The indoor AC GN38-12 changeover disconnectors are intended to make and break, without load, individual sections of a medium-voltage network up to 12 kV (50 Hz), and to provide safe earthing of the disconnected sections. The GN38-12 series are three-pole, vertical-break (changeover) devices with a compact layout, designed for installation in KRU/KSO panels and distribution switchgear cabinets where footprint, reliability and ease of maintenance are critical.

Purpose and application

The GN38-12 disconnector is used to create a visible break for operational switching, maintenance and repair on 6–12 kV distribution assets: on incoming feeders and sections of KRU/KSO, in busbar chambers, in feeder bays (cable, line, transformer), as part of main and distribution substations. The device provides:

• operational isolation of the de-energized section (visible break);
• workzone delimitation by earthing the circuit via the built-in earthing switch (if so equipped);
• sectionalizing and maintenance switching without load;
• interlocks to prevent personnel errors via mechanical and key-type interlocks.

The compact design allows GN38-12 to be used in small KSO-type cubicles, modular switchgear, shallow cabinets and retrofit bays without re-engineering the entire panel. Thanks to the three-position logic (ON – OFF – EARTHED), the device integrates easily into typical distribution schemes, and the availability of different operating mechanisms gives flexibility in design.

Technical data

Service conditions

GN38-12 disconnectors are intended for indoor installations under the following (typical medium-voltage) conditions:

• Location category: indoor installation (MV switchgear rooms, KRU/KSO, cabinets);
• Ambient temperature: -25 °C to +40 °C (short-term excursions per project), without condensation during operation;
• Altitude: up to 2000 m (above this, recalc of insulation clearances and test levels is required);
• Relative humidity: up to 95% (daily) with no condensation;
• Atmosphere: free from corrosive vapours/gases in concentrations harmful to insulation and metals; no conductive dust or aerosols;
• Vibration and shocks: not exceeding the levels specified for MV switchgear mechanical robustness (per IEC/GOST);
• Environmental category: U2 (per legacy GOST classification).

When designing the switchgear, consider ventilation modes (natural/forced), possible local hot spots inside the cabinet, minimum creepage distances and clearances between live parts, and the impact of heating/dehumidification on dielectric strength.

Design and construction

The GN38-12 is a three-pole unit on a welded base frame including the following major assemblies:

• Bushing insulators (upper/lower) – provide mechanical strength and dielectric insulation of live parts from the frame and cabinet;
• Changeover current-carrying blade (vertical-break type) – forms a visible break and makes connection to the earthing contact in the “EARTHED” position;
• Contact system – fixed and moving contacts with enhanced wear resistance; spring elements maintain contact force;
• Earthing switch (option) – located on the fixed or moving contact side, mechanically interlocked with the main blade;
• Linkage system – transmits force from the mechanism to all three poles, ensuring synchronism and positive position latching;
• Three-position operating mechanism (e.g., type ZQL or equivalent) – provides “ON”, “OFF”, “EARTHED” positions; supports sealing and limit switches.

Current-carrying parts are selected for low contact resistance and long-term stability (electro-technical copper/copper alloys with galvanic coating). Insulators and insulating panels are sized with adequate creepage and withstand levels for indoor service and the site’s pollution degree. The design requires minimal upkeep: periodic visual checks, tightening of bolted joints, insulation cleaning and mechanism inspection.

GN38-12 disconnectors are manufactured with or without a built-in earthing switch. The main blades and the earthing blade are driven by a single three-position mechanism with fixed positions: “disconnector closed”, “disconnector and earthing switch open”, “earthing switch closed”. The mechanism incorporates interlocks that prevent an incorrect sequence of operations. Interlocking with the circuit breaker of the respective bay is provided.

Mechanical endurance before first major overhaul is at least 2000 operations. The interval to a medium overhaul is at least 1000 cycles with a service period up to 4 years. Nominal service life - 25 years, subject to the maintenance schedule and service conditions.

Safety and interlocks

Personnel safety is ensured by a combination of design and procedural measures:

• Three-position logic: prevents simultaneous energization of live parts and closing of the earthing blade;
• Mechanical interlocks of the mechanism: blocking “ON” when the earthing switch is engaged, and vice versa;
• Key and mechanical interlocking with the circuit breaker and bay doors (keylocks, position limit switches);
• Visible break for visual confirmation of the de-energized state before work;
• Sealing of the operating handle to fix operational status;
• Provision for portable earthing points to support safe work procedures.

When engineering interlocks, consider the switching sequence, access to the handle, the blade travel envelope, and the requirements of electrical safety rules for locking, labelling of controls and position indication.

Variants and options

The GN38-12 is supplied in various construction and equipment options to fit a specific switchgear, bay dimensions and customer requirements:

• with a built-in earthing switch or without it (on the fixed or moving contact side);
• left- or right-hand mechanism location; different blade orientations;
• connection options: for busbar packs, cable lugs, flexible connections;
• insulator versions: porcelain/epoxy (indoor), increased creepage distances;
• installation of limit switches (dry contacts) for position telesignals;
• optional motor-operator (per project) for remote control;
• anti-skew provisions through adjustable links and position latches.

Standards compliance

Design and manufacture of the GN38-12 follow applicable standards for medium-voltage apparatus:

• IEC 62271-102 / EN IEC 62271-102 - AC disconnectors and earthing switches (requirements, type tests);
• IEC 62271-1 - Medium-voltage switchgear and controlgear - Common specifications;
• EN/IEC 60721-3-3 - Environmental conditions for indoor locations (replaces legacy GOST 15150 categories for indoor use);
• General mechanical robustness - according to enterprise specifications and applicable IEC guidance;
• Electrical installation rules - applied as relevant to 6–35 kV MV switchgear;
• Enterprise standards (drawings/specs) - interface dimensions, interlocks, TS/remote control interfaces.

Engaging contractors and partners

We welcome cooperation with electrical equipment manufacturers, KRU/KSO switchgear integrators, design and installation firms, as well as investors interested in localizing/organizing production of the GN38-12 series. We offer:

• transfer of design document packages (from preliminary documentation to a full set for serial production);
• adaptation of design solutions to your site’s manufacturing capabilities (tooling, machine park, plating, painting);
• selection and qualification of the supply chain (insulators, stamping/machining, subassembly);
• advice on type/routine tests, FAT/SAT methodologies, and preparation of programs and reports;
• support for initial series, staff training, commissioning support.

Documentation offered

Available preliminary technical documentation for tenders (questionnaires, specifications, explanatory notes) and a full set of manufacturing documentation for production at your site:

• assembly and detail drawings (DWG/DXF, BoMs, parts lists);
• 3D models of parts and assemblies (STEP/IGES/Parasolid (x_t), SolidWorks, Inventor);
• electrical diagrams, interlocking maps, TS/remote control wiring, cable schedules;
• work instructions for assembly/adjustment, inspection routes, test programs;
• typical O&M documentation (datasheet, manual, test records).

On request, documents can be tailored to the project requirements and manufacturing capabilities (busbar thicknesses, interface dimensions, mechanism type, limit switch and cable gland locations, insulator type, etc.).

Why work with us

- No need for a large in-house engineering team: you receive a ready-to-build documentation set.
- No “pilot dead-ends”: our experience enables starting from series with minimal tweaks.
- Expert advice on all nuances of manufacturing and testing the GN38-12, assistance with tooling and quality control programs.

For additional information on GN38-12 disconnectors: inbox@proekt-energo.com

...as is well known, an error made at the design stage costs ten times more in manufacturing and a hundred times more in operation - it is best to allow for everything in advance.

PDF - Download technical information for the GN38-12 disconnector.