Wye / Delta Motor Connection

[7EA]

Needing a real motor expert to chime in on this one. At our power plant, we have two 60 HP 480v oil pumps as part of a steam turbine oil pump skid (european manufacture). The motors are connected across the line start. Recently we had a failure of one of the motors due to a broken plastic cooling fan and subsequent overheating of the motor. We replaced it with a motor of the same manufacturer but slightly different configuration. The biggest change was that the motor connections in the peckerhead of the old motor was by terminal blocks & jumpers and the new simply had motor leads. The new motor is a 12 lead motor and we connected it in the delta (run) high voltage configuration. When the new motor was started, it repeatedly tripped the instantaneous trip breaker in the bucket. We bumped the instantaneous trip point up two settings and still it would not start. Not until after we had pulled the new motor out and sent it back to our local vendor for testing was it discovered that the old motor had been connected in the wye (start) configuration. This was the connection from the factory and we have since confirmed the other pump is the same way. I have never seen a 12 lead wye start delta run motor left to run continously in the wye connection. I understand this will not allow the motor to deliver the same torque but it is currently running fine (and starting beautifully!) and driving the pump as it needs to. Current readings are approx. 42 amps and nameplate is 69. The load is constant and does not vary. Is there anything detrimental to leaving it in this configuration? Is the motor essentially "derated" but since it is driving the load properly and is well under nameplate current all is well? Thanks in advance.

 

[templdl]

Needing a real motor expert to chime in on this one. At our power plant, we have two 60 HP 480v oil pumps as part of a steam turbine oil pump skid (european manufacture). The motors are connected across the line start. Recently we had a failure of one of the motors due to a broken plastic cooling fan and subsequent overheating of the motor. We replaced it with a motor of the same manufacturer but slightly different configuration. The biggest change was that the motor connections in the peckerhead of the old motor was by terminal blocks & jumpers and the new simply had motor leads. The new motor is a 12 lead motor and we connected it in the delta (run) high voltage configuration. When the new motor was started, it repeatedly tripped the instantaneous trip breaker in the bucket. We bumped the instantaneous trip point up two settings and still it would not start. Not until after we had pulled the new motor out and sent it back to our local vendor for testing was it discovered that the old motor had been connected in the wye (start) configuration. This was the connection from the factory and we have since confirmed the other pump is the same way. I have never seen a 12 lead wye start delta run motor left to run continously in the wye connection. I understand this will not allow the motor to deliver the same torque but it is currently running fine (and starting beautifully!) and driving the pump as it needs to. Current readings are approx. 42 amps and nameplate is 69. The load is constant and does not vary. Is there anything detrimental to leaving it in this configuration? Is the motor essentially "derated" but since it is driving the load properly and is well under nameplate current all is well? Thanks in advance.

If I can take a guess the motor that failed was probably an older motor prior to the high efficiency motors of today. The inrush required to start the original motor was much lower than the replacement. Check this out. Keep in mind that the purpose of the MCP is to protect the motor circuit should the motor experience a winding failure. The intent is to take the motor off line should there be a winding to ground winding failure and before it could escalate into a phase to phase winding failure. You want to set the MCP such that the magnetic pickup is just above the inrush required to start the motor. It is interesting to note that you did state that you "bumped" the magnetic pick up setting up 2 but then neglected to state what that setting was. You will note that for a design B energy efficient motor you are allowed to set the MCP up to 17 times the FLA of the motor which should be 69 x 17=1173a. It is interesting that you included a great deal of information but did not state what the MCP size was and where you had set it which makes a bit difficult to address your question. Is the MCP 150a? If so it should have a mag setting of up to 1500a . A C-H HMCP has setting has setting A-H, A=450 and H=1500. You would select E=1050a If you had a 100a MCP you would set ti at the highest setting available.

Please refer to NEC art 430-52(C)(3)
Exception No. 1: Where the setting specified in Table
430.52 is not suff?cient for the starting current of the motor,
the setting of an instantaneous trip circuit breaker shall be
permitted to be increased but shall in no case exceed
1300 percent of the motor full-load current for other than
Design B energy eff?cient motors and no more than
1700 percent of full-load motor current for Design B energy
eff?cient motors. Trip settings above 800 percent for
other than Design B energy eff?cient motors and above
1100 percent for Design B energy eff?cient motors shall be
permitted where the need has been demonstrated by engineering
evaluation. In such cases, it shall not be necessary
to first apply an instantaneous-trip circuit breaker at
800 percent or 1100 percent.

 

[7EA]

Thank you for the education on the allowable settings of the MCP. The failed motor was not terribly old, 2004 vintage. In hindsight, the real reason why the old motor would start with the old settings of the MCP and the new motor would not is that the old was connected in the wye configuration and we were connecting the new in the delta. The wye is typically the starting configuration for a wye/delta reduced voltage motor starter and it will transfer over to delta (either open or closed transition) after a time delay. It now makes perfect sense that we couldn't get the new motor to start with the old MCP settings because the starting current (and also torque) in the wye is approx. 30% of the motor in the delta. My question is really a basic one in regards to any 12 lead motor and not specific to the current, etc of this motor and MCP. What are the effects of leaving the motor to run continously in wye? Keep in mind, this is not a wye delta starter but an ATL. In my education, if you are starting a motor ATL it should be connected in the delta (run) configuration.

 

[topgone]

Thank you for the education on the allowable settings of the MCP. The failed motor was not terribly old, 2004 vintage. In hindsight, the real reason why the old motor would start with the old settings of the MCP and the new motor would not is that the old was connected in the wye configuration and we were connecting the new in the delta. The wye is typically the starting configuration for a wye/delta reduced voltage motor starter and it will transfer over to delta (either open or closed transition) after a time delay. It now makes perfect sense that we couldn't get the new motor to start with the old MCP settings because the starting current (and also torque) in the wye is approx. 30% of the motor in the delta. My question is really a basic one in regards to any 12 lead motor and not specific to the current, etc of this motor and MCP. What are the effects of leaving the motor to run continously in wye? Keep in mind, this is not a wye delta starter but an ATL. In my education, if you are starting a motor ATL it should be connected in the delta (run) configuration.

The reason why there are 12 lead motors is for the product to be applicable to two voltage levels. You can configure the motor to run on 230V (double-delta) or on a 460V (series delta).
On your original question, if you leave a motor running on wye configuration when the required connection should have been delta, your motor will deliver less torque as the motor torque is proportional to the square of the voltage. The voltage impressed on the motor windings will be 57% when connected in wye, and you're motor will give you just 33%(0.57^2) of the rated torque. This torque may allow you to start motors driving fans or pumps, but you will not be able to run mills and other equipment that require 100% torque. The point is to supply the right voltage to the motor.

 

[7EA]

Thank you topgone. I'm certainly not asking you to put your "blessing" on this application, but since this motor is running a pump; and the oil flow and motor currents are well within specs, can I reasonably assume that leaving the motor(s) in wye will not affect motor life/reliability? It has been suggested that the manufacturer did this with the intent of greater reliability and for less mechanical stress on startup, etc. If I spoke Swedish I would call the manufacturer and ask, but that has proven to be a challenge at times.

This torque may allow you to start motors driving fans or pumps, but you will not be able to run mills and other equipment that require 100% torque. The point is to supply the right voltage to the motor.

 

[templdl]

Thank you for the education on the allowable settings of the MCP. The failed motor was not terribly old, 2004 vintage. In hindsight, the real reason why the old motor would start with the old settings of the MCP and the new motor would not is that the old was connected in the wye configuration and we were connecting the new in the delta. The wye is typically the starting configuration for a wye/delta reduced voltage motor starter and it will transfer over to delta (either open or closed transition) after a time delay. It now makes perfect sense that we couldn't get the new motor to start with the old MCP settings because the starting current (and also torque) in the wye is approx. 30% of the motor in the delta. My question is really a basic one in regards to any 12 lead motor and not specific to the current, etc of this motor and MCP. What are the effects of leaving the motor to run continously in wye? Keep in mind, this is not a wye delta starter but an ATL. In my education, if you are starting a motor ATL it should be connected in the delta (run) configuration.

There is no doubt that you certainly have a handle on the Y-D starter application. Yes, a 2004 motor must have been energy efficient. If you configure the motor in a way that it would be for a Y-D starter but leave it in Y mode if you think about it you are applying 480v across two windings in series for each phase, that is the windings are connected from the 'A' to the center point of the 'Y' to 'B' putting the 'A' winding in series with the 'B' winding. Then the 'B' in series with the 'C' and the 'A' in series with the 'C'. Thus each winding essentially will see 1/2 on the 480v. As such, what performance can you expect from a motor that is rated with 480v across each winding when configured in a delta?
And, yes as topgone indicated, the motor could be configured such that it could be applied with 230v. the 12 leads allows you to spit each winding which allows tou to apply 230v to each part of the winding thus the "double delta" as described by topgone. And I agree with topgone that the performance will be far less when configured to run in a 'Y' than a delta as he pointed out.
But what I still have not been made aware of is what MCP is being used and what the setting is. It's hard to provide an answer when neither of those answers have been provided. You are questioning why the MCP is tripping aren't you?

 

[7EA]

Templdl, sorry if my question wasn't clear. We were perplexed why the new motor would not start with the same settings as the old. Now that we realize the the old was wye, and the new delta, It makes sense. We re-connected the new wye and everything works beautifully with the "old" settings. I was more concerned of the effects of leaving a motor running when permanently connected wye. I am not near the motor at this time, so I can't be sure of what the MCP settings are. It is a CH 150a MCP and I know we went as high as 1050 with no luck (over 15x nameplate). Most likely, had we went to the next step, we could have gotten the motor to start ATL delta. We were "nervous" because of the disparity between the two, and the fact that if for some reason, had we tripped the MCC main, we would have tripped the plant, (and 250 MW on the spot market doesn't come cheap!)

 

[templdl]

Templdl, sorry if my question wasn't clear. We were perplexed why the new motor would not start with the same settings as the old. Now that we realize the the old was wye, and the new delta, It makes sense. We re-connected the new wye and everything works beautifully with the "old" settings. I was more concerned of the effects of leaving a motor running when permanently connected wye. I am not near the motor at this time, so I can't be sure of what the MCP settings are. It is a CH 150a MCP and I know we went as high as 1050 with no luck (over 15x nameplate). Most likely, had we went to the next step, we could have gotten the motor to start ATL delta. We were "nervous" because of the disparity between the two, and the fact that if for some reason, had we tripped the MCC main, we would have tripped the plant, (and 250 MW on the spot market doesn't come cheap!)

Darned, that's strange. You have everything covered with the HMCP150 set at 1050 which should be setting 'E'. There has to be something more going on there. I would have no problem with setting it higher as the highest setting is 1500a. As far as the upstream devices they must have an instantaneous that is higher than 1500a. However if you did try 1500a and it still tripped the MCP you most have a real issue.
I would try the next high setting and if still trips the MCP try the next. I can't see any reason that you would damage anything except the number of starts per hour allowed when attempting to practice re-staring the motor. I certainly wouldn't exceed 7 attempts.
Tripping the MCP isn't going to hurt anything if the motor is not defective. If you are successful at setting the MCP higher and starting the motor on a consistent basis then you most likely would be in violation of the NEC with a setting higher than 17x. Personally I don't see any danger in that but I would still bird dog the reason that there is such a high inrush which I find strand. I would consult the motor manufacturer with this issue telling them what you are doing and the issues that you are having with the HMCP while trying to not exceed the 17x the FLA of the NP of the motor.
If you an instrument that was capable of capturing the peak current such as on old brush recorder was capable of doing you may get an idea what the actual instantaneous current that you are dealing with.

 

[Jraef]

Darned, that's strange. You have everything covered with the HMCP150 set at 1050 which should be setting 'E'. There has to be something more going on there. I would have no problem with setting it higher as the highest setting is 1500a. As far as the upstream devices they must have an instantaneous that is higher than 1500a. However if you did try 1500a and it still tripped the MCP you most have a real issue.
I would try the next high setting and if still trips the MCP try the next. I can't see any reason that you would damage anything except the number of starts per hour allowed when attempting to practice re-staring the motor. I certainly wouldn't exceed 7 attempts.
Tripping the MCP isn't going to hurt anything if the motor is not defective. If you are successful at setting the MCP higher and starting the motor on a consistent basis then you most likely would be in violation of the NEC with a setting higher than 17x. Personally I don't see any danger in that but I would still bird dog the reason that there is such a high inrush which I find strand. I would consult the motor manufacturer with this issue telling them what you are doing and the issues that you are having with the HMCP while trying to not exceed the 17x the FLA of the NP of the motor.
If you an instrument that was capable of capturing the peak current such as on old brush recorder was capable of doing you may get an idea what the actual instantaneous current that you are dealing with.

I agree that it's strange.

But, maybe that was the INTENT of the pump mfr, i.e. they sized the motor KNOWING it would run in Star with 480V applied and they KNEW the shaft HP would be lower, but it would not trip out the breaker on magnetizing inrush. I have seen a couple of OEMs do stuff like this. Seems wasteful, but if they had repeated problems with the motors tripping breakers on 480V systems (as opposed to 380V systems which would inherently have lower magnetizing inrush), they may have elected to solve it by using a larger motor and connecting it ion Star to avoid call-backs.

 

[StarCat]

Wye-Delta

Wye-Delta

Here is an article I found useful.

http://electromotores.org/PDF/InfoT...ifferences Estrella Delta vs Part Winding.pdf

 

[topgone]

Templdl, sorry if my question wasn't clear. We were perplexed why the new motor would not start with the same settings as the old. Now that we realize the the old was wye, and the new delta, It makes sense. We re-connected the new wye and everything works beautifully with the "old" settings. I was more concerned of the effects of leaving a motor running when permanently connected wye. I am not near the motor at this time, so I can't be sure of what the MCP settings are. It is a CH 150a MCP and I know we went as high as 1050 with no luck (over 15x nameplate). Most likely, had we went to the next step, we could have gotten the motor to start ATL delta. We were "nervous" because of the disparity between the two, and the fact that if for some reason, had we tripped the MCC main, we would have tripped the plant, (and 250 MW on the spot market doesn't come cheap!)

You should look at the whole setup, not just the electrical setup, IMO. Did your crew check if the driven pump was not "backpedalling" when it was started? A faulty one-way valve at the discharge side of the pump can give you starting problems. There are other items to investigate: recirculation valve control failing, deadheading, motorized discharge valve slow to open, or piping not properly lined up for pumping operations, etc.