- Frequency of Fault Occurrence in Different Links of a Power System
- Fault in Overhead Lines
|Sr. No.||Type of Short Circuit Fault||Percentage Occurrence|
|1.||Single phase to ground (L-G)||70|
|2.||Phase to Phase fault (L-L)||15|
|3.||Two phases to ground (L-L-G)||10|
|4.||Phase to phase and third phase to ground||2 or 3|
|5.||All the three phases to ground||2 or 3|
|6.||All the three phases shorted||2 or 3|
- The ratio of minimum fusing current and the current rating of fusing element is known as fusing factor.
- Fusing factor always greater than unity.
Types of Fuse
- Rewirable fuse (Kit Kat fuse), Standard ratings of fuse are 6, 16, 32, 63 and 100A.
- Cartridge Fuse
- HRC Fuse
- Switch Fuse (The ratings of switch of fuse units are in the range of 30, 60, 100, 200, 400, 600 and 800 Amperes).
- A circuit breaker is a device, which can (i) make or break a circuit either manually or by the remote control under normal conditions. (ii) Break a circuit automatically under fault conditions. (iii) make a circuit either manually or by remote control under fault conditions.
Classifications of Circuit Breaker
Oil Circuit Breaker,
- This type of circuit breaker employs some insulating oil (e.g. transformer oil) for arc extinction.
- Oil circuit breakers are divided into two types (1) bulk oil circuit breaker (2) Low oil circuit breaker
- Bulk oil circuit breaker has two types (a) plain break oil circuit breakers (b) Arc control oil circuit breakers
- Plain break oil circuit breakers are used for low capacity installation for voltage not exceeding 11KV.
Air Blast circuit Breaker,
- In which high pressure air-blast is used for extinguishing the arc.
- Air blast circuit breaker used upto voltages of 15KV and capacity of 2,500MVA.
Sulphur Hexafluoride (SF6) Circuit Breaker
- Sulphur Hexafluoride (SF6) gas is used for arc extinction.
- Sulphur Hexafluoride (SF6) gas has electronegativity property.
- Sulphur Hexafluoride (SF6) circuit breaker can be used from 3.3KV to 760KV.
- Sulphur Hexafluoride (SF6) circuit breakers require maintenance once in four to ten year.
- 145KV SF6 Circuit breaker need only about 30 Kg of SF6 gas for first filling and no replacement is required for about 5 Years.
Vacuum Circuit Breaker
- In this type of circuit breaker vacuum is used for arc extinction.