International and Indian Standards for Ring main Unit

Ring main units are integral parts of High voltage system.

These are used in HT system where there are different HT customers on same line. By using ring main unit these HT loads will be easily catered.

Ring main unit serves both purposes i.e. for supply to Transformers and also for protection of Transformers.

Ring main unit consists of following parts:-

1. Load break switch/ Circuit breaker

2. Earth switch

3. Isolators

Circuit breaker/Load break switch may be of Vaccum type of SF6 gas type.

Ring main units are usually maintenance free. Only concern is to look at SF6 gas indicator when there is gas at red indicator this means you doesn't operate the breaker otherwise explosion may takes place.

There are following codes and standards which are applicable on Ring main unit 

For Ring Main Units applicable Codes, Standards, rules, Acts:-

Standard or rule	Title
Indian Electricity rule	With latest Amendments
Indian Electricity act	2003
IS 3427	A.C. Metal Enclosed switchgear and control gear for rated voltages above 1 KV
IS 9920 Part 1,3 &4	High voltage switches above rated voltage 1 KV
IS 13118	General requirements of circuit breakers above rated voltage 1 KV
IS 3231	Electric relays for Power system protection
IEC 60265 part 1	High Voltage switches
IEC 60056	High voltage alternating current circuit breaker
IEC 60059	Preferred current ratings of high voltage switchgear
IEC 60185	Current Transformers
IEC 60694	Specifications of High voltage Switchgear
IEC 60298	A.C. Metal enclosed Switchgear
IEC 60129	A.C. Dis-connector and earth Switches
IEC 60529	Classification of degree of protection provided by enclosures
IS/IEC 62271-102 (2003)	High-Voltage Switchgear and Controlgear, Part 102: Alternating Current Disconnectors and Earthing Switches [ETD 8: High Voltage Switchgear and Controlgear]
IEC 60255	Electrical relays

Above list describes each and everything about Ring main units. These standards not only provides technical details during manufacturing but also provide details about how to ensure safety and protection system in HT switchgear.