RNDZ-27.5 Sectioning disconnector for 27.5 kV overhead contact system

The RNDZ-27.5 series sectioning disconnectors are intended for operational switching of previously de-energized 27.5 kV AC sections and for their subsequent safe earthing by integrated earthing switches. The design provides a clearly visible isolating gap. Units are supplied in single-, double- and triple-pole versions; the pole coupled to the operating mechanism is the leading pole. Operation is via manual or motor drives; provision is made for fitting limit switches and auxiliary contacts for remote control and telemetry.
Environmental and service conditions - in accordance with EN 50125-2 (fixed installations). Permissible operating parameters:
- installation altitude ≤ 1000 m a.s.l.;
- ambient temperature -60 to +40 °C;
- wind speed up to 40 m/s without icing and up to 15 m/s with ice up to 10 mm thick;
- average annual relative humidity 80% at +15 °C;
- max. wind pressure 700 Pa (≈34 m/s) without icing;
- max. wind pressure 140 Pa (≈15 m/s) with ice sheath up to 10 mm;
- total permissible mechanical load on one pole’s terminals (including wind/ice loads) - 500 N with uniform distribution.
Insulation performance meets the requirements of the 27 kV voltage level per EN 62271-1; test methods per IEC 60060-1. External creepage distance of porcelain insulators on standard versions:
- pollution level I - not less than 60 cm;
- pollution level II - not less than 105 cm.
On request - execution with polymer insulators type ОСК8–35–Б–2 with creepage ≥ 105 cm. Mechanical endurance - at least 2000 “close-open” cycles.
The disconnectors are not intended for operation under pronounced vibration, impacts or other dynamic effects exceeding industry norms.

Technical data

Rated voltage, kV	27.5
Highest voltage for equipment (Um), kV	30
Rated current, A	1000; 1600
Rated peak withstand current, kA	63
Rated short-time withstand current, kA	25
Short-time duration, s - main blades - earthing blades	3 1
Frequency, Hz	50
Creepage distance of external insulation, cm	≥ 60
Allowable horizontal conductor tension, N	≤ 800
Environment / installation category	per EN 50125-2 / outdoor
Mass (typical), kg	1 pole ~53/62; 2 poles ~118
Overall dimensions (typical), mm	height 960 / 1300; width 750 / 840 / 930

Application and use

AC overhead contact system sectioning disconnectors of the RNDZ type are high-voltage devices for performing operational switching with no load current. Their primary task is to connect/disconnect previously de-energized sections of the OCS while ensuring electrical safety during maintenance, installation and inspection. In the open position the device provides a visible isolating distance that confirms physical separation of the work section from the power supply - a requirement of EN 50122-1 and operating rules.

As an option, fixed earthing switches are installed to reliably earth isolated sections and eliminate hazards due to induced voltages or inadvertent energization. The term “sectioning” reflects the function - dividing the OCS into electrically separated zones for flexible operation and fault containment.

Design and operating principle

General arrangement

RNDZ units are two-column, horizontally rotating disconnectors for outdoor installation. This kinematics is well suited for railway infrastructure: the rotary motion effectively “breaks off” icing and minimizes installation height. Versions - single- and double-pole (a three-pole set comprises one leading and driven poles coupled via inter-pole rods).

Main assemblies

Frame (base). Welded steel load-bearing structure carrying the rotary bases of the insulator columns, the drive assemblies and, where fitted, the earthing-switch mechanism.
Support/insulator columns. Each pole uses two porcelain columns to provide the required clearances and mechanical stiffness. The columns are mounted on cast-iron rotary bases with bearing units for smooth rotation about the vertical axis.

The horizontal-rotation layout improves contact reliability under icing and reduces overall height compared with “shear-type” or vertical-rotation designs.

The contact system defines the resistance of the main current path and the device’s durability. It comprises main blades and earthing blades. Main blades: Half-blades mounted on the upper insulator flanges meet at ~90° rotation. Current transfer is via a demountable lamella (laminated) contact: a spring-loaded pack of copper lamellae provides stable contact pressure, lowering contact resistance and the risk of local overheating. For 1600 A ratings the contact pieces have silver overlays; the assembly is enclosed by a metal hood against precipitation and icing. Earthing blades: An independent frame-mounted unit: a plate-type moving blade on a rotating shaft with a fixed counter-contact. The shaft runs in bronze bearings for smooth, wear-resistant motion; a flexible copper bond connects the blade to the common earthing system. Operated by a separate drive.

Drive and kinematics

Manual or electric drives are used. Force is transmitted via a vertical pull-rod to the shaft of the leading pole and then via inter-pole tie rods to the driven poles. Rod lengths are adjustable to synchronize the moments of contact engagement/disengagement.

Mechanical interlocks - safe operation

The interlock is purely mechanical: profiled cams/discs on the operating shafts of the main and earthing blades block motion in inadmissible positions; shaped cut-outs permit movement only in the correct sequence.

Standards compliance

EN 62271-102 - High-voltage disconnectors and earthing switches.
EN 62271-1 - High-voltage switchgear and controlgear - Common specifications.
EN 50119 - Railway applications - Fixed installations - Overhead contact systems.
EN 50122-1 - Railway applications - Fixed installations - Protective provisions relating to electrical safety and earthing.
EN 50125-2 - Railway applications - Environmental conditions - Part 2: Fixed installations.
IEC 60060-1 - High-voltage test techniques - Definitions and general requirements.
EN 60529 - Degrees of protection provided by enclosures (IP Code).
EN ISO 1461 / EN ISO 12944 - Corrosion protection (hot-dip galvanizing / protective paint systems) - as specified.

Collaboration with contractors, manufacturers, investors

We are open to cooperation with manufacturing and installation companies and with investors for series production and/or localization of the RNDZ-27.5. We provide the complete design dossier, routing sheets, specifications, purchased-parts lists, material/coating requirements and FAT procedures. Delivery of sub-assemblies (contact system, earthing switch, tie-rod mechanisms, drive units) and partner training are available.

For contractors - site supervision, author’s supervision, commissioning and training of O&M personnel. For investors and production organizers - cost calculation, recommendations on shop equipment (presses, welding, galvanizing, test rigs), and pilot-batch support.

Documentation offered (drawings, 3D models, CAD)

Available formats: DWG/DXF (AutoCAD), SLDDRW/SLDPRT/SLDASM (SolidWorks), STEP/Parasolid, PDF. On request we provide 3D models for BIM, data sheets, connection/layout diagrams, and installation/adjustment/operation manuals. The documentation package is adapted to the project requirements and manufacturing capabilities.

Your advantages

- No need to maintain a large team of senior engineers: you receive a production-ready documentation set usable by mid-level engineers.
- Prototypes not strictly required: our experience enables direct launch of series production from the documentation.
- When working to our documents, your specialists receive full process support for manufacturing the RNDZ-27.5 sectioning disconnectors.