Since I've had rather too many light bulbs 'popping' on turn-on recently, I
decided to monitor the mains voltage by leaving my Brennenstuhl
volt/amp/watt meter plugged into a socket.

Whereas it sits at just under 240v for most of the time, it has been showing
quite a lot of variation - this morning getting up to about 248v for a
while.

What are the acceptable limits? Is the voltage controlled locally in each
sub-station - or does that just transform it down in a fixed ratio? The
thought occurs to me that if power stations generate a constant voltage, the
voltage arriving at domestic premises will vary depending on what load is
being drawn en-route - and large fluctuations may occur when factories start
up and shut down (not that there are any very close to me).

Can anyone throw any light on this subject?
--
Cheers,
Set Square
______
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"Set Square" wrote in message
...
Since I've had rather too many light bulbs 'popping' on turn-on recently,
I
decided to monitor the mains voltage by leaving my Brennenstuhl
volt/amp/watt meter plugged into a socket.

Whereas it sits at just under 240v for most of the time, it has been
showing
quite a lot of variation - this morning getting up to about 248v for a
while.

What are the acceptable limits? Is the voltage controlled locally in each
sub-station - or does that just transform it down in a fixed ratio? The
thought occurs to me that if power stations generate a constant voltage,
the
voltage arriving at domestic premises will vary depending on what load is
being drawn en-route - and large fluctuations may occur when factories
start
up and shut down (not that there are any very close to me).

Can anyone throw any light on this subject?
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.



By telling the huge hamster to either slow down or speed up in his wheel

Set Square wrote:

Whereas it sits at just under 240v for most of the time, it has been showing
quite a lot of variation - this morning getting up to about 248v for a
while.

What are the acceptable limits? Is the voltage controlled locally in each

Depends on what you mean by acceptable... and to who? ;-)

It ought to be no more than 230 + 10% or less than 230 - 6%, so
technically yours is borderline out of spec.

sub-station - or does that just transform it down in a fixed ratio? The

IIUC the transformers have multiple taps that allow a range of voltages
to be preselected. The supplier presumably choosing an appropriate tap
based on the length and average load of the circuit.



--
Cheers,

John.

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"Set Square" wrote in message
...
Since I've had rather too many light bulbs 'popping' on turn-on recently,
I
decided to monitor the mains voltage by leaving my Brennenstuhl
volt/amp/watt meter plugged into a socket.

Whereas it sits at just under 240v for most of the time, it has been
showing
quite a lot of variation - this morning getting up to about 248v for a
while.

What are the acceptable limits?

Maximum permissable is 253 volts.


Is the voltage controlled locally in each sub-station

Either there or on the pole top transformer if you have one.


or does that just transform it down in a fixed ratio?

Well it's fixed at installation. But most can be adjusted so that they can
ensure the nearest house is under max and the furtherest over min.


The
thought occurs to me that if power stations generate a constant voltage,
the
voltage arriving at domestic premises will vary depending on what load is
being drawn en-route - and large fluctuations may occur when factories
start
up and shut down (not that there are any very close to me).

Far worse is adverts in Coronation St and times like that. Every kettle in
the land suddenly coning on is far worse a load variation than any factory
can manage. In fact the contracts with major industrial users of power
insist they don't suddenly turn everything on or off in one go.

On Mon, 24 Jan 2005 18:55:32 -0000, Set Square wrote:

snip

Can anyone throw any light on this subject?

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.

11kv to lv transformers normally have five off-load taps, which give a
range +5% to - 5% of nominal 11kv. One of the skills in distribution
engineering is to work out where along the circuit transformers need to be
connected at say 11kv +2 & 1/2%, 11kv + 0% or 11kv -2 & 1/2%.

The theory is that your supply voltage will remain within statutory limits
regardless of load on the 11kv system. Where it usually goes wrong is when
load has gradually crept up over the years and the circuit hasn't been
checked for voltage drop.

Well, you did ask..........

:-))

--
the dot wanderer at tesco dot net

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?


--
Cheers,

John.

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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Upper limit is 253Volts, although most lightbulbs will burn out quickly
at that level.

In the UK the limit is 230 (stated voltage) plus 10%. In my opinion
this is an unrealistic level - it gives far too much leeway to the
suppliers.

-Km


Set Square wrote:
Since I've had rather too many light bulbs 'popping' on turn-on
recently, I
decided to monitor the mains voltage by leaving my Brennenstuhl
volt/amp/watt meter plugged into a socket.

Whereas it sits at just under 240v for most of the time, it has been
showing
quite a lot of variation - this morning getting up to about 248v for
a
while.

What are the acceptable limits? Is the voltage controlled locally in
each
sub-station - or does that just transform it down in a fixed ratio?
The
thought occurs to me that if power stations generate a constant
voltage, the
voltage arriving at domestic premises will vary depending on what
load is
being drawn en-route - and large fluctuations may occur when
factories start
up and shut down (not that there are any very close to me).

Can anyone throw any light on this subject?
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

kmillar wrote:

Upper limit is 253Volts

In the UK the limit is 230 (stated voltage) plus 10%.

Errm, spotted any inconsistency in those two statements by any chance ;-)





--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Mon, 24 Jan 2005 21:43:36 +0000, 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?

Yup, stage 1 and stage 2 load shedding (3% and 6% voltage reduction) is
done these days by telecontrol from central control rooms, by making the
system transformers lower the tapping. It happens - or used to - much more
frequently than you might think, especially during winter months.

Stage 3, rota disconnections - 3 hours off 3 hours on - is also largely
done by telecontrol, something we haven't had for some years now.


--
the dot wanderer at tesco dot net

John Rumm wrote:

kmillar wrote:

Upper limit is 253Volts
In the UK the limit is 230 (stated voltage) plus 10%.

Errm, spotted any inconsistency in those two statements by any chance ;-)

No, I don't see what you're getting at! 230 + 10% = 253?

Andy Burns wrote:

John Rumm wrote:

kmillar wrote:


Upper limit is 253Volts
In the UK the limit is 230 (stated voltage) plus 10%.


Errm, spotted any inconsistency in those two statements by any chance ;-)


No, I don't see what you're getting at! 230 + 10% = 253?

Yup, brain fart, unable to multiply by 1.1 (somehow came up with 248...
think I will go lie down in a quiet room)

--
Cheers,

John.

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| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

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?
--
Cheers,
Set Square
______
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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.
--

Reply address is spamtrapped. Remove theobvious for valid e-mail address

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

In article 1106658377.6477361036c3636354041bdde6782eb8@teran ews,
"Paul King" writes:

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.

Not for at least 50 years (the age of some of my supply distribution
books). When mechanical switches were used, a second coil allows for
smooth switching with no shorting. SCR's have been used for on load
tap switching for perhaps couple of decades now, and their diode
properties mean there's no shorting current even without the secondary
coil. They do zero voltage switching in any case (not that this
mechanism is used to prevent shorting).

--
Andrew Gabriel

John Rumm wrote:


Yup, brain fart, unable to multiply by 1.1 (somehow came up with 248...
think I will go lie down in a quiet room)

Yeah, but at least it was an ISO-9001, DoD-STD-2167A *quality-assured*
brainfart, right? ;-)

Stefek Zaba wrote:

....DoD-STD-2167A *quality-assured*

Eeeeek, not that please! (20 pages of design document, 150 pages of
cross reference later ;-))

--
Cheers,

John.

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