motor troubleshooting

[eadd9]

I recently installed a vfd on motor. I brought 480 directly off a 30a breaker into the vfd then supplied 480 to the motor i also wired in a remote pot.
everthing worked fine until i left ( of course ) got a call about the motor not working. I tested the motor independent of the vfd the breaker tripped instantly what tests can i do to the motor to see if it is any good now?
Will a thermally protected motor trip a breaker instantly if not allowed sufficient time to cool?

 

[mdshunk]

Will a thermally protected motor trip a breaker instantly if not allowed sufficient time to cool?

Nope, it sure won't. I think you toasted the motor. My guess, whithout knowing anything else, might be that this was a TEAO or TEFC motor and they had it running too slowly to cool itself. Now, it's toast. You need a TEBC motor if it is to run real slow, or use a gearbox along with the VFD.

 

[eadd9]

motor troubleshooting

we shouldn't have to run the motor any less than 40 hz but i didn't set this as the min freq parameter before i left and i think the operator ran the motor under load at 10 hz for god knows how long anyway no problem about the motor i have another just don't want to ruin another the vfd is a baldor why didn't it realize the motor was overloaded and shut it down before it burnt up?
you probably need more info to determine that just tell me what you need for specifics thanks.

 

[mdshunk]

we shouldn't have to run the motor any less than 40 hz but i didn't set this as the min freq parameter before i left and i think the operator ran the motor under load at 10 hz for god knows how long

What type of motor was it, anyhow? Fan cooled motors aren't really supposed to go under roughly 40%, and good design says not to even take them below 50%.

anyway no problem about the motor i have another just don't want to ruin another the vfd is a baldor why didn't it realize the motor was overloaded and shut it down before it burnt up?

Beats me. Did you program everything you needed to? I didnt' even know Baldor made drives.

 

[eadd9]

motor troubleshooting

yeah baldor makes drives and there tech support is pretty good same guy everytime i call though. it is a 480v 9.3a 7.5h 3 phase motor fan cooled yes but heres the thing (i wish i could draw a schematic of what i did)
30a breaker feeds vfd vfd feeds motor i know the breaker is way to big but i thought the vfd would act as the overloads if the current was excessive probably like you said earlier i need to adjust some parameters in my vfd.

If i burn up another motor i may be asking you if you want to super size that?:smile:

 

[mdshunk]

probably like you said earlier i need to adjust some parameters in my vfd.

You betcha. Never walk away from any VFD without going through each and every parameter. When in doubt, err on the conservative side to save equipment. Better a callback for a setting change than a toasted motor.

 

[eadd9]

motor troubleshooting

hard lesson but a good one some things just arn' t (excuse english) cut and dry.

 

[Psychojohn]

Does the motor have a thermal OL that can be tied into the drive?
I have had motors burn up that were not overloaded, but they burnt up due to lack of cooling of just faulty insulation.

 

[iaov]

yeah baldor makes drives and there tech support is pretty good same guy everytime i call though. it is a 480v 9.3a 7.5h 3 phase motor fan cooled yes but heres the thing (i wish i could draw a schematic of what i did)
30a breaker feeds vfd vfd feeds motor i know the breaker is way to big but i thought the vfd would act as the overloads if the current was excessive probably like you said earlier i need to adjust some parameters in my vfd.

If i burn up another motor i may be asking you if you want to super size that?:smile:

It probably was not overloaded. Lack of cooling caused the insullation on the windings to melt down. Bummer!

 

[frenchelectrican]

Really my thumb of rules if any motor run below 50% of base speed either use motor thermosat or seperated cooling fan motor to keep it from getting overheating especally on slow speed operation.

Or get some sorta like timedelay sensor so for so many X minutes it will give a warning signal if approching the limit of the tempture rise.

Merci,Marc

 

[mdshunk]

Really my thumb of rules if any motor run below 50% of base speed either use motor thermosat or seperated cooling fan motor to keep it from getting overheating especally on slow speed operation.

Or get some sorta like timedelay sensor so for so many X minutes it will give a warning signal if approching the limit of the tempture rise.

Merci,Marc

That's good rules, right there. People don't realize that even though you can easily and pretty accurately slow down an AC motor, you're cooking that thing unless you have other cooling provisions in mind.

 

[weressl]

I recently installed a vfd on motor. I brought 480 directly off a 30a breaker into the vfd then supplied 480 to the motor i also wired in a remote pot.
everthing worked fine until i left ( of course ) got a call about the motor not working. I tested the motor independent of the vfd the breaker tripped instantly what tests can i do to the motor to see if it is any good now?
Will a thermally protected motor trip a breaker instantly if not allowed sufficient time to cool?

Bunch of nonsense unqualified advice follows your questions.

The sign of insanity is to keep repeating the same thing and expecting different results.

I suggest that you ask the installation be reviewed by an electrical AND a mechanical engineer who specializes in ASD applications.

 

[petersonra]

I would suggest that the so called "rules of thumb" being quoted regarding how low you can run the VFD without damaging the motor are just bad ideas that are perpetrated by those who do not want to look real close at their application, or perhaps do not know how to do so.

Modern motors do not have as much iron in them as older motors did. This makes them more efficient, and sometimes cheaper to make. It also can make them somewhat more susceptible to overheating if run at low speeds and relatively high loads.

The thing is that when a motor is run at low speeds off a standard VFD, it rends to do a lot less work, and typically does not generate all that much heat, so the cooling issue tends to not be as big a deal as you might think. It doesn't go away, but it may not be a problem. Note the use of the word "tends".

Vector drives, OTOH, can really generate some serious heat in a motor at lower speeds. It is generally a good idea to have some kind of temperature sensing device in the motor winding(s) when using a vector drive at low speeds, and you may even want to add external cooling fans, although the design of some motors does not always require them.

Motors and VFds tend to be designed conservatively enough that for many applications it is not necessary to look real close. Some applications need that closer look.

 

[bsh]

Per NEC 430.126 you have to have some type of temp sensing between the motor and drive. Since most smaller motors don't have any temp feedback it is up to the drive to figure this out. Some drives have circuitry built-in that will model the temp (AB Powerflex does, the 1330 does not).

 

[Jraef]

It probably was not overloaded. Lack of cooling caused the insullation on the windings to melt down. Bummer!

That is probably one of the top ten failures in VFD installations. People ASS-U-Me that the OL protection in the VFD will protect the motor from over heating. The problem is, the OL protection is based solely on current. It ASS-U-es that the motor temperature is dependent upon current, but if the motor is running too slow, the current will be low but the heating effect will be higher than you would expect and as mentioned previously, the cooling of the motor is diminished with lower speed. So the motor overheats, even though the current is well within normal as far as the OL circuit is concerned.

In IEC countries, they tend to insist on using Thermistors embedded in the motor to detect actual motor winding temperature as a supplement to the OL circuit. Most VFDs now come with a Thermistor input as standard. A good idea, but unfortunately here in the US you pretty much have to remember to order the motor with the Thermistors installed in advance, it's difficult to add them after the fact.

 

[weressl]

That is probably one of the top ten failures in VFD installations. People ASS-U-Me that the OL protection in the VFD will protect the motor from over heating. The problem is, the OL protection is based solely on current. It ASS-U-es that the motor temperature is dependent upon current, but if the motor is running too slow, the current will be low but the heating effect will be higher than you would expect and as mentioned previously, the cooling of the motor is diminished with lower speed. So the motor overheats, even though the current is well within normal as far as the OL circuit is concerned.

In IEC countries, they tend to insist on using Thermistors embedded in the motor to detect actual motor winding temperature as a supplement to the OL circuit. Most VFDs now come with a Thermistor input as standard. A good idea, but unfortunately here in the US you pretty much have to remember to order the motor with the Thermistors installed in advance, it's difficult to add them after the fact.

That is not exactly corect. The thermal protection model in the ASD software takes into consideration the speed and the load characteristcs. The thermistor is to protect against misapplication or rather to extend the motor application to conver all possible scenarios. I would say 95% of aplications could live without thermistors and it is an unnecessary expense. It is very useful in hazardous(classified) aplications, even though it is not required.

 

[steveng]

That is not exactly corect. The thermal protection model in the ASD software takes into consideration the speed and the load characteristcs. The thermistor is to protect against misapplication or rather to extend the motor application to conver all possible scenarios. I would say 95% of aplications could live without thermistors and it is an unnecessary expense. It is very useful in hazardous(classified) aplications, even though it is not required.

what does asd mean?
thanks

 

[mdshunk]

Bunch of nonsense unqualified advice follows your questions.

Huh? I guessed it was probably a lack of cooling, you say that's nonsense. Then Jref brings it up and you say "exactly right". You're just mean.

 

[crossman]

why didn't it realize the motor was overloaded and shut it down before it burnt up?

Do we know the motor was overloaded? Or was it normal load, but running so slowly that the fan wasn't cooling it enough?

 

[quogueelectric]

I recently installed a vfd on motor. I brought 480 directly off a 30a breaker into the vfd then supplied 480 to the motor i also wired in a remote pot.
everthing worked fine until i left ( of course ) got a call about the motor not working. I tested the motor independent of the vfd the breaker tripped instantly what tests can i do to the motor to see if it is any good now?
Will a thermally protected motor trip a breaker instantly if not allowed sufficient time to cool?

Put your nose to the windings. If it looks like a duck walks like a duck and talks like a duck its a duck. Or a cooked goose but you can smell it.