System Listings

HV Switchgear & Equipment

System Overview

High Voltage (HV) switchgear is equipment that is used on the HV side of the supply or substation transformer serving a site.

HV supplies are used extensively in the supply industry as the principle means to distribute electricity due mainly to the fact that losses are minimised and cables are smaller that they would be at Low Voltage.

There are international voltage definitions which technically define 11kV (the most common voltage used for local HV distribution) as medium voltage. However, in the UK when engineers say "HV" they usually mean 11kV

HV distribution & control as a vast topic and further information and learning resources can be obtained from the South Bank University.

Systems Available and Applications

As far as the building services designer is concerned it is usually only necessary to be fully conversant with the following types of HV equipment. This is because the equipment may come as part of a packaged substation, or may need specification by the premises designers/users for technical reasons.

Ring Main Units - Self contained devices with two open ring isolators and an integral circuit breaker. Commonly used to serve a transformer. These can be free standing or attached to a Transformer in a packaged sub station.
Circuit Breakers - These are complex protection devices which interrupt faults (including short circuits) at High Voltages. A system of protection relays will detect a fault using current transformers and related equipment. Once a fault is detected, the circuit breaker contacts are opened, hence interrupting the fault.
These days there are two common types of circuit breaker - Vacuum and Sulphur Hexafluoride (SF6). These are discussed at greater length elsewhere on this server.
Transformers - A transformer essentially converts one voltage to another. The usual ratio for a commercial building is 11,000v down to 415v. The transformer may be located internally or externally. It may also form part of a packaged substation.
Packaged Substation - A composite unit comprising HV circuit breakers (or an RMU), one or more transformers and LV switchgear. Commonly used throughout the industry in private substations.

Other equipment and more complex variations of the above would normally be designed and specified by the parties responsible for the HV network.

View of a typical packaged substation

Legislation & Guidelines

There are numerous items of legislation relating to the design, installation and maintenance of HV switchgear & equipment.

British Standards.

Also refer to The British Standards Institution

BS 4752:1977 "Circuit Breakers". This covers the manufacture and application of Circuit Breakers for use with voltages up to and including 1000V a.c and 1200V d.c. (Supersedes BS862:1939 & BS936:1960)
BS 3659:1963 "Heavy Duty Air Breaker Systems for AC Systems". This covers specialised HV Air Circuit Breakers which are rarely if ever used at 11kV.
BS 6878:1988 "Specification for high-voltage switchgear and controlgear for industrial use" Cast aluminium alloy enclosures for gas-filled high-voltage switchgear and controlgear
BS 6626:1985: "Code of practice for maintenance of electrical switchgear and controlgear for voltages above l kV and up to and including 36 kV". Procedures for principal components and guidance on replacement parts, precautions to secure safety of personnel and to minimise hazards to plant.

Combined Standards

BS EN 60694:1997 "Common specifications for high-voltage switchgear and controlgear standards". Gives specifications covering ratings, design and construction type tests, routine tests for indoor and ou...

BS EN 60517:1997 "Gas-insulated metal-enclosed switchgear for rated voltages of 72.5 kV and above" Requirements for indoor or outdoor switchgear utilising gas other than air at atmospheric pressure

International Standards