Description
Star-delta systems
During direct start-up, electric motors can draw a current from the mains significantly exceeding its rated value In. This current is called the motor starting current and its value ranges up to Ir = 10In. Therefore, starting systems are used for engines with higher power. The star-delta system is a simple and cheap way to limit the inrush current of the motor.
- ready set for connection
- execution up to 800kW
- solutions on a rail, mounting plate or cabinets
When the motor windings are connected in a star pattern, the starting current of the motor is three times smaller, but also the starting torque is three times smaller. After switching on the supply voltage and accelerating the motor to a rotational speed close to synchronous speed, the windings are automatically switched to delta configuration. The engine then accelerates to the rated speed and goes from starting to rated operation.
This has the advantage of reducing the duration of the surge currents, which can lead to excessive heating and mechanical stresses in the windings, which can lead to motor failure. An additional advantage is the relative simplicity and cheapness of the solution. The main disadvantage is the reduced starting torque, which means that such a start-up is only applicable to motors that are not loaded with the rated torque at the time of start-up, e.g. when driving fans or belt conveyors.
Current graph depending on the start-up method:
Diagram of selection of LS contactors for a star-delta circuit and diagrams:
We recommend a star-delta type MPC-TTZ-U240-216 relay for the circuits
