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Transformer Current Inrush

October 17th Fact-of-the-Day

AC power may happen to be applied to the primary winding of a power transformer at any point in the voltage cycle. Excessive current inrush can result if the primary voltage suddenly goes from zero to a high value rather than increasing sinusoidally as it does during normal operation. Excessive inrush current to a large transformer may not only blow a fuse, trip a breaker, cause a sharp dip in mains voltage, damage transformer windings, or damage electrical supply circuits, it also induces a very large voltage spike in the transformer secondary winding. Large secondary voltage spikes can breakdown winding insulation, damage rectifiers, and damage other power supply components. A common remedy in large commercial transmitters is to initially apply AC power through one or more low-value, high wattage resistors that are short-circuited after a few AC cycles. ©2004 Martek International All rights reserved.

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