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Phased Zero Voltage Start for Transformer Input

IP.com Disclosure Number: IPCOM000091331D
Original Publication Date: 1968-Jan-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Koranye, TD: AUTHOR

Abstract

This circuit minimizes the initial line current surge to a core of transformer T by selecting the polarity of the first energizing cycle. If the last energizing cycle is always of one polarity and the first cycle at turnon is of the opposite polarity, the core does not go into saturation and core magnetizing current is held to a minimum.

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Phased Zero Voltage Start for Transformer Input

This circuit minimizes the initial line current surge to a core of transformer T by selecting the polarity of the first energizing cycle. If the last energizing cycle is always of one polarity and the first cycle at turnon is of the opposite polarity, the core does not go into saturation and core magnetizing current is held to a minimum.

The circuit shows a three-phase, four-wire, switched power supply system with load 1 in phase one that is energized only when contacts 6 and relay points 4 are closed. A zero phase-shift detecting and delay circuit 5 assures the closure of relay points 4 at a zero voltage crossover point of phase one.

If, after relay points 4 close due to closure of switch 11, the phase one voltage goes positive, transformer 7 does not produce in its secondary winding a voltage of sufficient amplitude to turn on SCR3. When the phase one voltage goes negative, SCR2 is turned on via closed relay points 4 to energize load 1 via transformer T. When switch 11 is opened, SCR2 turns off on the next zero voltage crossover point of phase one, the current in load 1 is near its maximum value. This current results in a voltage in the secondary winding of transformer 7 of sufficient magnitude and of the correct polarity to turn SCR3 on for the following positive half cycle. Due to the fact that SCR3 fires automatically after SCR2 turns off, it is always the last to turn off and the required conditions for contro...