Energy Efficient Motor How Reduce Losses

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Different Losses are Minimized In Energy Efficient Motor

Q. How Different Losses are Minimized In Energy Efficient Motor.

Different Losses are Minimized In Energy Efficient Motor

Measures adopted for energy efficiency address each loss specifically as under :

(A) Core Losses :

  1. Core losses are found in the stator-rotor magnetic steel and are due to hysteresis effect and eddy current effect during 50 Hz magnetization of the core material.
  2. These losses are independent of load and account for 20-25% of the total losses.
  3. The hysteresis losses which are a function of flux density are be reduced by utilizing low-loss grade of silicon steel laminations.
  4. The reduction of flux density is achieved by suitable increase in the core length of stator and rotor. Eddy current losses are generated by circulating current within the core steel laminations Core losses are reduced by using thinner laminations.

(B) Stator and Rotor I’R losses : 

  1. These losses are major losses and typically account for 55% to 60% of the total losses. I’R losses are heating losses resulting from current passing through stator and rotor conductors. I’R losses are the function of conductor resistance and the square of current.
  2. Resistance of conductor is a function of conductor material length and cross-sectional area. The suitable selection of copper conductor size will reduce the resistance.
  3. Reducing the motor current is most readily accomplished by decreasing the magnetizing component of current. This involves lowering the operating flux density and possible shortening of air gap. Rotor I2 R losses are a function of the rotor conductors (usually aluminium) and the rotor slip Utilization of conductors will reduce the winding resistance. 
  4. Motor Operation closer to synchronous speed will also reduce rotor I2 R losses.

(C) Friction and Windage Losses : 

  1. Friction and windage losses results from bearing friction, windages and circulating air through the motor and account for 8-12% of total losses. 
  2. These losses are independent of load. The reduction in heat generated by stator and rotor losses permit the use of smaller fan. The windage losses also reduce with the diameter of fan leading to reduction in windage losses.

(D) Stray Load Losses :

  1. These losses vary according to square of the load current and are caused by leakage flux induced by load currents in the laminations and account for 4 to 5% of total losses. These losses are reduced by careful selection of slot numbers, tooth/ slot geometry and air gap. 
  2. Energy efficient motors cover a wide range of ratings and the full load efficiencies are higher by 3 to 7%. The mounting dimensions are also maintained as per IS 1231 to enable easy replacement.
  3. As a result of the modification to improve performance the costs of energy efficient motors are higher than those of standard motors. The higher cost will often be paid back rapidly in saved operating costs, particularly in new in new applications or end-of life motor replacements.
  4. In cases, where existing motors have not reached the end of their useful life, the economics will be less clearly positive. 
  5. Because the favorable economics of energy-efficient motors are based on savings in operating costs, there may be certain cases which are generally economically ill-suited to energy efficient motors.
  6. These include highly intermittent duty or special torque applications such as hoists and cranes, drives punch presses, machine tools and centrifuges. In addition energy efficient designs of multi-speed motor are generally not available. 
  7. Furthermore energy efficient motors are not yet available for many special applications, e.g. for flame-proof operation in oil-field or fire pumps or for very low speed applications. 
  8. Also most energy efficient motors produced today are designed only for continuous duty cycle operation. 
  9. Given the tendency of over sizing on the one hand and ground realities like, voltage, frequency variations, Efficacy rewinding in case of a burnout, on the other hand, benefits of EEMs can be achieved only by  careful selection, implementation, operation and maintenance efforts of energy managers.

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