What’s he relationship between triangle and star connection and its advantages and disadvantages?

The same three-phase motor can be connected by triangle connection, corresponding to low voltage; It can also be connected according to the star connection method, corresponding to high voltage; The high voltage is 3 times the square root of the low voltage. For example, a 380V motor with a triangular connection, if connected by a star connection, the corresponding voltage is 660V. The specific connection should correspond to the power supply voltage.

The star-connected motor does not generate circulation inside, which is theoretically better than the triangular connection.
Because the three-phase winding can not be absolutely balanced, there is always a small difference in 3-phase motor voltage, which will form a circulation inside the triangle, resulting in motor heating and efficiency reduction. The triangular connection is also made for historical reasons, that is, the so-called star-triangle start, star-triangle start can effectively reduce the starting current, but it will reduce the starting torque, so it can only be used in light load or no-load starting state.

We see that the fan pump motor can be started by star-triangle, but there is certainly no star-triangle start on the crane, the lifting is mostly started by winding rotor series resistance, why make so much trouble, there is a reason. Of course, the current conditions of frequency conversion starting has completely solved such problems.

Regardless of three-wire or four-wire system (without ground), the electrical Angle between the three-phase voltages is 120 degrees phase difference under ideal conditions. It is assumed that because of periodic interference, 3N harmonics are generated in the phase winding of the load terminal, 3N*120=360N, indicating that the three-phase 3N harmonic voltage phase is exactly the same, if the amplitude is the same, the 3N harmonics of the three groups of line voltage will be completely cancelled out, that is, there is no integer multiple harmonics of 3 in the voltage between the lines.

For the triangle connection, the above 3N harmonic currents in the same phase are short-circuited in this triangle and are kept in this triangle to form an infinite circulation. Therefore, for the presence of harmonics, the triangular or star connection can be selected according to whether the 3N harmonics are possible in the voltage or current.