STAR DELTA 3 PHASE MOTOR

HI EXPERTS

SOMEBODY ASKED ME TO CHANGE THE ROATION OF A STAR DELTA 3 PHASE MOTOR
HOW THIS IS POSSIBLE ON A REGULAR DIRECT ON LINE STARTING SYSTEM TWO PHASES ARE INTERCHANGED BUT AS YOU KONW ON STAR DELTA SYSTEM 6 WIRES FROM CONTROL ARE CONNECTED TO 6 TERMAINAL OF THE MOTOR NOW DOES IT MEAN THAT IF I INTERCHANGE TWO WIRES ON EACH BANK THEN THE MOTOR DIRECTION WILL BE CHANGED.

THGANKS EXPERTS

The star - delta system itself is supplied by 3 wires. Swap two of these.

For 415v Star Connection voltage is effectively reduced to 58% or 240v. The equivalent of 33% that is obtained with Direct Online (DOL) starting.


If Star connection has sufficient torque to run up to 75% or %80 of full load speed, then the motor can be connected in Delta mode.

When connected to Delta configuration the phase voltage increases by a ration of V3 or 173%. The phase currents increase by the same ratio. The line current increases three times its value in star connection.

During transition period of switchover the motor must be free running with little deceleration. Whiler this is happening "Coasting" it may generate a voltage of its own, and on connection to the supply this voltage can randomly add to or subtract from the applied line voltage. This is known as transient current. Only lasting a few milliseconds it causes voltage surges and spikes. Known as a changeover transient.


As you can see the supply itself is still 3 phase and if you change any 2 of those you will change direction. The reason for six wires is to convert from star to delta. To understand the connections for this look at:http://www.patchn.com/tutr-mot.htm

It may be easier to change the leads to the starter rather than at the motor or starter output.

you change a normal 3Ph motor by changing two of the phases over
on star/delta you do the same thing but the 2 phases you change on one side you do the same to the other side, or as previously said just change two phases over on the incoming supply.

michael