Each circuit breaker bay for gas-insulated switchgear includes the full complement of isolator switches, grounding switches (regular or proven), instrument transform-ers, control and protection equipment, in-terlocking and monitoring facilities, com-monly used for this type of installation (See chapter GIS, page 1/8 and following).
Circuit breakers for air-insulated switch-gear are individual components and are assembled together with all individual electrical and mechanical components of an AIS installation on site.
All Siemens circuit breaker types, whether air- or gas-insulated, consist of the same components of a parts family, i.e.:
■Interrupter unit
■Operating mechanism
■Sealing system
■Operating rod
■Control elements.
SF6-insulated circuit breakers
Control elements
Interrupter units
Operating mechanism
Sealing systems
Parts family
Fig. 38: Circuit breaker parts family
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Circuit Breakers for 72 kV up to 800 kV
The blast cylinder (4) encloses the arc-quenching arrangement like a pressure chamber. The compressed SF6 flows ra-dially into the break by the shortest route and is discharged axially through the noz-zles (6). After arc extinction, the contact tube (3) moves into the open position.
In the final position, handling of test volt-ages in accordance with IEC and ANSI is fully guaranteed, even after a number of short-circuit switching operations.
Major features
■Erosion-resistant graphite nozzles
■Consistently high dielectric strength
■Consistent quenching capability across the entire performance range
■High number of short-circuit breaking operations
■High levels of availability
■Long maintenance intervals.
The operating mechanism
The operating mechanism is a central module of the high-voltage circuit breakers.
Two different mechanism families are avail-able for Siemens circuit breakers:
■Electrohydraulic mechanism for all AIS and GIS types
■Spring-stored energy mechanism for AIS types up to 170 kV.
The electrohydraulic operating mechanism All hydraulically operated Siemens circuit breakers have a uniform operating mecha-nism concept, whether for 72 kV circuit breakers with one interrupter unit per pole or breakers from the 800 kV level with four interrupter units per pole. Identical operat-ing mechanisms (modules) are used for single or triple-pole switching of outdoor circuit breakers.
The electrohydraulic operating mecha-nisms have proved their worth all over the world. The power reserves are ample, the switching speed is high and the storage capacity substantial. The working capacity is indicated by the permanent self-monitor-ing system.
The interrupter unit Current-path assembly
The conducting path is made up of the terminal plates (1 and 7), the fixed tubes (2) and the spring-loaded contact fingers arranged in a ring in the moving contact tube (3).
Arc-quenching assembly
The fixed tubes (2) are connected by the contact tube (3) when the breaker is closed. The contact tube (3) is rigidly cou-pled to the blast cylinder (4), the two to-gether with a fixed annular piston (5) in between forming the moving part of the break chamber. The moving part is driven by an operating rod (8) to the effect that the SF6 pressure between the piston (5) and the blast cylinder (4) increases.
When the contacts separate, the moving contact tube (3), which acts as a shutoff valve, releases the SF6. An arc is drawn between one nozzle (6) and the contact tube (3). It is driven in a matter of millisec-onds between the nozzles (6) by the gas jet and its own electrodynamic forces and is safely extinguished.
1
2 3 6
4 5 2 8
7
Arc Breaker in
closed position
Precompression Gas flow during arc quenching
Breaker in open position
Upper terminal plate
Fixed tubes Moving contact tube
Blast cylinder Blast piston Arc-quenching nozzles Lower terminal plate
Operating rod 1
2 3 4 5 6 7 8
Fig. 39: The interrupter unit
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Circuit Breakers for 72 kV up to 800 kV
The force required to move the piston and piston rod is provided by differential oil pressure inside a sealed system. A hydrau-lic storage cylinder filled with compressed nitrogen provides the necessary energy.
Electromagnetic valves control the oil flow between the high- and low-pressure side in the form of a closed circuit.
Main features:
■Plenty of operating energy
■Long switching sequences
■Reliable check of energy reserves at any time
■Switching positions are reliably maintained, even when the auxiliary supply fails
■Excessive strong foundations
■Low-noise switching
■No oil-leakage and consequently environmentally compatible
■Maintenancefree.
Description of function
■Closing:
The hydraulic valve is opened by elec-tromagnetic means. Pressure from the hydraulic storage cylinder is thereby applied to the piston with two different surface areas. The breaker is closed via couplers and operating rods moved by the force which acts on the larger sur-face of the piston. The operating mech-anism is designed to ensure that, in the event of a pressure loss, the breaker remains in the particular position.
■Tripping:
The hydraulic valve is changed over electromagnetically, thus relieving the larger piston surface of pressure and causing the piston to move onto the OFF position. The breaker is ready for instant operation because the smaller piston surface is under constant pres-sure. Two electrically separate tripping circuits are available for changing the valve over for tripping.
M
P P
M
Oil tank Hydraulic storage
cylinder
Operating cylinder
Releases Operating piston
Pilot control
On Off
N2
Main valve Auxiliary
switch Monitoring unit
and hydraulic
pump with motor P P
Fig. 43: Schematic diagram of a Q-range operating mechanism Fig. 40: Operating unit of the Q-range AIS circuit
breakers
Fig. 42: Operating cylinder with valve block and magnetic releases
Fig. 41: Q-range operating unit for GIS circuit breaker 8DN9
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Circuit Breakers for 72 kV up to 800 kV
The spring-stored energy operating mechanism
Optional to the hydraulic operating mecha-nism, Siemens circuit breakers for voltages up to 170 kV can be equipped with spring-stored energy operating mechanisms.
These drives are based on the same prin-ciple, which has been proving its worth in Siemens low and medium voltage circuit breakers for decades. The design is simple and robust with few moving parts and a vibration-isolated latch system of highest reliability. All components of the operating mechanism, the control and monitoring equipment and all terminal blocks are arranged compact and yet clear in one cabinet.
Depending on the design of the operat-ing mechanism, the energy required for switching is provided by individual com-pression springs (i.e. one per pole) or by springs that function jointly on a triple-pole basis.
The principle of the operating mechanism with charging gear and latching is identical on all types. The differences between mechanism types are in the number, size and arrangement of the opening and clos-ing sprclos-ings.
Major features at a glance
■Uncomplicated, robust construction with few moving parts
■Maintenancefree
■Vibration-isolated latches
■Load-free uncoupling of charging mechanism
■Ease of access
■10,000 operating cycles
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Corner gears Coupling linkage Operating rod Closing release Cam plate Charging shaft Closing spring connecting rod Closing spring
Hand-wound mechanism Charging mechanism Roller level
Closing damper Operating shaft Opening damper Opening release Opening spring connecting rod Mechanism housing Opening spring 1
2
3
4
5 6 7
8
18 17 16 15 14 13 12 11 10 9
Fig. 44
Fig. 45: Combined operating mechanism and monitoring cabinet
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