Page 69 - Electric Drives and Electromechanical Systems

62 Electric Drives and Electromechanical Systems

FIG. 2.14 Distortion in the supply input to a drive system due to externally generated harmonics or chopping.
(A) Distortion of the supply caused by chopping. (B) Distortion caused by the addition of externally generated
harmonics to the supply.
spikes may cause a hardware (particularly in power semiconductors) failure in
the equipment. Manufacturers of critical equipment often provide a certain degree of
protection by including surge arrestors or snubbers in their designs. However, spikes of
very large magnitude in combination with a higher frequency may result in a stress-
related hardware failure, even if normal protection standards are maintained. A
chopped voltage and harmonics have the potential to interfere with a drive system if it
is not designed to be immune from such effects.
Power conditioning provides an effective way of suppressing some or all of the
electrical disturbances other than the power outages and frequency. Typical methods of
providing power conditioning include:

Metal-oxide varistors, which provide protection against line-mode voltage spikes,
Electromagnetic interference filters, which help to prevent the effect of the
chopped waveforms on the equipment as well as to prevent the equipment from
conducting high-frequency noise into supply