Once the efficiency of the motor is addressed, it is important that it be installed in such a way that the energy efficiency potential of the motor is realized and reliability is maximized. As noted at the beginning of this chapter, the system may account for a greater share of the energy use characteristics than the motor itself. The installation parameters considered in this section include motor speed, shaft alignment, electrical supply, and motor operating characteristics.

• Motor Speed
• Alignment
• Electrical Supply
• Operating Characteristics

Motor Speed

The first thing to check when installing any new motor is its operating speed. While (on average) energy-efficient motors have higher full-load speeds than standard motors, there is a significant variation in speed within all types of motors. Installing a motor with a higher operating speed can result in increased energy consumption on centrifugal loads (e.g., fans and pumps). This speed change can sometimes lead to overloading of the motor, which can result in premature failure.

Ideally, the first step in the replacement process is to characterize the actual load requirements. This determination frequently requires monitoring and engineering analysis, and as a result is only justified for major applications. At a minimum, the operating speed of the equipment with the new motor should be as close to the old motor as possible. For belt-driven equipment, the speed difference can be compensated for by changes in pulley size. The flow of direct-drive pumps can be adjusted by trimming impellers. These approaches are a low cost, preferred solution to maintaining speed for constant load applications.

If a more complete characterization is desired, it should include whether the present flow (air or water) is correct and whether there is any significant variation in the flow requirements. As an example, for a main HVAC distribution fan, the temperature rise/drop across heat exchanger and register discharge pressure should be measured to determine if the flow is appropriate to the equipment design specifications. Dampers should be checked to ensure that they are not substantially closed. If the flow is varied by dampers, the maximum and minimum flows should be measured and an estimate of the frequency of the flow change made. If the ratio between maximum and minimum flow is greater than two to one, some means of varying the motor speed should be considered.

For fluctuating loads with significant annual run times, an adjustable speed drive should be considered. These devices allow the motor speed to be varied to follow the load and thus minimize energy consumption. ASDs can more than double motor system cost but the energy savings from properly designed applications can be impressive, sometimes exceeding 50 percent. If the load is not continually varying but is operated in two specific operating regimes (e.g., a HVAC system with a lower flow requirement during heating and a higher requirement during the cooling season), there are other less costly options that can be considered. Dual pulleys can be installed on the motor and fan drive-shafts, and the speed can be changed manually as part of the seasonal change-over (although these options are generally available only in standard-efficiency models). In some applications, a two-speed motor may be an option. (A multi-speed motor has multiple windings allowing the motor to be operated at two or more different speeds by switching how the electricity is supplied to the motor.) In general, these motor are less efficient and more costly than single-speed motors but the energy savings from reduced operating speed will frequently make this an attractive option.

ASDs have gained an undeserved reputation for unreliability. Most of these problems can be traced to problems with the electrical supply (discussed below) or a mismatch between the drive and motor. If the drive and motor are not electrically compatible, harmonics can cause the motor to overheat or experience excessive vibration, both of which will lead to premature failure. These problems can be avoided by checking with the motor and drive manufacturers before installing the ASD. To address this potential problem, many of the motor manufacturers are now offering matched motor/ASD packages. EPRI and BestPractices Motor Systems are now making available a design and selection tool, ASDMaster.

Alignment

Proper motor-shaft alignment reduces motor load and extends bearing life, and increases the torque delivered to the load. Perfectly aligned motors lose less than 1 percent of transmitted torque while each degree of misalignment increases torque loss by 1 percent. Beyond 5 degrees, bearing failure results. Misalignment is in fact the leading cause of bearing failure. Most coupling and transmission systems allow for some flexing but this flexing among the components results in increased friction that robs the load of torque and produces energy losses.

The best shaft alignment procedure involves first securing the driven equipment, then working back to the motor. The recommended alignment tolerance is 5/1,000 of an inch at the coupling but many experts feel that the tolerance should be measured at the bearings for a more precise alignment. For maximum energy and reliability benefit, however, the misalignment should be as close to zero as possible.

There are a number of alignment methods in use ranging from a crude "straight edge" method, to dial indicators, to laser alignment. The straight edge method is appropriate only for low speed (i.e., no greater that 300 rpm) and belt systems where other alignment methods are impractical. The dial indicator method is the most widely used and with appropriate attention to detail produces good results for all systems except high-speed equipment (i.e., about 3,600 rpm) where the greater cost of the laser systems is required (Energy-Efficient Motor Systems Handbook).

Electrical Supply

The equipment that supplies electricity to motor systems can produce energy losses and adversely affect the reliability and life of the motor. Ideally, the electricity driving a motor should be at the design voltage and frequency, and have a sinusoidal wave form. Unfortunately these conditions frequently are not met. These deficiencies can adversely affect both the efficiency and the life of the motor.

System deficiencies fall into the following four broad categories:

1. Voltage imbalances in three-phase systems;
2. Excessively high or low system voltage;
3. Low power factor; and
4. Power quality problems (most frequently voltage transients and harmonics).

Voltage imbalances can result from imbalanced circuits in the facilities, frequently resulting when single-phase lighting is all operated off a single leg of the primary three-phase service. In some cases, the phase imbalance may result from problems in the utility supply system, especially if the facility is relatively far from the nearest substation. Transient imbalances, or loss of one or two phases, can result from a utility equipment failure such as the loss of a transformer. This problem, often referred to as "single phasing," often occurs due to lighting strikes and can result in electrical failure of the motor. Devices called phase monitors are available that measure the differences between the phases and will shut down the circuit if the difference reaches levels that can cause damage. If a facility is in an area prone to outages, such as rural areas, these devices should be considered for large motors and expensive devices such as refrigeration compressors.

One solution to many under-voltage conditions is to increase the size of cabling. In addition to reducing voltage drops in the cable, the increased conductor diameter has the added benefit of reducing line losses. Low power factor can be corrected by using capacitors connected to the motor or at the point of electricity distribution. Improving system power factor yields significant electricity bill savings by reducing utility charges for low power factor. It can also result in electricity savings by reducing line currents, which in turn reduce cable and transformer losses (Dorhofer, F.J., and W.H. Heffington. 1994. "Electrical Energy Monitoring in an Industrial Plant." In Proceeding of the 16th National Industrial Energy Technology Conference, 269-274. Houston, Tex.: Texas A&M University.). Power quality problems can result from electricity supply problems external to the facility but are frequently associated with equipment at the facility such as switching power supplies used in adjustable speed drives and computers. Various types of filters and surge suppressors can be used to address these problems but if the problem is not correctly identified, the solution can make the problem worse. As a result, a technician experienced with these problems is required to correctly diagnose the problem and propose the correct solution. Many utilities have developed teams of experts to help deal with these problems in customer facilities.

ACEEE has estimated that improvements to electric supply systems can result in a 1 to 5 percent savings in motor loads, along with improved reliability and extended motor life. Many of these improvements will also result in additional energy savings and improved reliability in non-motor electrical loads (Energy-Efficient Motor Systems Handbook).

Operating Characteristics

Some efficient motors may cause breakers to trip because they have a higher starting current spike. This current is too short lived to trip hybrid or thermal breakers but may cause problems with magnetic breakers. If magnetic breakers trip, the problem can be addressed by adjusting the set point on the breakers or by replacing the breakers with new models.