Siemens Gas-Insulated Switchgear up to 550 kV, 63 kA, 5000 A Type 8DQ1
Siemens.com/energy
Leading worldwide due to innovative technology
The Siemens gas-insulated switchgear (GIS) is an extremely successful product concept. Since its introduction back in 1968, Siemens has installed more than 28,000 indoor and outdoor switchgear bays worldwide, and well over 300,000 bay-years of operation have been recorded.
Since 1974, Siemens has supplied gas-insulated substations for voltage levels of up to 420 kV. Continuous improvement has led to the current 8DQ1, suitable for a voltage range of up to 550 kV.
Intense research and development have resulted in the current generation of gas-insulated, metal-encapsulated switchgear, a world leader in terms of:
- Economic efficiency
- High reliability
- Safe encapsulation
- High degree of gastightness
- Long service life
- Low maintenance costs
- Easy access and ergonomic design
- High availability
- Reliable operation even under extreme environmental conditions
The 8DQ1 switchgear, designed for rated voltages up to 550 kV, meets modern requirements for performance and reliability.
Flexibility thanks to modular design
A fundamental feature of the gas-insulated switchgear is its high degree of flexibility provided by a modular system. Components are arranged in pressure-resistant, gastight enclosures according to their functions. All customary bus schemes can be implemented with a small number of active and passive modules.
The 8DQ1 switchgear (up to 550 kV) features a single-phase, metal-enclosed design that minimizes dielectric and dynamic loading. The encapsulation material is corrosion-resistant aluminum. O-ring seals, a proven construction principle since 1968, guarantee gastightness.
Coupling contacts absorb temperature-related length changes in conductors. The insulating and arc-quenching medium is sulfur hexafluoride (SF6). The extremely tight casing prevents environmental pollution. Static filters in the gas compartments absorb moisture or decomposition products. Rupture diaphragms prevent excessive pressure buildup, with diverter nozzles directing expelled gas safely.
Typical double busbar feeder
With only a few modules, all typical switching configurations can be implemented.
Components:
- Circuit-breaker interrupter unit
- Stored-energy spring mechanism
- Circuit-breaker control unit
- Busbar I
- Busbar disconnector I
- Busbar II
- Busbar disconnector II
- Work-in-progress earthing switch
- Work-in-progress earthing switch
- Outgoing-feeder disconnector
- Make-proof earthing switch (high-speed)
- Current transformer
- Voltage transformer
- Cable sealing end
Circuit-breaker module
The central element of a switchgear bay is the single-phase encapsulated circuit breaker, designed for single-pole automatic reclosure. It consists of an interrupter unit and a stored-energy spring mechanism.
The design is based on time-tested identical constructions used in air- and gas-insulated switching technology, ensuring high reliability.
Stored-energy spring mechanism
This mechanism provides the force to operate the circuit breaker. It features a compact, corrosion-free aluminum housing and a simple, reliable principle of operation. Both opening and closing springs are visible. The drive unit is separate from the SF6 compartment. Maintenance-free components and vibration-isolated latches enhance reliability.
Advantages:
- Identical construction principle for rated voltages from 72.5 to 550 kV
- Low operating energy
- Simple principle of operation
- Switching state controllable at all times
- Low maintenance, economical with a long service life
Interrupter unit and Arc-quenching principle
The interrupter unit operates using the dynamic self-compression principle, requiring minimal operating energy and reducing mechanical stress.
Current path
In the closed position, current flows through the main contacts. Arcing contacts are in parallel. During breaking, the main contacts open, and current commutates to the arcing contacts. An arc forms, compressing SF6 gas. This compressed gas flows through a heating volume and a nozzle to extinguish the arc.
Interruption of fault currents
For short-circuit currents, the arc heats the gas, increasing pressure. When current passes zero, the gas flows back through the nozzle to quench the arc. A valve prevents high-pressure gas from entering the compression volume, reducing the energy required from the operating mechanism.
Disconnecting switches
Disconnecting switches ensure a dielectrically safe gap between system parts at different potentials. Cast-resin bushings hold the contact system, with pressurized gas as the high-voltage insulating medium.
Up to two earthing switches can be installed simultaneously. Disconnecting switches can be built in separate gas compartments or combined with surrounding modules.
Earthing switches
Earthing switches connect de-energized live parts to the grounding system. Make-proof versions are used for inductive and capacitive currents. They are also used for measuring and testing protection relays.
The 8DQ1 switchgear features pin-type earthing switches. They can be integrated into common housings with disconnecting switches or installed separately. Make-proof earthing switches use a stored-energy spring mechanism.
Common features of disconnecting and earthing switches:
- Three poles are coupled mechanically and operated by a single motor drive.
- Alarm switches and ON/OFF indicators are directly connected to the drive shaft.
- Identical motor drives are used for both types of switches.
- Manual emergency operation is integrated.
- Enclosures can be fitted with inspection windows.
Instrument transformers
Current and voltage transformers are used for measuring and protection.
Current transformer
These are single-phase inductive types, often located on the outgoing side of the circuit breaker. The high-voltage conductor serves as the primary winding. The SF6 gas provides primary insulation.
Voltage transformer/RC-voltage divider
Each single-phase inductive voltage transformer is encapsulated in its own housing. Key components include the primary winding, secondary windings, and an iron core. Pressurized gas and film insulation provide high-voltage insulation.
Resistive-capacitive voltage dividers (RCVD) use oil-impregnated capacitive elements. They are ferroresonance-free and offer excellent transient characteristics, mapping high voltage linearly over a wide frequency range.
Surge arrester
Encapsulated surge arresters limit overvoltages. Their active parts are metal-oxide resistors with a non-linear current/voltage characteristic. They are typically flange-jointed to the switchgear via a gastight bushing.
Termination modules
Termination modules connect the gas-insulated switchgear to transformers, reactors, cables, or overhead lines, providing the transition from SF6 gas insulation to other media.
Transformer termination
Enables direct SF6/oil tube connection from the GIS to an oil-insulated transformer or reactor. Expansion joints absorb movements.
Cable termination
Connects the metal-enclosed GIS to high-voltage cables compliant with IEC 62271-209. Includes a connection flange for cable testing.
SF6/air termination
Connects the GIS to air-insulated components or overhead lines via a bushing (porcelain or composite insulator). This module combines an angle-type module with an SF6 bushing.
Extension and angle-type modules
These modules are used for connections within a bay and for conduit lead-outs, with shapes and numbers depending on the circuit and bay layout.
Busbar module
The 8DQ1 switchgear features a single-phase encapsulated passive busbar. Busbar disconnecting switches, sectionalizers, and earthing switches are housed in separate gas compartments. Expansion joints connect adjacent bays, accommodating movements.
Control and monitoring – a reliable and flexible control and protection system
Robust electrical components are used for control and monitoring. All necessary elements are incorporated locally in the high-voltage devices. Factory testing minimizes commissioning time and on-site failures.
Gas monitoring
Gastight partitions create separate gas compartments. Density monitors with red/green indicators provide alarm and blocking signals.
Reliable and flexible control and protection system
The control unit is housed in a local control cubicle for easy access. Feeder protection can optionally be included. Shielded cables and coded plugs ensure reliable cabling.
Siemens offers high-voltage switchgear with various digital control and protection systems. Standard interfaces allow connection of:
- Conventional control systems
- Digital control systems with user-friendly bay controllers
- Intelligent, fully networked digital control and protection systems
Siemens provides customized concepts from a single source.
Transport, installation, commissioning, maintenance
Transport
Switchgear assemblies are split into optimized shipping units for easy handling and transport. All units are tested before dispatch. Operating-mechanism attachments are preset at the factory. Flanges are protected against corrosion.
On-site installation
The modular design and few shipping units reduce installation time and effort. Detailed instructions and special tools allow easy and rapid installation, even by customer personnel under Siemens supervision.
Commissioning
On-site testing of switching devices and electrical circuits ensures proper function. Flanges are checked for tightness. High-voltage tests verify installation work. All tests comply with IEC standards.
Maintenance
The gas-insulated switchgear is designed for optimum balance in design, materials, and maintenance. The hermetically sealed enclosure requires minimal maintenance. Visual inspections are recommended, with the first major inspection due after 25 years.
Quality assurance
A consistent quality management system ensures high-quality gas-insulated switchgear. The system has been certified according to CSA Z299, DIN EN ISO 9001, and DIN EN ISO 14001. Test labs are accredited according to ISO/IEC 17025.
Quality and environmental protection systems cover all product life cycles. Regular reviews and audits ensure system efficiency and continuous improvement.
Special "clean" areas in production and comprehensive inspections contribute to high quality. Mechanical and high-voltage tests verify compliance with standards. Suitable packing ensures safe arrival.
Switchgear bay examples
The modular system allows for customary circuit arrangements and individual solutions for specific building dimensions and system extensions.
Double busbar arrangement
Bus coupling arrangement
Double busbar arrangement with transfer bus
Double busbar arrangement with bypass
1½ circuit-breaker arrangement
Technical data
| Switchgear type | 8DQ1 |
|---|---|
| Rated voltage | up to 550 kV |
| Rated frequency | 50/60 Hz |
| Rated short-duration power-frequency withstand voltage (1 min) | up to 740 kV |
| Rated lightning impulse withstand voltage (1.2 / 50 µs) | up to 1,550 kV |
| Rated switching impulse withstand voltage (250 / 2,500 μς) | up to 1,175 kV |
| Rated normal current busbar | up to 5,000 A |
| Rated normal current feeder | up to 5,000 A |
| Rated short-circuit breaking current (< 2 cycles) | up to 63 kA |
| Rated peak withstand current | up to 170 kA |
| Rated short-time withstand current (up to 3 s) | up to 63 kA |
| Leakage rate per year and gas compartment (type-tested) | < 0.1 % |
| Driving mechanism of circuit breaker | stored-energy spring |
| Rated operating sequence | O-0.3 s-CO-3 min-CO / CO-15 s-CO |
| Bay width | 3,600 mm |
| Bay height, depth (depending on bay arrangement) | 4,800 mm x 10,000 mm |
| Bay weight (depending on bay arrangement) | 21 t |
| Ambient temperature range | -25 °C up to +55 °C |
| Installation | indoor |
| First major inspection | > 25 years |
| Expected lifetime | > 50 years |
| Standards | IEC / IEEE / GOST |
Other values on request.
