Adjacent Feeder Voltage Sag

When there is a fault condition on a circuit, the transformer at the substation will attempt to supply current to the fault for a very brief period until the line is cleared or de-energized.

The excessive current draw will depress the voltage at the substation for the length of time the transformer is trying to "feed" the load. Any other circuits on the same buss will see a sympathetic voltage drop. In many cases, this sympathetic will be large enough to cause computer and other microprocessor based equipment to drop off line. This means customers miles from the circuit problem and on entirely different feeder could experience the symptoms of a momentary outage. The actual magnitude of the voltage drop will be dependent upon impedance of the transformer and circuit. Low impedance transformers will lessen the impact of the voltage drop.