E-ASR for Slip Ring Induction Motor

E-ASR for Slip Ring Induction Motor

  • We use closed loop control using a PLC
  • We offer electronic auto slip regulator to solve the problem of productivity of crushing capacity, especially in sugar and cement industries
  • As shown in Fig 2., the load on fiberize/leveller/crusher is very erratic in nature where the motor encounters sudden kick load due to irregular cane loading
  • Additional slip is required (up to 15% slip) to smoothen the kick load. Rotational kinetic energy along with motor power will contribute to overcome the kick load
  • KE contribution = 1/2x(MI)x(Dw) 2, where, MI = Moment of Inertia, (Dw) = Reduction in speed up to 15%
  • Conventional buffer resistance has helped to stabilize the kick load (as shown in fig.3.) but creates loss in the resistance equal to 15% of motor running load
  • Old-ASR was able to save the energy compared with fixed type buffer resistance. However, it is observed that old electromagnetic ASR suffers from poor P.F. regulation of motor (i.e from 0.5 to 0.6 approx.) being an inductive scheme. This also reduces the torque capacity of the motor as shown in fig.4.
  • This leads to motor underutilized by a factor of around 20-25% and it affects the net crushing capacity of the sugar/cement factory. This also reduces the motor torque
  • E-Auto Slip Regulator Principle

  • As shown in Figure 5, the e-ASR scheme consists of resistances connected in series which are switched on and off using fast thyristors across resistances depending on the load of the motor.
    When the load is high then resistances are added thereby increasing the slip as shown in Figure 6. When the load is reduced, resistances are taken off thereby reducing the slip, saving energy
1 KW 318 kW 386 kW
2 KVAR 464.5 kvar 344 kvar
3 KVA 563.3 kVA 517 kVA
4 PF 0.568 lag 0.742 lag
5 Current 827.7 A 750 A
6 Crushing Rate 3600 Tones/Day 4100 Tones/Day

This data was recorded with old-ASR and e-ASR panels through power analyser and average values are given.

Advantages of e-ASR:

  • Restores the motor P.F. to rated P.F
  • Improves the motor torque by addition of variable resistance in rotor circuit as shown in fig.A
  • Increases the life of motor due to reduction is current
  • Saves energy up to 10% when compared with constant buffer resistance. Even when compared with ASR of electromagnetic type, extra 3-5% energy saving potential exist
  • Improves the crushing rate of sugar and cement plant


  • Do I need e-ASR even after adding P.F capacitor to motor?

    Here it is important to note that adding P.F. capacitor on motor terminal will improve line P.F but motor P.F will remain poor due to inductive nature of old-ASR
    To improve motor P.F, e-ASR must be added
  • Will this e-ASR generate Harmonics?

    The answer to this is NO.
    Although it works based on power electronic thyristors, it does not generate any harmonics because it works on the principle of integral cycle control and not the phase angle control. Hence there is no scope for any harmonics from e-ASR
  • It is reliable to use e-ASR?

  • We are using thyristors having a peak inverse voltage of at least 2 kV which makes the e-ASR more reliable. This is because during the running operation of motor the voltage on the rotor side never goes beyond 10% of the rotor voltage
  • This e-ASR being installed to rotor circuit of motor, the thyristor units are not subjected to any direct surge from line side of motor