Why does the direct start-up of high power motors affect the voltage of the grid
Because the instantaneous starting current of the three-phase machine is five to seven times the rated electric current, the voltage of the line is reduced, and the voltage of the power grid and the zhou wave are low. Therefore, the high power motor should be initiated by star/Angle to reduce the starting current and avoid the large fluctuation in the voltage of the grid. The star triangulation is initiated by changing the connection of the motor winding, and the pressure is actuated. When activated, the main contactor will give the power to the three ends of the motor winding, which will close the three ends of the motor winding. Winding becomes a star connection, after the completion of the start, time relay action, star contactor disconnect, contactor operation will be three of the power supply to the motor winding end. The winding becomes a delta connection. The motor is fully pressed. During startup, the asterisk contactor and the operating contactor must be interlinked. Image: KT - time relay, KM1 - star contactor, KM2 - the main contactor, KM3 - the operating contactor.
Cage motor direct starting current is rated current of 6 ~ 7 times, large motor starting current is up to thousands of A, caused the high current on the pressure drop caused by power grid voltage drop.
Because of the asynchronous motor starting, the rotor has not turned up, the stator rotating magnetic field cutting speed relative to the rotor conductors, in rotor induction electric potential is very big, so the current is very big, if starting directly from grid, starting current can reach 4 to 7 times the rated current, and is the most current inductive current, this would have had a big impact on the grid: 1) the large starting current will be produced on the transmission line, the larger voltage drop; 2) because so much of the starting current, most of it is a perceptual current, will cause a demagnetization effect on the grid, and will also cause the grid voltage to fluctuate.
The ac motor starts with a current of 5 to 7 times the rated current. The effect of the high power motor directly on the voltage of the grid; The main consideration is that a large start current will reduce the voltage of the grid and cause a ripple effect. Normally, the power grid transformer capacity is over 180kVA, and the power of the motor is below 7kW. At present 4-100kw motor multi-purpose delta voltage drop starting..
