75kva transformer not putting the right voltage or is utility the problem.

[Elect117]

I got a call because the walk-in cooler condensing motor had been replaced by the HVAC guy, two of the new motors burned that had been replaced.
Motor will run at minimum 200v
While taking voltage reading they been reading 193volts between phase.


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I know you will be able to solve their issue with all of the advice already given, but I would add to the list verifying the the HVAC guy's motor voltage minimum, conductor sizing, and maximum current rating.

200V rated motors should be okay within a range. Or at least that has always been my understanding. If the voltage is on the lower side of the rating, then the current increases to compensate. The cheapest solution is still to get the service voltage increased, or change the dry type transformer taps, but I would, if you had the time, verify the conductor and motor ratings.

My concern is that you will get the voltage fixed, but the motors might still fail if the issue is the combination of the conductor sizing and voltage. I wonder if he replaced the motors twice, checked voltage and it was within range those times, but this time needed to find something to blame. And since it is summer, and very hot (at least here), the voltage is lower. Those other times, it could have been winter and the voltage was fine. Or there is dust accumulation, the walk in door isn't sealing properly causing the motor to run for extended periods, etc. Upping the wire size can help with the effects of overloading. If the conductor is already oversized to the MOCP then that is definitely not it.

 

[kwired]

I'd look for the problem before opening that can of worms.

Definitely.

Several years ago (maybe year 2000ish) a nearby school had some work done (by out of area EC) over the summer months. They updated several feeder panels and ran several new circuits which majority of the new load was through the wall AC units. This was first AC to ever be in most those rooms in a building constructed in 1950.

At the time I was the EC they often called for smaller projects and service calls. I got call within first couple days of fall semester classes saying the bell that rings at beginning and end of class periods wasn't very loud, particularly later in the day. It is a 24 volt AC system for these bells.

I came later in the day to check it out, been long enough ago I don't recall actual voltage but that 24 volts was extremely low which explained why the bells not working right, then I checked the 120 volt primary side and it was proportionally low, eventually determined service voltage in general was pretty low. If you haven't guessed yet - it was due to the addition of all the AC loads. The service equipment happened to be sufficient for the load but POCO transformer was well under sized after this new load was added along with their overhead service conductors were pretty undersized as well.

 

[qcroanoke]

Definitely.

Several years ago (maybe year 2000ish) a nearby school had some work done (by out of area EC) over the summer months. They updated several feeder panels and ran several new circuits which majority of the new load was through the wall AC units. This was first AC to ever be in most those rooms in a building constructed in 1950.

At the time I was the EC they often called for smaller projects and service calls. I got call within first couple days of fall semester classes saying the bell that rings at beginning and end of class periods wasn't very loud, particularly later in the day. It is a 24 volt AC system for these bells.

I came later in the day to check it out, been long enough ago I don't recall actual voltage but that 24 volts was extremely low which explained why the bells not working right, then I checked the 120 volt primary side and it was proportionally low, eventually determined service voltage in general was pretty low. If you haven't guessed yet - it was due to the addition of all the AC loads. The service equipment happened to be sufficient for the load but POCO transformer was well under sized after this new load was added along with their overhead service conductors were pretty undersized as well.

How long did it take to convince POCO it was their problem?
But knowing you you had all your ducks in a row when you called them.

 

[ptonsparky]

I worked with a small town school that was forced to install a fire alarm system. VD was so bad it would drop out on alarm. IDR what had been added besides that but we installed a new service. POCO transformer and feed was too small so we came in from a different direction. We did manage to pull out the old lead covered SE cable that had also been installed in a rigid conduit. CCC project i believe. At the same time I got to restore the BB scoreboard that was original to the building. Once I got everything clean and lubed up it worked as new. We did an EG. It would have been close to 60 years old at that time. Fun project.

 

[kwired]

How long did it take to convince POCO it was their problem?
But knowing you you had all your ducks in a row when you called them.

didn't take much to convince them there was problems.

working out a solution and who pays for what was a different story.

Ended up being resolved the following summer, the new AC load went away after about a month once outside temps started dropping and load conditions weren't really any different than they had been for several years for the rest of the school year. Bigger padmount and closer location to the building and underground instead of overhead conductors to the existing service equipment.

 

[ptonsparky]

How long did it take to convince POCO it was their problem?
But knowing you you had all your ducks in a row when you called them.

The importance of having '...all your ducks in a row' cannot be understated.

 

[Jraef]

And the utility is probably within limits. Most have rules that are about 10% of the designated voltage. Most supply closer to 5%.

Utility rules are different from utilization rules. The utilities are supposed to keep within +-5% (with allowances for brief temporary excursions). So 463 out of a 480 service is roughly 3-1/2%, so well within their normal tolerance. They will not likely even respond to a request to “fix” it.

The 193V L-L on the secondary of the 208V transformer is about a 7.2% drop and would be an issue, except they (the utility) are not responsible for the secondary of the owner’s site transformer, because their rules only apply to the SERVICE POINT, meaning voltage drop WITHIN a facility is not their problem.

Bottom line on this, I wouldn’t be looking to the utility to solve this problem, it’s not theirs.

So back to your original question, CAN temperature affect the output voltage of a transformer? Yes, but not at the levels you are observing here. 95F is not yet even at the rated operating temperature of that transformer. That has Class H insulation with a 115deg RISE over ambient. Ambient for transformers is 40C, so 104F. 115deg RISE means you should not see a problem up to 155C, which is 311F! Now that is at the internal core, surface temperature can be 20-30% lower, but you are still talking about 200+degF surface temperature as being “tolerable”. So don’t bother going down that rabbit hole either…

Wire resistance does change with temperature, which is why under sizing conductors can quickly become a problem. Temperature goes up, resistance goes up, voltage drops, induction loads pull MORE current, which raises the conductor temperature, which increases resistance, which drops voltage, etc. etc. I would be looking at the LOAD on that transformer and the conductor sizes involved. They may have added too much to it after it was installed.

 

[Hv&Lv]

Utility rules are different from utilization rules. The utilities are supposed to keep within +-5% (with allowances for brief temporary excursions). So 463 out of a 480 service is roughly 3-1/2%, so well within their normal tolerance. They will not likely even respond to a request to “fix” it.

The 193V L-L on the secondary of the 208V transformer is about a 7.2% drop and would be an issue, except they (the utility) are not responsible for the secondary of the owner’s site transformer, because their rules only apply to the SERVICE POINT, meaning voltage drop WITHIN a facility is not their problem.

Bottom line on this, I wouldn’t be looking to the utility to solve this problem, it’s not theirs.

So back to your original question, CAN temperature affect the output voltage of a transformer? Yes, but not at the levels you are observing here. 95F is not yet even at the rated operating temperature of that transformer. That has Class H insulation with a 115deg RISE over ambient. Ambient for transformers is 40C, so 104F. 115deg RISE means you should not see a problem up to 155C, which is 311F! Now that is at the internal core, surface temperature can be 20-30% lower, but you are still talking about 200+degF surface temperature as being “tolerable”. So don’t bother going down that rabbit hole either…

Wire resistance does change with temperature, which is why under sizing conductors can quickly become a problem. Temperature goes up, resistance goes up, voltage drops, induction loads pull MORE current, which raises the conductor temperature, which increases resistance, which drops voltage, etc. etc. I would be looking at the LOAD on that transformer and the conductor sizes involved. They may have added too much to it after it was installed.

I would still ask the utility.
Occasionally we have a regulator the raise/lower motor goes bad, or the capacitor is bad so the motor won’t work. If it's stopped at a lower step, sometimes we don’t know until we do inspections or a customer calls in with voltage complaints.

 

[ptonsparky]

We had a regulator serving our small town get stuck high. POCO appreciated the call and it was fixed PDQ.
I don't remember now what caused me to check.

 

[electrofelon]

I would still ask the utility.
Occasionally we have a regulator the raise/lower motor goes bad, or the capacitor is bad so the motor won’t work. If it's stopped at a lower step, sometimes we don’t know until we do inspections or a customer calls in with voltage complaints.

We "found" a bad regulator last year after installing a solar system. Voltage was high and kicking out the inverters. Battled with POCO for a week with him saying it was some problem with the PV system. Turned out it was a bad regulator 4 miles down the road.

 

[Hv&Lv]

We "found" a bad regulator last year after installing a solar system. Voltage was high and kicking out the inverters. Battled with POCO for a week with him saying it was some problem with the PV system. Turned out it was a bad regulator 4 miles down the road.

You know, a lot of times it takes way less time to go check something out rather than argue with the customer about it..
After all, the service trucks run the entire system every day

 

[kwired]

I was troubleshooting an item for a customer in my shop when I happened to discover my service voltage was like 263ish. Might have never known otherwise. Called POCO, after they checked things out they got back to me and said there was a regulator issue.

I don't know if their newer metering system would have told them there was a problem or not, seems possible. They will know pretty much when any service on their system is with no voltage and this system integrates with a map on their web site that anyone could look at and see what areas have no power - particularly useful after a storm

 

[Hv&Lv]

I was troubleshooting an item for a customer in my shop when I happened to discover my service voltage was like 263ish. Might have never known otherwise. Called POCO, after they checked things out they got back to me and said there was a regulator issue.

I don't know if their newer metering system would have told them there was a problem or not, seems possible. They will know pretty much when any service on their system is with no voltage and this system integrates with a map on their web site that anyone could look at and see what areas have no power - particularly useful after a storm

Our metering system will do that. I get an email every night with an all system voltage check abnormalities. I can tell if a capacitor bank is stuck in by the clusters of high voltages, and if regulators are out of sorts, again by the clusters of abnormalities on the map.
Our in house online map has WAY more detail than the outage map the public sees on our website.

 

[electrofelon]

Our in house online map has WAY more detail than the outage map the public sees on our website.

I'd LOVE to have access to that.....