Constant Torque Motor Wiring Question 1

[eatme3452]

I have a constant torque, two speed, 460V motor with six unmarked leads. I have figured out which three leads are one speed and which three leads are the other speed, but not which group is high or low. How do you determine which trio is the high speed and which trio is the low speed without running it?

 

[jraef]

I take it there are no markings whatsoever on the leads? Is there any nameplate information, i.e. is it 2 speed one winding or 2 speed 2 winding? Since you mentioned Constant Torque it is probably 1 winding, but you should be sure. If so, and it is a standard NEMA design motor (again, an assumtion because you said it was 460V), low speed would be connected to 1, 2 and 3, with 4, 5 and 6 open. High speed would be connected to 4, 5 and 6, with 1, 2 and 3 shorted together.

"Venditori de oleum-vipera non vigere excordis populi"

 

[aolalde]

For one winding constant torque the connection is 2 Wye for high speed and 1 Delta for low speed. The six terminals must give continuity against each other.
As a second check we will separate the terminals belonging to each speed measuring resistance.
Randomly assign (tag) T1 to one lead and measure resistance against the remaining five terminals. You will have three resistance values, High once, medium twice and lower twice. Tag the remaining five terminals as follows:

One high resistance --- T5
Two medium resistance T3 and T2 (randomly)
Two lower resistance T4 and T6 (randomly)

Apply 460 Volts three phases to T1, T2 & T3 leaving open and insulated T4,T5 and T6.
The motor must run smooth at the low speed. If it is noisy and erratic to catch speed we have inverted selection of the terminals. Interchange randomly T1, T2 & T3 by T4, T5 and T6 (the three at the same time,at this step the order is not important).
Verify resistances again and check that the resistance values are as in step two matching the new terminal assignment. Run again the motor applying 460 Volts to T1,T2 &T3 ( T4,T5,T6 individually open and insulated) now the motor must run smooth at low speed.

Now note (tag) the line sequence L1 to T1, L2 to T2 and L3 to T3 and the shaft rotation.

Make the connection for high speed ( T1&T2&T3 tie together neutral) and apply 460 volts to T4,T5 and T6 note the shaft rotation.
If the rotation matches that of the low speed chech that L1 is on T4, L2 with T5 and L3 with T6.
If the shaft rotation was reverse, interchange two lines and verify that the rotation matches that at low speed. T4,T5 andT6 match in order L1,L2,L3 for your final identification.

 

[aolalde]

If you already identified each trio it means it is two windings?
Measure phase resistance to each trio, the one with lower line to line resistance is the high speed winding. This is because the power it will provide is higher proportional to the speed.
(Constant torque T) HP=T*rpm/5252. Then test phase sequence as above.

For a single winding construction you can not make this test since the phases of each speed are interconnected.