Figure 3.5-1 DC System Grounding | Figure 3.5-2 Box Frame Ground |
3.6. DC Power Output Over-Current Protection
There are several different options for DC output power distribution. Distribution provides a convenient method of connecting the load cables as well as over-current protection.
DC Plug-in Circuit Breakers
A standard 48-position plug-in circuit breaker tier provides -48V distribution. Various circuit breaker sizes from 1 to 100 amps are available, with 60-100 amp breakers requiring two positions and a circuit breaker adapter kit. Each rectifier bay has two 24-position breaker tiers. Each breaker tier is connected at its center to the -48V DC bus, and each side of the tier has a total current capacity of 300A. Each breaker tier has a total current capacity of 600A. Each rectifier bay has a total current capacity of 1200A. It is therefore necessary to balance the load on the rectifier bay to avoid overloading any section of the output bus. Also when planning the output installation, take into consideration the configuration of the plant and the number of rectifiers installed.
Any combination of up to 48 single (1-50 Amp) or up to 24 double (60-100 Amp) breakers may be installed. If all rectifier bays are installed with snap-in breakers, up to 192 single or 96 double breakers may be installed. In the main bay a pair of ribbon cables routed directly to the controller backplane handles alarming. In the expansion bays, each 24-breaker tier is alarmed as a group of breakers. A two-pin connector on each tier connects to the Circuit Breaker expansion board in each bay. Circuit breaker alarms can be monitored by attaching the other end of the alarm wire to the gray Wago connector on the Circuit Breaker / LVD Expansion board. Since the normally open contacts are monitored, any tripped breaker will give an alarm. Install the alarm wire in the Wago connector on the expansion board. Jumper the pins behind
