Energy Conservation Techniques to be Adopted to Reduce Losses in the Induction Motor

Energy Conservation Techniques to be Adopted to Reduce Losses in the Induction Motor

Q.  List out the energy conservation techniques to be adopted to reduce losses in the induction motor. 

(A) Improving  Power Quality :

• Motor performance can be increased by maintaining the voltage level within in BIS standards i.e. within the tolerance limit of  ± 6 % and keeping the frequency within the tolerance of ± 3 %. This is achieved by avoiding voltage unbalance, maintaining voltage and frequency values and avoiding harmonic distortion.

Voltage unbalance :

• 3-phase motors are designed to operate on balanced supply. Unbalance voltage causes excessive heating and vibrations. This leads to increase I2R losses. Remedy on this is to distribute single-phase loads on 3-phases.

Harmonic filters are used to reduce harmonics in the system, maintaining frequency as constant.

(B) Motor Survey :

• Motor survey is important aspect in energy conservation. Conducting a motor survey is the best way to correctly size a replacement motor.
• A motor survey should begin by reviewing and cataloging the nameplate information on the existing motor to obtain the parameters such as rating of motor, rated speed, efficiency, full-load current, etc.
• The motor nameplate is the first step of a motor survey. It gives available information, such as speed and full-load current, which is helpful while selecting the right size motor.
• Motors operate most efficiently near full load, so determining load requirements accurately is important.
• The highest efficiency is achieved above 80 percent of full load torque, below that efficiency starts to drop dramatically. 

(C) Matching Motor with Loading :

• The characteristics of motors vary widely with their load and the type of duty they are expected to perform.
• For example, the applications like constant speed, constant torque, variable speed, steep/ sudden start, continuous/ intermittent duty, frequent start/ stops, etc. should be taken into consideration carefully when deciding for the type of a motor for that specific application.
• Proper selection of the range of the motor according to load requirements will reduce the power consumption.
• The efficiency of motors operating at loads below 40% is likely to be poor and energy savings are possible by replacing these with properly sized motors, new or interchanging with another load.
• An incorrect selection of motor always leads to various problems such as premature failure of the motor causing severe production loss.

(D) Minimizing the Idle and Redundant Running of Motor :

• By minimizing the idle and redundant running of motors, prolonged idle running of machine tools, conveyors, exhaust fan, lights etc. can be avoided. Idle running of auxiliaries like cooling towers, air compressors, pumps etc. during prolonged stoppage of production machines can be avoided.

(E) Operating in Star Mode :

• In loads operating at less than 30 % of the full load, i.e. at light loads, operation of “Delta’ connected motor in “Star’ connection can save energy. If a motor is over sized and continuously loaded below 30 % of its rated shaft load , energy can be saved by permanently connecting the motor in Star.
• In many cases, the load is below 30 % most of the time, but sometimes the load exceeds 50 % in this condition automatic Star-Delta changeover switches can be installed.
• This can save upto 5 to 15 % of the existing power consumption.

(F) Rewinding of Motor :

• Rewinding of electric motors when they fail can be a cost-effective option in man ways.
• While the rewinding process is expected to be extensive and capable of bringing the motor back to a like-new condition, most rewinders do not follow every step or the precision needed to be followed in every step of rewinding. 
• This has major impact on the efficiency of a rewound motor. Rewinding will decrease the efficiency by 2-5% in most of the motors.
• New technologies are available which help reduce the losses in a rewound motor, rare cases have shown that a motor’s efficiency increased after being rewound.
• A common problem occurs when heat is applied to strip old windings : the insulation between lamination’s can be damaged, thereby increasing eddy current losses. 
• A change in the air gap may affect power factor and output torque. 
• Efficiency an be improved by changing the winding design though the power factor could be affected in process. 
• Using wires of large cross section would reduce stator losses thereby increasing efficiency.

(G) Energy Efficient Motor

• An EEM generates the same shaft output power, but uses less input power than a standard efficiency motor. 
• Energy efficient motors apply less electricity and last longer than standard motors of the same size. 
• Energy-efficient motors are defined as the motor in which design improvements are incorporated specifically to increase efficiency of motors.
• Design improvements focus on reducing intrinsic motor losses.
• Improvements include the use of lower-loss silicon steel, a longer core to increase active material), thicker wires (to reduce resistance), thinner laminations, smaller air gap between stator and rotor, copper instead of aluminium bars in the rotor, superior bearings and a smaller fan, etc.
• Energy-efficient motors now available in India operate with efficiencies that are typically 3 to 4 percentage points higher than standard motors.

(H) Periodic Maintenance

• Machine cleaning : To ensure that ventilation and motor cooling is proper. 
• Machine set up and alignment : To ensure that the belt drives and couplings are set up properly.
• Bearing lubrication : Verify that they are lubricated and sealed properly
• Condition assessment : Vibration, unusual temperature rise etc. indicate problems.  
• Performance assessment : Regularly measure supply voltage variations. Voltage imbalance leads to high losses.
• Maintenance of electrical connections in the starter and motor terminal box : The loose connections unsafe and source of heat losses. 

This will definitely save the energy in induction motor. 

Other factors are : 

(i) By phase balancing. 

(j) Matching the motor in star-mode.

(k) Use high quality bearings to reduce friction losses. 

(l)Use small cooling fan to reduce fan load. 

(m) Lower air gap reduces magnetic losses.