O&M of HV Switchgear Types of Operating Principles
Types of Operating Principles
Bulk Oil
Minimum or Small Oil
SF6
Vacuum
Bulk Oil Circuit Breaker
Three interrupter poles housed in a common metal tank filled with insulating oil.
Commonly called the DEAD TANK design.
Bulky, thick steel walls provided to withstand the tremendous gas and oil pressure created within the arc chamber by the arc during short circuit.
The interrupter, solely depends on the turbulent flow of oil and gas bubbes to quench the arc, is known as a “Plain break Interrupter”.
Bulk Oil Circuit Breaker
The insulating oil
Helps to cool and quench the arc
Insulates live parts from the tank
An example:
(cont’d)
Reyrolle LMT2 6.6kV switchgear (4 panels) would need 1 drum of oil for replacement of oil.
The Circuit Breaker can be supplied with solenoid (eg. Reyrolle A5T) or spring mechanism for closing and tripping.
Pictures of Reyrolle C-series BOV and Reyrolle LMT2 BOV
Ring Main Unit – Typical Features
Normal Current – 800A, voltage 22kV & below
Available in bulk oil, vacuum and SF6 versions
No relay protection, only earth fault indicator
Single stroke manual closing; available also in motor charged version
“Idiot proof” interlocks
Usually dead-tank, sealed and suitable for outdoor installation.
Ring Main Unit –
Load Break Switch
Features
Quick-Acting-Fault-Making Switch
No interrupter
Capabilities
Making: Up to rated short circuit making current
Breaking: Only rated normal current
Ring Main Unit – Fuse Switch or Switch Fuse
Features
Quick-Acting-Fault-Making Switch
Current limiting fuse link and isolator
Capabilities
Making: Up to rated short circuit making current
Breaking: Up to fuse rating
Small Oil Volume (SOV) Circuit Breaker
Oil is purely used for arc quenching and NOT for insulation
Insulation is provided by the dielectric material of the pole.
In general, replacement of oil in SOV circuit breaker is recommended after every fault interruption.
Small Oil Volume (SOV) Circuit Breaker
During the opening operation, the piston assembly effectively causes oil rush into the arc quenching device to expedite arc extinction
Example: CalorEmag ZE4
Properties of SF6 (Sulphur Hexafluoride)
Colourless, odourless, non-toxic, non-flammable
Five times heavier than air
Chemically inert up to 150 degC.
Decomposes into SF4, SF2, S2, F2, S, F etc at high temperature
No carbon component
Good di-electric strength, good arc quenching medium
Types of SF6 Circuit Breaker
Single Pressure Puffer
Double Pressure Puffer
Uniform pressure in SF6 gas compartment; gas compressed and discharged through puffer during circuit interruption.
High and Low pressure SF6 gas compartments; high pressure gas discharged through puffer into low pressure region during circuit interruption.
Rotating Arc Quencher
Magnetic coil assists quenching of arc during
Single Pressure Puffer
Types of SF6 Circuit Breaker
Construction of SF6 circuit breakers of late, adopt the same structure of a small oil volume circuit breaker in that the three interrupter poles are housed in insulated “live” poles. Eg Y-SF6 22kV circuit breaker
The poles are filled with pressurised SF6 (1-5 bars) supplied from a common reservoir Any gas leakage can be monitored through a pressure gauge.
Vacuum Circuit Breaker
Vacuum interrupters employ no insulant like oil or gas in its arc quenching device.
No maintenance
Require relatively smaller mechanical energy for contact closing and opening.
Interrupting device:
A pair of flat contacts housed in a completely sealed bottle kept at a pressure of 10-3 mm of mercury. With absence of any conducting material, contact gap kept as small as 15mm.
Vacuum Circuit Breaker
Arc extinction: After a natural current zero, the remaining metal vapour condenses on the shields of the vacuum bottle and the dielectric strength builds up rapidly across the parted contacts to prevent a RESTRIKE. The uniquely high dielectric strength of vacuum ensures that the current is almost always interrupted on the first current zero encountered. Result: CURRENT CHOPPING. If improper control => OVERVOLTAGE (2 – 3 times normal voltage) OR cause damage to transformer
Vacuum Circuit Breaker
Advantage as compared to other circuit breakers:
Very short contact travel Elimination of clumsy drive rod and piston system
Movement of the contact within the bottle is permitted by the use of stainless steel bellows at the base of the bottle.
Size of vacuum bottle is determined by external factors:
Requirements on creepage clearance
Basic Impulse Level
Gas Insulated Switchgear
IEC 517 Metal enclosed switchgear in which the insulation is obtained, at least partially, by an insulating gas other than air at atmospheric pressure.
Features
Constant environment
Filled with SF6 gas at 1-1.5 bars
Vacuum interrupter
Metal-clad or metal enclosed
Compact
Gas Insulated Switchgear Problem #1
Compact CT Chamber Switchgear can be compact because it is designed with static relay protection system in mind – smaller relay mounting less CT burden requirements and smaller size & weight o CT. With the use of electromechanical relays for distribution switchgear, the size of Current Transformer will definitely be large. An example can be found in Siemens 22kV GIS
Gas Insulated Switchgear Problem #2
Compact cable chamber and special terminations Switchgear are all designed with pre-moulded plug-in type of cable termination. As termination plug is short, its reliability depends very much on the care exercised by the jointers in adhering to the correct dimensions and cleanliness of the terminations. Also the switchgear is designed for single core cable system. As such, termination of cable plug is more difficult for our three-core cable system.
Gas Insulated Switchgear Operating Mechanisms
Manual- or motor-charged spring operating mechanisms (VCB)
Manual or electrical operating system (VCB) Open/Close circuit breaker at high speed
CB ON
CB OFF
Isolator OFF
Ready-to-
Earthed ON
Gas Insulated Switchgear Operating Mechanisms
3PDS (Three-position disconnector system with closed/ open/earthing positions) is operated manually (for Meiden GIS) or electrically (for Siemens GIS) 8 Three-position switch Switching positions -a. Closed b. Opened c. Ready-to-earth Siemens GIS
Perform status indications.
Gas Insulated Switchgear Construction
Barrel Type
Single phase encapsuated
No possibility of phase to phase fault
More O-ring seals
Drum & Cubicle Type
3 phases encapsualted
Phase to phase fault possible
Less compartment, less possibility of leaks
Less space of terminating cables
Barrel type
