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Electrical Power Supply

Minimizing The Effects Of Line-voltage Changes

Power-line voltages normally fluctuate randomly for a variety of reasons. A special voltage-regulating transformer can improve the voltage stability of the primary power. This transformer's action is based on a coil winding that includes a capacitor which tunes the trans former's inductance into resonance at the power line frequency. When the line voltage is too high, the circulating current in the transformer's resonant winding tends to saturate the magnetic core of the transformer, reducing its efficiency and causing the voltage to fall. When the line voltage is too low, as on a hot summer day when air conditioners are taxing the capabilities of the generators and power lines, the circulating current is reduced, raising the efficiency of the transformer. The voltage regulation achieved by these transformers can be helpful even though it is not perfect. An early TV brand included resonant transformers to prevent picture-size variations that accompanied normal line-voltage shifts.

Resonant power transformers waste energy, a serious drawback, and they do not work well unless heavily loaded. A regulating transformer will dissipate nearly its full rated power even without a load. They also tend to distort the alternating-current waveform, adding harmonics to their output, which may present a problem when powering sensitive equipment.

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