What is the difference between high efficiency and premium efficiency motors are

As a result, premium efficiency motors are typically larger and heavier than standard electric motors. Other common characteristics of premium efficiency motors include:. Copper is a valuable material in a premium efficient design because it produces higher electrical conductivity compared to other metallic conductors.

According to the U. Department of Energy, it would only take ten years for the NEMA premium efficiency motor program to:. To put this into perspective, the results would be the same as keeping 16 million cars off the road.

Premium efficiency motors can help to significantly lower global greenhouse gas emissions. However, motor buyers generally concentrate on price, not electricity consumption. It goes without saying that more-efficient motors will consume less energy and reduce their owners' electric bills over the long run, but a rapid return on investment is most likely when the motors operate at high duty cycles. Motors that operate intermittently may or may not save enough to justify replacement except in cases where utility rates are especially high.

But, in evaluating motors that operate at a high duty cycle, or continuously, replacement with energy-efficient motors can usually result in very rapid payback, and save many times their initial cost. Today, many industrial organizations are seeking ways to display their concern for the environment. Establishing and implementing a policy to use high-efficiency motors is one way to demonstrate environmental concern and, at the same time, save energy and money.

In fact, numerous companies have already won national recognition by including high-efficiency motors in their corporate energy policies. As to the cost of the motors themselves, a number of utilities and state agencies now offer incentive programs in the form of rebates and cost-sharing programs that encourage their customers to install the efficient devices. Utilities benefit from these demand-side management programs because the improved motors reduce the need to bring new power sources on line.

Electric motors are simply devices that convert electrical energy into mechanical energy. Like all electromechanical equipment, motors consume some "extra" energy in order to make the conversion. Efficiency is a measure of how much total energy a motor uses in relation to the rated power delivered to the shaft. A motor's nameplate rating is based on output horsepower, which is fixed for continuous operation at full load. The amount of input power needed to produce rated horsepower will vary from motor to motor, with more-efficient motors requiring less input wattage than less-efficient models to produce the same output.

Electrical energy input is measured in watts, while output is given in horsepower. This convention applies in the USA; output power for motors manufactured in other countries may be stated in watts or kilowatts.

One horsepower is equivalent to watts. There are several ways to express motor efficiency, but the basic concept and the numerical results are the same. For example:. The ratio describes efficiency in terms of what can be observed from outside the motor, but it doesn't say anything about what is going on inside the motor, and it is what's happening inside that makes one motor more or less efficient than another.

For example, we can rewrite the equation as:. Their magnitude varies from motor to motor and can even vary among motors of the same make, type and size. Power losses and stray load losses appear only when the motor is operating under load. They are therefore more important - in terms of energy efficiency - than magnetic core losses and friction and windage losses, which are present even under no-load conditions when the motor is running, of course.

Power losses appear as heat generated by resistance to current flowing in the stator windings and rotor conductor bars and end rings. Rotor losses, another form of power losses, are also called slip losses because they are largely - but not entirely - dependent on the degree of slip the motor displays. Slip is the difference in rpm between the rotational speed of the magnetic field and the actual rpm of the rotor and shaft at a given load.

Rotor losses are reduced by decreasing the degree of slip. Conductivity is an important characteristic of the rotor. Conductor bars in large motors are normally made from high-conductivity copper. Conductor bars in small-to-intermediate size motors, up to about hp, depending on manufacturer, are in the form of a die-cast aluminum "squirrel cage" that gives these motors their common name.

Increasing the mass of the die-cast bars requires changes in the slots in the rotor laminations, through which the bars are cast, and that changes the rotor's magnetic structure. The fact that high-efficiency motors tend to have less slip run faster than standard-efficiency motors must be taken into account in certain applications.

For example, energy consumption by centrifugal loads such as fans and rotary compressors is proportional to the cube of rotational speed. If such loads are driven at the higher speed of a low-slip, high-efficiency motor directly replacing a standard motor, energy consumption can actually increase.

This situation can sometimes be resolved by lowering rotational speed with a variable-speed drive, gears or pulleys. There are other parameters, such as torque or starting current, that can vary among motors of the same nominal horsepower.

It is important to properly engineer the application of any motor to the intended task. Magnetic core losses arise from hysteresis effects, eddy currents and magnetic saturation, all of which take effect in the steel laminations.

In general, efficiency levels become higher as motor horsepower increases, as shown in the following table from NEMA:. This table is for motors operating at full-load. Although efficiency gains may seem small when upgrading to a higher motor class, consider that the power loss reduction is significant. Motor efficiency gains between classes seem small when viewed as percentages, but the benefits are evident once percentage gains are translated to kilowatts and power bill savings.

Like with any energy efficiency upgrade , it is important to carry out a detailed technical and financial assessment before purchasing NEMA Premium Efficiency motors. Consider the following recommendations before proceeding with a purchase:. IEC efficiency classes cover motors from 0.

Motors can have 2, 4 or 6 poles, and can be designed to operate at 50 Hz or 60 Hz. NEMA Premium Efficiency motors can yield thousands of dollars in yearly savings when deployed in commercial and industrial facilities, and even higher savings are available if they are complemented with a variable frequency drive VFD. However, keep in mind motors must also be a good match for their application to guarantee efficient operation and a long service life, so professional guidance is highly recommended before any motor upgrade.

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