Siemens makes gas-insulated and air-insulated medium-voltage switchgear. The 8DJH is the gas-insulated switchgear for secondary distribution up to 24 kV (with an 8DJH36 version and a blue GIS version free of fluorinated gases); NXAIR is the air-insulated switchgear for primary distribution; NXPLUS C and 8DA10/8DB10 are gas-insulated switchgear for primary distribution, in single-busbar and double-busbar versions.
What it is and where it is used
The Siemens 8DJH, NXAIR, NXPLUS C and 8DA10/8DB10 switchgear covers almost the entire medium-voltage range. The 8DJH is the gas-insulated switchgear for secondary distribution (customer substations, rings, buildings, wind and solar plants). NXAIR is the air-insulated switchgear for primary distribution. NXPLUS C and 8DA10/8DB10 are gas-insulated switchgear for primary distribution where space, pollution or altitude matter. SIMOSEC is the range of air-insulated switchgear for secondary distribution. SIVACON is the low-voltage switchboard.
It is found in distribution substations, industry, mining, infrastructure and generation. For the general principle, see medium-voltage switchgear and GIS substations.
Variants: 8DJH, 8DJH36, NXAIR, NXPLUS C, SIMOSEC and 8DA10/8DB10
| Model | Application | Main difference |
|---|---|---|
| 8DJH | Secondary distribution up to 24 kV | Gas-insulated; ring, transformer and circuit-breaker panels |
| 8DJH 24 blue GIS | Secondary distribution up to 24 kV | Clean Air insulation, no fluorinated gases |
| 8DJH Compact | Secondary distribution | Smaller version |
| 8DJH36 | 36 kV secondary distribution | Single busbar, indoor; 38 kV in the North American version |
| NXAIR | Primary distribution | Air-insulated, up to 17.5 kV and 40 kA |
| NXAIR H | 36 kV primary distribution | Air-insulated, up to 36 kV and 31.5 kA |
| NXPLUS C | Gas-insulated primary distribution | Single busbar, up to 38 kV, 31.5 kA and 2,500 A (North American version) |
| 8DA10 / 8DB10 | Gas-insulated primary distribution | Single busbar (8DA) and double busbar (8DB), up to 40 kA |
| SIMOSEC | Secondary distribution | Air-insulated |
| SIVACON | Low voltage | Distribution switchboard and MCC |
The values are those Siemens publishes for each range and region; the values for each installed unit are read from its nameplate.
Main characteristics
- Gas insulation (8DJH, NXPLUS C, 8DA/8DB): the live parts sit in a sealed tank, which reduces size and exposure to the environment. Versions with SF6 require monitoring of the gas density; the blue GIS uses clean air.
- Air insulation (NXAIR, SIMOSEC): withdrawable or fixed vacuum circuit breaker, separate compartments and internal arc classification according to IEC 62271-200.
- Transformer panels with fuses or with a circuit breaker and relay, depending on the rating and the selectivity required.
- Voltage indicators and plug-in cable connections on the gas-insulated switchgear, which change how cable and insulation tests are carried out.
Communications and integration
Communication is handled by the relay or the remote control unit of the switchgear: on Siemens switchgear it is common to find SIPROTEC and Reyrolle relays, integrated into SCADA through IEC 61850, IEC 60870-5-104 or DNP3. The 8DJH can be motorized to automate distribution rings.
8DJH catalog data
The 8DJH catalog HA 40.2 (2017 edition) defines it as three-phase, single-busbar, metal-enclosed indoor switchgear for secondary distribution up to 24 kV. Its applications are local rings, customer substations, wind and solar plants, hydroelectric plants, water plants, airports, train and metro stations, open-pit mining and high-rise buildings. The maximum values it publishes are:
| Rated voltage | 7.2 kV | 12 kV | 15 kV | 17.5 kV | 24 kV |
|---|---|---|---|---|---|
| Power-frequency withstand voltage | 20 kV | 28 kV | 36 kV | 38 kV | 50 kV |
| Lightning impulse withstand voltage | 60 kV | 75 kV | 95 kV | 95 kV | 125 kV |
| Short-time withstand current, 1 s | 25 kA | 25 kA | 25 kA | 25 kA | 20 or 21 kA |
| Peak withstand current, 50 / 60 Hz | 63 / 65 kA | 63 / 65 kA | 63 / 65 kA | 63 / 65 kA | 50 or 52.5 / 52 or 55 kA |
The rated current of the busbars is 630 A. That of the ring feeders is 400 or 630 A, and that of the circuit-breaker feeders is 250 or 630 A. The rated current of the transformer feeders is 200 A, set by the high-breaking-capacity fuse. The gas vessel has an IP65 degree of protection and is filled to 150 kPa absolute, with a minimum functional level of 130 kPa. The standard ambient service temperature ranges from -25 to +55 °C, and from -40 to +70 °C on request. Siemens estimates a service life of at least 35 years, probably 40 to 50 years, counting the tightness of the welded vessel. The limit is set by the switching cycles of the devices, according to the classes of IEC 62271-100, -102 and -103. The optional internal arc classification is IAC A FL for installation against a wall and A FLR for free-standing installation. In the Compact version, for substations without a control aisle, it is A F. Pressure relief is downward and, optionally, to the rear or upward. The switch-disconnectors have three positions, with mechanical position indicators built into the mimic diagram on the front.
NXAIR catalog data
Siemens publishes NXAIR in several catalogs according to short-circuit current and voltage. HA 25.73 (2023) covers up to 17.5 kV and 40 kA, and HA 25.74 (2023) up to 17.5 kV and 50 kA. The NXAIR M catalog is for 24 kV up to 25 kA and the NXAIR H catalog for 36 kV up to 31.5 kA. In all versions the switchgear is declared with internal arc classification IAC A FLR (front, lateral and rear access) and loss of service continuity category LSC 2B. Its partition class is PM, that is, metallic partition. According to the catalog for up to 40 kA:
- Arc confinement: up to 31.5 kA for 1 s, the internal arc can be confined to the compartment where it occurs, as an option beyond the standards.
- Shutters and testing: the shutters are positively driven and can be locked separately, and cable tests can be carried out without isolating the busbar.
- Remote operation: establishing the isolating distance and earthing the feeder and the busbar can be controlled remotely.
- Degree of protection: up to IP51.
- Endurance of the devices: the withdrawable vacuum circuit breaker is declared with classes E2, M2 and C2, and the isolating distance with class M0. The manufacturer presents it as maintenance-free.
- Measurement and protection: standard block-type current transformers or, as an alternative, low-power sensors with a Rogowski coil, and a SIPROTEC 5 bay controller with a three-input arc protection module for point or line optical sensors.
- Service life: more than 30 years, according to the catalog.
These data explain why two “NXAIR” switchgear units can have different short-circuit ratings and installation requirements: the name covers several platforms. The exact type designation is on the nameplate.
Frequently asked technical questions
- 8DJH documentation: Siemens publishes the 8DJH and 8DJH36 catalogs; the instructions are issued per version.
- Cable tests on gas-insulated switchgear: they are carried out through the plug-in connectors or the test points provided, never by opening the tank. See diagnostic cable testing.
- Gas pressure or density alarm: do not operate the switchgear until the cause is known. See SF6 density monitor.
How we help
We do not sell switchgear. At Tiza Group we test air-insulated and gas-insulated medium-voltage switchgear (circuit breakers, insulation, gas, interlocks, cables and instrument transformers) and support commissioning, in substations and in industry, in Colombia or elsewhere on request. See circuit breaker testing within testing and commissioning. Write to us through the contact page.
Related guides
- Medium-voltage switchgear
- GIS substation
- Medium-voltage switch-disconnector
- SF6 density monitor
- SF6 gas analysis
- Diagnostic cable testing
References
- IEC 62271-200, AC metal-enclosed switchgear and controlgear for rated voltages above 1 kV and up to and including 52 kV.
- IEEE C37.20.7, internal arc testing of medium-voltage switchgear.
- Siemens, product pages for 8DJH 24 blue GIS, 8DJH36, NXPLUS C and 8DA10/8DB10, 8DJH 24 kV and 8DJH36 catalogs, NXAIR and NXAIR H brochures.
Frequently asked questions
What is the Siemens 8DJH switchgear?
It is gas-insulated medium-voltage switchgear for secondary distribution up to 24 kV, built from ring, transformer and circuit-breaker panels. Siemens also offers the 8DJH36 for 36 kV, the smaller 8DJH Compact and the 8DJH 24 blue GIS, which insulates with Clean Air instead of fluorinated gases.
What is the difference between NXAIR and NXPLUS C?
NXAIR is Siemens' air-insulated switchgear for primary distribution, up to 17.5 kV and 40 kA in its base version; NXAIR H reaches 36 kV and 31.5 kA. NXPLUS C is single-busbar gas-insulated switchgear that Siemens publishes up to 38 kV (North American version), 31.5 kA and 2,500 A. The choice depends on space, environment and voltage.
Where can I find the Siemens 8DJH manual?
Siemens publishes the 8DJH and 8DJH36 catalogs as PDFs, and the installation and operating instructions for each version. For switchgear already in service, the manufacturer's documentation for its exact type designation is the document that counts.