ABB Zenith ZTS T Series, Operation, Maintenance, And Installation Manual

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O PER AT I O N , M A I N T EN A N C E , A N D I N S TA L L AT I O N G U I D E
A07
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2
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2.5 Sequence of Operation
2.5.1 Switching sequence / Automatic
(Open / Delayed transition)
2.5.1.1 SOURCE 1 Priority
(SOURCE 2 = Generator)
The switching sequence can be
summarized in the following steps:
1. An anomaly occurs on SOURCE 1
2. Override momentary S1 outage delay
3. Generator start
4. SOURCE 2 OK
5. Transfer from S1 to S2 delay
6. Pre-transfer signal on
7. Load shed signal on
8. Pre-transfer S1 to S2 delay
9. Load shed delay
10. Transfer switch (SOURCE 1) to
position O
11. Center-off delay (only with Delayed
transition I - O - II type)
12. Transfer switch (SOURCE 2) to
position II
13. Post-transfer S1 to S2 delay
14. Pre-transfer signal off
The re-transfer sequency can be
summarized in the following steps:
1. SOURCE 1 is restored
2. Transfer from S2 to S1 delay
3. Pre-transfer signal on
4. Pre-transfer S2 to S1 delay
5. Transfer switch (SOURCE 2) to
position O
6. Center-off delay (only with Delayed
transition I - O - II type)
7. Transfer switch (SOURCE 1) to
position I
8. Load shed signal off
9. Generator stop delay
10. Post-transfer S2 to S1 delay
11. Pre-transfer signal off
12. Generator stop
13. SOURCE 2 off