ABSTRACT
Power frequency disturbances can last anywhere from one complete cycle to several seconds or even minutes. The effects of power frequency disturbances vary from one piece of equipment to another and with the age of the equipment. One of the most common power frequency disturbances is voltage sag. Voltage sag is an event that can last from half of a cycle to several seconds. Arc furnaces are an example of loads that can produce large voltage sags in electrical power systems. Arc furnaces employ large inductors to stabilize the current due to the arc. Flicker is a low-frequency phenomenon in which the magnitude of the voltage or frequency changes at such a rate as to be perceptible to the human eye. Isolation transformers do not help in curing voltage sags or swells; they merely transform the voltage from a primary level to a secondary level to enable power transfer from one winding to the other.
