on their corresponding voltage waveform, and
within the same cycle interval, set all three timers to the same value. This will result in A-phase
closing first, B-phase second, and C-phase third. If you want a different order, add a 1-cycle
offset to the phase that needs to be delayed.
Zero-Crossing Timers Pickup (ZCApu, ZCBpu, ZCCpu)–Scheme 2
The logic closes the relay output contact at a negative going zero crossing when it detects no
trapped charge. The positive going zero-crossing element is not used. ZCApu provides the
delay for the breaker close time and any offset to move the closing point to another point on the
wave.
For example, with a Tclose (nominal closing time of the breaker) time of 33 ms (2 cycles), and a
setting of ZCApu = 0, the breaker will close at the zero crossing 2 cycles after the output contact
closes. However, if the Tclose time is 29 ms (1.75 cycles), the breaker would close 1/4 cycle
before the zero crossing.
The zero-crossing timers work like the peak-crossing timers. Refer to Figure 4.10 for a timing
diagram. The difference is that the output of the relay occurs at the zero crossing instead of the
peak.
Setting of the B-phase timer is similar to that for the A-phase timer. The relay performs the
adjustment for the 120° shift from A-phase to B-phase. Refer to the A-phase calculations. If all
three phases are to close at the same point on their corresponding voltage waveform, and within
the same cycle interval, set all three timers to the same value. This will result in A-phase closing
first, B-phase second, and C-phase third. If you want a different order, add a 1-cycle offset to the
phase you need to delay.
Setting of the C-phase timer is similar to that for the A-phase timer. The relay performs the
adjustment for the 240° shift from A-phase to C-phase. Refer to the A-phase calculations. If all
three phases are to close at the same point on their corresponding voltage waveform, and within
the same cycle interval, set all three timers to the same value. This will result in A-phase closing