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What is difference between star connection and delta connection of three-phase asynchronous motor

Date:2023-07-25   Author:XINDA MOTOR
A three-phase asynchronous motor is a commonly used motor type. When using this kind of motor, people often choose star connection or delta connection. So, what is the difference between star connection and delta connection? Let's discuss it in detail below.

First of all, we need to understand what is a three-phase asynchronous motor. A three-phase asynchronous motor, also known as a squirrel-cage asynchronous motor, is a motor powered by alternating current. Compared with DC motors, three-phase asynchronous motors have the characteristics of simple structure, long life, and convenient maintenance, so they are widely used. When using a three-phase asynchronous motor, we need to choose two connection methods: star connection and delta connection. Star connection and delta connection are two basic connection methods of motors, and they have different characteristics and scope of application.

The delta connection method of the motor is to connect the windings of each phase end to end in turn, and lead out each connected point as three phase lines of three-phase electricity. In the delta connection, the phase voltage of the motor is equal to the line voltage; the line current is equal to the phase current which is three times the root sign. The star connection method of the motor is to connect one end of each phase winding to one point, and their other ends are used as lead wires, which are three phase wires respectively. In star connection, the line voltage is three times the root of the phase voltage, and the line current is equal to the phase current. Due to the small output power of the star connection, it is often used for small power, high torque motors, or motors with high power when starting, so that the loss of the machine is small, and the delta connection is used after normal operation. This is what is often referred to as a star-delta start.

△When wiring, each winding of the three-phase motor bears the line voltage (380V), while when connecting Y, each phase of the motor bears the phase voltage (220V). In the case of the same motor power, the winding current of the motor in the △ connection is smaller than that of the Y connection motor. In the Y-type connection, the starting torque of the motor is only half of that of the △ connection, and the current is only about one-third of that of the △ connection. △The starting current is 4-7 times of the rated current, but the torque is large. The speed is the same, but the torque is different.

The choice of motor connection is a three-phase motor, and the single-phase motor does not have the above two connection methods. Generally, motors below 3KW are more star-connected, and motors above 3KW are generally delta-connected. According to regulations, motors larger than 15kw need star-shaped starting angular operation to reduce/lower the starting current. In our country, generally smaller motors below 3-4KW (kilowatts) are required to be connected in a star shape, and the larger motors above are required to be connected in a delta.