Sources of sags and interruptions

Sources of sags and interruptions:

 A sudden increase in load results in a corresponding sudden drop in voltage.

 Any sudden increase in load, if large enough, will cause a voltage sag in:

o  Motors

o  Faults cause the voltage sag.

o Switching operation

 Since the electric motors draw more current when they are starting than when they are running at their rated speed, starting an electric motor can be a reason of voltage sag.

 When a line-to-ground fault occurs, there will be voltage sag until the protective switch gear operates.

 Some accidents in power lines such as lightning or falling an object can be a cause of line-to-ground fault and voltage sag as a result.

 Sudden load changes or excessive loads can cause voltage sag.

 Depending on the transformer connections, transformers energizing could be another reason for happening voltage sags.

 Voltage sags can arrive from the utility but most are caused by in-building equipment. In residential homes, we usually see voltage sags when the refrigerator, air-conditioner or furnace fan starts up.