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Post by noddymac on Jan 15, 2021 13:57:46 GMT
It looks as though the rectifier issue at Newbury Park will be resolved next week as I received an email from my manager stating there will be a reduced service on the east end of the Central line on the Hainault loop due to the rectifier issue being sorted. I believe this is expected to start from start of traffic on the 18th and finish at the end of traffic on Friday the 22nd.
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Post by sawb on Jan 15, 2021 17:53:28 GMT
What is the purpose of a rectifier and what is the issue with the one at Newbury Park?
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hobbayne
RIP John Lennon and George Harrison
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Post by hobbayne on Jan 15, 2021 19:12:40 GMT
What is the purpose of a rectifier and what is the issue with the one at Newbury Park? On Saturday 19 September 2020, one of the two rectifiers (used to supply direct current (DC) traction to the railway), at Newbury Park substation packed up.
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rincew1nd
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Post by rincew1nd on Jan 15, 2021 19:17:12 GMT
What is the purpose of a rectifier and what is the issue with the one at Newbury Park? A rectifier converts AC electricity to DC, AC is what LU takes from the National Grid, DC is what powers the trains.
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Post by zbang on Jan 15, 2021 21:44:41 GMT
On Saturday 19 September 2020, one of the two rectifiers (used to supply direct current (DC) traction to the railway), at Newbury Park substation packed up. And they're just getting to it? (assumed that sourcing replacement parts is the issue, power semiconductors don't grow on trees, as it were)
This kind feeds back to the discussion of stabling and robbing trains for parts to fix others.
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Post by Dstock7080 on Jan 15, 2021 22:13:54 GMT
And they're just getting to it? (assumed that sourcing replacement parts is the issue, power semiconductors don't grow on trees, as it were) Tucked away in this post was the initial response: districtdavesforum.co.uk/post/496583
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Post by zbang on Jan 16, 2021 0:43:43 GMT
The engineer in me really wants to see the failure analysis (large transformer are more than just uncommon), but I suspect I won't.
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class411
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Post by class411 on Jan 16, 2021 12:06:37 GMT
Is 'rectifier' one of those English words that LU choose to mean something entirely different to its normal use?
In normal electrical terminology a rectifier - as Rincew1nd states above - is a device for converting AC to DC. Presumably LU use bridge rectifiers to keep the Grid happy and ensure the supply is not too lumpy.
A lot of the posts above seem to be implying that it is a transformer that has failed.
Rectifiers are easy to source and it would be sensible for LU to stock spares. Even with the current involved they would be easy to transport and uninstall/install.
The type of transformer used by LU, on the other hand, would be very large, probably not viable to backup with spares, and difficult to transport and uninstall/install.
Given all that, and what has been said and referenced above, it looks very much as if it is a transformer that has failed.
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Post by dm1 on Jan 16, 2021 12:45:58 GMT
Perhaps they mean a rectifier with an integrated transformer to go from medium voltage grid AC to low voltage DC. You can't rectify e.g. 11kV AC to 750 DC without a transformer and/or power electronics.
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class411
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Post by class411 on Jan 16, 2021 14:06:15 GMT
Perhaps they mean a rectifier with an integrated transformer to go from medium voltage grid AC to low voltage DC. You can't rectify e.g. 11kV AC to 750 DC without a transformer and/or power electronics. That makes a lot of sense. Back in the day, before the advent of solid sate electronics, the rectifier(s) would have been a fairly complicated, large (and possible quite impressive) piece of engineering. So it would make sense to consider the transformed 'just' some simple lump bolted on the back. Nowadays it's a bit confusing, and it makes LU seem somewhat incompetent (being unable to source a simple thing like a solid state rectifier array), whereas the reality seems to be that they need to source and transport as massive transformer, which could quite reasonable take several days or even longer.
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Post by Dstock7080 on Jan 16, 2021 15:51:35 GMT
even the article linked above, swaps between terminologies: "Thought I’d share some pictures of the ongoing works to replace a defective 22kv high voltage transformer on the east end of the Central Line": lifted out: universal spare rectifier coming in:
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Post by zbang on Jan 16, 2021 16:34:03 GMT
In power engineering usage*, the generic word "rectifier" quite often refers to the entire assembly converting high-voltage AC to lower-voltage DC (transformer(s), conversion electronics, controls & monitoring, etc). Yes, it also could refer to the diodes/etc contained within, but often they're called by a more specific term (e.g. thyristor or diode). *at least in railways & transit, motion picture projection (for arc lamps), electro-plating, DC-powered cranes, etc
ETA- It's common for transformers larger than a maybe a MW to be built-to-order from a stock design, if not outright custom-designed. Those can take many months to produce, and with the cost vs failure rate (v. low if maintained), ready spares are seldom produced.
Another ETA 7 hrs later- A correspondent tells me that his company (a public utility in the US) ordered a 15MW high-voltage transformer- 1 year(!) lead time and over $600k, and we'll take half that now, please. That's not the kind of thing you keep many spares of, and even the spares need maintenance (keep the oil clean and dry, the insulators clean, etc).
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class411
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Post by class411 on Jan 18, 2021 11:23:00 GMT
In power engineering usage*, the generic word "rectifier" quite often refers to the entire assembly converting high-voltage AC to lower-voltage DC (transformer(s), conversion electronics, controls & monitoring, etc). Yes, it also could refer to the diodes/etc contained within, but often they're called by a more specific term (e.g. thyristor or diode). Never heard it used way over here apart, or course, from LU apparently). 'Power supply, power pack or just 'the DC' would be more usual - or 'substation' in railway usage. Google also seems ignorant of the usage. Seems odd that engineers would deliberately use a synecdoche that is likely to lead to confusion. Engineer A: The rectifier's blown. Engineer B: What's wrong with it? Engineer A: The rectifier's blown.
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Post by zbang on Jan 18, 2021 16:33:59 GMT
Seems odd that engineers would deliberately use a synecdoche that is likely to lead to confusion. Engineers can be an odd bunch , we do it all the time; in context these things tend to be clear enough. Not so different from calling things by the manufacturer's name (e.g. Tannoy).
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Post by Dstock7080 on Jan 24, 2021 11:41:28 GMT
The refurbished HV transformer at Newbury Park was successfully reinstated on Friday 22 January and full power available in the area.
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Post by modeng2000 on Jan 24, 2021 12:53:46 GMT
So just to be clear, was it a faulty transformer?
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Post by Dstock7080 on Jan 24, 2021 13:35:33 GMT
So just to be clear, was it a faulty transformer? Transformer within the rectifier, yes.
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class411
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Post by class411 on Jan 24, 2021 13:39:51 GMT
So just to be clear, was it a faulty transformer? Yes. It was the transformer. The rectifiers were fine. Had it been the rectifiers there would have been a much quicker solution.
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Post by zbang on Jan 24, 2021 18:41:36 GMT
I wonder what the fault analysis says (not that I expect to see it), usually the only thing that will fault a large transformer is gross overheating, a lightning strike, or lack of maintenance (usually leads to contaminated oil).
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Post by spsmiler on Jan 24, 2021 23:54:32 GMT
The refurbished HV transformer at Newbury Park was successfully reinstated on Friday 22 January and full power available in the area. Good news! I now look forward to the day when I can actually benefit from its repair.
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Post by modeng2000 on Jan 26, 2021 10:31:05 GMT
Ive been thinking about the electricity supply for the traction and realise that I have no idea about the amount of power that these sub stations provide.
Quite a long time ago I visited a Southern Railway sub station that had three or four rotary converters and used to collect fuses that blew from time to time usually when there was a lot of pickup-shoe arcing during frosty weather. I seem to remember fuse ratinge of 700 amps.
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Post by superteacher on Jan 26, 2021 11:34:35 GMT
Ive been thinking about the electricity supply for the traction and realise that I have no idea about the amount of power that these sub stations provide. Quite a long time ago I visited a Southern Railway sub station that had three or four rotary converters and used to collect fuses that blew from time to time usually when there was a lot of pickup-shoe arcing during frosty weather. I seem to remember fuse ratinge of 700 amps. 700 amps - wow!
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Post by zbang on Jan 26, 2021 18:26:09 GMT
A loaded train could take 2+ MW to move- at 620 volts that's over 3000 amps (but only 100 amps at 22kv). (Representative numbers, not looking up actuals at the moment. I know the Washington Metro third rail can supply something over 4000 amps in a given section @ 750v.)
Anyway, it's a lot of power.
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Post by modeng2000 on Jan 26, 2021 19:18:04 GMT
A loaded train could take 2+ MW to move- at 620 volts that's over 3000 amps (but only 100 amps at 22kv). (Representative numbers, not looking up actuals at the moment. I know the Washington Metro third rail can supply something over 4000 amps in a given section @ 750v.) Anyway, it's a lot of power.
Thanks I really had no idea.
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Post by modeng2000 on Jan 26, 2021 19:24:50 GMT
As I remember it, I was still at school then, the 700 amp fuse was around 6" long and maybe 1" diameter and filled with sand. There were metal end sections for the connections. Half way along the fuse body was an indicator that vaporised when the fuse failed.
Sorry if this has gone off topic.
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roythebus
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Post by roythebus on Apr 19, 2021 13:30:08 GMT
1st engineer: what's the problem with the rectifier?
2nd engineer: It's f****d.
1st engineer: OK.
But yes, there's a lot of amps needed to move a train. I read that a typical Eurostar train would use more power for the "hotel" slices on board than it uses for moving along.
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Post by grumpycat on Apr 27, 2021 8:42:17 GMT
1st engineer: what's the problem with the rectifier? 2nd engineer: It's f****d. 1st engineer: OK. But yes, there's a lot of amps needed to move a train. I read that a typical Eurostar train would use more power for the "hotel" slices on board than it uses for moving along. I seem to remember they couldn't full throttle the class 373s since those would set the transformers on fire or something.
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