To AM

sorry cut off mid edit.

read with my last post - try this SP doc    PM= pole mount on page 10, GM = ground mount on next page

If you cannot identify the transformer,   

PM1 (Single Phase)500VA (Aw diddums - wont be that small!)
PM2 (Single Phase) 25kVA
PM3 (Split phase)   50kVA
PM4 (Split phase)   100kVA
PM5 (Three Phase)  50kVA
PM6 (Three Phase)  100kVA
PM7(Three Phase)   200kVA   (heavy - expect to see 2 poles and a cross bar rig.)


all about 4.5 % drop at full load   perhaps 4.75% on the largest.

You can ignore the baby 500s. They are used to supply other DNO pole-mounted equipment when there is nothing else local to use, I don’t think they would ever be used to supply customers. They do however seem a bit more robust to lightning than the little resin block versions that some have used. The resin block ones are known to go off like a grenade in some circumstances. 


Regards,


Alan.

Same construction as my 110-volt tool transformers?


Remind me not to use them during a storm!


 Andy Betteridge

So let's see if I got this right there are 43 houses in my street times by 10 is 430 so the steady current should be 430 amps is that correct or should it be 43 divided by 3 then x 10  either way I wouldn't fancy putting a fuse in on a live circuit

Its a non post, the poster just wants the DNO to do the calculations, we get it all the time. This is clearly an additional load, and we require a declaration.

We we going off on a tangent here? If what the OP said is true - given a 50A steady load the voltage drops below ESQCR permitted levels - then there is surely a problem with the DNO's supply. Additional or disturbing loads may well cause additional problems - but that shouldn't cloud the basic underlying issue.


  - Andy.

normally, but not in a few very old roads originally wired for DC, the houses will share along the phases 1,2,3,1,2,3, and repeat..


Round here (SSE, the southern bit - other DNOs will vary, and realise that cities are something else again)


For a half megawatt transformer on the ground of the kind found in a fenced compound at the end of the road, there may be 70 houses per phase or more like 50 if there are also a few shops and things that take a 3 phase supply from the same transformer.

You might think 400A per phase, = 400* 3 * 230 = 270KVA, and on a 500KVA unit  in practice you may see two branches going off from each phase fused at 400A each.  (so yes, 25- 35  houses on 400A fuse)

Anything much less than 400A would not always discriminate well with 100A downstream once things are loaded up.



For a suburban housing estate, larger -say 1MVA plus -  transformers make little sense, as the length of the LV to cover all the properties is voltage drop limited. So,  two smaller units a few hundred yards apart are more economic , 11kV line is cheaper than the weight you would need to go a long  way at LV.

High rise blocks however may have enough users to need most or all of a transformer each, and then larger transformers and still quite close together, make more sense.

Spread out rural has the reverse - with a low rated pole pig  for each cluster of buildings that are within transformer sharing distance, and 11kV yompoing over the fields.

Very very  spread out (only seen in Scotland, but maybe used elsewhere) it becomes worth having 33kV phase to phase, rather than 11kV,  and then the 33k-400V transformer at the last pole before the village.

DNO have been aware of the extra load since the outset, and an upgrade price of £8k would be a bargain. What it has done so far for me is to confirm my thoughts on heat pumps generally, and particularly as the weather gets colder and COP perhaps drops to less than one, ie, less than that of a resistive heating load, and far less efficient too! I'm talking to the manufacturer about this and already have some usefull data coming from them! Defrost cycles also more frequent too in the cold weather, add further to their inefficiency. I'm pursuing that seperatelly.   

It's also got me wondering about Ze and pfc measurements generaly, particularly with standard multitester or look tester kit, Measurements are sunstancially affected by other paralled loads on the supply network, I never did get this mentioned on the 2391 course!

Thanks again Alan, I will be looking into that as I'm hoping for a meeting with the DNO enginner, so will also check this out then. It does not though excuse the low voltage at say half the supply fuse rating, or does it?