Anyone who skiers knows that a sudden, sharp pull can make a person fall.On the industrial side, many businesses waste millions of dollars a year on this sudden, sharp start of the motors they use (to drive fans, crushers, agitators, pumps, conveyor belts, etc.), and countless ALTERNATING current motors are unnecessarily burdened each day.
The sudden and violent start of a Big Power Motor will mainly cause losses in the following aspects:
(1) Voltage and current transients generated by direct online starting or star-delta starting may easily lead to electrical faults.Transient phenomena of voltage and current can lead to overloading of the local grid, resulting in undesirable voltage changes and ultimately affecting other electrical equipment in the same grid.
(2) Mechanical failure of the entire drive chain from the motor to the starting equipment and to the strong stress.
(3) Operating faults: such as pressure vibration of pipeline system, damage to products on the conveyor belt, and discomfort of elevator ride.
In addition, the problem of economic benefits is also obvious: every technical problem, every failure, will cause economic losses due to maintenance or even suspension of production.In the production of industrial enterprises, this will lead to the increase of off-budget production costs
Another early solution was the slip-ring motor, which was started by a starting rheostat connected via a slip-ring to a rotor circuit.In this way, although the motor's torque can still be maintained at the level necessary to start the load, the starting current has been reduced.
During the starting process, the motor gains speed, and the rotor resistance gradually decreases. Once the rheostat is completely off the circuit, the motor can reach its maximum speed, and the rotor winding shortens at this point. Therefore, the motor starts to operate as an ordinary squirrel cage motor from this point.
The advantages of slip-ring motor are high torque and limited starting current. It is mainly suitable for motors with high starting load, such as crusher and mill motor.The disadvantage is that its mechanical and electrical structure is too complex, and the use of brushes, slip rings, resistors and joints increase costs (including maintenance costs) and reduce reliability.
