Set Square wrote:
In an earlier contribution to this discussion,
John Rumm wrote:

Wanderer wrote:

As far as you, the domestic customer is concerned, it happens at
primary substations, (33kv/11kv) Current and voltage transformers
are connected to relays that detect the load being drawn on the 11kv
network and either step or step down the 11kv voltage. The
transformers have multiple taps that can be changed on load.

When a line is lightly loaded, the notional supply voltage close to
the prmary sub might be about 11,200, to say 10,800 right at the end
of the circuit. As the load goes up, the notional voltage increases
to allow for voltage drop in the circuit.

Interesting stuff...

So is this where they would tinker with the voltage if they wanted to
shed some load, or would that be done further back in the network?


This is really what I was getting at - even if my question wasn't
explicit enough. I was interested in knowing whether any automatic
*dynamic* adjustments are made - as opposed to leaving transformers
on fixed tappings, once installed. It sounds as if dynamic
adjustments *are* made.

Could this account for the momentary outages which occur from time to
time? Could these be caused by a transformer switching to a different
tapping to adjust the voltage?

Yes. Those dips are called "brown-outs" and are caused when the transformer
tappings are changed. Since the switching contacts are "make before break"
(otherwise you'd get a very momentary blackout) the transformer experiences
a momentary "shorted turns" episode. This causes *HUGE* currents to flow
within the (shorted) transformer windings, creating the brown-out.
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