On the inclusion of a three-phase motor in a single-phase network, which facilitates starting. Scheme, description

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On the inclusion of a three-phase motor in a single-phase network, which facilitates starting. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Electric motors

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When starting powerful (2 ... 7 kW) and high-speed (3000 rpm and more) electric motors, our craftsmen experience serious difficulties. Most of these motors are designed for a three-phase network, and they have to be powered from a more affordable single-phase one.

At the moment of starting a powerful high-speed motor, the current in the line increases many times, which causes heating of the supply wires and a sharp drop in voltage. If you turn on the protection on the bulbs [1] in series with the engine, then the engine will definitely never start. To facilitate starting, powerful cables are used and the motor shaft is manually unwound using a cord. But wires suitable for the cross section are not always at hand, and spinning with a cord is a dangerous and inconvenient task, since in most cases the engine is located inside a metal frame or housing.

On the inclusion of a three-phase motor in a single-phase network, facilitating start

Until now, I considered circuit [2] to be the best solution to the problem, but then I came across another circuit solution, which, after a little refinement, surpassed [2]. According to the new scheme, starting switching has been simplified, now it is enough to turn the SA1 switch handle (see figure), and the engine will reach its operating speed. Engine spin-up is carried out automatically according to the "star" scheme. The direction of rotation is set by the capacitor.

By excluding the capacitor from the circuit and connecting the third phase (dashed line in the figure), we get a star-delta switch for quickly adapting the electric motor to various voltages of a three-phase circuit.

References:

Goreiko N.P. Protection of cable lines//Radioamator-Electric. 2000. - No. 12. - C2-3.
Bearded Yu. Inclusion of a three-phase motor in a single-phase network, facilitating the launch // Radioamator-Electric. - 2000. No. 8. - P.15.

Author: Yu.Borodaty

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