On Tue, 25 Jan 2005 13:04:15 -0000, Paul King wrote:

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.

Nope! System transformers are fully capable of changing tap on load with no
discernable effect for the customer (other than an increase or decrease in
supply voltage). It's a while now since I had anything to do with system
transformers, but if memory serves, Ferranti Transformers first came up
with a surge divertor mechanism a good few decades ago.

The dips or 'brown outs' are usually caused when automatic switchgear
usually operating at 11kv or higher, clears a fault on a circuit that is
*electrically* close to the circuit feeding you, i.e. normally on an
adjacent feeder connected to the 11kv busbars at the primary substation..
The fault level or 'available energy' to be dissipated into the fault and
the 'closeness' of the electrical interconnection will usually determine
how much of a dip you see.

Here's a poser for those interested. Two primary substations, with 11kv
inter-connected radial circuits, normally with an open point between them.
System transformers can sense load and adjust voltage accordingly. What
might happen when the open point is closed, say to carry out maintenance?

--
the dot wanderer at tesco dot net