TP-6714 4/1030 Section 3 Operation
3.8 Sequence of Operation,
Service Entrance Models
Service entrance models operate in programmed-
transition mode, with a pause in the off position during
transfer. The time in the off position is set through the
off-to-standby and off-to-preferred time delays. If the
OFF time delay is shorter than the time required for the
circuit breaker to open, the transfer time will be
controlled by the circuit breaker operation time.
3.8.1 Preferred Source Loss and
Return, Service Entrance Models
Preferred Source Fails
1. Load control contacts open.
2. Engine start time delay expires.
3. The generator is signaled to start (engine start
contacts close).
4. The generator starts and the standby source
becomes available.
5. Preferred-to-standby time delay expires.
6. Source 1 circuit breaker opens.
7. Off-to-standby time delay expires.
8. Source 2 circuit breaker closes.
9. Post-transfer load control time delays expire.
10. Load control contacts close.
Preferred Source Returns
1. Pre-transfer load control time delays expire.
2. Load control contacts open.
3. Standby-to-preferred time delay expires.
4. Source 2 circuit breaker opens.
5. Off-to-preferred time delay expires.
6. Source 1 circuit breaker closes.
7. Post-transfer load control sequences and engine
cooldown time delay expire.
8. Load control contacts close.
9. The generator is signaled to stop (engine start
contacts open).
3.8.2 Exerciser Operation,
Service Entrance Models
Unloaded Exercise
The unloaded exercise sequence is the same as for
standard transition. See Section 3.6.2.
Loaded Exercise Sequence Starts
1. Exerciser timer begins.
2. The engine start contacts close, signaling the
generator set to start.
3. The generator starts and the standby source
becomes available.
4. Pre-transfer load control time delays expire.
5. Load control contacts open.
6. Preferred-to-standby time delay expires.
7. Source 1 circuit breaker opens.
8. Off-to-standby time delay expires.
9. Source 2 circuit breaker closes.
10. Post-transfer load control time delays expire.
11. Load control contacts close.
Emergency Source Fails (Normal Source is
available)
1. Immediate failure to acquire standby alarm.
2. Exerciser is deactivated.
3. Load control contacts open.
4. Source 2 circuit breaker opens.
5. Off-to-preferred time delay expires.
6. Source 1 circuit breaker closes.
7. Post-transfer load control time delays expire and
load control contacts close.
8. Engine cooldown time delay expires and engine
start contacts open.
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