Retrofit is the modernization or partial re-equipment of KRU/KSO switchgear by replacing obsolescent components with modern ones while preserving the switchroom architecture and the existing interfaces to busbars, foundations and cable terminations. For the KRU-2-10 series, the greatest effect is achieved by replacing the withdrawable truck (drawout unit) with an oil circuit-breaker by a modern vacuum or SF₆ circuit-breaker with a spring-operated or electromagnetic operating mechanism. Such a replacement eliminates oil handling, increases switching endurance and reduces operational risk while keeping the cubicle layout and service interfaces unchanged.

Purpose and application

KRU-2-10 is used for receiving and distributing electric power in three-phase AC networks, 50 Hz, at 6 kV and 10 (12) kV, in systems with isolated neutral or earthed via an arc-suppression (Petersen) coil. The retrofit of the withdrawable unit is intended to extend the life cycle of existing substations without full switchgear replacement, which is especially relevant when:

• fault-clearing reliability needs to be increased and scheduled maintenance reduced;
• existing cubicles must be brought into line with current IEC/EN requirements;
• budgets and/or outage windows are constrained;
• there is a need to increase switching endurance and ensure predictable maintenance.

Applications: MV distribution at industrial facilities, power utilities (6–10 kV distribution substations), mining and oil & gas, transport and municipal infrastructure, telecom sites, data centers, etc. Owing to the standardized geometry of KRU-2-10 cubicles, a new-generation withdrawable truck retrofit allows the existing connections, door openings, shutter mechanisms and interlocks to be retained, or replaced by factory adapters with minimal intervention in the enclosure.

Technical data (typical ranges for KRU-2-10 retrofit)

Service conditions

Retrofit kits and replacement withdrawable units are designed for standard indoor MV switchgear environments:

• ambient air temperature typically from -5 °C to +40 °C (extended ranges with space heaters if required);
• relative humidity up to 80 % at +15 °C without condensation (anti-condensation heaters available);
• altitude up to 1000 m a.s.l. (higher on agreement with insulation coordination adjustment);
• installation category per EN/IEC 60721-3-3 / similar indoor category (non-aggressive, non-hazardous atmospheres);
• pollution degree as per project (enhanced insulation, IP executions and anti-corrosion coatings are available).

Subject to local codes, the retrofit may include replacement/addition of ventilation, heating and micro-climate control (temperature and humidity sensors, signaling to SCADA/DCS) to prevent condensation and insulation moisture ingress, which is especially relevant for old indoor substations and damp basements.

Layout and design solutions

The baseline scope for a KRU-2-10 withdrawable-unit retrofit includes removal of the existing truck with an oil (low-oil) circuit-breaker and installation of a new truck with a vacuum or SF₆ circuit-breaker, as well as adjustment/replacement of interfacing assemblies:

• power-contact and guide adapters, alignment of heights/projections of main tulip contacts;
• rework/replacement of the shutter mechanism and mechanical interlocks, synchronization of the positions “insert/test”, “service”, “open/earthing”;
• modernization of the earthing switch operating mechanism (if required) and integration of position indication;
• replacement/adaptation of the secondary plug, transfer of control, signaling and interlock circuits to the new scheme;
• deployment of digital protection relays (IEDs) with IEC 61850/IEC 60870-5-104 per project, with settings verification;
• check of main-contact transition resistance, earthing scheme, and dielectric tests per IEC/EN.

To speed up implementation, three typical scenarios are available:

1. On-site CB replacement using an adaptation kit (cross-members, contact blocks, transition plates) with updated interlocks and secondary plug. The most cost-effective option, but requires precise adjustment of the operating mechanism and some supervision time.
2. Complete withdrawable-unit replacement with a new truck fully compatible with KRU-2-10 dimensions and interfaces. Interlocks and logic are identical to the native design; installation time is minimal. The removed oil-CB truck may be kept as a spare.
3. Factory “Retrofit Frame” / “OneFit” module - a ready frame assembly with circuit-breaker, integrated shutters, interlocks, current sensors and type tests per IEC 62271-1/-100. The solution provides identical kinematics, improved insulation coordination and reduces the impact of human factor in operation.

Retrofit options comparison

Safety

Retrofit enhances personnel and electrical safety through:

• sealed vacuum/SF₆ interrupting chambers - no oil leakage, minimal fire risk;
• modern interlock systems preventing mal-operations during racking-out/racking-in, switching onto the earthing switch, etc.;
• improved indication of device positions, voltage presence, and test plug insertion;
• option to equip arc-detection sensors and high-speed tripping schemes based on microprocessor IEDs;
• enhanced insulation coordination and coordinated creepage distances for dusty/damp rooms.

Manufacturing options

On request, executions are available for feeder rated currents of 630–1600 A (for selected feeders up to 2000 A) and breaking capacities of 20/25/31.5 kA; rated busbar current 1250–3150 A. We supply withdrawable trucks with circuit-breakers from leading manufacturers, adapter kits for your KRU-2-10 cubicles, and ready frame modules. As per project, we can supply protection relays (e.g., families with IEC 61850 support), measuring current/voltage transformers, breaker-failure and backup protection, ATS/AR, control/indication panels, as well as busbar kits and bus bridges for sectionalizing and incoming feeders.

Options: VPIS (voltage presence indicating system) integration, door viewing windows, truck position monitoring systems, space heaters, anti-corrosion coatings, higher-IP executions, seismic anchoring, cable terminations tailored to your cable types, and sets of service sticks and transport trolleys.

Compliance with standards

Retrofit solutions are engineered and manufactured in accordance with applicable norms. In the project and test documentation we follow (selectively, per supply scope):

• IEC 62271-200 - metal-enclosed switchgear and controlgear for voltages above 1 kV and up to and including 52 kV (MV switchgear);
• IEC 62271-100 - AC circuit-breakers (medium-voltage range per project);
• IEC 62271-102 - earthing switches and disconnectors;
• IEC 62271-1 - common specifications for MV switchgear and controlgear;
• IEC 60529 - degrees of protection (IP code);
• IEC 60071 (or current replacements per IEC TC 28/TC 17) - insulation coordination.

If required, compliance with national standards and customer-specific industry requirements can be demonstrated by type and routine test protocols. For environmental categories formerly referenced as GOST 15150 (e.g., U3/U1), we apply the EN/IEC 60721 series (e.g., EN/IEC 60721-3-3 / EN/IEC 60721-3-4) as applicable to the installation.

Engaging contractors and investors

We are open to cooperation with electrical equipment manufacturers, assembly plants, service and EPC/installation companies, as well as investors interested in series production of retrofit kits for KRU-2-10. Various collaboration models are possible: contract manufacturing of assemblies, supply of design documentation and tooling, licensing, staff training, site supervision, support during certification and type testing. For EPC contractors we provide complete design inputs, 3D models for coordination, material take-offs and cable/wiring schedules.

Delivered documentation (drawings, 3D models)

The documentation package includes: overall and interface drawings (DWG/DXF), 3D models (STEP/Parasolid), single-line and secondary circuit diagrams (AutoCAD Electrical/ECAD), bills of materials, questionnaires, installation/commissioning/operation manuals, dielectric-test and commissioning procedures, catalog sheets for relays/sensors, and lists of purchased items. All materials are adapted to your manufacturing capabilities and project requirements; localization to your corporate CAD and document standards is available.

Benefits of working with us:

- No need to maintain highly qualified engineering staff - you receive a complete documentation set for the product to be manufactured, suitable for an engineer of average qualification. 
- No need to build pilot prototypes - our experience allows launching serial production successfully from the start.
- Working to our documentation, your specialists will receive consulting on all nuances of replacing the KRU-2-10 withdrawable unit.

For additional information on KRU-2-10 withdrawable unit replacement (retrofit), please contact: inbox@proekt-energo.com

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