network fault monitoring

[bernardgreen]

I thought that the 'final' transformers in the UK were 3-phase HV to single-phase LV

When supplying a small single phase load ( 1 to 3 houses ) the primary is fed by two of the three HV phases. Some pole routes are two phase and some are three phase for customers who have a need for three phase LV and/or to spread several pole transformers over the three HV phases.

 

[JohnD]

if you wanted to monitor such a fault at a remote location, I think you'd need some kind of (probably mobile phone tech) signalling equipment as you couldn't do it through the network cables.

It's done at some Utilities lnstallations, but AFAIK not yet at every little pole-mounted transformer.

PMR is used for more important signalling, as it will work even after a major incident.

 

[AdrianUK]

Are you talking about a transformer fed by one phase of the HV? I thought that the 'final' transformers in the UK were 3-phase HV to single-phase LV (the pole-mounted one which supplies me is certainly fed with all three HV phases, and I'd always assumed that all three were 'connected'). If the later, what is meant by the 'phase' of a 3-phase supply?

Kind Regards, John

Most distribution transformers are three phase delta to three phase star, the star point being the neutral & being solidly earthed.

Only "small" (say 15kVA) pole mount transformers are single phase. These are fed line-line on the primary side & usually have one end of the secondary grounded. The secondary may be centred tapped at 230-0-230 in which case its known as a split phase supply. Note that this is not "two phase" - these are opposite ends of the same coil.

There is no transformer configuration which can supply a single phase load from a three phase supply & load all phases equally.

 

[JohnW2]

Most distribution transformers are three phase delta to three phase star, the star point being the neutral & being solidly earthed.

Indeed, and I see that I worded my previous post very badly - when I wrote "3-phase HV to single-phase LV", what meant (had in my mind) was "3-phase HV to 3 x single-phase {i.e. 3 phases, used separately, and a neutral} LV" - the point I was making being that the primary was fed with all three phases of the HV supply.

However, my question remains - what did Simon mean when he spoke of the 'phase' of the 3-phase HV supply feeding the primary of the transformer (or, come to that, the 'phase' of the 3-phase supply coming out of the secondary)?

Kind Regards, John

 

[ban-all-sheds]

The secondary may be centred tapped at 230-0-230 in which case its known as a split phase supply. Note that this is not "two phase" - these are opposite ends of the same coil.

But if you use the centre tap as your point of reference the two ends are out of phase, therefore they are not the same phase, therefore there are two phases.

 

[SparkyTris]

I've certainly seen that done, although possibly not primarily for the reason you're discussing.

what other reasons, John?

 

[JohnW2]

what other reasons, John?

I'm not really sure, but I saw it done decades ago, largely (if not completely) before the days of TN-C-S (which is what creates the greatest potential concerns).

I suppose it could have been that they wanted to remain 'in control' of the extent and arrangement of the RF earth (e.g. concentrated beneath a 'long wire' antenna), without the 'confusion' being caused by it be connected to some other 'earth'.

Kind Regards, John

 

[AdrianUK]

But if you use the centre tap as your point of reference the two ends are out of phase, therefore they are not the same phase, therefore there are two phases.

No.

One end is inverted with respect to the other, agreed, but it is ONE sinewave.

Look at it another way.... the secondary is driven from a single sinewave.... how it generate two phases?

 

[JohnW2]

No. One end is inverted with respect to the other, agreed, but it is ONE sinewave. Look at it another way.... the secondary is driven from a single sinewave.... how it generate two phases?

We've been over this ground countless times before, and it's really only a matter of some people's view of 'conventional terminology' - 180° out-of phase is not conceptually different from 120°, 90° or any other phase difference between two voltages.

For what it's worth, Fig 3.3 of BS7671 depicts three different variants of "Two-phase" arrangements - with the two phases 180°, 90° and 120° degrees apart. The first of those (often called 'split phase') is the one you assert is not "Two-phase". Is BS7671 wrong? (wouldn't be for the first time!).

Kind Regards, John

 

[ban-all-sheds]

https://www.diynot.com/diy/threads/quick-question-reg-number-prohibiting-sp-rcbos-on-tt.328187/

 

[SimonH2]

We've been over this ground countless times before, and it's really only a matter of some people's view of 'conventional terminology' - 180° out-of phase is not conceptually different from 120°, 90° or any other phase difference between two voltages.

Indeed, and my guess would be that's it's one of those terminology things where the terminology is there to avoid the confusion that could otherwise arise - to those in the industry, "2 phase" and "split phase" would instantly conjure up the appropriate mental image of what was being discussed.

At a previous job, the local DNO came along and asked if we'd be prepared to have a fault reporting box on our premises. AFAICT it was just a simple mains monitor that dialled up to report if the power failed. It was part of their attempts to automate end user level fault reporting and allow them to have a better view of faults and the scale of their affects. IIRC I asked them a few years later if they still wanted it installed, and they said it didn't matter any more.
In reality, I think that sort of thing would be the only way of monitoring for broken neutrals - looking for significantly out of spec N-phase voltages which seems to be the hallmark of many "lost neutral" incidents blowing up users' electronics.