Siemens 8DN8, 8DN9 and 8DQ1 GIS Substation

Short answer

The 8DN8 is the Siemens Energy gas-insulated switchgear (GIS) for high voltage, with catalog ratings up to 145 kV and 170 kV. The family continues with the 8DN9 up to 245 kV and the 8DQ1 up to 550 kV, and is completed by the 8VN1 Blue GIS, which uses clean air and vacuum switching. They are used where space is short: cities, industrial plants, power stations and transmission substations.

What it is and where it is used

The Siemens 8DN8 GIS is a gas-insulated switchgear from Siemens Energy, the company that since 2020 has brought together the energy business formerly part of Siemens AG. Alongside the 8DN8 are the 8DN9, for 245 kV, and the 8DQ1, for 420 and 550 kV. Recent projects also feature the 8VN1 Blue GIS, which uses no SF6. All of them combine circuit breaker, disconnectors, earthing switches, instrument transformers and busbars inside metal enclosures filled with pressurized gas.

They are installed where space comes first: urban substations, power stations, industrial plants, mining, coastal or polluted areas, and extensions of existing substations. For the general concept of this technology, see GIS substation.

Variants: 8DN8, 8DN9, 8DQ1 and 8VN1 Blue GIS

Model	Application	Main difference
8DN8 (up to 145 kV)	High voltage, indoor or outdoor	Up to 40 kA short-circuit and 3,150 A in feeders, per the data sheet
8DN8 (up to 170 kV)	High voltage, indoor or outdoor	Up to 63 kA and up to 4,000 A in feeders
8DN9	Up to 245 kV	Next step of the 8D series in SF6
8DQ1	245, 420 and 550 kV	GIS for transmission and extra-high voltage; up to 63 kA at 550 kV
8VN1 Blue GIS	Up to 145 kV	Clean-air insulation and vacuum switching, no fluorinated gases

Siemens Energy also states that its DC GIS is based on the 8DQ1 technology and that the 8VM3, designed for wind turbines, is derived from the 8DN8 design. The manufacturer’s medium-voltage switchgear is outside the scope of this sheet.

Main features

Circuit breaker with spring-operated mechanism and an auto-reclose operating sequence, with interrupting times below three cycles according to the 8DN8 data sheet.
Separate gas compartments, each with its own density supervision. Siemens Energy declares an annual leakage rate per compartment below 0.1% in type tests. See SF6 density monitor.
Service life and maintenance: the data sheet speaks of more than 25 years until the first major inspection and more than 50 years of expected life.
Local control cabinet built into the GIS or separate, with conventional control or a digital bay controller, and options for density sensors, breaker monitoring and controlled switching (point-on-wave).
Instrument transformers, conventional or low-power (LPIT), which Siemens Energy also offers for these GIS.
Standards: IEC and IEEE, with the IEC 62271 series as the reference for high-voltage switchgear.

The pressures and compartments of a GIS are explained in GIS pressures and gas compartments, the internal fault in internal fault in a GIS and arc test, and the interfaces with cables and transformers in GIS interfaces with cables and transformers.

Construction and data from the 8DN8 series brochure

The German-language brochure «Gasisolierte Schaltanlagen, Baureihe 8DN8, bis 170 kV, 63 kA, 4000 A» (Siemens AG, Energy Sector, 2011, order no. E50001-G620-A122-V1) describes the construction in more detail than the commercial data sheets. It is a 2011 document: use it to understand the design and confirm the project values with Siemens Energy.

Technical data it publishes, for rated voltage levels of 72.5, 145 and 170 kV:

Item	72.5 kV	145 kV	170 kV
Power-frequency withstand voltage (1 min)	140 kV	275 kV	325 kV
Lightning impulse withstand voltage (1.2/50 µs)	325 kV	650 kV	750 kV
Rated current, busbars and feeder	2500 A	3150 A	4000 A
Short-circuit breaking current	31.5 kA	40 kA	63 kA
Rated peak withstand current	85 kA	108 kA	170 kA

For all levels it gives bay widths of 650, 800, 1000 and 1200 mm and a frequency of 50 or 60 Hz. It gives the rated operating sequence O-0.3 s-CO-3 min-CO or CO-15 s-CO and a DC auxiliary supply of 48 to 250 V. The ambient temperature runs from -30 to +40 °C, the expected life is more than 50 years and the standards are IEC, IEEE and GOST. The declared leakage rate is 0.5% per year per compartment in the routine test and 0.1% in the type test. The brochure makes clear that other values are available on request.

How it is built:

Three-phase enclosure of cast aluminum, with flanges at every module joint and O-ring seals. The joints have sliding contacts that absorb the thermal expansion of the conductors, and gas-tight assembly covers.
Gas compartments separated by insulating barrier bushings, each with its own density supervision. Each compartment carries static filters that retain moisture and decomposition products, and rupture discs with a deflector that direct the gas outlet away from personnel if the pressure rises above the permitted level.
Self-compression (auto-puffer) breaker: on opening, the main contact separates first and the current continues through the arcing contact, which protects the main contacts. The gas compression comes from the movement of the cylinder and, at high fault currents, from the heating of the gas by the arc itself. That is why the spring mechanism needs little energy. The brochure states that the mechanism can be three-pole or single-pole operated; the single-pole version allows single-pole opening and auto-reclosing.
Spring mechanism with the closing and opening springs visible, separate from the SF6 spaces. It holds its position if the auxiliary supply fails and allows opening regardless of the state of the closing spring.
Three-position device that combines disconnector and earthing switch: the pivot connects the conductor either to the disconnector blade or to the earthing contact, so the two functions are mechanically interlocked with each other. There is a third, neutral position with both open. The three poles move together with a motor, with manual emergency operation and optional viewing windows to see the position of the three phases. The earthing contact is brought out insulated from the enclosure for testing.
Fast-acting earthing switch of the pivot type, with a motor-charged spring, optional at the feeder.
Instrument transformers: the current transformer is of the conventional inductive type, with the high-voltage conductor as primary and independent cores, and is preferably placed right after the breaker. The voltage transformer is foreseen on the busbars and at the feeder, and there is a «Power VT» version designed to apply test voltage on site throughout the life of the GIS, for example after an extension. Resistive-capacitive dividers and sensors are also available for digital equipment.
Connection modules: to cable (plug-in or conventional), to overhead line through air/SF6 bushings, and to a transformer or reactor with a direct connection through a bushing sealed against oil and gas pressure, with compensators for thermal movement and differential settlement of the foundations. The cable terminations can be disconnected internally for the high-voltage test. See on-site withstand voltage test and partial discharge test.

Transport, assembly and maintenance according to the brochure: the bays leave the factory assembled and tested, with up to six single bays or three double bays per shipping unit, and travel in standard containers or by truck. On site, what remains is the wiring between bays, the connection to the control system, the leak test of the whole installation and the equipment tests per IEC with a test report. The manufacturer describes the GIS as virtually maintenance-free under normal conditions and recommends a first inspection after 25 years. For gas monitoring see SF6 gas analysis, and for verifying timing and contacts see the circuit breaker timing test and the contact resistance test.

Configurations it mentions: single busbar, double busbar, ring, H and 1½ breaker, plus a mobile solution in an H configuration. At 145 kV, the brochure states that the footprint today is about a quarter of that of the first designs from 1968.

Communications and integration

The GIS is not an IED in itself, but its local control cabinet does integrate into the automation system. When it carries a digital bay controller, the positions, gas alarms and lockouts reach SCADA over IEC 61850 or another protocol of the system, and the density and partial discharge monitoring can send their alarms over the same network. Coordinating the GIS internal interlocks with the controller logic is a point we review in every project. See bay controller.

Frequently asked technical questions

Where is the 8DN8 GIS documentation? The data sheet and the brochure are public; the operation manual and the drawings belong to the project. Request them with the serial number, because they change with the bays, the operating mechanism and the cabinet.
SF6 low-density alarm: first confirm it against the density gauge reading and the affected compartment; a real leak is located before topping up, and gas quality is checked with an SF6 gas analysis.
Field tests: a new or extended GIS is tested with on-site withstand voltage, partial discharge, contact resistance and breaker timing, in addition to the functional control tests. See partial discharge test and circuit breaker operating time tests.
SF6 or clean air: the decision depends on the voltage level available in each product line and on the environmental regulation of the country. In Europe, the fluorinated gas rules already set dates for new equipment.
Extending an existing GIS: it requires confirming the compatibility of the busbar and control interfaces with the manufacturer before designing the new bay.

How we help

At Tiza Group we test and commission GIS substations at medium, high and extra-high voltage, for both utilities and industry. We test the breaker, the instrument transformers and the control, and carry out commissioning tests in coordination with the utility. See testing and commissioning and circuit breaker testing. If the GIS is part of an extension or a replacement, we do the engineering under engineering design and studies. Field work is done in Colombia, or elsewhere on request. Write to us through the contact page.

References

IEC 62271-203, gas-insulated metal-enclosed switchgear for rated voltages above 52 kV.
IEC 62271-1, common specifications for high-voltage switchgear.
Siemens Energy, 8DN8 GIS data sheet, 8DQ1 data sheet, brochure «Gas-insulated switchgear 72–550 kV» and 8VN1 Blue GIS sheet.

Frequently asked questions

What voltage does the Siemens 8DN8 GIS handle?

The Siemens Energy data sheet presents the 8DN8 at two levels: up to 145 kV, with short-circuit currents up to 40 kA, and up to 170 kV, with up to 63 kA and feeder currents up to 4,000 A. For 245 kV the family continues with the 8DN9, and for 420 and 550 kV with the 8DQ1.

Where can I get the Siemens 8DN8 manual in PDF?

Siemens Energy publishes data sheets and brochures for the 8DN8 and 8DQ1 on its website. Operation and maintenance manuals are delivered with each project, because they depend on the bay configuration, the operating mechanism and the local control cabinet; request them with the project or serial number.

Does the 8DN8 use SF6?

Yes, the 8DN8, 8DN9 and 8DQ1 are SF6-insulated GIS. For those who want to avoid that gas, Siemens Energy offers the Blue line, such as the 8VN1 up to 145 kV, which uses clean air as the insulating medium and vacuum interrupters for switching.