Copper saves moremoney in the long runThere is a capital investment that can repaymany times its original value over the next 20years. And at the same time, improve equipmentreliability, reduce downtime and repair costs, andresult in lower releases of carbon dioxide to theatmosphere.The formula is straightforward: install high efficiencymotors having the highest electrical energyefficiency commensurate with your needs.High efficiency motors pile up savings worth manytimes their purchase cost for as long as they remainin service.
Understanding or its equivalent, Efficiency, % = Watts (Input ) - Watts (Losses) x 100Electrical Efficiency Watts (Input) “Losses” stands for all the energy “fees” the motorElectric motors are simply devices that convert charges in order to make its electrical-to-mechanicalelectrical energy into mechanical energy. Like all energy conversion. Their magnitude varies fromelectromechanical equipment, motors consume motor to motor and can even vary among motors ofsome “extra” energy in order to make the conversion. the same make, type and size. In general, standardEfficiency is a measure of how much total energy a motors have higher losses than HEMs.motor uses in relation to the rated power deliveredto the shaft. Types of LossesA motor’s nameplate rating is based on output Energy losses in electric motors fall into fourhorsepower, which is fixed for continuous operation categories:at full load. The amount of input power needed to • Power lossesproduce rated horsepower will vary from motor to • Magnetic core lossesmotor, with high-efficiency motors (HEM) requiring less • Friction and windage losses, andinput wattage than less-efficient models to produce • Stray load losses.the same output. Electrical energy input is measuredin watts, while output is given in horsepower. (This Power losses and stray load losses appear onlyconvention applies in the USA; output power for when the motor is operating under load. They aremotors manufactured in other countries may be therefore more important than magnetic core lossesstated in watts or kilowatts.) One horsepower is and friction and windage losses, which are presentequivalent to 746 watts. even under no-load conditions.There are several ways to express motor efficiency, Power losses, also called I²R losses, are the mostbut the basic concept and the numerical results are important of the four categories and can account forthe same. For example: more than one-half of a motor’s total losses. PowerEfficiency, % = 746 x Horsepower (output) x 100 losses appear as heat generated by resistance Watts (input) to current flowing in the stator windings and rotor conductor bars and end rings.Efficiency, % = Watts (output) x 100 Watts (input) Stator losses make up about 66% of power losses, and it is here that motor manufacturers have achievedThe ratio describes efficiency in terms of what can significant gains in efficiency. Since increasingbe observed from outside the motor, but it does the mass of stator windings lowers their electricalnot say anything inside that makes one motor more resistance (and therefore reduces I²R losses), HEMsor less efficient than another. For example, we can typically contain about 20% more copper thanrewrite the equation as: standard models of equivalent size and rating.Efficiency, % = Watts (output) x 100 Watts (output) + Watts (Losses)
Rotor losses, another form of power losses, are also High electrical conductivitycalled slip losses because they are largely (but notentirely) dependent on the degree of slip the motor Conductivity is an important characteristic of thedisplays. Slip is the difference in rpm between the rotor. Conductor bars in large motors are normallyrotational speed of the magnetic field and the made from high-conductivity copper. Conductoractual rpm of the rotor and shaft at a given load. bars in small-to-intermediate size motors, up toS = Ns - N about 200 hp, depending on manufacturer, are in Ns the form of a die-cast aluminum “squirrel cage” thatWhere “S” is “slip”, “N” is “output speed under load” gives these motors their common name. Increasingand “Ns” “synchronous (no-load) speed, rpm”. the mass of the die-cast bars requires changes in the slots in the rotor laminations, through which theRotor losses are reduced by decreasing the degree bars are cast, and that changes the rotor’s magneticof slip. This is accomplished by increasing the mass structure. Lowering rotor I²R losses in what are typicallyof rotor conductors (conductor bars and end-plates) aluminum alloy squirrel cage motors is therefore notand/or increasing conductivity, and to a lesser a simple task.extent by increasing the total flux across the air gapbetween rotor and stator. Copper has higher electrical conductivity than aluminum, and it would be an ideal conductorMagnetic core losses arise from hysteresis effects, bar material except for the fact that it is difficult toeddy currents and magnetic saturation, all of which die cast. A process to produce die-cast coppertake effect in the steel laminations. Magnetic losses rotors has recently been developed and, when fullycan account for up to 20% of total losses. With commercialized, it will enable the production ofproper design, use of better materials and stringent motors with even higher efficiencies than the bestquality control, these losses can be reduced models currently available.considerably. The fact that HEMs tend to have less slip (run faster)The most effective means to reduce hysteresis and than standard motors must be taken into account insaturation losses is to utilize steels containing up to certain applications.4% silicon for the laminations in place of lower-costplain carbon steels. The better magnetic properties For example, energy consumption by centrifugaloffered by silicon steels can reduce core losses by loads such as fans and rotary compressors is10 to 25%. proportional to the cube of rotational speed. If such loads are driven at the higher speed of a low-slip,Reducing the laminations’ thickness also helps: HEM directly replacing a standard motor, energysubstituting 26-ga or 29-ga steel for the 24-ga steel consumption can actually increase. This situationfound in standard motors lowers core losses by can sometimes be resolved by lowering rotationalbetween 15 and 25%. Lengthening the lamination speed with a variable-speed drive, gears or pulleys.stack, which reduces the flux density within the stack, There are other parameters, such as torque oralso reduces core losses. Eddy current losses can be starting current, that can vary among motors ofreduced by ensuring adequate insulation between the same nominal horsepower. It is important tolaminations, thus minimizing the flow of current (and properly engineer the application of any motor toI²R losses) through the stack. the intended task.