Star-delta start of a three-phase electric motor. Scheme, description

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Star-delta start of a three-phase electric motor. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Electric motors

When using high power motors with high starting currents, to reduce the starting current, the star-delta motor control scheme is used, in which starting occurs with low starting currents "star connection" and after a certain time switching to normal operation "delta connection ". Let's consider this scheme in more detail.

Control scheme

Three-phase star-delta start
Fig. 1

Connection of the auxiliary voltage, through the contact of the time relay K1 and the contact K2, in the circuit of the coil of the contactor K3.

Turning on contactor K3 opens contact K3 in the coil circuit of contactor K2 (blocking erroneous switching on), contact K3 closes in the coil circuit of contactor K1 combined with the contacts of the time relay.

Turning on the contactor K1, closes the contact K1 in the coil circuit of the contactor K1 (self-feeding), at the same time the time relay turns on, opens the contact of the time relay K1 in the coil circuit of the contactor K3, closes the contact of the time relay K1 in the coil circuit of the contactor K2.

Switching off contactor K3, contact K3 closes in the coil circuit of contactor K2.

Turning on contactor K2 opens contact K2 in the coil circuit of contactor K3 (blocking erroneous switching on).

Power plan

Three-phase star-delta start

Connection scheme "star"

Turning on the contactor K3, closes the power contacts K3, the ends of the windings are closed on the bar of the electric motor W2 U2 V2.

Turning on the contactor K1, closes the power contacts K1, power is supplied to the ends of the windings on the bar motor U1 V1 W1.

Connection diagram "delta"

The time relay is activated, the contactor K3 is turned off, the contactor K2 is turned on, the power contacts K2 are closed, power is supplied to the ends of the windings on the bar motor W2 U2 V2.

Publication: electro.narod.ru

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