Discuss Star delta testing help needed in the Industrial Electrician Talk area at ElectriciansForums.net

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Kj14

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Hi I need some help I haven't work on star delta motors since my 1st year apprenticeship. How do you test the motor from the panel i.e check that the windings are balanced?

Any help much appreciated
 
Depending on the type of load you may find doing a current test on each phase does not always give the answer you may expect. It may be fine on a load such as a fan, but I have a customer that manufactures compressors and we always get out of balance current readings.

Testing in the panel across each set of windings with a good quaility meter should give a matching resistance across all three windings, so test between U1 & U2, V1 & V2, W1 & W2. Then megger test each winding to earth.
 
Hi,depending on constraints,if it was the motor i was wanting to test,i would not include the wiring from panel to motor. Check as described,but at disconnected motor.

This way,any troubling readings are the motor,and not any included part of the connections.
 
Hi,depending on constraints,if it was the motor i was wanting to test,i would not include the wiring from panel to motor. Check as described,but at disconnected motor.

This way,any troubling readings are the motor,and not any included part of the connections.

Testing at the motor with it disconnected would always be my preference, but the OP did ask how to test from the panel so I assumed there were constraints.
 
Hi I need some help I haven't work on star delta motors since my 1st year apprenticeship. How do you test the motor from the panel i.e check that the windings are balanced?

Any help much appreciated
No such animal as a Star Delta Motor, it's the method of starting that Star Deltahttps://www.youtube.com/watch?v=KsS1v_i2YtU
Best way to check the Windings would be to disconnect the 6 leads at the Motor terminal box, make sure you mark the leads, to avoid malfunctions
 
The motors getting hot and tripping out Ive insulation resistance tested and that's fine, just want to check the motor is balanced. Need to rule out electrical fault before fitters will look it
 
Can you turn the rotor to make sure it turns free and smooth, is there any noises coming from it when it's on, if there's a belt on it is that ok and tight enough. Also check if the overload is set properly
 
How can you say it's not the starter? I have seen motors that have been stuck in star either because of a failed timer or even a welded star contactor and boy does the motor run hot!
if my thinking right the current (in star) of each phase runs across two sets of wiring doubling the resistance and reducing the current therefore why would it be getting hot
 
if my thinking right the current (in star) of each phase runs across two sets of wiring doubling the resistance and reducing the current therefore why would it be getting hot

Because of the load on the motor, it cannot deliver the required power, torque and will not achieve its maximum running speed when running in star hence the motor will be overloaded.
When the motor is connected in star, the motor will be effectivly rated at approximately a third of its motor plate rating, so a 7.5kw rated motor will have an output of about 2.5kw. So if the motor is being asked to deliver 7.5kw of power but only capable of delivering 2.5kw it will effectively be overloaded and get rather warm! The control system will not normally detect this as usually the overload relay is shorted out by the star contactor during start up.
 

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