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First, the triangle connection and star connection

Connect the ends of the three windings of the three-phase power supply, X, Y, and Z together to form a common point O, and lead three end lines from the beginning ends A, B, and C. This connection is called "star connection method". "Y-shaped connection method".

The three-phase power supply is a system in which three sinusoidal power sources having the same frequency, equal amplitude, and phase difference by 120° are connected in a certain manner to the external power supply.

The three-phase power supply has two types of connection: Y-shaped and Δ-shaped.

Both the star connection and the delta connection refer to the winding connection of the motor itself. The star connection method refers to connecting the three-phase ends of the motor winding together, the three-phase head end is the power supply end; the delta connection method refers to the three-phase winding end-to-end Connected to each other, the three terminals are power terminals; no matter which connection, there must be three-phase sinusoidal AC power supply with 120-phase phase difference of 120 degrees, and 220V can not be used instead.

Because the three-phase live line (A, B, C) of the three-phase alternating current has a voltage of 220V, the phase difference between them is 120 degrees, and the voltage between the three phases differs by 380V, using three in-phase FireWire is not a substitute.

Second, the three-phase power star connection

The symmetrical three-phase four-wire YY system is a commonly used system with three fire lines and one center line. In the three-phase connection of the star connection, the line voltage is 3 times the root of the phase voltage, and the line current is equal to the phase current. When the three-phase load is balanced, even if the neutral line is connected, no current flows through it. When the three-phase load is unbalanced, the neutral line should be connected, otherwise the load of each phase will be divided.

The star connection is mainly used in high-voltage large or medium-sized motors, and the stator windings only lead to three wires. For the star connection, the load of each phase is balanced, and the sum of the current vectors flowing through the three phases at any time is equal to zero.

Third, the motor two wiring method diagram

As can be seen from the above figure, the upper and lower piles are connected in a triangle, and the top three piles are connected together in a star shape, such as a motor without a junction box.

First phase winding head tail on 1.4

Second phase winding head tail on 2.5

Third phase winding head tail on 3.6

Star connection: 456 connected together, 123 connected to the power supply

Delta connection: 1 connection 6, 2 connection 4, 3 connection 5, become the three outlets of the motor

Fourth, the description

(1) Because there is no neutral point when the motor is connected to the delta, the specific method is that the head and the tail of the three-phase winding of the motor are respectively connected. At this time, there is only one voltage level, the line voltage is equal to the phase voltage, and the line current is equal to the phase current. 1.73 times

(2) When the motor star connection method has a neutral point (the motor is generally a three-phase symmetrical load, the neutral line is generally not drawn). The specific method is that the three tails of the three-phase winding of the motor are connected together, and the three heads are connected. The power supply, at this time, has two voltage levels, namely the line voltage and the phase voltage, and the line voltage is equal to about 1.73 times the phase voltage, and the line current is equal to the phase current.

(3) It should be noted that the motor of the original star connection cannot be connected to a triangle. (If it is connected to a triangle, the phase voltage rises to about 1.73 times, and the motor will be burned for a long time.)

(4) Similarly, the motor with the original delta connection cannot be connected to a star shape. (If it is connected to a star, the phase voltage is reduced to about 1.73 times, which does not reach the normal power. If the rated load is used, then it is overloaded. For a long time, it will inevitably burn the motor).

(5) In China, the smaller motors below 3-4KW (kW) are generally required to be connected into a star shape. The larger motors above are required to be connected into a triangle.

(6) Why the larger power motors are connected in a triangle shape, the advantage is that when the light load is started, in order to facilitate the step-down start (the star is connected at the start, the triangle is changed when the operation is running, and the motor start time is extremely short and connected to the star. The advantage is that the starting current can be reduced to 1/3 and so on.

The star-connected phase current is equal to the line current, the line voltage is 3 times the root of the phase voltage, the delta connection, the line voltage is equal to the phase voltage, the line current is 3 times the root of the phase current, and the connection is connected to the three-phase symmetric load. .

Five, the comparison of the two methods

(1) Delta connection method: It helps to improve the motor power, shortcomings, large starting current, and large winding withstand voltage (380V). Increased insulation rating.

(2) Star connection: It helps to reduce the winding withstand voltage (220V) and reduce the insulation level. Reduced startup current. Disadvantages, motor power is reduced. Therefore, most of the low-power motors below 4KW use planetary connection. More than 4KW is used in the delta connection.

The motor with delta connection adopts Y-â–³ start at light load start to reduce the starting current! The light load is the condition, because the Y connection torque will become smaller, the starting current is reduced for the purpose, and the starting current is reduced by the Y connection method. The power of the delta connection is large, the starting current is also large, the power of the star connection method is small, and the starting current is also small.