I need a wiring diagram for a star-delta start.

Need a wiring diagram for the star-delta start

When starting, the main circuit of the motor needs to be cleverly connected with 6 wires. Among them, three wires need to be connected to L1, L2, and L3 at the power end (implemented through KM), and the other three wires need to be connected together through the starting contactor (star KM1) to achieve reduced voltage start.

The function of the main contactor loop remains unchanged during operation and is still connected to L1, L2, and L3 of the power supply. The difference is that the other three wires are connected to the run contactor (KM2) instead of the main contactor. In this way, the six wires of the motor are connected by two contactors (KM and KM2) into a triangle voltage full voltage operation mode connected end to end.

Extended information:

Star-delta starting is a method of reducing starting current, which is achieved by sacrificing power. Whether or not to use star-delta starting cannot be determined solely by the power of the motor. The nature of the load must also be considered. Generally speaking, when the load is light when starting and the load is heavy when running, you can consider using star-delta starting. For squirrel-cage motors, the starting current is usually 5-7 times the running current. Therefore, when selecting the starting method, it is necessary to comprehensively consider the motor power, load characteristics and the applicability of star-delta starting.

In order to avoid excessive impact on the grid voltage when the motor is started, a common method is to use star-delta starting. The voltage requirements of the power grid are generally plus or minus 10%. When the power of the squirrel-cage motor exceeds 10% of the rated power of the transformer, star-delta starting is required.

Star-delta starting circuit diagram with relay time

Triangle start circuit diagram:

Y—△Reduced voltage starting control

Press the start button SF, the time relay KT and the contactor KM2 are connected at the same time

Electrical pull-in, the normally open main contact of KM2 is closed, and the stator winding is connected in a star shape, and its

The normally open auxiliary contact is closed and contactor KM1 is connected. The normally open main contact of KM1 is closed, the stator is connected to the power supply, and the motor is in star shape

Start under connection. A pair of normally open auxiliary contacts of KM1 are closed and self-locking. After a certain delay, the normally closed contact of KT is disconnected, KM2 is reset after power off, and contactor KM3 is powered on and closed. The normally open main contact of KM3 winds the stator

is connected in a triangle so that the motor operates at rated

Figure 5-18 Y-△Reduced voltage starting control Normal operation under voltage. The function of the normally closed auxiliary contact of KM3 in series with button SF is: when the motor is running normally, the normally closed contact is disconnected, cutting off the path of KT and KM2. Even if SF is pressed by mistake, KT and KM2 will not be energized. , so as not to affect the normal operation of the circuit. If you want to stop, press the stop button SS, the contactors KM1 and KM2 will be powered off and released at the same time, and the motor will stop rotating after disconnecting from the power supply.

Principle of star-delta step-down startup

The star-delta starting principle is because the motor starting current is proportional to the power supply voltage. At this time, the starting current provided by the power grid is only 1/3 of the full voltage starting current, but the starting torque is also only 1/3 of the full voltage starting torque. Star-delta starting is a step-down starting, which is achieved by sacrificing power in exchange for reducing starting current.

The three-phase winding of the motor with star-delta step-down starting has six external terminals, A-X, B-Y, C-Z (the following takes a motor with a rated voltage of 380V as an example). In star-shape starting, X-Y-Z is connected, and the three terminals A, B, and C are connected. The three-phase AC voltage is 380V. At this time, the voltage of each phase winding is 220, which is greatly reduced compared with directly adding 380V to the starting current, avoiding the impact of excessive starting current on the power grid.

The torque at this time is relatively small, but the motor can reach a certain speed. Star-delta operation: After the motor reaches a certain speed after star-starting for a period of time (about tens of seconds), the electrical switch converts the six terminals into a delta connection and connects it to the 380V power supply again. The voltage of each phase winding is 380V. , the torque and speed are greatly increased, and the motor enters the operation process under rated conditions.

The voltage reduction startup here means that the voltage drops from 380 to 220 at the beginning, which is the star connection method. One end of the motor is connected separately, and the three wires at the other end are connected together. After a certain time of startup (usually 30 seconds to one minutes), disconnect the star terminal and connect the triangle terminal. Generally, star-delta start can be used when the load is light when starting is required and when the load is heavy.

Generally, the starting current of a squirrel-cage motor is 5-7 times the operating current, and the voltage to the grid should generally be plus or minus 10%. In order to avoid excessive impact on the grid voltage, star-delta starting is required. , generally when the power of the squirrel cage motor exceeds 10% of the rated power of the transformer, star-delta starting is used.

Extended information;

Star-delta starting is required for three-phase asynchronous motors with a capacity of 7.5KW or more. If the voltage fluctuation of the grid caused by the motor at the moment of starting is less than 10%, it can be relaxed to 15% for motors that do not start frequently. The three-phase winding of the star-delta step-down motor has six external terminals, A-X, B-Y, and C-Z (the following uses a motor with a rated voltage of 380V as an example).

A star start, X-Y-Z is connected, the three terminals A, B, and C are connected to the three-phase AC voltage 380V. At this time, the voltage of each phase winding is 220, which is greatly reduced compared with directly adding 380V starting current, avoiding excessive starting The impact of current on the power grid. The torque at this time is relatively small, but the motor can reach a certain speed.

B diagonal operation, after star starting the motor for a period of time (about tens of seconds) to reach a certain speed, the electrical switch converts the six terminals into a delta connection and connects the voltage of each phase winding to the 380V power supply again. For 380V, the torque and speed are greatly increased, and the motor enters the operation process under rated conditions.

Reference source; Encyclopedia--Star-Delta Initiation & Principle

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