Dear Boyu,

TfL Ref: 1862-2122

Thank you for your request received by Transport for London (TfL) on 10 November 2021. Please accept my apologies for the considerable delay in acknowledging your correspondence.

We will aim to issue a response by 8 December 2021 in accordance with the Freedom of Information Act 2000 and our information access policy.

We publish a substantial range of information on our website on subjects including operational performance, contracts, expenditure, journey data, governance and our financial performance. This includes data which is frequently asked for in FOI requests or other public queries. Please check http://www.tfl.gov.uk/corporate/transpar... to see if this helps you.

We will publish anonymised versions of requests and responses on the www.tfl.gov.uk website. We will not publish your name and we will send a copy of the response to you before it is published on our website.

In the meantime, if you would like to discuss this matter further, please do not hesitate to contact me.

Yours sincerely

Jasmine Howard
FOI Case Officer
FOI Case Management Team
General Counsel
Transport for London

dangos adrannau a ddyfynnir

Dear Boyu,

 

TfL Ref: 1862-2122

 

Thank you for your request received by us on 10 November 2021 asking for
information about the rail electrification system for London underground,
plus associated images.

 

Your request has been considered in accordance with the requirements of
the Freedom of Information Act and our information access policy.  I can
confirm that we hold the information you require. You asked for:

 

the full explanation on the rail electrification system for London
underground and the mode of electrification for different lines.

 

We can advise that the lines are electrified with a four-rail Direct
Current (DC) system. The configuration and potential of the conductor
rails varies across the network. As of 2020, there are three different
conductor rail configurations:

 

The original configuration is nominally 630 V (voltage), with a −210 V
centre conductor rail and a +420 V outside conductor rail. This is the
default configuration wherever deep-level tube trains operate.

 

Beginning in 2016, sections of the sub-surface network were reconfigured
to a 750 V configuration (−250 V and +500 V rails). As of 2019, the entire
sub-surface network uses this configuration except for Uxbridge to
Finchley Road (via Harrow) as 1973 Stock and 1996 Stock (of the Piccadilly
and Jubilee lines respectively), share the railway.

 

In areas where London Underground and third rail rolling stock share
tracks, the centre conductor rail is electrically connected to the running
rails. This still results in a 750 V voltage but in a 0 V/+750 V
configuration. Lines configured in this manner include:

 

o Between Gunnersbury and Richmond on the District line, shared with the
London Overground between East Putney and Wimbledon on a section of
the District line that was transferred from British Rail

 

o Between Queen's Park and Harrow & Wealdstone on the Watford DC line,
served by the Bakerloo line and London Overground trains.

 

The four rail system was first used in the early twentieth century. The
isolated traction current return allowed a train's position to be detected
using DC track circuits, and reduced any earth leakage currents that could
affect service pipes, telephone cables, or cast iron tunnel liners.

 

The traction current has no direct earth point but there are two resistors
connected in series across the traction supply. The positive resistor is
twice as great as the negative resistor, since the positive rail carries
twice the voltage of the negative rail. The junction point of the
resistors is earthed, establishing the reference point between the
positive and negative rails by voltage division. The resistors are great
enough to prevent large currents flowing through the earthed
infrastructure.

 

Also, it will be great if you have data and images for the electrification
system

 

Please see the following link which provides a semi-geographical overview
of the London Underground network with the detailed track layout in place
at the time these images were produced at:

 

[1]https://www.whatdotheyknow.com/request/1...

 

In accordance with section 21 of the FOI Act, we are not obliged to supply
you with a copy of the requested information as it is already accessible
to you elsewhere.

 

If this is not the information you are looking for, or if you are unable
to access it for any reason, please do not hesitate to contact me.

 

Please see the attached information sheet for details of your right to
appeal as well as information on copyright and what to do if you would
like to re-use any of the information we have disclosed.

 

Yours sincerely

 

 

 

Jasmine Howard

FOI Case Officer

FOI Case Management Team

General Counsel

Transport for London

 

From: BOYU PAN <[2][FOI #805411 email]>

Sent: 10 November 2021 22:49

To: FOI <[3][email address]>

Subject: Freedom of Information request - About the technical information
and data on electrification system of London Underground

 

Dear Transport for London,

 

I wish to get the full explanation on the rail electrification system for
London underground and the mode of electrification for different lines.
Also, it will be great if you have data and images for the electrification
system.

 

Yours faithfully,

 

BOYU PAN

 

 

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References

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1. https://www.whatdotheyknow.com/request/1...
2. mailto:[FOI #805411 email]
3. mailto:[email address]
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