AC Controls

Solid-State Reduced Voltage Starters

General

Operation

The solid state motor controller uses silicon 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.

Shorted SCRa

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 Stopa

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.

Class 70 / 71

Siemens-Furnas Class 70 / 71 combines Digital Signal Processor control and silicon controlled rectifier (SCR) technologies 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 control 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.

aAvailable on 2000+ Starter

3-Phase Control Configuration

When SCR triggering is delayed, the voltage 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

15

Controls AC

CSI Section 16160

Siemens Electrical Products and Systems

307

 

Specification Guide