Star to Delta conversion

[Robert P]

Hi.
I need to alter the configuration of this motor wiring from star to delta so that I can use a VFD to control it (hopefully). If I remove the star connection from the N terminal am I safe to assume that these 3 wires will be in the correct orientation/ polarity to make the delta connection i.e. they will be w2, u2 and v2? Hope I've explained myself properly. Can I also assume that the connections A = W1, B= U1 and C = V1?

 

[James]

hard to see from the picture

but assuming it is a 3 phase induction motor.
if you remove the 3 wires from the N terminal then
test continuity between A and each of the 3 wires in turn you should find the other end of winding A (call it A2)
repeat for B and then C

you should then have identified each of the winding pairs.

take the wire A2 and join it to terminal B
take wire B2 and join it with terminal C
take wire C2 and join it with terminal A

Terminals A,B,C then will be your U,V,W connections
if the motor turns the wrong way then just swap any 2 of the motor cables between inverter and motor, leaving the windings configured the same way at the motor end.

 

[Robert P]

hard to see from the picture

but assuming it is a 3 phase induction motor.
if you remove the 3 wires from the N terminal then
test continuity between A and each of the 3 wires in turn you should find the other end of winding A (call it A2)
repeat for B and then C

you should then have identified each of the winding pairs.

take the wire A2 and join it to terminal B
take wire B2 and join it with terminal C
take wire C2 and join it with terminal A

Terminals A,B,C then will be your U,V,W connections
if the motor turns the wrong way then just swap any 2 of the motor cables between inverter and motor, leaving the windings configured the same way at the motor end.

Thanks James. It is a 3 phase induction motor. I was just a bit worried that there could be a chance that the start and end of the windings could be the wrong way round. So hopefully all A, B and C will be (let's say) the start of the winding and A2, B2 and C2 (the ends currently connected to the N terminal) will be the end of the winding. I'm assuming it wouldn't currently work in Delta if they were the wrong way round?

 

[ACB33]

Hi, if coil identification is a bit problematic you could do a 'flick test' on the 3 coils to definitely identify the magnetic polarity of each of the windings - its many years since I've done this but the interweb should have some info - essentially you apply a 9 volt battery across coil A for an instant and with an old achool analogue meter ( avo) connected to coil B the needle should flick left to right, you then repeat for coil C - labelling up each coil end e.g A1 & the other end A2, B1 & B2, C1 & C2 - the motor will then run fine on the vsd without 'growling' or burning out - if the needle on the meter flicks backwards then that coils magnetic polarity is reversed and the labels just need swapping - James could probably elaborate more on the flick test, its many years since i was doing this on motors... the good old days of the Avometer!

 

[Robert P]

Hi, if coil identification is a bit problematic you could do a 'flick test' on the 3 coils to definitely identify the magnetic polarity of each of the windings - its many years since I've done this but the interweb should have some info - essentially you apply a 9 volt battery across coil A for an instant and with an old achool analogue meter ( avo) connected to coil B the needle should flick left to right, you then repeat for coil C - labelling up each coil end e.g A1 & the other end A2, B1 & B2, C1 & C2 - the motor will then run fine on the vsd without 'growling' or burning out - if the needle on the meter flicks backwards then that coils magnetic polarity is reversed and the labels just need swapping - James could probably elaborate more on the flick test, its many years since i was doing this on motors... the good old days of the Avometer!

Thanks. That's handy info to know. I've seen something on the web about applying a very low ac voltage and then measuring and then measuring across the remaining coils.

 

[Lucien Nunes]

If one coil is reversed then you have what is basically a shorted transformer pitting two phases of the of the incoming supply head-to-head with the third. So long as you proceed as above, pairing each of the wires that had been attached to the star point with another that had been a line wire, you will end up correct in delta.

 

[gordy ere]

Thanks James. It is a 3 phase induction motor. I was just a bit worried that there could be a chance that the start and end of the windings could be the wrong way round. So hopefully all A, B and C will be (let's say) the start of the winding and A2, B2 and C2 (the ends currently connected to the N terminal) will be the end of the winding. I'm assuming it wouldn't currently work in Delta if they were the wrong way round?

after changing to delta you may need some kind of surge protection