volt drop calcs and 230 v

[Knobhead]

do the transformers have to be de energised to change taps or do they bang it live ?

its done live.

Switched live they will go bang, don’t even think about it.

On load tap changers are normally at the 33/11KV transformers.

Off load

On load

 

[Guest55]

Switched live they will go bang, don’t even think about it.

On load tap changers are normally at the 33/11KV transformers.

nice animated diagram.

recently read a HSE report that was linked on the IET forum that reported on the death of a sub station worker that was killed changing the taps manually - the mechanism connected to the operating handle failed , jammed between 2 of the contact points , chamber overheated , explosion with hot oil ensued with no warning - terrible way to go , DNO's subsequently changed their proceedures etc.
your 2nd pic is exactly the same as the technical video shown by the HSE

 

[Knobhead]

nice animated diagram.

recently read a HSE report that was linked on the IET forum that reported on the death of a sub station worker that was killed changing the taps manually - the mechanism connected to the operating handle failed , jammed between 2 of the contact points , chamber overheated , explosion with hot oil ensued with no warning - terrible way to go , DNO's subsequently changed their proceedures etc.
your 2nd pic is exactly the same as the technical video shown by the HSE

That was terrible and I feel so sorry for the guy’s family.

There was a known fault on the tap changer and he operated it live.

Operating a tap changer isn’t a nice experience, the transformer sounds like its being violently sick.
It would be very rare you did it using manual control, they are normally under the control of a automatic voltage regulator.
If you watch the animation there are times where there are shorted windings which is where the two reactors (inductors) come in to play. They limit the current in the shorted windings.

 

[7029 dave]

Im pretty sure that the minimum is 216V for tolerances allowable if l remember correctly. Please put me right if im talking piggie-excrement. I think its nominal voltage 230 -6%=13.8V which is 216.2V to +10%=23V which is 253V...

correct.

 

[Flanders]

Im pretty sure that the minimum is 216V for tolerances allowable if l remember correctly. Please put me right if im talking piggie-excrement. I think its nominal voltage 230 -6%=13.8V which is 216.2V to +10%=23V which is 253V...

I ask this question to the DNO just the other day and that's the answer they gave me too, The customer had a load of them GU10 compact florescent lamps that were only lasting a few months (the voltage was around 149 volts at the lamps and 151 at the incomer) The lamp supplier said that due to the higher voltage the lamps could be over heating ,mind you they are discontinuing these lamps so suggested fitting LED lamps instead.

 

[timclarkx]

Nominal voltage 230v permitted tolerance +10% / -6% 216.2 v - 253.0 v (bs7671, appendix 2, section 14).

Volt drop- 3% for lighting circuits, 5% for other circuits.

Probably repeated what others have said earlier..so apologise if so.

 

[7029 dave]

149/151 volts are you sure?

 

[Flanders]

149/151 volts are you sure?

yes used 2 different tester to check

 

[Jabbajaws]

yes used 2 different tester to check

Is this for real Flanders? Was everything operating within the dwelling correctly?

Im curious to know the answer that's all.... :33:

 

[Flanders]

Yes it was a shop must of been next to the transformer , that's why I a spoke to the DNO but they assured me it was all ok

 

[7029 dave]

With that kind of voltage it should be no supply, nothing will work just too low!!

 

[Flanders]

With that kind of voltage it should be no supply, nothing will work just too low!!

7just realised Typo should of been 249 volts 251 volts:81:

 

[7029 dave]

yes lol coz I had job last year nothing working but had polarity, measured 155 v on the screws passed over to DNO joint had gone down in street.

 

[Jabbajaws]

yes lol coz I had job last year nothing working but had polarity, measured 155 v on the screws passed over to DNO joint had gone down in street.

Now this makes more sense. Nothing working which l didn't think it would....

 

[Knobhead]

Never mind the IET and EU harmonisation.

The specification for a DNO local transformer is for up to 1000KVA, 11/.433KV 4.5% reactance. 1500KVA the reactance rises to 5%

433V not 400V

 

[cmac70]

You could always do the good old way a taste to see what flavour voltage it is 230 or 400.

 

[Knobhead]

You could always do the good old way a taste to see what flavour voltage it is 230 or 400.

Which planet are you on?

230 = 400/√3, to all intense and purpose the same.

Which flavour of vanilla?

If you really want to be pedantic 230.94 = 400/√3

 

[Silly Sausage]

If you really want to be pedantic 230.94 = 400/√3

If you want to be really pedantic 230*√3 = 398.37

 

[Engineer54]

No idea what you're all arguing about you'll never going to be seeing 230 Volts or 400 volts in the UK or Europe for literally 10's of years, if ever!! lol!! It's all just fantasy world stuff!!

 

[Knobhead]

It could be done using the voltage regulators on the 33KV OLTC’s. The knock on would be disastrous. The LV network can’t cope with the current loading as it is now.

I tried lowering the voltage on an 80MVA system, I soon put it back to where it was.