What voltage is used on the London Underground?

Question

What voltage is used on the London Underground?

Answer 1

630 V DC

(+420 V DC on one rail and -210 V DCon the other, creating an overall Potential Difference of 630 V DC)

Answer 2

Total electricity supplied 1091 (gigawatt hours)

Substations output voltage

630v DC

Nominal track voltage

630v DC

Answer 3

44,000 volts

Answer 4

LUL use a four rail system to run trains. The two running rails are used for signalling and as a traction earth. The two conductor rails have a nominal pole to pole voltage of 630v DC. This voltage is then referenced to earth by the introduction of resistor banks (known as bleed resistors) for earth fault detection purposes only. Otherwise it is an earth free system.

The earth reference is Pos to earth +420v, Neg to earth -210v. Both rails are equally dangerous and can kill.

The advantage of this system is that you can continue to run trains under earth fault conditions. Should say a tin can get wedged under say the pos rail then an earth fault would be created. The positive to earth voltage would be 0v. The negative to earth voltage would be -630v. The train would still see the pole to pole voltage of 630v and operate normally.

On the mainline railways an earth fault on the positive rail would cause the circuit breaker to trip and the supply would be cut.

In addition to the above most track sections are fed from two sub-stations (one at each end). Should there be a supply problem at one sub-station then the other sub-station can still feed the section of track and trains will continue to run.

If one of the electric rails fails for any reason, all 630 volts will be transferred to the other rail, with no effect on the running of the train – and so no delays for passengers. On the main line a power failure to its single ‘traction’ rail would simply stop the train.

Answer 5

.as much as they can afford, get, and have.