Magnetic Starter

Update date:2018-03-09 Source:MAXGE

Magnetic Starter

Overload protection means that when the load of the motor exceeds its rated load and exceeds a certain allowable time, the electromagnetic starter can automatically cut off the power of the motor. Loss-of-voltage protection means that the electromagnetic starter is turned on. After the motor is started and put into normal operation, the electromagnetic starter can automatically break the circuit when the power supply is cut off to prevent the motor from starting when the power supply is re-energized. Damage and personal injury.


Electromagnetic starters are classified into two types, irreversible and reversible. The former is used to start an induction motor that does not need to be reversed; the latter is used in an induction motor that needs to be reversed. Electromagnetic starters operate with buttons. The irreversible electromagnetic starter has two buttons: "start" and "stop"; the reversible electromagnetic starter has three buttons: "forward rotation", "reverse rotation" and "stop".


In order to prevent the normal control contactor and the reverse control contactor in the reversing starter from being energized at the same time, so that a power short circuit occurs, an electrical interlock is generally provided in the control circuit, and sometimes a mechanical interlock is additionally provided to ensure that only when the starter is When one of the contactors is in the open position, the other contactor may be energized and the motor only operates in one direction.

Starting mode


1, direct start. However, when the three-phase asynchronous motor is directly started, the current can reach 6-7 times of the rated current, which has a great impact on the power grid, especially the high-power motor.

2, step down start. Step-down starting is mainly a hot auto-pressure start and Star Delta step-down start.

Thermal auto-reduction start-up refers to reducing the motor voltage at start-up through the auto-transformer and reducing the starting current. It is generally reduced to about 55% to 75% of the rated voltage. The advantage is that the starting voltage can be easily changed by changing the number of taps of the self-turning transformer. The disadvantage is that it requires the use of self-turning transformers, which is costly.

3, frequency sensitive resistance starts. Frequency-sensitive resistance start-up means that the frequency-sensitive resistance is connected in series in the main circuit when the motor starts, thereby reducing the starting current. The frequency sensitive resistor can smoothly change the starting current and has less impact on the power grid. It is an ideal starting method. However, current high-frequency frequency-sensitive resistors are all in the form of inductors, so they will generate large electromagnetic eddy currents when in use, which will reduce the power factor of the power grid.

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