Electrical Confusion

How did the mfr know that the voltage was too high, rather than some other cause?

230 x 1.1 = 253, so theoretically your voltage is still within tolerance, even though a bit high.

I haven't the slightest idea how he knew. He just said it was the probable cause of the failure. The engineering manual for the motor doesn't spell out what the maximum voltage for the motor should be. It just says 220 / 240 volts.

I'm suspicious a 15% over voltage from 220 is the actual root of your problem. I suspect something completely different is your problem. Possibly the starter windings did not turn OFF once the motor got up to speed. That is if this 3Φ motor has starter windings. Another possibility is the protection circuitry failed when one of the phases disappeared with the transformer replacement.

Thanks. I don't know if this motor has starter windings. each incoming wire has its own fuse and all the fuses are still ok. (had them tested) At the current voltage input, I am afraid to hook the motor back up.

I had planned on talking to So Cal Edison Monday. But, I didn't know what to ask them to do. Thank you.

220/415 motors are designed to be connected, in delta for 220volts and, star for 415 volts. The connections are usually accomplished by Links within the terminal box. If the motor is connected in Delta and 415 volts is applied, the motor will burn out. Perhaps this is what the manufacturer is referring to when they mention that the motor has been subjected to high voltage......!! Norm.

As pointed out you need to call utility company and request them to change the tap setting of the transformer if high voltage is the reasons for equipment failure. Sometimes it could have happened due to sudden voltage fluctuations but mottos are designed to withstand . Surge arresters are used for sensitive electronic equipment like bio medical equipment.

3 phase motors have no use for starter winding. They use of a set of contactors for forward rotation, and another set for reverse if needed. A missing phase does no good to the health of a motor. Additionally, while it ought not to, a motor can be a bit substandard, and draw too much current at the high end of its voltage range. If it is additionally fully loaded, the coils are cooking, and have short life.

By the way, you will know what excursions are on the feed, if it is recorded / logged for a week or two. Such devices can be rented quite reasonably. see Yellow pages for test and measuring equipment rental.

Or, simply ask ConEd to lower the voltage tap on you. But, do you have any equipment known to be sensitive to undervoltages??

All the motors I have are in industrial sewing machines. The one that burned up had been in constant use for more than twenty years without a problem. I will call ConEd Monday and get the problem resolved. Thanks everyone.

you should be able to use any motor that is rated within _-10% of the plate rated voltage on the motor. 10% of 240 is 24 of course 24 +240 is well within range of your measured voltage. to answer your direct question your electrician can install a "buck transformer" in a few minutes that can get you almost any desired lower voltage, good luck, yor poblem is bot a tough one

I don't believe that the high voltage is responsible for the motor failure. The motor fuses should protect it from both overload and short circuit faults. I believe that your power company made a change in the phase arrangement that was not tolerated by your motor. I would have the power company sort this problem out.

p a bit.....I too highly doubt your failure was do to excessive voltage, sounds like an attempt to shift irresponsibility back on to you. I also agree that having Edison return and adjust their tap points would be a good option (and no cost to you for an electrician and buck t-former, But I have dealt with SCE for decades over voltage issues in Orange county.Fullerton and older parts of Santa Ana are ell known for Low voltage especially during heat waves, you of course have great voltage that doesn't seem to have "sagging" issues. I'd try to get SCE back first, if they wont(which wouldn't surprise me, get a quote or 2 from electricians to install a buck T-former if were just talking about a single load with excessive voltage. If it's a system wide issue demand SCE re-tap your supply service t-former, good luck

SCE came to the facility today. They told me that the transformers had no tap adjustments. The transformers are from back in the 60's somewhere. They are coming back on Wednesday and I am not sure what they can do. Can anyone tell me what danger there is in putting the machine back on line for one or two days. The company that rewound the motor tells me that they don't think short term use would lead to problems.

Not only that. As the voltage rises, the core will enter saturation more deeply. That heats the core, that heats the coils. The Increased current resulting from the decreased inductance (due the saturation) increases current. The coils will bake, reducing lifetime.

Allaround bad idea.

Byron Jay,

I appreciate your continuing to follow-up this post. Utility companies have to met a target range of voltages in their distribution system. This means that close to the transformer the voltage will be high, while near the end of the line it will be low. However, at both ends it should be within the range of voltages posted in their Service Standards. As other(s) have noted, this voltage will also vary depending on the load (time of day) and season (worse in summer in SoCal). They will typically use automatic tap-changing transformers to keep the voltage in their system within the set standards.

I have had a motor or two burn out from an imbalance in the supplied voltage. In one case, although the phase-to-phase voltages were all within the specified range, there was about a 4-5% imbalance between them. This caused the motor currents to vary by a much greater percentage. Although the currents were all within the motor's nameplate rating, this current imbalance caused circulating magnetic fields within the motor's core and overheated it... (At 500Hp, it was expensive! The lineman who initially responded to our trouble call was quite respectful towards us afterwards, because it took 3 field crews and 2 supervisors about 5 hours to find the failed splice about 1-mile away on their primary distribution network.) Neither fuses nor standard NEMA-style starters will detect this sort of a problem; however an IEC-style starter will detect it and give your motor the needed protection.

From your comments, it sounds like your motor rewind people and your electrician are all "OK". Have your electrician check to see if there is any voltage imbalance greater than about 2%. Consider the use of an IEC-style starter (perhaps one with a NEMA rating). I agree that the rental of a recording meter--from Fluke, Dranetz, and others--may be a good idea also.

--JMM

Today: I bought a volt meter and tested the three legs of the voltage into the newly rewound motor. (I haven't turned the motor on yet) Leg 1 125.5 volts, Leg 2 125.5 V and Leg 3 131.7 volts. Is this what you are talking about when you talk about imbalance? All of you have a great deal of help. Also, SCE is coming tomorrow to follow up on their first visit. They have a computer hooked up to the incoming lines to measure the voltage and voltage fluctuations. By tomorrow after noon I should know

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Sir,

The voltage imbalance from your measurements is calculated as

(worst-average)*100/worst.

This gives the imbalance as a %. From your numbers I calculate 3.1%. This is significant but not outside the range of acceptable values for a motor's operation. If you use a clamp-on ammeter for your motor, the current should not vary by more than 10-12%. However, if the currents are relatively low, then you are also going to face limits to the meter's resolution.

The voltages themselves are on the high side of the normal range. Perhaps they will do something. It sounds like your utility is being responsive to your problem.

--JMM

First, let me thank all of you for trying to help me. Today, SCE technician found the problem. The feed from the transformer to the building had a short in it and it worked intermittently. Also there was enough feedback through the off and on switch that it fooled the electrician. The only problem is that it ruined two $15,900.00 sewing machines. Now all I have to do is convince SCE to replace them.

Happy Thanksgiving to all of you. Again, I want to express my thanks for the help.

Byron,

The terminology used in the diagnosis seems incorrect.

A short circuit in a feed would be phase to phase, or phase to ground. In either case it would not be intermittent because the massive current surge would have taken out upstream components. What you had was an intermittent open circuit, likely a bad connection, switch or splice, temporarily stopping the flow of current in that leg.

In electrical terminology short, and open are opposites.

I hope I have not come across as a nit picker. Terminology can enhance or detract from clear communication.

Happy Thanksgiving,

Ace

I thought exactly the same thing, you just aren't as lazy as I am today

Try to limit your trips to the dining table today!

I assume you are reading these voltages phase to ground. You said the electricinn got 253 volts. If you are on a Y Delta system with the voltages you indicate you would only have about 210 volts phase to phase. This is low but well within acceptable levels. If you are on a floating system (no connection to ground) then reading voltages to ground is meaningless. Either way the motor only sees phase to phase voltage so that is what you should check. Leg 1 to leg 2, leg 1 to leg 3, and leg 2 to leg 3.

The problem has been solved. Thanks everyone.