Connecting industrial electrical motors

Industrial motors with a power over 4kW generally have a 400-690V connection. Small motors generally have a 230-400V connection. A typical feature is that the higher the voltage, the lower the current.

A 690V connection may use thinner wires, which is cost-saving. Large factories with heavy machine parks and their own transformer station have these connections. Companies active in the heavy industry obtain the required voltage level by installing a transformer station, which is subject to strict regulation.

Star or delta connection

Motor’s nameplates with large drives or AC motors generally display an indication such as 230-400V or 400-690V. The lowest voltage level indicates the motor winding of the motor. These drives are generally applied in 3 phase current three phased connections, with a line current of 400V.

Specialist knowledge is required while wiring-up the junction box of large motor drives utilising star or delta connections. In star connections the voltage is distributed over the three windings. In delta connections each winding has the same voltage level.

Example of star and delta connection

Let’s take the example of a 230-400V electrical motor. In a delta connection the total line current of 400V is distributed over the winding, in a star connection this is 230V. If there is a 230-400V indication each winding can hold a maximum capacity of 230V. The total capacity is 400V. In a line current of 400V the electrical motor will have a star connection. If the electrical motor indicates 400-690V, each winding can have a maximum capacity of 400V and in a line current of 400V the electrical motor can be delta connected.

Limit starting voltage in starting-up motors

Motors with a high starting voltage draw high peak current at starting-up. The star-delta connections determine the starting voltage levels. To ensure that your electrical installation can handle this load it is recommendable to limit the starting current surge. If you start an electrical motor the nominal load can be twice as high in star connections and even 6 to 7 times higher in delta connections.

A motor protection switch (MPS) bridges the short peak current without cutting off the current. In high-voltage appliances we advise you to apply a softstarter or frequency switch allowing the motor to start using less current. In this way your electrical installation will not get overloaded.

Incorrect connections of electrical motors have huge consequences

Incorrect connections of electrical motors have huge consequences. In a delta connection of a 230-400V motor each winding will have the same voltage level. However, in a 230-400V electrical motor each winding will have a maximum load of 230V. In a line current of 400V each winding will have a 400V load. This results in overloading the coils and the windings will burn.

Using a star connection in a 400-690V motor will damage the electrical motor. The total voltage will be distributed over the three windings. In a 400-690V star connected motor undervoltage will occur, which is not directly noticeable. Undervoltage means that the motor needs a lot of voltage to supply the required power level. The motor will eventually overload and, if there is no motor protection, the windings will burn.

Connecting motors to 400-690V is a specialist skill and requires compliance with applicable legislation and standards. The engineers of Beemster provide the best advice. For more information about our work, please feel free to contact us.

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