There are two kinds of wiring methods for gear motor, which are delta connection and star connection. The delta connection is that the three-phase windings are connected end to end. The star connection is that the head is connected to the head or the tail is connected with the tail.
Delta connection:
The delta connection method is to connect the winding of each phase head to tail in turn and draw out each connected point, which is the three-phase line in three-phase electricity. The phase voltage is equal to line voltage; the line current is equal to the square root of 3 times the phase current.
The delta connection is helpful to improve power, the drawback is that the start current is large. The winding that needs to withstand voltage is very large.
Star connection:
The star connection is that one end of each phase is connected to one point, and the other end of them is taken the outgoing line, which is divide into three-phase lines. The line voltage is equal to the square root of 3 times the phase voltage, the line current is equal to the phase current.
Due to the small output power, the star connection is used in the small efficiency, high torque motor, or when the high power motor starts, so the loss of motor is small. After the normal operation, the delta connection is used. This is a star-delta start.
The advantage of the star connection is that it can reduce the voltage that the motor should withstand, the insulation level, starting current; but the motor power is small.
The method of choosing wiring mode:
Generally, the star connection is more used in motors below 3kw, while the angle connection is more used in motors above 3kw. According to regulations, motors above 15kw need star connect start and angle connection operation, to reduce starting current.
For the small motor which is angle connection, if it is connected to three-phase 220V power supply voltage, this must use star type.
Conclusion:
1, There is no neutral point in the delta connection, the specific method is that the head and tail of the three-phase windings of motor are connected respectively. There is only one voltage level, the line voltage is equal to the phase voltage, the line current is about the 1.73 times of phase current.
2, There is the neutral point in the star connection(generally, the motor is three-phase symmetrical load, so the neutral line is not led out), the specific method is that the three tail of three-phase windings of motor is connected, and three heads are connected to the power supply. At this time, there are two voltage levels. Namely, the line voltage and phase voltage, the line voltage is equal to the 1.73 times of phase voltage, the line current is equal to the phase current.
3, it should be noted that the motor which is the star connection can’t be connected with delta connection. (if using delta connection, the phase current will rise to about 1.73 times, and the motor will burn down in the long run time)
4, Of course, the motor which is connected by delta connection cannot be connected with star connection. (if using the star connection, the phase motor will be reduced to about 1.73 times, the normal efficiency can’t be reached. If there exists a rated load, it will be in overload status. The motor will be burned down in a long time)
5, In China, the motor whose power is lower than 3kw are required to be connected by star wiring. The power which higher than 4kw should be connected by delta connection.
6, The advantage of the delta connection is that when the motor starts under light load, it is convenient to start by reducing voltage.
The phase current of star connection is equal to line current, the line voltage is the square root of 3 time of phase voltage. It can improve the working voltage of each phase and power.
