8DC System, UPS
8.1 Project Requirements
DC power maintains readiness of the electrical switchgear and the plant control system during the plant operation and plant outages. DC power is one of the first systems to be commissioned as it facilitates testing of the power distribution system, which in turn allows the mechanical equipment to be powered and tested.
In large plants, DC system and its equipment is needed in several places. In the case of this industrial project (see Chapter 1), it is needed in the main substations and the process plant. The plant DC system must produce the following voltage supplies:
- 125 Vdc for switchgear breakers and disconnect switches in the main substation.
- 125 Vdc in the process plant for the plant switchgear breakers.
- 125 Vdc for the critical emergency lube systems.
- 24 Vdc for field transmitters and distributed control system (DCS) I/O's at the process plant. 24 Vdc will be obtained directly from 125/24 V dc/dc converters.
- 120 Vac uninterruptible power supplies (UPS) for DCS at several locations of the process plant.
In the IEC countries, the equivalent DC voltage is 110 Vdc.
Evidently, these low‐voltage sources cannot be transmitted from one building to the ...
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