Rockwell Automation 2364E Non-Regenerative DC Bus Supply Unit (NRU) - Manual (Page 17)

Publication 2364E-5.01 April 2002
Overview 1-3
How Does An NRU Work? To help you to understand the theory behind how an NRU works, read
this section for descriptions of the primary electrical components, a
conceptual schematic, and a discussion of rectifier bridge operation.
Primary Electrical Components of the NRU
The primary electrical components of the NRU are:
• a 3-phase circuit breaker or motor circuit protector, depending
upon NRU rating
• AC line, current-limiting fuses
• a six-pulse, full-wave, 3-phase-diode-bridge rectifier unit
• a DC bus choke
• a control power transformer
• primary and secondary control transformer fusing
Motor Circuit Protector
The motor circuit protector is the switching device between the NRU
and the 3-phase AC source used to turn power to the system on and
off; it also provides magnetic overload protection. Motor circuit
protectors are standard features in 180A DC and 350A DC NRUs.
3-Phase Circuit Breaker
The 3-phase circuit breaker is the switching device between the NRU
and the 3-phase AC source used to turn power to the system on and
off; it also provides overcurrent trip and magnetic overload
protection. 3-phase circuit breakers are standard features in 900A
DC, 1500A DC, 2000A DC, 2500A DC, and 3000A DC NRUs.
AC Line, Current-Limiting Fuses
These fuses are located between the circuit breaker (or motor circuit
protector) and the diode-bridge rectifier unit. This fusing protects the
diodes from excessive currents and provides a current-limiting action
that permits a circuit breaker or motor circuit protector (with a
withstand rating less than 65,000A AC fault current available) to
effectively provide an AIC rating of 65,000A AC.