Burned a 3 phase motor

[=sparky=]

I recently wired 2 3phase motors of 2HP and 10HP for a spray booth in a paint shop. The 10HP motor is for the air compressor and is 208-230/460Volt 30-28/14Amp, and is fed from a 3phase 40 Amp Mag starter from a 3phase 40Ampfused disconnect, which in turn is fed by a 40Amp 3pole breaker in a 240 Volt 3phase; 3 wire; delta panel. Leg A and C measure 120 Volts to ground, Leg B measures 208 Volts to ground, and 240 Volts phase to phase. The Compressor is wired for Low Voltage Delta I joined wires A-1-7-6, B-2-4-8, C-3-5-9. The mag starter coil is activated by a pressure switch on the compressor. The T-wires in the pecker head of the 10Hp motor on the compressor were black and lightly burned when I had made the connections. I inserted the wires through heat shrink, and relabeled them after half an hour of the process of elimination and troubleshooting with the knowledge that the previous shop was a 240Y 3W system. The 3pole 40amp breaker at the panel trips after the compressor runs for 10 seconds. I checked the rotation of the fan on the compressor and everything checks out. What else can I do to get this motor running and is there a possibility that the windings are going to smoke out?

Now the 2HP motor is a fan motor installed for the spray booth, and it is 3phase 230/460Volt 6.2/3.1Amp. It is fed from a 15Amp fused disconnect, which in turn is fed from a 20amp fused 3p CB. I also wired this motor for low voltage delta. I ran the motor for 10 seconds the check rotation. I did this a couple more times for the owner of the paint shop. The next morning I received a rather devastating call that the fan motor smoked out, and needed to be replaced with the money from my pocket. Both motors were previously wired for Low Voltage Wye because the previous shop had 240V 3W Wye available power. I've checked all my connections and nothing has turned out to be wrong what can I do? Now I have to call an industrial service electrician for a second opinion just to prove to the customer that the motor burned out through no fault of my own. I've attached pictures of my work. Please help me I don't know what I could have done wrong.

 

[benaround]

Sparky,

I think you should reconnect the motors in the wye configuration. Agian ( I think ) what

you have done is change the coils in the motor from wye to delta. I don't think a motor

knows the difference between delta and wye power. Also, the nameplate voltage seems

to indicate a wye 208/230-460 where delta would be 240. An amp reading should let you

know what is going on.

 

[don_resqcapt19]

First you can't change a motor from a wye to delta connection unless you have a 12 lead motor. With a 9 lead motor it is either a wye or a delta and that cannot be changed in the field. Second the motor does not know or care if the supply is wye or delta. It just needs the correct 3 phase voltage. If the motor is a 9 lead with an internal wye connection, you will damage it if you attempt to run it connected like a low voltage delta. The low voltage connection for a standard 9 lead wye motor is the lines to 1&7, 2&8, 3&9 and 4,5&6 connected together.

 

[don_resqcapt19]

A standard dual voltage 3 phase motor has 6 windings. In a standard motor with a wye internal connection leads 10, 11 & 12 are connected together internally. If the motor is delta connected, you will have 1&12, 2&10 and 3&11 connected internally.

If you connect a wye motor using the low voltage delta connections, 3 of the 6 motor windings will see the line to line voltage and the other 3 will see the line to line voltage divided by 1.73.

 

[Jraef]

Looks as though you have a 9 lead dual voltage motor. Unfortunately, the motor can be one of two different types: Y connected or Delta Connected. Both are dual voltage, the difference is only in the design used by the manufacturer. So the first thing you must determine is EXACTLY which type you have. The connections you indicate that you performed would be consistent with a Delta wound motor, used in the Low Voltage configuration, just as you apparently thought you were doing. If you really did that, and it really is a Delta wound motor, there should not have been a problem (in that part of the installation anyway). If however the motor was wound as a Y connected Dual Voltage motor, that configuration was all wrong.

Check out this trouble shooting guide. It steps you through a process of determining how the motor was wound if it is not identified on the nameplate.

As the others have said, the configuration of the supply is irrelevant, don't waste any more time on that side of the issue. As long as you measure 240V phase-to-phase, you have what you need.

BUT, if as you say, the previous owner had wired them in Y because that was what the supply was, one of you is/was wrong! So either the motors are Y and you wired them as if they were Delta, or they are Delta wound but USED TO BE wired wrong and although you have now connected them correctly, the damage was done before you got them.

Other potential issues on the compressor:
1) The hysteresis setting (aka differential, or cut-in / cut-out) on the pressure switch is set too close. It must be NO LESS THAN 7# between the two, but you should definately consult the manual for that compressor. That makes the motor cycle on and off too often. The OL relay SHOULD stop it from being damaged, but basic low-cost compressor packages don't come with the best of OL relays.
2) It sounds as if you moved and installed this, and it had been running in another location. You may also want to double check the selection of heater elements. What often happens, especially when there is some other problem such as the hysteresis setting, is that the OL relay trips, as it should, but rather than solve the REAL problem, someone just puts in higher amperage heaters. This then allows the motor to smoke before they trip.

As per the fan, #2 could also apply, especially if the fan was under sized from the get go. There also could be a flow problem in that there was supposed to be an inlet vane but it was removed. The restricted flow would have required less HP but someone thought that they could get more air flow by removing the restriction, not realizing that this would cause the motor to overload. I have seen that numerous times.

 

[wirenut1980]

Is the main difference between a 9-lead internally connected wye motor and a9-lead internally connected delta motor the voltage magnitude it expects? If not what is the reason for having wye and delta motors?

 

[LarryFine]

Is the main difference between a 9-lead internally connected wye motor and a9-lead internally connected delta motor the voltage magnitude it expects? If not what is the reason for having wye and delta motors?

No.

A dual-voltage motor is, electrically speaking, basically two motors that share the same framework, much like dual-voltage transformer windings.

Each 'half' of each winding must be wired the same way. If the 3-lead half is Wye, the 6-lead half must be wired the same way, and the same if Delta.

The 6-lead half must also be wired to the 3-lead half properly, either in parallel for LV or in series for HV. It sounds like the OP didn't do this correctly.

The wiring diagram for the motor must be followed carefully. It sounds like the OP didn't follow this correctly, and the mis-wired windings burned.

 

[Jraef]

As to why does a motor manufacturer pick one method over the other? I have never seen a good answer to that. It always seems to boil down to "because that's how we learned to do it". I've heard the voltage argument before, but I can't see how that would make much difference and I have seen other people with much more direct knowledge in motor winding say that the argument doesn't hold water. Maybe it did years ago when there might have been a big difference in the cost of the wire insulation, but now days the economy of scale means that there are really no tangible differences in voltage ratings in low voltage magnet wire.

 

[weressl]

I recently wired 2 3phase motors of 2HP and 10HP for a spray booth in a paint shop. The 10HP motor is for the air compressor and is 208-230/460Volt 30-28/14Amp, and is fed from a 3phase 40 Amp Mag starter from a 3phase 40Ampfused disconnect, which in turn is fed by a 40Amp 3pole breaker in a 240 Volt 3phase; 3 wire; delta panel. Leg A and C measure 120 Volts to ground, Leg B measures 208 Volts to ground, and 240 Volts phase to phase. The Compressor is wired for Low Voltage Delta I joined wires A-1-7-6, B-2-4-8, C-3-5-9. The mag starter coil is activated by a pressure switch on the compressor. The T-wires in the pecker head of the 10Hp motor on the compressor were black and lightly burned when I had made the connections. I inserted the wires through heat shrink, and relabeled them after half an hour of the process of elimination and troubleshooting with the knowledge that the previous shop was a 240Y 3W system. The 3pole 40amp breaker at the panel trips after the compressor runs for 10 seconds. I checked the rotation of the fan on the compressor and everything checks out. What else can I do to get this motor running and is there a possibility that the windings are going to smoke out?

Now the 2HP motor is a fan motor installed for the spray booth, and it is 3phase 230/460Volt 6.2/3.1Amp. It is fed from a 15Amp fused disconnect, which in turn is fed from a 20amp fused 3p CB. I also wired this motor for low voltage delta. I ran the motor for 10 seconds the check rotation. I did this a couple more times for the owner of the paint shop. The next morning I received a rather devastating call that the fan motor smoked out, and needed to be replaced with the money from my pocket. Both motors were previously wired for Low Voltage Wye because the previous shop had 240V 3W Wye available power. I've checked all my connections and nothing has turned out to be wrong what can I do? Now I have to call an industrial service electrician for a second opinion just to prove to the customer that the motor burned out through no fault of my own. I've attached pictures of my work. Please help me I don't know what I could have done wrong.

• 10HP motor is 208-230/460Volt motor windings should be connected delta for 208-240V and wye for 460V
• 2HP motor is a fan motor is 3phase 230/460Volt motor windings should be connected delta for 230V and wye for 460V.

The above is true if you have 6 leads. When you have more than that, find and follow the manufacturers instructions. Don't get confused between the suply delta or wye configuration and the motor widning, the two has hardly have anything to do with each other.

 

[LarryFine]

• 10HP motor is 208-230/460Volt motor windings should be connected delta for 208-240V and wye for 460V
• 2HP motor is a fan motor is 3phase 230/460Volt motor windings should be connected delta for 230V and wye for 460V.

I beg to differ. The difference between 230 and 460 is not the difference between wye and delta from the supply; it's whether each phase's windings are in parallel or series.

 

[don_resqcapt19]

• 10HP motor is 208-230/460Volt motor windings should be connected delta for 208-240V and wye for 460V
• 2HP motor is a fan motor is 3phase 230/460Volt motor windings should be connected delta for 230V and wye for 460V.

The above is true if you have 6 leads. When you have more than that, find and follow the manufacturers instructions. Don't get confused between the suply delta or wye configuration and the motor widning, the two has hardly have anything to do with each other.

While I have heard of 6 lead motors being set up that way, it is not electrically correct. If the coils in the motor are 230 volt coils, they will see 277 volts when conneted in wye and to a 480 volt system. If the coils are 277 volt coils, they will see 230 volts when conneted in delta to a 230 volt system. The won't see the correct voltage at one of the voltages, at least with the standard voltage systems here in the US. I understand that some other countries use systems such as 220/380 where this is a correct use of a 6 lead motor on a dual voltage system.

 

[weressl]

I beg to differ. The difference between 230 and 460 is not the difference between wye and delta from the supply; it's whether each phase's windings are in parallel or series.

Don, Larry,

Sorry, you both right.

Brainflatulence?:roll:

 

[Besoeker]

The won't see the correct voltage at one of the voltages, at least with the standard voltage systems here in the US. I understand that some other countries use systems such as 220/380 where this is a correct use of a 6 lead motor on a dual voltage system.

The EU, for example, is now nominally 230/400V.
The 400V is 3-phase and the 230V single phase.
If you have a cage motor with six connections brought out it's most likely to permit star (wye) delta starting rather than to accommodate a dual voltage 3-phase systems.

 

[hurk27]

I was trying to visulize the effect of wiring a Y motor like that was done so I made a little digram in paint, after seeing it, I can see quit a few things that would have caused a failure.

 

[hurk27]

Just realized that the "red" Delta windings are only rated for 120 volts, that would have fried them leaving the Y "blue" windings running the motor at half the horse power? I think.

 

[don_resqcapt19]

Just realized that the "red" Delta windings are only rated for 120 volts, that would have fried them leaving the Y "blue" windings running the motor at half the horse power? I think.

It is a 230/460 dual voltage motor so all of the coils are rated for 230 volts. The red coils would see 230 and the other coils would see 133 volts based on the wye connection.

 

[hurk27]

It is a 230/460 dual voltage motor so all of the coils are rated for 230 volts. The red coils would see 230 and the other coils would see 133 volts based on the wye connection.

Yep thought about it at work and it was as I had put in my diagram, but even then I missed the Y figure, thats what I get for trying to post late

But do you see a phase angle differance from one 1/2 winding wired as a delta? and the other 1/2 a fixed Y

Keep me straight Don keep me straight:wink:

 

[don_resqcapt19]

Yep thought about it at work and it was as I had put in my diagram, but even then I missed the Y figure, thats what I get for trying to post late

But do you see a phase angle differance from one 1/2 winding wired as a delta? and the other 1/2 a fixed Y

Keep me straight Don keep me straight:wink:

I'm not sure if there would be a phase shift like in a delta/wye transformer. I expect that there would be.

 

[hurk27]

To me it would be like two motors tied together by the shaft but out of sync, with only the delta connected it would be find but at half HP, or only the Y connected, but to have both connected each would be trying to slip back into sync, but cant because of the two windings fixed on the same pole.