ABB A43, User Manual

Page: 51 / 295

Technical Description
2CMC48001M0201
51 A43/A44
Revision: C User Manual
Negative effects of harmonics
The presence of harmonics in voltages and currents can cause a number of prob-
lems:
•
Increased cable losses. At higher frequencies skin and proximity effects
increases, resulting in increased losses.
•
High current in the neutral wire.
•
Motor efficiency and product lifetime will decrease if the voltage contain
harmonics.
•
In transformers, harmonics will cause higher wire, hysteresis and eddy
losses, which could result in efficiency losses up to 50%.
•
Voltage harmonic can give higher peak voltages (higher crest factor),
causing overvoltage protection devices to trip and in worst case
destruction of devices.
•
Voltage harmonic can result in decreased product lifetime and in worst
case destruction of capacitor banks (used for power factor correction).
•
Voltage harmonic can cause malfunction of devices controlled by the
voltage, often zero crossings (voltage harmonics can give extra zero
crossings).
•
Voltage harmonics can produce disturbances within devices having its
power supply connected to the mains causing problems.
Eliminating negative effects of harmonics
Because of the negative effects of harmonics it may be necessary to take actions to
decrease the problems. This can be either done by decreasing the harmonics, and/or
taking actions that decrease the negative effects of the harmonics.
Suggested actions
•
Increase the size of the neutral conductor if the current is abnormally high
due to harmonics.
•
Install appropriate filters to isolate loads with high current harmonics.
•
Install filters to protect to protect loads that are sensitive to voltage
harmonics.
•
Oversize generators, motors and transformers to better cope with
harmonics.
•
Substitute equipment for equipment that generates less current harmonics
and is less sensitive to voltage harmonics.