Power Standards Lab - Other Disturbances

Tutorial

Other Power Disturbances

Some Other Common Disturbances

The most common disturbances on AC power systems are voltage sags or dips. Other problems, such as transient overvoltages and brief interruptions, occur almost everywhere. Problems with harmonics, voltage regulation, and flicker occur at a wide range of sites.

Some other disturbances that occur at specific locations include:

Frequency variations. On utility grids, these are rare events, usually associated with catastrophic collapses on the grid. However, at sites with back-up diesel generators, they are common.
High frequency noise. This can be caused by anything from arcing brushes on a motor, to local radio transmitters.
Mains signalling Some utilities intentionally place small signals on the mains voltage to act as control signals (for example, they may control a capacitor switch, or they may instruct revenue meters to go to a different rate structure).
EFT Extremely Fast Transients are nano-second range transient overvoltages. Due to their high frequency content, they do not travel well over the mains circuits, getting damped out within a few meters. However, they can be caused by nearby contact arcing.
Unbalance On three-phase systems, the voltages and currents on each phase should, in theory, match the voltages and currents on the other phases. Sometimes they don't.

For more information about other rare or unusual power disturbances, please contact me, and I will be glad to help.

Alex McEachern, 1/2004