Triangulation and star connection for geared motors
Nowadays, there are two kinds of motors commonly used in gear motors on the market. One is the delta connection method. The delta connection method is that the three-phase windings are connected end to end, and the connection torque is large. The starting method is to use the motor with the stator winding as a delta connection. At startup. The other is the star connection. The star connection is the head-to-head or tail-to-tail connection. The starting torque is small, which can reduce the starting current and voltage.
When the triangle is wired, each winding of the three-phase motor is subjected to the line voltage (380V), and in the case of the star connection, the motor is subjected to the phase voltage (220V). In the case of the same motor power, the winding current of the angle motor is smaller than that of the star motor.
When the motor is connected to the Y-type operation, the starting torque is only half of the delta connection, but the current is only about one-third of the triangular start. When the triangle starts, the current is 4-7 times of the rated current, but the torque is large. The speed is the same, but the torque is different.
Delta connection
The delta connection of the motor is to connect the windings of each phase end to end, and draw each connected point as three phase lines of three-phase electricity. The motor phase voltage is equal to the line voltage when the delta is connected; the line current is equal to 3 times the phase current of the root number.
Star connection
The star connection of the motor is to connect one end of each phase winding to one point, and the other end of the winding is used as a lead line, which is respectively three phase lines. When star connected, the line voltage is 3 times the root of the phase voltage, and the line current is equal to the phase current.
Due to its small output power, the star connection method is often used for low-power, high-torque motors, or when the motor with higher power is used at the beginning, so that the loss of the machine is small, and the triangle connection is used after normal operation. This is the star triangle that is often mentioned.
Motor connection selection
It is a three-phase motor, and the single-phase motor does not have the above two connections.
Generally, motors with a speed of 3 kW or less are more frequently connected to the star type, and motors of more than 3 kW are generally angularly connected. According to regulations, motors larger than 15kw require star-type starting angle operation to reduce the starting current.
There is also a small motor angle start, if it is connected to the three-phase 220V power supply voltage, it must be connected to a star.
In China, the smaller motors below 3-4KW (kW) are generally required to be connected into a star, and the larger motors above are specified to be connected in a triangle.
The delta connection helps to increase the motor power. The disadvantage is that the starting current is large and the winding withstand voltage (380V) is large! Increased insulation rating!
Star connection helps reduce the winding withstand voltage (220V), reduces the insulation level, and reduces the starting current; the disadvantage is that the 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 delta-connected motor uses Y-Δ start-up at light load start-up to reduce the starting current. Light load is a condition, because the Y connection torque will become smaller, and the starting current is reduced. The Y connection method reduces the starting current.
to sum up
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 about 1 of the phase current. , 73 times.
2. When the motor is connected to the star, there is a neutral point (the motor is generally a three-phase symmetrical load, so 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 to the power supply. At this time, there are two voltage levels, namely line voltage and 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 with the star connection cannot be connected to a triangle. (If it is connected to a triangle, the phase voltage will rise to about 1.73 times, and the motor will burn out when running 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. A long time will inevitably burn the motor).
5. In China, the smaller motors below 3-4KW (kW) are all specified as star-shaped, and the larger motors above are specified to be connected in 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 during operation, and the motor start time is extremely short and connected to a star. The advantage is that the starting current can be reduced to 1/3, etc.).
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. It can increase the working voltage of each phase and increase the power.
