Power outage strands trains

[whole diary]

[grahame]

From the BBC^» (British Broadcasting Corporation - home page)

The picture titles (below) give some idea of the problems cause yesterday - "Nearly a million people have been affected by a major power cut across large areas of England and Wales, affecting homes and transport networks."

* Passengers on a train near Kentish Town station got off and began walking along the tracks

* People walked in complete darkness at Clapham Junction station in London during a power cut

* Information was not showing on Waterloo departure boards

* All services in and out of King's Cross station were suspended

* A staff member guides train passengers with torch light at Clapham Junction station in London

* Passengers travelling on Thameslink were delayed

* London North Eastern Railway staff, pictured here at Peterborough station, was disrupted, with delayed passengers handed bottled water

[Electric train]

Yesterday while all this was happening, i travelled on the Hammersmith & City from Whitechapel to Paddington and then on to Maidenhead with no problems at all.   

The only thing mentioned by the H&C driver was when we got to KX & St P that the was not Victoria line due to a power failure, it was not until I got a BBC^» (British Broadcasting Corporation - home page) new alert on my phone that I became aware of the scale.

I did not get any calls on my work phone, although I'm not on call this week (phew)

Often when there are these types of power outages it is the signalling systems that take the time to restore, this is can be due to in built safety features, ie they do not want interlocking compromised.  The stations  take their supplies for the local "street" supplies larger ones like Clapham will have more than one but in essence will be the same bulk supply point.

The last major power outage was back in 2004 (if I recall correctly) which affected South London

[ellendune]

It was reported on the radio this morning that some trains needed "specialist engineers" to get them restarted. Surely this should not result from a temporary loss of power?

Also reported that one train delayed for 13 hours had no toilets after 5 hours delay.  Not good. 

[eightf48544]

Beaten to it but same question.

Heard on the BBC^» (British Broadcasting Corporation - home page) that stranded trains needed specialist engineers to restart them. Is this correct?

Or did they mean signal engineers to restore  the signalling system as mentioned by electric train.

[Timmer]

It was reported on the radio this morning that some trains needed "specialist engineers" to get them restarted. Surely this should not result from a temporary loss of power?

Also reported that one train delayed for 13 hours had no toilets after 5 hours delay.  Not good. 

The Thameslink class 700s which was the main cause of the chaos into and out of Kings Cross and St Pancras with EMT^» (East Midlands Trains - about) and LNER^» (London North Eastern Railway - about) trains stuck behind them.

The 9.52 Aberdeen to Kings Cross arrived into Kings Cross 499 minutes late! Due to arrive 1648, finally pulled in at 0107.

[IndustryInsider]

Another internal review by the TOCs^▸ (Train Operating Company) and promises of 'lessons learned' I expect!

[SandTEngineer]

Perhaps this might help a little bit (from the WNXX^▸ (Stored Unserviceable, Mainline Locos HQ All Classes) Forum).  Appologies for it being a 'bit technical':

On a system such as the National Grid all the generators (alternators, in reality) run at the same output frequency (same rotational speed). To ensure proper load sharing each individual alternator adjusts its output voltage to control the power flow. As a network reaches its capacity the alternators will start to slow down so the frequency reduces; at lighter loads the frequency increases. The UK^▸ (United Kingdom) limit is something like 49.5 to 50.5 Hz (+/- 1%).

Now if there's a fault somewhere the grid will split itself up to isolate the fault, to prevent the "cascade failure", that has happened in places like the US, where everything goes off. If this ends up with a network segment running at close to its full load the alternators will slow down and you may go beyond the normal limit. This can cause problems to all sort of system that rely on the frequency being correct.

(When I worked at Rugby we built "Uninterruptible Power Supplies" for critical industries. These took the AC in, converted it to DC^▸ (Direct Current) then inverted back to AC; the DC also charged a battery which could be used to create an output if the input failed. Normally the output would be frequency and phase locked to the input so that if the inverter failed a bypass switch could be switched in to continue feeding the load. However if the AC input went outside the acceptable frequency range the output would revert to 50.0 Hz until the input came back in range. The output frequency was actually controlled to minimise the time the output was not synchronised to the input.)

Most AC fed trains nowadays have a complex "front end convertor" (sometimes called four quadrant convertor, or PMCF, a French acronym) that allows power to be drawn or regenerated at unity power factor (separate discussion). This is done by chopping up the supply current at a much faster rate than 50 Hz - a commonly used multiple is 39 (it needs to be an odd number) which gives a switching frequency of 1950 Hz; this has to be phase locked to the 50 Hz for proper control of interference harmonics. So if the supply frequency reduces to 49.5 Hz, the chopping frequency reduces to 1930.5 Hz. If this chopping frequency gets too far out of range it could interfere with certain signalling systems, so there will be some extra protection, rather like the Interference Current Monitor Unit (ICMU) used on older DC-fed trains. It may be this protection circuit that has tripped out on the Siemens units.

As I recall, a "frequency fault" on a 390 or 334 will trip the Vacuum Circuit Breaker, but I think it's resettable so many times in so many minutes before you have to reboot the train. Maybe if the low frequency was present for a long time, this could trip the repetitive fault circuit.

[broadgage]

As above, the national grid have a legal duty to maintain the frequency between 49.5 and 50.5 cycles, and can be fined for failing in this duty.

However it must be accepted that under rare emergency conditions that the grid frequency can vary by more than that.

I would expect that a properly designed electric train should be able to work over at least the range from 48 cycles to 52 cycles, and preferably be able to work down to 47.5 cycles.
I do not know how low the frequency dropped this time, but in a PREVIOUS similar event about 10 years ago the grid frequency very briefly dropped to 48-75 cycles and remained below 49-5 cycles for 9 minutes.
I would expect that an electric train should work correctly under such conditions.

[didcotdean]

The drop has been reported to be to 48.89Hz.

Another fact that made the response difficult was that there was a high amount of renewables (strong wind) and relatively little thermal plant generating at the time with little inertia in the mix, so the imbalance from the production side needed to come from starting up generation from scratch. Pumped storage was turned on almost immediately followed by the open cycle gas turbines.

This is a known issue with greater reliance on renewables, and there is a contract out at the moment for fast response battery provision.

[Red Squirrel]

...

Another fact that made the response difficult was that there was a high amount of renewables (strong wind) and relatively little thermal plant generating at the time with little inertia in the mix, so the imbalance from the production side needed to come from starting up generation from scratch. Pumped storage was turned on almost immediately followed by the open cycle gas turbines.

This is a known issue with greater reliance on renewables, and there is a contract out at the moment for fast response battery provision.

Apparently two major generators - Little Barford gas-fired power station in Bedfordshire and Hornsea offshore wind farm - both went offline at about the same time. We should wait for the experts to establish how these events unravelled, but it is understood that the lower rotating mass of renewable sources causes grid managers to have sleepless nights.

Of course this is not an argument against renewables, but it may suggest that more investment in 'synthetic inertia' could be helpful.

[bobm]

When I was young we had good old fashioned power "cuts" (especially during the three day week) - now it seems we have new fangled power "outages".

[broadgage]

When I was young we had good old fashioned power "cuts" (especially during the three day week) - now it seems we have new fangled power "outages".

It is the modern trend, never use a short word like "cuts" when a longer word such as "outages" will do.

[onthecushions]

One wonders what happens when a modern signalling system loses power - does it fail right side, everything red including AWS^▸ (Automatic Warning System) and TPWS^▸ (Train Protection and Warning System), or not?

Restarting/booting must be a nightmare - all lines blocked initially but how does it know which sections to clear first, with most occupied with (possibly failed) but loaded passenger trains? Would it all be manual?

If this is to be the future then the phrases Bi-mode and UPS for ROC^▸ (Rail Operating Centre - a centralised location for railway signalling and train control operations for a specific route or region)'s spring to mind.

OTC

[broadgage]

Agree, they really need UPS systems and other back up power supplies for signalling control centers.
And whilst I don't think much of the IETs^▸ (Intercity Express Train) for reasons given elsewhere, they DO have the merit of being able to proceed when the power fails.
IMO^▸ (in my opinion), all new electric trains should have either a small diesel engine or a battery so as to permit of low speed operation to the next station, OR to power the air conditioning if unable to proceed.

[Red Squirrel]

And whilst I don't think much of the IETs^▸ (Intercity Express Train) for reasons given elsewhere, they DO have the merit of being able to proceed when the power fails.

...only as far as the first failed signal..!

IMO^▸ (in my opinion), all new electric trains should have either a small diesel engine or a battery so as to permit of low speed operation to the next station, OR to power the air conditioning if unable to proceed.

Wasn't there once talk of IETs being equipped with Transit-sized engines for 'limp-home' capability? Or did I dream that?

When I was young we had good old fashioned power "cuts" (especially during the three day week) - now it seems we have new fangled power "outages".

It is the modern trend, never use a short word like "cuts" when a longer word such as "outages" will do.

Doesn't 'cut' imply a deliberate, planned act, e.g. to save energy because (say) the miners were on strike (again)? I seem to remember we used the word 'failure' in other circumstances. 'Failure' has its origins in Old French, whilst 'Outage' is from an Old English word, for what it's worth...