Rockwell Automation 2364F Regenerative DC Bus Supply Unit (RGU) - Manual (Page 20)

Publication 2364F-5.01– October 2003
1-4 Overview
Descriptions of the Primary Electrical Components
Motor Circuit Protector
The motor circuit protector is the disconnect device between the RGU
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 J, K, and L-code RGUs.
3-Phase Circuit Breaker
The 3-phase circuit breaker is the disconnect device between the
RGU 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 M and
N-code RGUs.
AC Line, Current-Limiting Fuses
AC line, current-limiting fuses are placed between the circuit breaker
(or motor circuit protector) and the RGU power structure. This fusing
protects the bridge 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.
AC Line Reactors
AC line reactors reduce peak currents and harmonics in the AC line
and peak currents of the bridge circuit; they facilitate current flow
from the RGU to the 3-phase AC line during regeneration; and they
act as a known AC line impedance to the RGU which functions as a
power source while motoring or regenerating.
RGU Power Structure
The RGU power structure is the 3-phase power bridge which converts
the 3-phase AC power to DC and DC power to 3-phase PWM AC.
If the RGU is precharged (main contactor closed) but not enabled
(RGU not modulating), the RGU functions as a simple six diode
3-phase rectifier. The six diodes are the freewheeling diodes inside
the IGBTs, which are capable of supplying 100% motoring current to
the DC bus.