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Joined: May 2002
Posts: 382
H
Member
I thought that was the case C-H but I couldn't chase the info down. DJK makes a good point though - where do they get their power.

I think in the UK (as common elsewhere in the rail industry) the traction current and signal systems (where both are ac) are on different frequencies to prevent interference. I thought I read somewhere that the UK uses 83.333' Hz(?) in these cases, presumably solid-state derived.

Interesting that 16.666' is 1/3 of 50Hz - no interference protection there from harmonics.

Joined: Apr 2002
Posts: 2,527
B
Moderator
Before power electronics, I think the only choice for frequency conversion was motor-generator sets.

A previous employer had an 18,000HP motor-generator set that was 13.8kV 3ø in, and DC out. Excitation of the DC side could be varied rapidly, to ramp the output accordingly. It was a big DC power supply that could be controlled very tightly. It could only be started with clearance from the local electric utility.

Joined: Aug 2001
Posts: 7,520
P
Member
I've done a little searching, and it seems that the 25kV system in the U.K. has always been 50Hz, fed from the National Grid.

What I must have had in the back of my mind is this old 6.6kV 25Hz system.

From the same website:
Quote
The 15 kV a.c., 16 2/3 Hz, overhead system is used widely in Germany, Denmark and Austria.

In Germany the 16 2/3 Hz electricity supply comes from railway generating stations. Power is transmitted at 110 kV via overhead lines. The power is transformed from 110 kV to 15 kV at railway substations that feed the railway overhead system.

Joined: Sep 2002
Posts: 1,498
Likes: 1
C
C-H Offline
Member
Hutch,
16 2/3 Hz was adjusted to 16.7 Hz to avoid this problem. I left that part out

[This message has been edited by C-H (edited 08-08-2003).]

Joined: Aug 2002
Posts: 402
J
Member
Well Niagara Falls still has at least 1 turbine that puts 25hz for the big steel mills in Hamilton.

Joined: Dec 2002
Posts: 1,253
D
djk Offline
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Motor - Generator sets must be very inefficient... what kind of energy loss would you be looking at?

Joined: Jul 2002
Posts: 8,443
Likes: 3
Member
djk,
Motor-Gen Sets have a HUGE loss ratio.
This is only recuped where something like a Ward-Leonard type system is used to regenerate some of the losses lost in the Generator, but I am told that a normal Gen-set only runs at 60-70% efficient.
This is probably why they never really caught on as a real option for a UPS system.

Joined: Apr 2002
Posts: 2,527
B
Moderator
Trumpy—that is a very good point. Who's ever been in an equipment room with M-G sets that was "comfortable"—er, cool and quiet? I think though, that for many decades M-G sets were the most practical version of power conversion—until rugged SCRs came along.

[Mercury-arc rectifiers—like Ignitrons and Thyratrons—filled in between the two, but were a pain to keep running.]


[This message has been edited by Bjarney (edited 08-09-2003).]

Joined: Aug 2003
Posts: 1
S
Junior Member
Since Europe runs off the more common higher voltage system do they still require pole top transformers or is it done completely with the substations? Do you know where I can find some reference matterials about the pole top transformers that are in use in Europe.

Joined: Dec 2002
Posts: 1,253
D
djk Offline
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I don't know about the rest of Europe but here in Ireland we use substations in urban areas.

Power would come in from the grid at transmission voltages of up to 400kV to a large substation near a town/city. It's stepped down to a medium distribution voltage of either 38kV, 20kV or 10 kV and from there goes out to local substations.

Typically every new housing development or each area of a city would have one. They often provide a number of 3-phase +N (380V) circuits which would be distributed either underground or overhead.

Small commercial users (small stores etc) and domestic users typically take 1 phase + N (220V, nominally 230V)

Other users take 3 phases 380V (nominally 400V) +N

In rural areas a 3-wire (3phase) distribution system operates at 10kV or 20kV.

Pole top transformers are used to step the voltage down and to either provide 220V (domestic) or 380V (to larger farms/guest houses/hotels/schools etc)

You won't find pole top transformers in towns or even relatively small villages though. They'll always have a small substation.

Even where 2/3 houses are clustered together a larger pole mounted transformer may be used and a small 220/380V overhead distribution system will hook up the houses.

As for types of transformers used. It would depend on the country in question. I know ESB, the main PoCo here uses a lot of ABB and AEG substations.

They also use ABB Pole mounted transformers: (Oil filled can type)
[Linked Image from abb.com]

Here's the 3-phase version:
[Linked Image from abb.com]

Here's a typical small pad-mounted substations that are used to service a block of houses or a new housing development. You'll find them scattered around the place. They're just large green street cabinates. Often located at the side of a park, down a lane etc..

[Linked Image from abb.com]

All of the above are ABB

AEG and Siemens also supply similar set ups.

This is a bulkier looking Siemens transformer, something similar is seen in pole mounted applications here. Or as part offenced off substations.
[Linked Image from punchout.ptd.siemens.de]

The large substations that step-down from transmission voltages are pretty serious plant. Usually a large fenced off area with lots of transformers and switch gear.

for further information visit: www.siemens.com www.abb.com www.aeg.com www.alstom.fr
All of the above make transformers for the EU market.

I'm sure there are others too..



[This message has been edited by djk (edited 08-19-2003).]

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