Example: injection exclusion with multiple interconnected incoming feeders
The PLC can have the following characteristics:
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Number of digital inputs: is the number of circuit breakers for incoming feeder and for coupling. These inputs can be self-powered by the PLC or powered by an external power supply.
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Number of digital outputs: is the number of devices minus 1. These digital outputs can be electromechanical or solid-state outputs.
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Processing cycle is equal to 0.1 s or less.
Using a basic PLC to manage device exclusion allows to:
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Monitor continuously each part of ungrounded power system.
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Have a short response time to detect insulation faults.
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Be compatible with complex power systems with high number of incoming feeders and couplings.
Truth table:
|
Possible configurations 0 = open, 1 = closed |
Injection Inhibition 0 = injection, 1 = injection inhibited |
||||||
|---|---|---|---|---|---|---|---|
| D1 | D2 | D3 | C1 | C2 | IMD no.1 | IMD no.2 | IMD no.3 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 1 | 0 | 0 | 0 |
| ... | |||||||
| 0 | 1 | 1 | 1 | 1 | 0 | 0 | 1 |
| ... | |||||||
| 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1 |