They result because the system is either too weak for the desired voltage regulation or the voltage controls are inadequate. Incorrect tap settings on transformers can also result in system overvoltages. Undervoltages result from events which are the reverse of those causing overvoltages. A large load switching on or a capacitor bank switching off can cause undervoltage until voltage regulation equipment can bring the voltage back to within tolerances. Overloaded circuits can also cause undervoltages.
Imbalance can also be the result of blown fuses in one phase of a three-phase capacitor bank.
Waveform Distortion Waveform distortion is defined as steady-state deviation from an ideal sine wave of power frequency principally characterized by the spectral content of the deviation. There are five primary types of waveform distortion which are listed below. The presence of stray dc voltage or current in an ac power system is called dc offset. This can occur as a result of a geomagnetic disturbance or the effects of half-wave rectification. Incandescent light bulb life extenders, for example, may consist of diodes that actually reduce the rms voltage supplied to the light bulb by half-wave rectification.