Download Print this page

HP Class MMS and MRS User Manual page 24

Manual starters and switches

Advertisement

AC Controls
Solid-State Reduced Voltage Starters
Class 70 / 71
Siemens-Furnas Class 70 / 71 combines
Digital Signal Processor control and sili-
con controlled rectifier (SCR) technolo-
gies to provide optimum AC induction
motor starting and operation. It provides
soft start, energy savings,* soft stop,*
and added protective features.
The basic controller consists of electronic
circuit boards linked via flat cable connec-
tors. The main functions of the basic
assembly are to monitor the operating
parameters of the controller and to con-
trol the firing sequence of the SCR's.
The power module located below the
basic controller controls power to the
motor. The incoming and motor load
connections are made to terminal blocks
located on the top and bottom of the
power module.
The starters are available either as NEMA
Type 1, 12, or 4 enclosures. Units are
supplied with solid-state overload relays
as complete starters, or as combination
starters with fusible, non-fusible discon-
nect, or thermal magnetic circuit breakers
with or without shunt trip features.
Additional options are also available.
The Class 70 / 71 is designed to operate
3 phase AC induction motors at 208 to
575 volts and 6.1 to 960 amperes at 50
or 60 Hertz.
Available on 2000+ Starter
CSI Section 16160
Operation
The solid state motor controller uses sili-
con controlled rectifiers (SCR's) to control
the voltage to the motor windings. Each
SCR acts as a switch that can be turned
on with any electronic trigger signal at
any point on the voltage waveform and
turns off when the current waveform
crosses zero. Two SCR's are used in a
back-to-back arrangement in each phase
to allow alternating current to pass to
the motor.
3-Phase Control Configuration
When SCR triggering is delayed, the volt-
age to the load is reduced. This phase-
controlled operation provides soft starting
with stepless acceleration. Once the
motor is running, voltage reduction can
improve the motor's operating point at
partial load, saving energy and lowering
the reactive current.
3RW2 Phase Control
Siemens Electrical Products and Systems
Specification Guide
Shorted SCR
If one or more shorted SCRs are detect-
ed, the starter will not energize. A fault
LED will light and if provided with a
shunt trip, the main circuit breaker will
trip.
Pump Stop
This option eliminates water hammer in
pumping systems, by giving a controlled
decel to the motor voltage. This process
allows for smooth pressure reduction
and quiet check valve operation.
Phase Loss
The controller will trip off the line if one
or more phases is lost.
General
15
307

Advertisement

loading

This manual is also suitable for:

SmfF02K02MmsMrs