Eltech Engineering

Automatic Rotor Resistance Starter

Automatic Rotor Resistance Starter
Business Type Manufacturer, Exporter, Supplier, Retailer, Wholesaler
Technology As FCMA Technology
Input Voltage 415V to 15KV
Power 10KW to 6000KW
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Preferred Buyer From

Location Worldwide

Product Details

Slip Ring Induction
1 Year to 5 Years
Type of Design
Tailored Made

Generally Slipring Induction Motors are used for applications which needs High Starting Torque & same is achieved by connecting additional starting resistance in the rotor circuit. The resistance needs to be reduced continuously in steps to increase the speed of the Motor so that the required torque is maintained.


Slip dependent Rotor Resistance Starter / Controller are designed with lossy core & based on Rotor frequency dependant resistance design. This provides a low starting current with automatically reducing resistance which is inversely proportional to motor speed to provide enough starting torque & accelerate the motor with driven equipment to full speed smoothly without Electrical & Mechanical jerks.


Slip dependent Rotor Resistance Starter is connected to the Rotor Terminals of the motor, so that the starting current is limited to a low value with a high starting torque. Motor acceleration is smooth, step less and jerk less, as resistance reduction is step less and automatic. After reaching motor to full speed, Rotor Starter will be out of circuit with the help of inbuilt bypass contactor and during running motor will be acting as Squirrel cage induction motor.


These starters sense zero-speed automatically and offer high value (100%) of resistance at every new start. Thus avoid motor damage.


The Rotor Starter is designed in such a way that the resistance offered by it is frequency dependent. When the motor starts from zero speed the rotor frequency equal to supply frequency and the Rotor Starter resistance is maximum.


Salient Features:

  • Slip dependant Resistance provides automatic resistance variation during acceleration.
  • Low Starting current.
  • High starting torque.
  • Built in bypass contactor.
  • No moving parts & stepless cutting of Resistance.
  • No maintenance.


Data Required for Designing Starting Current:

  • Motor Data sheet with details of :- kW, I, V, F, N, PF, Effic, etc.
  • Driven equipment / Application details.
  • Motor Rotor Voltage (RV) & Rotor Current (RA).
  • Motor thermal withstand curve.
  • Motor current - speed curve.
  • Motor torque - speed curve.
  • Load torque - speed curve.
  • Motor Rotating Inertia (GD2).
  • Load Rotating Inertia (GD2).
  • Motor No. of starts per hour.
  • Ambient condition.



  • Cement industry - Ball mills, Wagon unloaders, Cement mills, Conveyors etc…
  • Steel industry - Ball mills, Conveyors etc…
  • Mines - Crushers, Conveyors, Pumps etc…
  • Sugar industry - Pumps, Fibrisors, Cutters, Levellers & applications which requires high starting torque.

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Comparison Table

Comparison Between Liquid Resistance Starters And Automatic Slip dependent Rotor Starters

Parameter LRS ARS
Operating Principle Resistance offered by resistive liquid, independent of rotor frequency Resistance created by eddy current loss dependent on rotor frequency
Starting current Vary between starts  depends on temperature of liquid  for same concentration and distance between electrodes Independent and constant starting performance for every start independent of temperature
life time of the starter

Depends on
1. No.of starts
2.Corrosive nature of atmosphere
3.Maintanances schedule

Independent and same as motor life
Moving parts involved in  operation in Power circuit Yes -Moving electrodes NO Moving parts
Time between starts depends on
1.Previous start
2.Ambient conditions
Independent and no limitations on between starts.
External Resistance variation Vs. Motor speed independent of motor speed . To made dependent on motor speed , one has to  go complex feed back mechanism By design principle itself  resistance is inverse proportional to motor speed
Starting Over currents Incase of counter load on motor is more , than possibility of over current bypass due to independent movement of electrodes NO possibility of over current , because resistance in circuit until motor reach full speed
Initial Cost Low High
Maintenance cost High No maintenance cost
Regular  maintenance Required Not required
Auxiliary motor Required for movement of electrodes Not required


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