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Transformers in Series, How does it effect the power?
6

Transformers in Series, How does it effect the power?

Transformers in Series, How does it effect the power?

(OP)
I have a step down transformer from the utility that supplies 480V to my facility. The utility say that it is rated for 500 KVA. I don't have any more information on the utility transformer.

Inside my facility, I have a step up transformer (to 2300V)  that is powering (only) a well pump rated for 450HP, 2300V

The inside transformer is a dry type 500 KVA unit with 5% impedance.

The utility transformer is operating at close to maximum rating when the pump is operating at capacity.

The problem is that when the well is started, the power is marginal to start the well pump motor. If the utility voltage drops slightly, the well motor may not start.

What size of transformer should the utility have supplied?

Does the impedance (of the transformers in series) have an effect on how much power comes through the transformers?

The utility was supplied with a load letter listing all equipment in the project. Now the utility rep is saying that there is no problem on their end, it is my fault. The utility is the one that sized the utility transformer.

Any comments?


 

RE: Transformers in Series, How does it effect the power?

Sounds like the utility transformer is probably sized pretty well for your load since you say that it is "near" capacity when the well pump is running.  Are you starting this pump across the line, or do you have compenstaion to limit the inrush from the start?

Alan

RE: Transformers in Series, How does it effect the power?

(OP)
The well motor is starting across the line, with about 4 times current during the start.

RE: Transformers in Series, How does it effect the power?

I am surprised that the utility will allow you to start the motor across the line, must not be affecting anyone else on the system.  I would expect your lights go out or almost on starting.  You really need to use starting compensation for a motor that large.

Alan

RE: Transformers in Series, How does it effect the power?

(OP)
Actually, I have an RVAT installed. However, the RVAT is programmed so that it is more or less an across the line start.

If the RVAT was set at the typical 80% voltage to start, it would drop the voltage further and make the motor starting problem worse.

As it is, the well pump motor takes 4 times the running current to start instead of 6 times for the typical motor. In addition, the well motor starts in 0.6 seconds as well. So the RVAT may not be necessary for this application.

I am more interested in answers to the questions in my first post.

What size of transformer should the utility have supplied?

Does the impedance (of the transformers in series) have an effect on how much power comes through the transformers?

The utility was supplied with a load letter listing all equipment in the project. Now the utility rep is saying that there is no problem on their end, it is my fault. The utility is the one that sized the utility transformer.

Any comments?




 

RE: Transformers in Series, How does it effect the power?

What does the project electrical engineer have to say about this?  If the utility transformer does not see 120% of nameplate for extended periods of time and you did not specifically ask for and pay for excess capacity then the utility transformer is not undersized.  The design on the customer side of the transformer has some serious problems though, should have been a 2400V service rather than a 480V service.

RE: Transformers in Series, How does it effect the power?

Every series device you put in an electrical circuit has impedance and will cause voltage drop across it when current is passed through it....especially at 4 times rated.  Both of your transformers are no doubt experiencing severe drop when you start the motor.

But David and the utility are correct in that you are causing the problem and it will be left for you to fix, or pay the utility to fix it for you.  They could install a larger trans. but your load does not indicate this is needed.  Larger utility trans. would help some, but possibly not enough.  The second transformer will continue to be a problem when starting across the line.  Should not be there!

Alan

RE: Transformers in Series, How does it effect the power?

You could also ask the utility for a second 2400 v service, but at this point they may charge you for the entire cost.

Alan

RE: Transformers in Series, How does it effect the power?

The xmfr z's will sum, making the voltage regulation even worse. I can see this will be a problem.

Check your power system + xmfr + cable voltage drop calculations at 100% and 400% of motor current. You may end up with such poor regulation you will burn up your pump motor.

Any way to start the pump with no/limited load?

@ 746 w/HP, your watts @ full load will be 335,700. Assume a .8PF, and that will be 419,625 VA. Is the 500,000 va transformer big enough depends many other factors including any other loads. If this is the only load, technically yes, it should be OK. But there are LOTS of other factors, like system z%, that we have not even discussed here yet.

These guys have given you some valuable insights and suggestions or maybe work arounds. If the only question you have is regarding the xmfr, technically it is probably OK.

You might need a power system study to fully answer everything-you have many variables here.

good luck
Steve
  

RE: Transformers in Series, How does it effect the power?

(OP)
I am not defending the designer, this is just the way that it is.

Actually, the voltage drop was measured. The incoming voltage drops to 440V on starting. The step up transformer voltage drop was not measured, but I don't think there is a problem there.

I also have an emergency generator and transfer switch 480V rated. The designer stated that he went with the lower voltage equipment because of the cost and servicablity factors. It is hard to get medium voltage service people.

All that is water over the dam now. I am just trying to resolve this the most cost effective way.

I also don't understand why the utility should not be providing enough power to start the motor. At some point, every motor has to start.



 

RE: Transformers in Series, How does it effect the power?

Utilities generally have policies banning DOL starting of motors more than some number of horsepower; typically in the 50Hp-200Hp range when served at 480V.  You need a 2400V VFD, or some other costly modification.  It isn't the utility's problem, though I'm sure they would be willing to let you pay for a larger transformer, and an additional monthly charge for excess capacity.  Better luck next time on the design.

RE: Transformers in Series, How does it effect the power?

If you cannot get your RVAT adjusted so that it will start the motor, and I would think you could, you might consider a VFD if it could work better.  Does anyone here think a VFD would be better?  The first thing I would do is find out why the RVAT does not do the job.  Does it have a problem?

Unfortunatley the utility will supply capacity for continuous loads, not inrush unless you can somehow persuade them (good luck) or pay them to do it.  They would probably add on a perpetual facility charge for the extra equipment.  This can be 2% of the extra installed cost every month (24%/year!) for the life of the facility.  Generally it is most cost effective for you to do it yourself.

When the utility sees your step up transformer, they will absolutely tell you that the second transformer is a major problem with the full voltage starts.

Alan

RE: Transformers in Series, How does it effect the power?

(OP)
Again, the RVAT was probably required by the utility to staisfy the across the line start issue. So, technically, I do not have an across the line start.

Practically, I do have an across the line start because of the way the RVAT is programmed.

Regardless, I do have a motor with less than the usual starting current demand. The motor also does not start at full load since the well drains back.

RE: Transformers in Series, How does it effect the power?

I don't see that the utility has done anything wrong here, unless there was some specific requirement regarding starting of this pump.  The real problem is the step-up transformer not the utility transformer.  Probably a severe lack of communications, but I don't think the utility is on the hook for a larger transformer.  But they might be willing to provide a larger one, for a cost, of course.

When you say the pump fails to start - what exactly is happening.  If this is a centrifugal pump, the motor should be able to start it at a fairly low voltage.  

With the captive transformer in series with the service transformer, there is a significant voltage drop across the two transformers during starting so I agree that a reduced voltage starter is just going to make things worse.  The captive transformer is already acting like a reduced voltage starter.  

Have you discussed the possibility of adjusting the primary tap on the utility transformer (and/or the captive transformer)?  Normally the utility transformer will have primary taps that allow +/- 5% adjustment of the secondary voltage.  You could try lowering the primary tap to boost the voltage on the low side up 2.5% or 5%, if that hasn't already been done.  You could also look to see if the captive transformer has taps.

"An 'expert' is someone who has made every possible mistake in a very narrow field of study." -- Edward Teller

RE: Transformers in Series, How does it effect the power?

bimr:
The short answer: A well pump motor with RVAT should not have any issues starting with the set up you are describing.

Long answer:

Firstly, it is not clear from your first post, if the problem really exists or you are antcipating an issue.

Your statement:

Quote:

If the RVAT was set at the typical 80% voltage to start, it would drop the voltage further and make the motor starting problem worse.
is not true. RVAT will reduce the starting voltage and so will the startikng torque and the current. The very reason RVAT exists. Well pumps typically have low starting torque requirements so even at 50% tap it should start OK. I would start out at 65% tap and go from there.



 

RE: Transformers in Series, How does it effect the power?

(OP)
The well pump motor manufacturer states that the well motor will not be able to start unless the voltage is at least 80% of nameplate. Therefore, the RVAT should be programmed only at the 80% tap.

The well motor  manufacturer generally recommends no RVAT since the motor starting current is only 4 times the operating current. However, some utilities specify that you have to use an RVAT.

Typically an RVAT would be programmed to transition from 80% to across the line once the motor has started. We have programmed this RVAT installation to automatically transition from 80% to line by the internal timer in the RVAT.

The problem that I have with the utility is that the utility transformer is operating at 90% of rated capacity with little reserve capacity to start the motor. All this information was listed on the load letter and the utility rep sized  the transformer too small. Now, the rep is trying to blame someone else.

Last weekend the voltage coming in from the utility was 4% less and the motor failed to start. The tap was changed on the transformer and the motor was then able to be started
 

RE: Transformers in Series, How does it effect the power?

(OP)
If you cannot get your RVAT adjusted so that it will start the motor, and I would think you could, you might consider a VFD if it could work better.  

A VFD would work, but a VFD would cost about $175,000.


When the utility sees your step up transformer, they will absolutely tell you that the second transformer is a major problem with the full voltage starts.

Why do you say that the step up transformer is the problem? The problem seems to be that not enough power is coming in from the utility transformer. The step up transformer is boosting the voltage.


 

RE: Transformers in Series, How does it effect the power?

Quote (bimr):

the utility transformer is operating at 90% of rated capacity
Then why do you keep implying that it is undersized?  It isn't even getting close to 120%.  Utilities size their transformers differently than customers.  For a service transformer that is not undersized and you won't get anywhere with the utility trying to tell them that it is undersized.  Your step-up transformer is the problem, this should have been a 2400V service.  It isn't, but that isn't the utility's problem, it is your problem.  You can fix your problem on your side of the meter, or you can pay the utility lots and lots of money to make your problem less of an issue, but you can't make it the utility's problem.

RE: Transformers in Series, How does it effect the power?

bimr:

I think you got the appropriate opinions here. You may not have read what you wanted to hear, but that is what it is.

For anything else hire another consulting engineers and take their advice.

 

RE: Transformers in Series, How does it effect the power?

(OP)
rbulsara (Electrical)   

I have already hired a 2nd engineer. The problem is not what the fellow is saying. The problem is that he does not respond in a timely manner. ie he does not return calls for 2 days. I left him a message yesterday  morning and he has not called back. Good way to lose a client.  So you are pinch hitting for someone that does not return calls.


davidbeach (Electrical)

Granted I am not an electrical engineer. Perhaps you are reading something into my posts. My sole purpose is attempting to understand the situation with the utility and who is responsible.

Should I go back and sue the electrical design engineer? What recourse do I have? Is he just going to say that it is the utility's problem?

Why does one bother to submit a load letter to the utility when they will just provide you with a standard commercial electrical setup. At some point, shouldn't the utility supply you with something that meets your needs? It is not like you are asking them to put it a major substation.

I have also seem similar problems on other projects where the utility does not furnish adequate equipment. Granted there may be design issues there as well. For instance, on one building the elevator motor caused the lights to flicker because the transformer was overloaded.

I don't see why the utility should be unhappy with the step up transformer since in the end, it uses electricity and they sell it.  I can see why the utility does not want the step down transformer since it has a power loss associated with it and it is on the utility's' side of the meter.
 

RE: Transformers in Series, How does it effect the power?

bimr:

Am I pinch hitting for someone? I did not even know he existed. Why are you keeping him? Find another one!

RE: Transformers in Series, How does it effect the power?

I don't know what recourse you have.  But you will find that nobody familiar with how utilities size service transformers will say that the utility transformer is undersized.  If at full load of your system, not transient conditions associated with motor starting, your 480V bus voltage is above 456V the utility has met their service obligations.  My guess is that you will find it much higher that 456V, and that you will find it closer to 500V than 480V when unloaded.  Most utilities have rules about how large motors are to be started, your 450HP is a bit much to be dealing with for a near full voltage start.

The utility doesn't give a hoot about your step-up transformer, they're happy to sell you the transformer losses.  Your motor on the other hand has a real problem with the step-up transformer.  If your motor won't start below 80%, your step-up transformer may leave you close to 80% during a "full voltage" start, throw in the RVAT starter and you will be well below 80%, that's why your step-up transformer is a serious mistake.  The utility's planning is probably for a motor that can start at 50% voltage, without the intervening step-up transformer, don't expect them to counteract bad design or unusual conditions on the customer side of the meter.

Probably your best option is to get a second, 2400V, service from the utility.  You'll be happier, your motor will be happier.  Probably can do that for well less than $175k.

The major point is that the utility service transformer is properly sized and the problem is elsewhere, even if that means the solution is more difficult.

RE: Transformers in Series, How does it effect the power?

Bimr:

Firstly, your aim should be to resolve the issue (it is not even established that it even exists), and not sue anyone.

If you are looknig for who to sue, consult a lawyer. You have come to a wrong forum!




 

RE: Transformers in Series, How does it effect the power?

Aha!

May be doing the same thing (asking the same question to same people) again and again would yield a different result?

 

RE: Transformers in Series, How does it effect the power?

BOTTOM LINE...This is NOT a utility problem!  Time to stop pointing in that direction.  It has become yours and your problem is the result of a poor design!  The utility appears to have provided the "industry standard" level of service.  Abuse of that service by poor design does not constitute a utility issue.

Does the step up trans. remain energized during periods of inactivity with the pump?  If so, get it turned off.  If energized 24/7 your customer/or you are paying for the no load trans. losses for 8760 hours per year.

One other issue we have not discussed is the run time on the pump.  You also have the trans. load losses when the pumps runs, and that in addititon can be significant if the pump has a high run time.

David is correct, you probably have 490 to 500 volts at your service.

Your comment about the step up transformer boosting voltage is correct, but it comes with a cost.  You say that your service voltage drops to 440 on pump start.  Probably so but it should still start if not for the additional voltage drop of 4 x %Z of the step up transformer.

Possible Solutions:

Just try setting the RVAT to a lower level and see if it works, forget the pump mfg. and do the test!  The pump should start unloaded.

Get a price from the utility for a second service at 2400 volts and compare that to the VFD insatlled cost.

The site obviously needs the pump and it is time to get it working.....as if you have not been trying right!

Alan

RE: Transformers in Series, How does it effect the power?

(OP)
davidbeach (Electrical) 26 Feb 09 20:16  
Wasn't this already beaten to death in thread238-228405: RVAT starting question for large well motor: RVAT starting question for large well motor?  

Not really. Since then the system has been tested by an electrical testing firm. The system has also been in operation for several months.

Racob above has added some additional comments that were not part of the discussion then
 

RE: Transformers in Series, How does it effect the power?

(OP)
racobb (Electrical)

You made many good comments.

"Does the step up trans. remain energized during periods of inactivity with the pump?  If so, get it turned off.  If energized 24/7 your customer/or you are paying for the no load trans. losses for 8760 hours per year."

How do I calculate the cost penalty for this? Is this a significant cost?

"One other issue we have not discussed is the run time on the pump.  You also have the trans. load losses when the pumps runs, and that in addition can be significant if the pump has a high run time."

The pump typically runs about 8 hours per day.

"Just try setting the RVAT to a lower level and see if it works, forget the pump mfg. and do the test!  The pump should start unloaded."

The RVAT is more or less out of the equation because of the way that it is programmed.  The well pump has been starting every day for 3 months without problem. Last weekend the voltage coming in from the utility was 4% less and the motor failed to start. The tap was changed on the transformer and the motor was then able to be started.

The utility has also recently offered a larger transformer for $10,000  plus $100 per month.

"Your comment about the step up transformer boosting voltage is correct, but it comes with a cost.  You say that your service voltage drops to 440 on pump start.  Probably so but it should still start if not for the additional voltage drop of 4 x %Z of the step up transformer."

Another good comment. I assume that this is really what the problem is. Is there a way to calculate the voltage drop through the step up transformer?
 

RE: Transformers in Series, How does it effect the power?

Yes, the % impedance stamped on the transformer nameplate is used to compute the voltage drop through the transformer.


 

"An 'expert' is someone who has made every possible mistake in a very narrow field of study." -- Edward Teller

RE: Transformers in Series, How does it effect the power?

"The system has also been in operation for several months."

Work load a little light?

"I do have a motor with less than the usual starting current demand."

Just how is this a problem?


 

RE: Transformers in Series, How does it effect the power?

(OP)


"I do have a motor with less than the usual starting current demand." What I meant is that the starting current for the motor is 4 times instead of the typical 6 times the operating current.

"Just how is this a problem?"

Last weekend the voltage coming in from the utility was 4% less and the well motor failed to start.
 

RE: Transformers in Series, How does it effect the power?

And the failure mode?

RE: Transformers in Series, How does it effect the power?

bimr:
4% utility voltage will not fail a motor to start. Utility supplies are entitled for 10% voltage variations. What and how exactly it "failed"?

There may be some other issue. If motor draws less starting current means that the "load" does not require a lot of starting torque.

You are trying to solve a problem which is not there, as far as I can read from your postings.




 

RE: Transformers in Series, How does it effect the power?

2
With two 500 KVA transformers in series with a 450 Hp pump, you almost have a system that inherently provides reduced current starting.
Have you considered an auto transformer to boost the input to the 480:2400V transformer when the incoming voltage is low? That may be your cheapest solution. You would want a closed transition or a very fast open transition to take the auto transformer out of service once the motor starts. A slow transition may result in mechanical damage to the pump or pump motor.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Transformers in Series, How does it effect the power?

(OP)
"And the failure mode?"

Well Motor will not start. If the well motor does not start in 5-10 seconds after the well motor is energized, the motor protection ciruit operates and ends the well start

At that point, the plant operator turned the generator on to run the well motor.

RE: Transformers in Series, How does it effect the power?

(OP)
rbulsara (Electrical)

"4% utility voltage will not fail a motor to start. Utility supplies are entitled for 10% voltage variations. What and how exactly it "failed"?"

I am telling you exactly what happened. Voltage normally has been 500V. For some unexplained reason, the utility voltage dropped to 480V which did not provide enough power to start the motor. I know the voltage reading is correct because there is a power monitor.

The utility then adjusted the transformer tap and that provided enough power to start the motor. The tap raised the voltage to 505V.
 

RE: Transformers in Series, How does it effect the power?

"Racobb above has added some additional comments that were not part of the discussion then."

Don't know that I have added much different than has already been said here, just beating the same old dead horse with a new hammer!
 

Alan

Democracy is two wolves and a sheep deciding what to have for dinner.  Liberty is a well armed sheep!
Ben Franklin

RE: Transformers in Series, How does it effect the power?

bimr:

As you write more it makes less and less sense. You could have adjusted the taps on your own transformer, IF that was the issue.

Can you elaborate what exactly happened, motor stalled? A fuse blew? Breaker opened? Breaker tripped before picking up speed?

 

RE: Transformers in Series, How does it effect the power?

(OP)
Starting sequence – when well pump fails to start
1.    Control system calls for well motor to start. Incoming utility voltage at 480V
2.    RVAT energizes well motor at 80% voltage. Nameplate voltage of motor is 2300V. Voltage to motor unknown. Design calls for 2400V.
3.    ~  2 seconds later, the RVAT transitions on timer signal to from 80% voltage to line voltage.
4.    Incoming utility voltage drops to 420V
5.    ~ 5 to10 seconds later, the motor protection device shuts off the well motor start because the motor is not .,running.


Starting sequence – when well pump is able to start
1.    Control system calls for well motor to start. Incoming utility voltage is at 500V
2.    RVAT energizes well motor at 80% voltage. Nameplate voltage of motor is 2300V. Voltage to motor unknown. Design calls for 2400V.
3.    ~  2 seconds later, the RVAT transitions on timer signal from 80% voltage to line voltage.
4.    Incoming utility voltage drops to 440V
5.    ~ .5 seconds later, the motor operating at normal speed
 

RE: Transformers in Series, How does it effect the power?

I'm assuming "not running" means motor is still accelerating at less than normal speed, not that the motor remains locked.

RE: Transformers in Series, How does it effect the power?

You just need(ed) to adjust votlage and timing.

You could wait for say 4 sec before applying full voltage. The whole purpose of the reduced voltat start is to start the motor at reduced voltage and revert to full voltage when the motor has picked up 70 to 80 % of the rated speed.

Also as stevenal suggest, you adjusted the tap of the wrong tranformer and exposing other "480V" loads to overvoltage conditions. You need to adjust the taps on the your tranfomer only feeding the motor.  

After all this efforts, how do you not know the rated voltage of the motor?? That would be the first thing needed to know. Adjust tap close to its rated voltage.

Using 80% tap on RVAT is waste of RVAT too.

 

RE: Transformers in Series, How does it effect the power?

(OP)
The motor starts in 0.6 seconds because of the way the pump is constructed. The pump has a long shaft with a narrow rotating element.  The well pump is either going to start or it will not. Lengthening the time for the motor to start will not make any difference.

The RVAT is typically required by the utility.  This utility requires that the RVAT be set at 80%

If you have a typical motor with 6 times the starting current, the RVAT would make more of a difference.

In this case with this well pump, since the starting current to operating current ratio is only 4 times, the RVAT is probably not necessary..

Part of the problem has been the motor protection device. The device requires a narrow window for operating voltage in order to operate. Too high a voltage will not allow the motor to start as well. The device also takes experienced staff to reprogram.

The tap was adjusted on the step up transformer at one point. Unfortunately because it is medium voltage equipment, you have to hire qualified personnel to change the taps.
 

RE: Transformers in Series, How does it effect the power?

Quote (bimr):

The device also takes experienced staff to reprogram.

Quote (bimr):

because it is medium voltage equipment, you have to hire qualified personnel to change the taps
Both very good things.  When you are playing around with equipment this expensive it is best to have people who know what they are doing.

RE: Transformers in Series, How does it effect the power?

bimr:

Quote:

The motor starts in 0.6 seconds because of the way the pump is constructed. The pump has a long shaft with a narrow rotating element.  The well pump is either going to start or it will not. Lengthening the time for the motor to start will not make any difference.

The RVAT is typically required by the utility.  This utility requires that the RVAT be set at 80%

None of your statement makes any technical sense, in fact they are not even believable. I am now convinced that you are not interested in technical issue, you some how after someone for reason only known to you.
 

RE: Transformers in Series, How does it effect the power?

deadhorse

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: Transformers in Series, How does it effect the power?

Your problem could possibly be that the step up transformer is of a cheep construction and is probally "primary turn compensated".
this would cause the voltage to drop when a 150% load is applied.
This transformer 2400/480 Y:Y was manafactured for stepdown applications.
See if I am correct.

wiretwister

RE: Transformers in Series, How does it effect the power?

(OP)
rbulsara (Electrical)

What part of this don't you understand?

"The motor starts in 0.6 seconds because of the way the pump is constructed. The pump has a long shaft with a narrow rotating element."  (This information is taken directly from Byron Jackson's product literature - the pump manufacturer)

http://www.flowserve.com/vgnfiles/Files/Literature/ProductLiterature/Pumps/ps-50-3-e.pdf

If the pump had a large diameter rotating element, the pump would take longer to get to speed. Simple physics, that an experienced engineer would understand.

When the motor is energized, it is either going to start or not start. Byron Jackson advice is to not keep the motor energized longer than 10 seconds, if the motor has not rotated.

"The RVAT is typically required by the utility.  This utility requires that the RVAT be set at 80% "(This 80% requirement is written into the utility customer service agreement by the utility).

RE: Transformers in Series, How does it effect the power?

(OP)
wiretwister (Electrical)

One of the electrical engineers also suggested this. The step up transformer has a 5% impedance and he was concerned about the impedance. Square D, the manufacturer of the transformer said that this is a standard impedance value for this type of transformer.

The other electrical engineer suspected that the utility was using a low quality transformer.

RE: Transformers in Series, How does it effect the power?

#1)From one of my previous posts:
"Your comment about the step up transformer boosting voltage is correct, but it comes with a cost.  You say that your service voltage drops to 440 on pump start.  Probably so but it should still start if not for the additional voltage drop of 4 x %Z of the step up transformer."

I was attempting to show you that voltage drop in the step up is also a huge problem....with Z=5% you have an additional 15 to 20 % voltage drop (3 to 4 times the %Z) on starting, just through the step up trans alone.  It needs to go!

#2)"The RVAT is typically required by the utility.  This utility requires that the RVAT be set at 80% (This 80% requirement is written into the utility customer service agreement by the utility)."

I think what you mean is that the RVAT may be set at a maximum of 80%....has nothing to do with settings less than 80%....utility is concerned about max, not min setting.

#3)"The other electrical engineer suspected that the utility was using a low quality transformer."

What a Crock!  I suspect he does not know the difference!

We can beat this up forever, but until you lower the tap on the RVAT and see if it will work, or until you replace some equipment, you will always be operating at the edge of the motor starting envelope and will continue to have problems.

If no one at the facility is willing to review these posts and make a decision, then they need to hire a consultant, pay him 10 to 20 grand, so he can tell them the same thing!

Alan

Democracy is two wolves and a sheep deciding what to have for dinner.  Liberty is a well armed sheep!
Ben Franklin

RE: Transformers in Series, How does it effect the power?

Too much conflicting advice in this thread....

Attached is power flow solution showing a 2300 V 450 hp motor starting across the line with two 500 kVA, 5 % transformers in series.

I assumed 6x Full load current at 0.2 pf at locked rotor.  

Voltage at the motor terminals at locked rotor is only 63%, ignoring voltage drop in the cable the motor.  A reduced-voltage starter is not a solution and would be part of the problem.  The utility can make all the rules on reduced voltage starting that they want, but they are still subject to the laws of physics like the rest of the universe.  

Voltage drop on the utility side of the service transformer is negligible - admittedly with a lot of assumptions, since there is no data.

If the motor can accelerate the pump with 40% of normal motor starting torque, then adjust the motor protection accordingly and let it start.  The fact that a relay tripped does not necessarily mean the motor cannot start safely.  If not, something will need to change.  Before you start spending money on new transformers, etc, you should get a EE to do an evaluation of the impact of the changes and probably a transient motor starting analysis.  

In my opinion, based on the limited information provided, the problems are on the customer's side of the service.  

Good luck.  

"An 'expert' is someone who has made every possible mistake in a very narrow field of study." -- Edward Teller

RE: Transformers in Series, How does it effect the power?

May be, you can think of having a run-of-the-mill 480 V VFD on the primary of the 2300 V trafo ? That shouldn't cost much.

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