15 kVa transformer good for what power?

[Andy]

After Joe’s post I have a question that has been bothering me for a while. We are running off a 15kVA transformer ( reading from the plate) powering three houses. I have also had the house fuse upgraded to 80A single phase.

Now I have my zappi set to limit incoming Amps to 60 despite the 80A fuse in order to be neighbourly. 60 amps is about 13.8 kW depending on voltage. 15kVa is about 13.5kW at 90power factor. So already I am supposedly using almost all the capacity of the transformer. So if I am charging batteries and the car and hitting these limits for 4 hours, is this a problem in reality? Both neighbours are currently very light users of the grid but this won’t always be the case.

I’m sorry I can’t remember who mentioned recently, maybe Stinsy, that DNO can demand a 60A limit for sustained loads. What happens if all three properties start doing this?

[Joeboy]

It takes a lot to melt the insulation in a transformer Andy. Although I have seen and smelled it. Even heard the pop. I'd be asking for a transformer upgrade by the dno? Can't do any harm?

[Andy]

I’m not sure how that’d go down well as I got it upgraded a few years ago because it was over voltage

I guess if the neighbours ever get an electric car I’ll let them know how much I am using.

[nowty]

Probably depends somewhat on the ambient temperature so in winter you can probably draw that little bit extra.

[Stinsy]

If I were you I’d keep an eye on voltage sag. Ie measure voltage with only trivial loads then charge your car, run your hob, etc., and measure the voltage again.

If the voltage drops too low you can complain to the DNO, but I believe they are only required to keep voltage between 216-253V so there is a lot of leeway,

[Andy]

The voltage sag isn’t too bad. It’s running between 230 and 240v fairly consistently now. I lose about 3v when maxed out.

We were hitting 256v on windy sunny days before the transformer got replaced.

[Stinsy]

Don't worry then!

[Oliver90owner]

15kVA is about 12kW resistive. I suspect that rating is a conservative value for each phase and each dwelling is fed from a separate phase.

Transformers do not like nearly 100% loading on one phase with little or nothing on the other legs, hence the conservative rating is very likely.

The transformers have different tappings for voltage selection and is a minor adjustment. It does not affect the kVA rating.

[Tinbum]

I don't think it will be per phase,

Our 100KVA transformer plate.

[Andy]

Don't worry then!

Roger I am a perpetual worrier and rule follower that constantly gets me in trouble compared to people I know who just crack on haha