scope:

This standard applies to all nominal 630V DC and 750V DC circuits derived from traction Substations including depots and sidings. The DC Traction Supply system nominal voltage shall be 630V or 750V as defined in LU Standard S1910 for the various Underground Lines, which includes the range of operating voltages to be expected. For the purposes of this standard, 'DC circuits' and 'DC protection' systems refer to these nominal voltages throughout this standard.

This standard specifically excludes any requirements for protective equipment on-board rolling stock. Non traction DC equipment is excluded other than the supply cable from traction substation DC switchboards.

This standard includes the requirements for:

a) protection systems

b) protection relays

c) direct acting protective devices

d) electronic protection within circuit breakers; including Moulded Case Circuit Breaker (MCCB)

e) fuses

f) protection current and voltage transformers

g) transducers

h) protection communications and intertripping.

This standard is applicable to all suppliers of new and modified DC protection systems.

This standard shall be read in conjunction with S1940.

Purpose

This standard:

a) describes the minimum performance levels required of electrical protection on London Underground's (LU's) Direct Current (DC) power distribution systems;

b) gives details of protection systems in terms of design principles and methods

c) provides the underlying principles applicable to protection systems in achieving minimum levels of safety, supply continuity and stability for DC power systems on the LU (DC) Power Distribution Network.