RETROFIT of the KRU K-15 roll-out element is an engineering replacement of the most “loaded” unit of the 6–10 kV cell (trolleys with a switch and primary/secondary interface) without dismantling the cabinet, without rebuilding the busbar and without transferring cable connections. In practice, the K-15 retrofit solves three key operational problems: (1) the exhausted service life of oil/low-oil circuit breakers and the shortage of repair kits, (2) increased fire and operational safety requirements, (3) the need to reduce maintenance time and eliminate “oil” regulations. As a result, the customer receives a modern withdrawable element with a vacuum (or SF6, as specified) circuit breaker, updated interlocks, and coordinated secondary circuits while retaining the base part of the switchgear.

Contents

• Purpose and scope of application
• What is included in the K-15 retrofit
• Technical data (typical)
• Initial data from the customer and survey
• Layout, interfaces, and compatibility
• Interlocks and operational safety
• Quality control, testing, PNR
• Design variants and options
• Comparison of modernization approaches
• Compliance with standards
• Documentation package and cooperation

Purpose and scope of application

The solution is designed to replace the withdrawable element (WE) of the K-15 series switchgear with a new WE compatible with a specific modification of the cell in terms of mounting dimensions, withdrawal/retraction trajectory, curtain system, locks, and secondary connector. Application — 6 and 10 kV switchgear, 50 Hz: substations and power distribution points of power systems, industrial GPP/CRP, infrastructure (water utilities, transport, mining, processing), facilities with high downtime costs. Retrofitting is relevant both for scheduled replacement of circuit breakers based on their service life and for reliability improvement programs (reducing switching equipment failures, reducing switching times, improving the reproducibility of shutdown characteristics).

The upgraded VE ensures normal switching operations and operation with existing control/signaling/ RZA circuits. Upon agreement, “selective” modernization of secondary systems is provided for: replacement of circuit breaker control circuits, transfer/replacement of trolley position limit switches, installation of new intermediate relays, introduction of measuring transducers and telemechanics interfaces.

What is included in the K-15 retrofit

• supply of a new roll-out element assembly (frame/trolley, switch, drive, roll-out/locking mechanism, primary plug-in contacts with adapters, curtain mechanism, interlocks);
• coordination of secondary circuits: transition plates or mating part of the connector, connection according to the control, signaling, and relay protection and automation circuits diagram;
• checking mechanical compatibility: guides, adjustment, locking in the “repair/test/operating” positions, access to manual controls;
• work on site (according to the project): installation/relocation of position sensors, replacement of curtains/grounding device drives, modification of the front panel, marking, updating of plates;
• set of operating materials: passport/RE for VE, installation and configuration instructions, test and measurement reports, connection diagrams.

Technical data (typical)

Initial data from the customer and survey

K-15 comes in various factory and “transitional” versions, so retrofitting should be done correctly based on the survey results. At the pre-project stage, the following are recorded: cell type and condition (K-15 modification, year/manufacturer, if available), the layout of the power compartment, the design of the curtains, the type of fasteners and fixings, the design of the earthing device, the location of the TT/TN, the format of the secondary connector, and the actual diagrams. Additionally, network calculation data is required: rated currents, short-circuit currents, neutral mode, requirements for APV/UROV, and blocking logic.

The result of the survey is a technical solution with references: a list of mechanical interfaces, a secondary switching circuit diagram, a list of cell modifications (if required), equipment specifications, and an agreed questionnaire for the switch/drive/secondary circuits.

Layout, interfaces, and compatibility

The new withdrawable element for K-15 is designed according to the principle of “replacement without cabinet reconstruction”: the mating parts of the main circuits, cable entries, and access to serviceable areas are retained. Compatibility is achieved by the following solutions:

• Primary contacts — plug-in node adapters with geometry specific to the K-15 cell; the required contact area and force during adjustment are ensured, misalignment and under-adjustment are eliminated;
• Movement mechanism — coordination of guides, stops, locks, control of gaps along the roll-out trajectory, preservation of service access to manual controls;
• Curtains — automatic closure of live parts when switching to “repair” mode, access blocking, restoration of normal curtain interaction logic with the trolley;
• Secondary circuits — transitional solutions for existing connectors (or replacement of the mating part while retaining the marking), linking of switch-on/switch-off circuits, block contacts, signaling, and relay protection circuits;
• Facade and indication — linking controls, inscriptions, and light signals to the layout familiar to personnel, updating plates and warning signs.

Special attention is paid to contact resistance, thermal conditions, and repeatability of adjustment: these parameters directly affect heating in the plug-in node area and the stability of the connection under prolonged load.

Locks and operational safety

When retrofitting the K-15, the task is not simply to “install a new switch,” but to ensure correct and unambiguous operation mechanics. A typical set of interlocks includes: prohibiting movement of the switch when the circuit breaker is closed; prohibiting the circuit breaker from being closed outside the “test/operating” position; interlocks between the circuit breaker and the earthing switch (depending on the cell diagram); blocking access to the compartment when the connection is turned on; fixing the positions of the trolley with visual indication. Safety enhancement elements are being implemented as required: voltage presence control, arc protection, emergency event logging, additional signaling of erroneous states.

Quality control, testing, PNR

To reduce the risk of “hidden” defects when replacing a roll-out element, it is advisable to formalize control at three levels: factory acceptance of the roll-out element, control at the facility before commissioning, and comprehensive checks as part of the cell.

• At the factory: checking kinematics and interlocks, checking adjustments, checking the electrical diagram of secondary circuits, functional on/off tests, measuring the resistance of control circuits.
• At the facility before applying voltage: measurement of insulation resistance, checking secondary circuits according to the diagram, checking interlocks and limit switches, measuring the transition resistance of the main contacts (micro-ohmmetry), checking phasing and marking. >As part of the connection: checking interaction with relay protection and automation (trip circuits, interlocks, automatic protection and automation according to the project), checking remote signaling/telemetry, checking the correctness of the “repair/test/operating” positions and the correct operation of the curtains.

If necessary, a test program and methodology are developed according to customer requirements (including extended checks of switch-on/switch-off times, control of coil and power supply parameters, and checking of emergency automation circuits).

Design variants and options

• Switch: vacuum — basic solution for most connections; SF6 — upon project request or for fleet standardization.
• Drive: spring-motor (with manual cocking and readiness indication) or electromagnetic — depending on the task and availability of operational power supply.
• Secondary circuits: “careful” integration into the existing scheme or modernization (replacement of intermediate relays, introduction of shutdown circuit control, expansion of signaling).
• RZA/ACS: implementation/replacement of terminals, arc protection (optics + current criterion), Modbus/IEC 61850 interfaces (according to the project), integration into the upper level.
• Environment-specific design: anti-corrosion coatings, galvanization/stainless steel elements, anti-condensation heating, temperature/humidity sensors in compartments.

Comparison of typical modernization approaches

Compliance with standards

The retrofit solution is developed taking into account the requirements for high-voltage equipment and switchgear. The project specifies the boundaries of responsibility (withdrawable element/circuit breaker/cell), as well as the list of applicable standards (specified for each facility):

• IEC 62271-1 — general requirements for high-voltage apparatus and complete devices;
• IEC 62271-100 — AC circuit breakers (service life, testing, switching capacity);
• IEC 62271-102 — Disconnectors and earthing switches (mechanics, interlocks);
• IEC 62271-200 — complete devices in metal enclosures 1–52 kV (LSC/IAC classification for new/upgraded solutions);
• IEC TS 62271-304 — indoor operating conditions with condensation/contamination;
• GOST 15150 — climatic versions and equipment placement categories.

Documentation package and cooperation

The standard package includes: working drawings and specifications, 3D models (STEP/Parasolid), secondary circuit diagrams, installation/configuration instructions, control cards, and test reports. Documentation can be provided both for in-house manufacturing (localization of parts and assemblies) and for the purchase of a ready-made roll-out element. For serial projects on K-15, cooperation is possible: delivery of design documentation with author's support, delivery of adaptation kits/assemblies, or turnkey work (survey, design, manufacturing, installation, commissioning).

We offer you documentation for replacing the KRU K-15 roll-out element (retrofit):

- Preliminary technical documentation for participation in tenders for the replacement of the KRU K-15 roll-out element. We will prepare the necessary information for you to assess the possibility of manufacturing products in accordance with the requirements of the tender documentation and questionnaires. - Working drawings, 3-D models, and other necessary documentation for the manufacture of the KRU K-15 roll-out element at your enterprise. If you do not plan to manufacture the product components and parts yourself, we will help you outsource their manufacture to third-party enterprises. Your enterprise will perform the general assembly and installation of the product. - All documentation will be adjusted as necessary in accordance with the project requirements and the technological capabilities of your enterprise. - If equipment from another manufacturer is installed at the substation, we will prepare documentation for the manufacture of similar equipment in addition to the installed equipment.

Advantages of working with us:

- No need to maintain highly qualified engineering and technical personnel - you will receive a set of documentation for the manufactured product, which can be handled by an engineer with average qualifications.
- No need to manufacture prototypes - our experience allows us to launch serial production of roll-out elements in compliance with mechanical and electrical compatibility requirements. - Working with our documentation, your specialists will receive advice on the nuances of linking the roll-out element to a specific K-15 modification (plug-in contacts, fine-tuning, curtains, locks, secondary connectors).

For more information on replacing the K-15 switchgear roll-out element (retrofit), please contact: inbox@proekt-energo.com

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