Connection schemeKnown widespread use of asynchronous electric motors, connected by "star" and "triangle". These connections are available at each production, three-phase motors, generators, transformers are connected with the “star”. The “triangle” is mainly used in engines of a long start-up and running cycle. It is also used in connection diagrams of transformers, mainly where there is a symmetrical load.

The joint inclusion of both star and triangle connections is used. when starting powerful electric motors. Starting starts with a "star" and then switches with a relay circuit to achieve speed to the "triangle" circuit. The engine continues to work for a long time on the "triangle".


  • 1 Connection of circuits according to the "triangle" scheme
  • 2 Connection of three-phase circuits according to the scheme "star"
    • 2.1 Special cases of application of the described connection schemes

Connection of circuits according to the "triangle" scheme

This connection is called a triangle only when both ends of the windings are connected to each other. Triangle connection is necessary when the mains voltage is suitable for such a consumer.

Electric motor start according to the "triangle" scheme, it is expressed by large values ​​of inrush currents and does not very well affect the durability of the windings. But when working on this connection, the power is equal to that stated in the passport of the consumer, which is sometimes necessary.

The "Triangle" scheme is divided into “Open” and “open”. The difference between the two types lies in the fact that an open triangle is a connection with a triangle with one point broken by the consumer. And open differs in that one winding is replaced by the consumer.

Connection of three-phase circuits according to the scheme "star"

Motor connection rulesThe following connection is called a “star” if the ends of the windings are concatenated into one node, which has the name “neutral point”, the second is called “neutral”. Connecting the engine for this type of engine power will be lower. Connecting these two types provides at what voltage your windings will work. Usually, a voltage is indicated on the motor for a particular connection method, as well as corresponding speed and power.

For example: take the network 380 to 220, the connection is a star, the voltage on the consumer is 220V. If you connect a delta circuit, the voltage on the windings will be 380, based on the voltage, the power P = UI will become greater. (In practice, the usual engine will burn, because the voltage will be 380V. However, 220/127 for this engine, the triangle is the normal mode, the star works with loss of power).

In the case of consumers working on a “star”, it is very important that there is no “phase skew”. If a neutral has, for example: poor contact, then a difference will arise - a load asymmetry at which one consumer will be under a certain voltage. This potential difference depends on the load distribution at the moment when the neutral wire is burned out. From this potential difference, consumers in the apartments turned out to be energized, causing an old television set to burn out or a refrigerator to fail. I think many people know such stories in the past.

Special cases of application of the described connection schemes

Application of star wiring:

  • Connection scheme by type A typical method of using this switch is used for asynchronous three-phase electric motors. Where three windings have equal load. With poor protection against current differences in the windings of the device very quickly fail. Frequently used frequency drives for protection and soft start. These chastotniki use the same connection scheme for different speeds. The speed varies by changing the frequency of the voltage applied to the windings, which greatly prolongs the life of the motors.
  • Three-phase transformers to supply consumers with phase voltage. When power networks 36kV and more midpoint is usually grounded to reduce the cost of insulation.
  • Tubular electric heaters are used in various boilers, boilers, various heaters.
  • Power supply to consumers of lighting and residential apartments in a four-wire scheme. It is necessary to distribute the phases to a more or less uniform load. The voltage between the phases is 380V, between the phase and the neutral 220V. To the four-wire connection scheme, usually the fifth ground wire is added. It plays the role of protecting people from electric shock and protecting equipment against short circuits.

The implementation of the triangle inclusion schemes:

  • Electrical circuitThe first most common use of the scheme in asynchronous. Of course, this scheme is not suitable for mechanisms requiring frequent switching off. But for mechanisms with a heavy start and working for a long time, this winding connection circuit is needed. For frequent inclusions, it is better to use frequency drives or soft starters. In practice, this connection is increasingly used in industry.
  • Also use the connection in the power networks of lighting and apartments.

Many questions arise from the difference between a star and a triangle. The difference, in my opinion, is in the constructive organization of the supply network. For the engine, the first method is preferable in those chains and mechanisms where there is frequent triggering. WITHIt should be remembered, with such a connection it is necessary to take into account the supply voltage, usually 380V. In the second case, the accounting for the supply voltage is available 220V. With such a connection, the motor has high starting currents, which wears it much faster.

Rarely found in industry compound triangle. More often low-powered engines work precisely on the star. Powerful engines are mostly equipped with frequency converters, and then the probability of failure of an expensive, custom-made engine is reduced to almost zero.

Powerful hydraulics engines, pneumatics use the star scheme at a metallurgical enterprise. Presumably, to exclude engine operation for wear. Engines are used in aggressive environments, therefore three protection levels are used: the first is fuses for each phase, the fuse should be semiconductor (it blows more quickly and does not allow it to heat up windings); the second is a circuit breaker, which, as a rule, works in extremely rare cases, if the fuse is not blown; third defense is temperature The thermal sensor is connected via a low voltage relay, which, when a sensor is triggered, breaks the relay in the winding supply circuit.