Pole mounted transformer question

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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Consulting Electrical Engineer - Photovoltaic Systems
Do pole mounted transformers have taps for secondary voltage adjustment? We have a residential customer with some equipment that is monitored externally (Tesla Powerwall Gateway), and the monitoring service is sending him messages that his service voltage is too high.
 
The Poco may have some responsibility to bring the supply voltage into spec. There are tariffs that specify what voltage the Poco is required to supply.
 
We ran into a similar issue a few years ago where the POCO simply claimed that the service voltage at the meter was within their contracted range, albeit very nearly at the top of it, so they bore no responsibility. Any voltage rise from PV inverters on the customer's side of the meter was not their problem.

But all that is really beside the point. My question remains: do pole mounted transformers have voltage adjustment taps like many pad mounted transformers have? Whose problem it is to ameliorate is not what I am asking.
 
I would guess not. It it helps, here is a image of the nameplate on the pole mounted transformer in front of my house. You can see they indicate a small set of field alterable connections on the secondary to place those windings in series or parallel, but do not show any secondary taps.

i-w9Tnd2Q-XL.jpg


I asked about these secondary connections in a post when my transformer failed and Hv&Lv said those connections are brought up above the oil and can be modified with the top off. Of course the transformer core itself would be submerged in oil and the taps we think about in dry type transformers are all right on the outside of the coils. So they’d be submerged if done like that, or all have to be brought above the oil, and I’d consider either unlikely. But I've been wrong before!

A possibility for your high secondary voltage might be a problem with a tap changer somewhere up stream of the transformer?
 
ggunn said:
We ran into a similar issue a few years ago where the POCO simply claimed that the service voltage at the meter was within their contracted range, albeit very nearly at the top of it, so they bore no responsibility. Any voltage rise from PV inverters on the customer's side of the meter was not their problem.

But all that is really beside the point. My question remains: do pole mounted transformers have voltage adjustment taps like many pad mounted transformers have? Whose problem it is to ameliorate is not what I am asking.
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In my experience, never say never, but mostly not. Often pad mounts do not have taps either, but yeah they do more often than pole mounts.
 
ggunn said:
Do pole mounted transformers have taps for secondary voltage adjustment? We have a residential customer with some equipment that is monitored externally (Tesla Powerwall Gateway), and the monitoring service is sending him messages that his service voltage is too high.
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You made it plain that you were simply asking the question, but at the risk of being a jerk, I'll comment that you may be able to use a small buck transformer to the Gateway.
 
Depends on the type of transformer.
We have some with taps and some (most) without.
They are just like dry pacs, +-5%
 
Hv&Lv said:
Depends on the type of transformer.
We have some with taps and some (most) without.
They are just like dry pacs, +-5%
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Hey, just curious... are these taps inside the oil? Or somehow brought up top and above the oil but below the lid?

I can't imagine anybody wanting to un-tighten, move, and re-tighten taps while elbow deep in mineral oil.

TIA.
 
GeorgeB said:
You made it plain that you were simply asking the question, but at the risk of being a jerk, I'll comment that you may be able to use a small buck transformer to the Gateway.
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You aren't being a jerk and of course bucking the voltage down with a transformer is a possible solution, but I was looking for something with zero hardware cost.
 
MD Automation said:
Hey, just curious... are these taps inside the oil? Or somehow brought up top and above the oil but below the lid?

I can't imagine anybody wanting to un-tighten, move, and re-tighten taps while elbow deep in mineral oil.

TIA.
Click to expand...
They are on the side. Simply de-energize the XF and turn the knob. Some tap changers change from say 7200V to 14,400V. Some are for (example) 14,400 volts, but change + or - 5% in 2.5% steps.

380130F8-27BC-4926-ACBF-C699DBAE4120.jpeg316CC7E1-A5DF-43E6-91A6-7098D91F0628.jpeg
 
Hv&Lv said:
They are on the side. Simply de-energize the XF and turn the knob. Some tap changers change from say 7200V to 14,400V. Some are for (example) 14,400 volts, but change + or - 5% in 2.5% steps.
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Thanks kindly. And how interesting. So you could eyeball this from the ground to know if the xfmr was adjustable. I must admit I look at a lot of pole mounted transformers (nerd) and I have never noticed something like that. Now I have a new hobby ;)

Around my Maryland area (BGE) I see pretty much only simple (budget?) pots with HV bushings up top, LV bushings on the side, and nothing else. No levers, light's or switches.

I would imagine it's not an inexpensive option to add something like that? And if I was a cheap POCO, I know what kind I'd keep in stock if I could get away with it.

Thanks again.
 
Just the curious Brit again. We seldom see pole transformers. I can recall just one in my trip to work .I'm sure there are others but not a lot.
How often do you guys get up and close?
 
Besoeker3 said:
Just the curious Brit again. We seldom see pole transformers. I can recall just one in my trip to work .I'm sure there are others but not a lot.
How often do you guys get up and close?
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I would assume for anybody other than a POCO Lineman, the answer is likely never, or certainly not often? In a typical service, it's before the meter and owned and maintained by the local POCO. I guess there are some situations where there could be customer owned pole transformer(s) beyond the meter. It's a good question, how often would an electrician run into a setup like that? Big facilities with some MV distribution?

The only reason I had a nice clear picture (post #5) of the nameplate on my house's xfmr was because the original failed and I started a thread about it last year. Here it is being replaced by a BG&E lineman, the black nameplate placard I posted above is visible on the lower mounting flange...
i-Fm54ZTM-XL.jpg
 
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MD Automation said:
Thanks kindly. And how interesting. So you could eyeball this from the ground to know if the xfmr was adjustable. I must admit I look at a lot of pole mounted transformers (nerd) and I have never noticed something like that. Now I have a new hobby ;)

Around my Maryland area (BGE) I see pretty much only simple (budget?) pots with HV bushings up top, LV bushings on the side, and nothing else. No levers, light's or switches.

I would imagine it's not an inexpensive option to add something like that? And if I was a cheap POCO, I know what kind I'd keep in stock if I could get away with it.

Thanks again.
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Look for the black knob on the back side. It’s a screw cap that covers and weatherproofs the actual mechanism.
Service Lights are going away.
single bushing tops (HV) are CSP and have a breaker inside them. There is a lever on the side to trip this breaker with a long stick.
Double bushing tops (conventional XFs) don’t have secondary protection and depend on the primary fuses to offer primary and secondary protection.
Generally speaking it’s about a $150 option to have a dual voltage switch added. That way they can be used on a 7200 circuit and a 13.2 or 14.4 circuit. Lots of POCOs have step down stations and it’s just easier to carry a DV transformer rather than have a yard full of all different kinds.
 
Hv&Lv said:
Look for the black knob on the back side. It’s a screw cap that covers and weatherproofs the actual mechanism.
Service Lights are going away.
single bushing tops (HV) are CSP and have a breaker inside them. There is a lever on the side to trip this breaker with a long stick.
Double bushing tops (conventional XFs) don’t have secondary protection and depend on the primary fuses to offer primary and secondary protection.
Generally speaking it’s about a $150 option to have a dual voltage switch added. That way they can be used on a 7200 circuit and a 13.2 or 14.4 circuit. Lots of POCOs have step down stations and it’s just easier to carry a DV transformer rather than have a yard full of all different kinds.
Click to expand...
My POCO here in NY has mostly 4800 and 7.62/13.2 distribution. Their pole mounts have a switch for either voltage
 
Hv&Lv said:
That’s an old delta system, right?
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Yeah tons of 4800 Delta distribution in upstate NY. Their strategy for upgrading these is/has been to upgrade the first half or third (very rough guess) of the line to 7.62/13.2 and have a pole platform bank there to serve the remaining 4800. My service is fed from such a line, it's 4800 single phase by the time it hits me.
 
ggunn said:
Do pole mounted transformers have taps for secondary voltage adjustment? We have a residential customer with some equipment that is monitored externally (Tesla Powerwall Gateway), and the monitoring service is sending him messages that his service voltage is too high.
Click to expand...
Many do, ours does, and we called them about his same over-voltage issue some time ago and they came out and reset our line to a lower voltage tap, but this depends on just what equipment your POCO uses.
 
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