KRUN K-6 (K-VI) - withdrawable unit replacement (retrofit)

Retrofit is the upgrade or partial re-equipment of metal-enclosed switchgear (KRUN) and single-sided service switchgear (KSO), replacing obsolete, end-of-life components with modern solutions.
The primary focus of modernization is the replacement of the most worn and simultaneously most critical device - the oil circuit breaker. New switching devices are modern breakers - vacuum or SF₆, with spring-stored energy or electromagnetic operating mechanisms. Unlike oil designs, they do not require regular servicing and offer significantly higher electrical and mechanical endurance. Comprehensive (extended) modernization is also possible: a modular replacement of the entire compartment, including a new withdrawable truck (draw-out unit), shutter mechanism, earthing (grounding) switch drive, door, protection & control panel, and other components.
The reliability of KRUN or KSO operation is directly determined by the reliability of its switching devices. This modernization path is a simple and economically sound way to address the wear of breakers in legacy distribution systems.
Retrofitting existing electrical equipment is financially more advantageous than purchasing new equipment, executing design and construction/installation work for its implementation, and compensating for losses caused by outages during a full replacement. Periodic maintenance of end-of-life oil breakers cannot ensure the required reliability of power supply, while the other parts of the cubicle often do not require replacement.
Equipment replacement options within a retrofit:
Replacement of the worn breaker on the existing withdrawable truck of the KRUN or KSO with a new device using an adaptation kit, refinement or replacement of interlocks, and adaptation of the breaker’s secondary plug-in connector. This is the most cost-effective option, but it requires more time and on-site labor.
Replacement of the entire withdrawable unit with breaker by a new one fully matching the dimensions and connection interfaces of the original, and fully identical in the set of interlocks. This approach is significantly faster to implement and requires minimal on-site work. An additional benefit is the possibility to keep the removed withdrawable unit with the oil (or minimum-oil) breaker as a spare.
Replacement with a factory-built “OneFit” retrofit module - a ready-to-install block with breaker, including implemented mechanical and electrical interlocks, protective shutters, and an adaptation system from standard plug-in primary contacts to the existing fixed contacts. This option is the most expensive, but it offers several advantages:
- improved dielectric performance;
- type-tested to IEC 62271-1;
- high reliability of the module’s mechanisms.

Technical data (typical values for a K-6 retrofit project)

Parameter	Typical value / range	Note
Rated voltage, kV	6 or 10	As per site network
Frequency, Hz	50/60	Compatible with protection & control
Rated continuous current of breaker, A	630–1250 (up to 1600 opt.)	Depends on VCB lineup
Rated short-circuit breaking current, kA	20–31.5	Selected per project spec
Mechanical endurance, operations	≥ 10,000	For modern MV breakers
Positions “Service / Test / Disconnected”	Yes	With interlocking system
Breaker operating mechanism	Spring-stored / electromagnetic	As specified by the project
Front door ingress protection	IP per project (e.g., IP31–IP54)	Depends on switchgear room
Secondary circuits interface	Removable multipin connector; unified to the original scheme	Labeling and pinout to be agreed
K-6 dimensional compatibility	Preservation of connection interfaces	Adapters / frames included
Protection relays	Microprocessor-based IEDs	Per Client’s ToR
Testing	Routine / acceptance per test program	At factory and/or on site

Purpose and application

Replacement of the withdrawable unit in KRUN K-6 (K-VI) is intended for comprehensive modernization of 6–10 kV medium-voltage distribution switchgear at industrial facilities, utility substations, transport and municipal infrastructure. The retrofit provides: higher switching reliability under short-circuits and overloads; reduced operating costs; lower risks associated with oil leaks and fire hazards; longer maintenance intervals; the ability to integrate modern microprocessor-based protection, automation and control (PAC) relays, as well as to build digital control schemes and remote monitoring (SCADA/DCS). The solution applies to standard K-series withdrawable cubicles (including K-6) while retaining existing busbars, foundations, cable terminations and most inter-cubicle partitions. This approach shortens commissioning time and minimizes downtime, including staged modernization of multiple cubicles without long outages of the switchgear.

Environmental conditions

The solution is designed for indoor MV switchgear rooms with normal service conditions for medium-voltage equipment: industrial-frequency AC 50/60 Hz, rated voltages 6–10 kV, installation altitude up to 1000 m above sea level (for higher altitudes, insulation is recalculated), typical ambient temperature range per project, and standard requirements for humidity and air cleanliness in the switchgear room. Where required, additional measures are provided such as increased enclosure IP rating, anti-condensation ventilation/heaters, seismic anchoring, and adaptation of secondary circuits to local operating conditions. Environmental classes and operating conditions are specified at the questionnaire/design stage and can be aligned with EN/IEC 60721-3-3 for stationary indoor installations and EN/IEC 60721-3-4 for stationary outdoor conditions, depending on project requirements.

Layout and design solutions

The baseline configuration of the withdrawable unit for KRUN K-6 includes: a modern breaker (vacuum/SF₆) on a standardized carriage; adapters for primary plug-in contacts matching the fixed parts of the cubicle; a new shutter mechanism and mechanical interlocks preventing incorrect operations; a modernized earthing (grounding) switch drive with a visual position indicator; a front door with viewing window, key interlocks and a new set of position sensors; a secondary plug-in connector panel/cassette matching the native K-series scheme; current and voltage transformers where replacement is required; sets of flexible/rigid bars for connections; intermediate cabling for adapting metering and PAC circuits; dust- and moisture-protective covers and seals. The withdrawable design ensures precise positioning in “Service / Test / Disconnected” with guides and latching assemblies rated for multiple racking cycles.
Vacuum breakers with spring-stored or electromagnetic mechanisms are preferred, offering high electrical/mechanical endurance, low operating costs and environmental safety. Compatibility with SF₆ breakers of the appropriate class is maintained if required by the project or fleet standardization. The mechanical layout allows installation of devices with varying dimensions provided tolerances for connection interfaces and pole spacing are met.

Safety

Personnel and equipment safety is achieved by a set of measures: mechanical and electrical interlocks exclude racking the withdrawable unit when the breaker is closed; the shutter mechanism automatically covers primary contact windows when the unit is moved to the test/disconnected position; visual position indicators and key interlocks ensure intentional operation; the earthing (grounding) switch is equipped with an independent drive and an interlock preventing erroneous closing onto live parts. Additionally, modernization of protection and automation is provided (replacement of electromechanical relays with microprocessor-based IEDs featuring measurements, fault recording and remote control). Materials and insulating parts are selected to meet flame resistance and tracking resistance requirements, and the enclosures ensure the specified IP degree for the intended service conditions.

Manufacturing options

Three typical modernization options are offered:
1) Breaker adaptation kit - installation of a new breaker on the existing withdrawable truck using transition frames, with modernization of interlocks and secondary plug-ins. Minimal capital cost, but precise supervision and adjustments are required on site.
2) New withdrawable unit in K-6 dimensions - a fully assembled withdrawable unit identical in connection interfaces and interlocks, enabling a plug-in replacement with minimal downtime. The removed unit can be retained as a spare.
3) Modular retrofit (“OneFit / OneFit-analog”) - a factory-built block with type tests, pre-installed interlocks and shutters, unified interfaces and full adaptation to the fixed parts of the cubicle. Maximum deployment speed, improved dielectric characteristics and factory-verified functionality.

Criterion	Adaptation kit	New withdrawable unit	Modular retrofit
Implementation time	Medium (depends on required rework)	Short	Minimal
Cost	Low	Medium	High
On-site work volume	Elevated	Low	Minimal
Type testing of the assembly	On site	Factory / on site	Factory type-tested
Geometric accuracy demands to cubicle	High	Medium	Medium / low
Breaker selection flexibility	High	High	High (within module range)

Compliance with standards

KRUN K-6 (K-VI) retrofit solutions are engineered and manufactured in line with applicable regulations for medium-voltage equipment. The scope of supply and the test program consider the requirements of, among others:
- IEC 62271-1 (general requirements for medium-voltage switchgear and controlgear);
- IEC 62271-100 (AC circuit breakers);
- IEC 62271-200 (metal-enclosed switchgear, AC, above 1 kV up to 52 kV);
- IEC 62271-102 (disconnectors and earthing switches);
- IEC 60529 (degrees of protection - IP code);
- Where necessary - national and industry standards, as well as environmental classes and service conditions per project documentation (e.g., EN/IEC 60721-3-3 for stationary indoor, EN/IEC 60721-3-4 for stationary outdoor).

Engaging contractors, manufacturers and investors

We are open to cooperation with manufacturing facilities and investors interested in producing withdrawable units and adaptation kits for KRUN K-6 retrofits. A partnership model is offered: licensing of detailed design documentation, training of technologists and installation personnel, supply of assemblies and critical components, author supervision and incoming quality control. For contractors, templates of manufacturing and test procedures (FAT/SAT), checklists and acceptance criteria are available, together with support during customer audits and operation. This enables rapid ramp-up of serial production and consistent product quality.

Deliverable documentation (drawings, 3D models)

The documentation package for the K-6 withdrawable-unit retrofit includes: questionnaires; preliminary technical documents for tenders; complete manufacturing drawings (DWG/DXF), 3D models (STEP/Parasolid), SolidWorks assemblies, bills of materials and purchased-parts lists; single-line and schematic diagrams; routing sheets and assembly/adjustment instructions; test programs and procedures; typical implementation projects; operation and maintenance manuals. Documentation is adapted to the project requirements and the manufacturing capabilities of your facility. Where needed, we provide nameplate/label templates, recommended spares lists and guidance on sourcing breakers, mechanisms and instrumentation.

We offer documentation for the replacement (retrofit) of the KRUN K-6 (K-VI) withdrawable unit:

- Preliminary technical documentation for participation in tenders related to the replacement of the K-6 (K-VI) withdrawable unit. We will prepare the information required to evaluate manufacturability in line with tender requirements and questionnaires.
- Working drawings, 3-D models and other necessary documentation to manufacture the KRUN K-6 (K-VI) withdrawable unit at your facility. If you do not plan to produce parts in-house, we will help source them from subcontractors. Final assembly and wiring can be carried out at your facility.
- All documentation can be adjusted, if required, to match the project requirements and your facility’s process capabilities.
- If different manufacturers’ equipment is installed at the substation, we will prepare documentation for manufacturing compatible units to complement the installed base.

Benefits of working with us:

- No need to maintain highly specialized engineering staff - you receive a documentation set for the product that can be used by a mid-level engineer.
- No need to build pilot prototypes - our experience allows successful launch of serial batches.
- Working to our documentation, your team will receive consultation on all nuances of replacing the KRUN K-6 (K-VI) withdrawable unit.