Optimization Of Sizing Of Motor For Energy Conservation by Tahir Saleem

1. Optimization Of Sizing Of Motor For Energy Conservation

7. Motor Efficiencies Efficiency 0% 100% Motor Load RED - This is a standard motor efficiency. White - Motor which gets very efficient very quickly thus power factor increases dramatically for small load change. (High Efficiency Motor) Yellow - Motor runs very inefficiently and power factor has a gradual increase. (Poor Efficiency Motor) 50% 100%

9. Description of Losses Loss Type Description Iron Losses Also referred to as magnetizing or core losses. The magnetic field essential to the production of torque in the rotor causes hysteretic and eddy current losses. Copper Losses Also known as electrical losses. Current flowing through the stator and rotor winding produce resistive heating losses (1 2 R) which are appox. Proportional to the current time the winding resistance. Friction and Windage Losses Mechanical losses occurs in the Bearings and brushes of the motors. Stray Losses Include leakage Fluxes, space harmonics, and saturation effect in the stator and rotor.

10. Motor Design Improvement Technology Efficiency Improvement More Copper Improves cooling and reduces operating Larger Conductor Cross Section Temperatures and power losses Larger Rotor Bars and Rings Reduces resistance and lowers stator resistive heating losses Improved Core Design Lower flux density and increased cooling capacity reduces magnetic losses Lamination Steel Premium grade gives low core losses New Slot Design Improve both efficiency and power factor Optimized Air Gap Give lower current requirement and stray load looses Improved Fan Design Reduces windage losses and improve air flow

11. Summary Of Motor Losses: Typical NEMA B Design Motor, 10 – 20 hp; 85% Efficiency Losses Primary I2 R losses (stator) 5.6 Secondary I2 R losses (rotor) 2.7 Iron core losses 3.0 Friction and Wind age losses 1.4 Stray losses 2.3 Losses sub total 15.0 Useful Power 85.0 TOTAL 100%

13. Electric Motor Systems Motor Sizing: Motor can be correctly sized to match the load they are expected to drive.

14. Motor Selection: High efficiency motors, with improved efficiency ratings of up to 10% can be substituted for standard construction motors. Motor Controls: Where the driven equipment does not have to meet a constant demand, controls can be used to reduce capacity and improve system efficiency.

15. Motor Drive Selection and Sizing Motors and driven machines must be looked at as a “system”. To achieve an energy efficient installation, when selecting a motor or a motor control system) it is essential to:

17. Motor Sizing: The efficiency can be expressed as Motor efficiency = Output Mechanical Power Input Electrical Power The efficiency of a standard motor is a function of many factors include.

29. KW Saved =kW x %Load x 100 - 100_ Old eff. new eff. Annual Cost Savings = kW Saved x Operating Hours x Electricity Cost Simple Payback Period = Motor and Installation Cost Annual Cost Savings

30. Example: A 7.5 kW motor is rated at 1450 rpm at full load. The measured was 1480 rpm and the measured power 3.7 kW. Fraction of full load = (1500rpm - 1480rpm) =40% (1500rpm - 1450rpm) Motor Efficiency = Output Mechanical Power Input Electrical Power Motor Efficiency = 7.5 kW x 0.4 = 81% 3.7 kW

31. Example A 30 kW motor on a supply air fan operates at 30% of rated load (9 kW) which gives rise to an operating efficiency of 75%. The motor runs for 6000 hours per year. A 15 kW motor costing Rs. 30000/= to purchase and install, is proposed for this duty. The operating efficiency of the down sized motor will be 85%

32. KW Saved = 30kW x 0.3 x ( 100 - 100 )= 1.413 kW 75 85 Annual cost savings =1.413kW x 6000hrs x Rs 6 =Rs 50868 Year kWh kWh Simple payback period = six month