NR NR/L2/ELP/27722 ISSUE 1 PDF

The system to be protected

The scope of this standard is to define the principles for the design of protection systems and the requirements for the protection scheme concept for ac electrified railways (electric traction systems).

This standard applies to protection systems for either of:

a. new electric traction systems;

b. changes to existing electric traction systems, where advised by the Regional Engineer (E&P) 

Note: the designer should advise the Regional Engineer (E&P) where the changes affect the operation or coordination of the existing protection scheme.

The system to be protected within the scope of this standard is the electric traction system and its interfaces as shown in figure 1.

The electric traction system and its interfaces are conceptually depicted in figure 1 as a classic 1x25 kV system. The scope of this NR/L2/ELP/27722 standard applies to other electric traction systems such as 2x25 kV autotransformer electric traction systems.

Figure 1 – Electric traction system and its interfaces 

{based on Figure 1, BS EN 50633:2016} 

The electric traction system that the protection system applies to is comprised of: 

a) incoming feeder circuit-breakers; 

b) traction substation busbar(s) and bus-section circuit-breaker; 

c) outgoing track feeder circuit-breakers or disconnectors; 

d) outgoing autotransformer feeder circuit-breakers or disconnectors; 

e) along-track-feeders (e.g. interconnecting feeders, independent feeders or bare feeders); 

f) contact line system; 

g) autotransformers; 

h) traction return circuit; 

The electric traction system has interfaces to other parts of the railway system. 

System interfaces

General 

Interfaces with the electric traction system include interfaces with the: 

a) traction supply; 

b) rolling stock; 

c) electrical installations fed by the electric traction system, such as PSPs; 

d) adjacent electric traction systems.

Traction supply 

The protection of the traction supply substation and upstream transmission or distribution system are covered by the protection principles and system of the transmission or distribution system operator. The interfaces take into account the following aspects: 

a) protection coordination; 

b) communication; 

c) reclosure; 

d) direction of power flow (consumption and regeneration). 

Rolling stock 

The traction unit circuit-breaker on the rolling stock is the interface between the electric traction system and the rolling stock. This means that the current carrying collector is considered as being part of the system to be protected. 

Protection of electric rolling stock against faults within the rolling stock itself, is not the primary role of the protection system of the electric traction system. The protection system of the electric traction system can, however, provide some degree of remote backup protection for such faults.

Electrical installations fed by the electric traction system 

Electric installations not directly related to traction power e.g. auxiliary power supplies, are not part of the electric traction system, although they may be fed by the electric traction system. 

The disconnecting device (e.g. switch, fuse, circuit-breaker, disconnector) of the electrical installations fed by the contact line or the traction substation is the interface between these two systems. 

The bonding connection between the electrical installation and the traction return circuit can also be regarded as being part of the interface between the two systems. 

In accordance with BS EN 50633, the protection system of the electric traction system shall be coordinated with the protection of the electrical installation. However, detection of internal faults within the electrical installations fed by the electric traction system is not the primary function of the electric traction system’s protection system. The protection system of the electric traction system can, provide some degree of remote backup protection for such faults.

Adjacent electric traction systems 

Other adjacent electric traction system may be two adjacent electric traction systems that are both: 

a) operated by Network Rail (with different protection systems);or 

b) one operated by Network Rail and the other operated by a separate entity. 

The disconnector is normally the interface between the two adjacent electric traction systems.

Exclusions from scope 

The scope of this standard, does not directly apply to: 

a) upstream transmission or distribution installations within the distribution/ transmission system operator network itself – other than the protection coordination between the upstream protection system and the protection system of the ac electric traction system; 

b) AC/DC interfaces; 

c) the internal and integral protection system forming part of an SFC (with the exception of the inherent backup protection of the supply substation); 

d) the detection of internal faults within the traction unit itself (with the exception of the inherent backup protection of the electric traction system); 

e) the detection of internal faults within non-traction electrical installations fed by the electric traction system (with the exception of the inherent backup protection of the electric traction system); 

f) other subsystems such as signalling or communication systems that can be influenced by the electric traction system; 

g) the methods of maintenance or work instructions for the protection system; 

h) operational procedures. 

The protection systems of the electric traction system and the upstream supply system may provide backup protection and will need to be coordinated. 

Purpose 

The purpose of this standard is to define the fundamental design principles that support the design and development of electrical protection systems provided for ac electric traction systems. 

This standard is aligned with and supports the requirements as obliged in: 

a) National Technical Specification Notice – Energy; 

b) BS EN 50633; 

c) BS EN 50122-1; 

d) BS EN 50388; 

e) ENA P24 ( and ENA EREC P24 Issue 2, 2020, Final v3.1). 

This standard, therefore, supports compliance with the Health and Safety at Work Act 1974 and the Electricity at Work Regulations 1989. 

This standard provides a common strategy to demonstrate compliance and support the optimisation of the design for railway subsystems in line with the requirements of: 

NR/L2/ELP/27275 ‘A.C. Electric Traction Energy Subsystem – System Design Principles’ and NR/L2/ELP/21085 ‘Earthing and Bonding on A.C. Electrified Railways’ 

It is not the focus of this NR/L2/ELP/27722 standard to reiterate legislation and governing standards.