Motor stalling

[T.M.Haja Sahib]

As long as the power delivered starts the motor and there is no other problems the undersizing of the transformer is likely POCO's problem.

Does the capacity of a transformer has any thing to do with motor stalling ?

Suppose the under capacity transformer is able to start the loaded motor. Would not the motor stall due to excessive voltage drop as a result of under capacity of the transformer ?

 

[renosteinke]

Get yourself a car with the biggest, mostpowerful engine you can find, then feed it through the narrowest tubing you can find.

Come back and let me know if an inadequate supply can affect the performance.

 

[kwired]

Does the capacity of a transformer has any thing to do with motor stalling ?

Suppose the under capacity transformer is able to start the loaded motor. Would not the motor stall due to excessive voltage drop as a result of under capacity of the transformer ?

How is it a motor will be able to start yet load is so great it will stall? Opening of a protective device is not stalling, I'm talking about stalling because not enough torque is available to move the load, not because some protective device opened the circuit. In order for motor to start moving enough torque must be produced to allow load to move. Accelerating to proper speed is another issue but not being able to reach that speed is not stalling.

If voltage drop is excessive enough that the motor is not going to accelerate to full speed, current will be high, voltage drop will be even worse, something is going to give and it will shut down or burn up.

If connected to a variable speed drive then we have a different situation - starting current will be low, overloading will start to happen somewhere before full rated speed is reached. The transformer will attempt to deliver the load that is demanded but will have increased heating as a result. If transformer is not able to deliver power needed voltage will drop, current will go up - making voltage drop even worse - something will either respond and shut it down or something will eventually burn up.

 

[T.M.Haja Sahib]

How is it a motor will be able to start yet load is so great it will stall?

The loaded motor, fed by an under capacity transformer, is able to start because the rated voltage is available to the motor at the instant of starting.But voltage drops soon after due to under capacity of the transformer.This could cause stalling of the motor.

 

[ActionDave]

The loaded motor, fed by an under capacity transformer, is able to start because the rated voltage is available to the motor at the instant of starting.But voltage drops soon after due to under capacity of the transformer.This could cause stalling of the motor.

One space after each punctuation mark. The rule is the same for either commas or periods. If you have no thumbs to strike the space bar that would be sad, but you can hit it with an index finger as a substitute.

In regards to thoughts about a loaded motor- If a loaded motor is able to start then there is enough capacity for it to run.

 

[T.M.Haja Sahib]

One space after each punctuation mark. The rule is the same for either commas or periods. If you have no thumbs to strike the space bar that would be sad, but you can hit it with an index finger as a substitute.

Sorry, I can't help it. You better bear with me or quit reading me.

If a loaded motor is able to start then there is enough capacity for it to run.

This may not be true in all cases.

 

[eric7379]

Sorry, I can't help it. You better bear with me or quit reading me.

This may not be true in all cases.

Can you cite a case in which this might occur?? I have never seen a case in which there was enough of a voltage drop (under capacity transformer) to cause a motor to stall after the motor had already started. The highest "drop" would be when the motor is first starting up, not after the initial inrush.

 

[T.M.Haja Sahib]

Can you cite a case in which this might occur?? I have never seen a case in which there was enough of a voltage drop (under capacity transformer) to cause a motor to stall after the motor had already started. The highest "drop" would be when the motor is first starting up, not after the initial inrush.

See below.

If connected to a variable speed drive then we have a different situation - starting current will be low, overloading will start to happen somewhere before full rated speed is reached. The transformer will attempt to deliver the load that is demanded but will have increased heating as a result. If transformer is not able to deliver power needed voltage will drop, current will go up - making voltage drop even worse - something will either respond and shut it down or something will eventually burn up.

 

[Besoeker]

Does the capacity of a transformer has any thing to do with motor stalling ?

Suppose the under capacity transformer is able to start the loaded motor. Would not the motor stall due to excessive voltage drop as a result of under capacity of the transformer ?

Seems like a d?j? vu moment...

If the motor is connected direct on line you have this sort of characteristic:

Clearly, the highest current is at starting. Thus is a double whammy for the supply voltage. Not only is it the highest current but it is at poor power factor which results in greater voltage regulation than the same current at good power factor. Then you're also hit about the lowest torque per amp. If the motor can get past that, things get better all round, so stalling isn't like to be caused by transformer capacity.
This is just confirming what others have already pointed out.

If the motor is fed by a variable frequency drive (not mentioned in your original post) and the supply voltage drops then so will the DC link voltage. Most VFDs default to fixed V/f ratio so there at at least a couple of possible outcomes. Depending on how low the voltage is I can see a couple of possible outcomes. The low DC link might prevent the motor getting maximum frequency thus limiting its speed. And if it's lower than the drive settings the drive will trip. Again, the motor stalling isn't a likely outcome.

 

[T.M.Haja Sahib]

..... the motor stalling isn't a likely outcome.

With VFD drive and under capacity supply transformer,when will the motor stalling be likely?

 

[Besoeker]

With VFD drive and under capacity supply transformer,when will the motor stalling be likely?

I can't foresee any circumstances where it would.

 

[T.M.Haja Sahib]

I can't foresee any circumstances where it would.

Okay. Let us take a star/delta starter. Is motor stalling likely with an under capacity transformer?

 

[eric7379]

Why don't YOU tell us when a situation like this can occur?? You ask one question, you get multiple responses, then you try to change the original question by "well, but what about, or what if this...."

You asked a question...you got an answer. When do YOU suppose a situation can occur in which a motor can stall after it has already started?

 

[T.M.Haja Sahib]

eric;
Are you not enjoying the way the discourse on the subject conducted here? Please join with us wholeheartedly.
As for your last question, I dare say with star/delta starter, motor stalling is possible with under capacity supply transformer. However, Bes would raise objections to it for your enjoyment also.

 

[Besoeker]

As for your last question, I dare say with star/delta starter, motor stalling is possible with under capacity supply transformer.

If you already knew the answer, why ask the question?

 

[T.M.Haja Sahib]

If you already knew the answer, why ask the question?

To know the answer better by hearing from experts like you in this forum.

 

[kwired]

eric;
Are you not enjoying the way the discourse on the subject conducted here? Please join with us wholeheartedly.
As for your last question, I dare say with star/delta starter, motor stalling is possible with under capacity supply transformer. However, Bes would raise objections to it for your enjoyment also.

Why is this any different than other motors we have already mentioned? The greatest amount of power will be needed to accelerate the motor from a state of rest. Once that first turn of the shaft occurs the current needed and the power factor both go down rapidly. If the voltage supply is able to get past that point, things only get better the closer the motor comes to normal operating speed.

 

[T.M.Haja Sahib]

That may be true for closed transition star/delta starter. In case of open transition star/delta starter, higher current could result during change over to delta and it may cause motor stalling with under capacity transformer.

 

[kwired]

That may be true for closed transition star/delta starter. In case of open transition star/delta starter, higher current could result during change over to delta and it may cause motor stalling with under capacity transformer.

The reason for part winding or wye delta starting is to reduce the intitial starting current. The motor should already have accelerated some with the first stage, the inrush of the second stage should be less than what it was for first stage otherwise the reasoning for using that starting method was not accomplished.

If the motor failed to accelerate in the first stage then it did not stall in the second stage - it was already stalled before that stage happened.

 

[T.M.Haja Sahib]

The reason for wye delta starting is to reduce the intitial starting current. ....... the inrush of the second stage should be less than what it was for first stage

This is not always the case with open transition wye delta starting.