Power quality test instruments are used when electronic devices are suspected of polluting power supply circuits. Some symptoms of line pollution include motors overheating for no apparent reason, premature winding failure, current-caused ball bearing failure, tripped breakers, hot conduit and/or neutral, and damaging voltage spikes. Figure 8.15 shows an instrument for testing power quality.
Circuits which power large numbers of computers are a problem for supply transformers if no correction is done. Electronic motor controls cause
FIGURE 8.15 An instrument for checking a circuit’s power factor and power quality. EXTECH Instruments.
even greater damage to them than the computers because higher amperes are involved. Remedial equipment (reactors, etc.) is essential for preventing equipment breakdown.
The tests should be done over a long enough period of time to cover all possible conditions.
Identifying and installing remedial equipment is a service that is often outsourced. The use of these test instruments requires specialized training and experience. It is often a one-time service. Safety training for personnel doing these tests is very important because the tests are done with live power.
The meter in Fig. 8.15 is used to determine the phase angle needed for power factor calculating. The consequence of a low power factor can be expensive penalties from the power supplier. A low power factor also affects motors by causing low voltage.
Low power factor is corrected with specially designed capacitors or with synchronous motors. Many industries outsource this procedure because it is normally a one-time service and takes special training. Some electric motor repair centers offer the service. Safety training is very important for personnel doing these tests because they are done with live power lines.
Vibration Sensors
Vibration is the leading cause of bearing failure. It is also an indication of impending bearing failure. Portable instruments work well for spot-checking, but continuously operating machinery should be monitored by attached sensors (Fig. 8.16.)
8.16 This instrument will check vibration, and has noncontact tachometer capability. EXTECH Instruments.
Vibration sensors will automatically give a warning when a preset level of vibration is reached. Corrective action can then be scheduled before catastrophic failure occurs. Electric motor repair centers balance repaired motors in accordance with EASA specifications. Some also offer in-plant machinery balancing. The service is often outsourced because it takes special training.
Laser Alignment
Laser alignment is the most accurate of all alignment methods (Fig. 8.17). It has been used successfully on multilevel shaft applications that require exact precision. It is easy to use and virtually eliminates mistakes that are common with other alignment procedures.
8.17 Laser alignment equipment. SKF USA Inc.
Flexible couplings are designed for a small degree of misalignment. Experience has shown, however, that vibration will occur unless alignment is nearly perfect.