Experience in connecting industrial electric motors to a household network. Scheme, description

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Experience in connecting industrial electric motors to a household network. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Electric motors

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Today, modernization and electrification of farms and small industries is in full swing in the countryside. In this regard, many novice electricians have questions. How to connect the electric motor correctly? What to do if the electric motor does not develop its power? What to do if a serviceable electric motor heats up quickly even at idle? These are the most common questions, so let's try to answer them.

For the convenience of connecting 3-phase motors, there are 6 threaded contacts in the junction box, which allow you to change the operating voltage (Fig. 1). When connected with a "triangle" (Fig. 1, a), the operating voltage is minimal, and when connected with a "star" (Fig. 1, b), it is maximum for a given motor. Typically, motors are made for the two most commonly used voltages: 220 V - delta and 380 V - star, but there are exceptions.

In modern electric motors, only three connecting contacts can be found.

This means that the ends of the motor windings are not brought out to the junction box, but are connected inside the motor housing. When connecting such motors, two troubles happen:

1) the engine starts, but does not develop sufficient power, as it operates at a reduced (220 V, not 380 V) voltage. Such an engine must be converted from a star to a delta;

2) the engine starts, but quickly heats up, as it operates at an increased (380, not 220 V) voltage. Such an engine must be converted from a delta to a star.

How to convert highly specialized engines? The question is very relevant, since most modern and imported electric motors have only three outputs.

To access the internal connections of the working windings, it is necessary to remove the front cover of the electric motor. It is located closer to the connection box. If it was not possible to remove the working body from the engine shaft (gear, clutch, pulley, etc.), then you will have to remove the cooling impeller (and hence the casing of the cooling system) and pull out the engine rotor along with the front cover.

The motor winding is impregnated with varnish and tied with insulating material (thread, ribbon, keeper tape, etc.), which must be cut to remove the internal connections. Only the connections of three wires are removed to one point; connections of two wires are not required to alter the operating voltage of the engine.

If the windings have only one 3-wire connection, they are connected in a star, if three - in a delta. To disconnect the wires, it is necessary to remove the insulation from them, bite off the bead formed by thermal welding of copper with wire cutters (Fig. 2), and unwind the wires.

For a star, it is enough to solder three conductors to the wires and bring them to the connection box. The standard connection of the beginning and end of the windings is shown in Fig. 3 (the groups of the beginning and end of the windings are separated by a solid line, the ends of the windings are connected by a broken line).

Since the accepted standard connection has symmetry, it is almost impossible to confuse anything in it. Next, you should connect the ends of the windings as indicated in Fig. 1, a, and the engine, having received sufficient power, will develop its power.

When switching a 3-pin electric motor from delta to star, it is important not to confuse the beginning and ends of the windings.

To do this, first remove the stranded conductor leads from the output connections. Then the remaining three connections are developed, but not disconnected (Fig. 4), the ends of the windings of the same name are marked with a “ringing”.

To do this, put a label (a) on any output of one of the pairs. Then, using a tester, another output of the winding marked in this way (b) is determined and the end paired with it (c) is marked. Then everyone repeats: find the conclusion (d), mark (e). Now we know that the ends a, c, d are of the same name (the beginning or ends of the windings) and, connecting them together, we get the inclusion of the motor windings with a star. To the remaining three conclusions outlined, you should solder the stranded wire leads. Now the engine will not overheat. It is possible, of course, to derive all 6 conclusions according to Fig. 3, but in practice this is not done, and whoever spent three “phases” for himself will no longer suffer with single-phase power supply of 3-phase motors.

A convenient star-delta switch is described in [1], information on reversing motors is contained in [2,3].

References:

1. The inclusion of a 3-phase motor in a single-phase network, facilitating the start//Electrician. - 2000.- №8.- P.15.
2. Reversing AC motors//Electric.2001.-№2.- P.20.
3. Safe woodworking machine//Designer. - 2001. - No. 3. - P.9.

Author: Y. Bearded

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