Retrofitting the roll-out element (RE) of the K-33 series switchgear involves replacing the connection trolley with a switch and connection units (primary plug-in contacts, secondary connector, interlocks, curtains, adjustment and fixing elements) with a modern kit while retaining the main switchgear cabinet. The most common reason for modernizing the K-33 is wear and tear of the switching apparatus and roll-out mechanics, an increase in interlock failures, and an increase in maintenance time. Installation of a new WE with a vacuum (or SF6, as required) switch transfers the connection to modern switching technology: no maintenance of the “oil system,” with a long service life, predictable shutdown characteristics, and the possibility of expanding secondary systems (RZA, arc protection, monitoring) .

• When is K-33 retrofitting most justified?
• Compatibility: what must match in K-33
• New roll-out element device: components and specifics
• Scope of delivery and design options
• Technical data (standard)
• Questionnaire: what data is required from the customer
• Secondary circuits and connectors: connection scenarios
• Interlocks, curtains, and safe operations
• Quality control and acceptance: measurable criteria
• Typical work plan and downtime minimization

When is retrofitting K-33 most justified?

• Switch service life: permissible operating hours/time exceeded, unstable switching times observed, shortage of spare parts or complexity of inspections.
• Overheating of the plug-in unit: increase in contact resistance, local heating due to wear/misalignment, traces of burning on contact surfaces.
• Problems with interlocks and curtains: “false” prohibitions, incomplete closure of curtains, wear of rods/cam mechanisms, inability to ensure a safe sequence of operations.
• Requirements for secondary system modernization: the need to install arc protection, event recording, relay protection and automation terminals, and telemechanics interfaces without reconstructing the entire switchgear.

Compatibility: what must match in K-33

K-33 comes in different factory and facility modifications, so the key stage is linking the new VE to a specific cell. The following compatibility points are important in practice:

• Geometry of the plug-in node: position of phase contacts, insertion depth, adjustment stroke, ensuring the required pressure and dielectric distances.
• Trolley support bases: guides/rollers, height marks, elimination of skew during insertion, stability in extreme positions.
• Repair/test/operating positions: reproducible locking, position monitoring with limit switches, compliance with locking and release logic.
• Curtain mechanism: coordination of curtain drives with trolley kinematics, elimination of jamming, correct coverage of access to live parts.
• Secondary connector: compatibility by type/pinout or use of an adapter solution while retaining circuit labeling.
• Connection to the grounding device (if provided): “switch-trolley-grounding device” interlocks, prohibitions on conflicting positions.

New roll-out element device: components and specifics

The new roll-out element for K-33 is supplied as a functionally complete connection module and includes the following components:

• Frame (trolley) with reinforced bases ensuring repeatable insertion and stable geometry of the plug-in unit throughout its service life.
• Switching device: 6/10 kV vacuum circuit breaker (or SF6 circuit breaker on request) with spring-motor or electromagnetic drive; drive readiness circuits, block contacts, manual cocking/control devices (depending on the version) are provided.
• Primary contacts: a set of plug-in contacts/adapters for the mating parts of a specific K-33 cell. The following are specified at the design stage: contact force, permissible contact resistance, resistance to dynamic forces during short circuits, and availability of control measurements (micro-ohmmetry).
• Adjustment and locking mechanism: ensures “soft” entry into the working position, locks the trolley, prevents spontaneous movement out of position during vibrations, and ensures correct operation of the limit switches.
• Curtains: mechanism for automatically closing the openings of current-carrying parts when the trolley is moved to the “repair” position; access blocking elements are provided in case of position mismatch.
• Locks: mechanical and/or electromagnetic elements that prevent incorrect sequences of operations and ensure a clear connection status.
• Secondary interface: connector/terminal module with an adapter for existing control, signaling, and relay protection circuits, with preserved labeling and controlled pinout.

Scope of delivery and design options

The standard delivery of the K-33 retrofit is based on the principle of maximum readiness for installation:

• roll-out element assembly (trolley, switch, drive, primary contacts with adapters, adjustment/fixing, curtain assembly, locks, limit switches);
• secondary connector and/or transition strips, circuit correspondence table (I/O matrix), marking kit;
• passport, installation/configuration/operation manual, VE test reports;
• set of plates, pictograms, and warning signs for updating connection markings.

The project allows for on-site work: replacement of the mating part of the secondary connector, relocation of position sensors, partial replacement of curtain mechanism elements, adjustment of the front panel, and local modernization of secondary circuits (without interfering with the bus compartment).

Technical data (typical)

Questionnaire: what data is required from the customer

To link the new VE to K-33 and reduce the risk of non-compliance, it is recommended to collect the following initial data:

Secondary circuits and connector: connection scenarios

For K-33, there are three practical scenarios for connecting secondary circuits that allow you to avoid “reworking” the cabinet:

1. Compatible “1 to 1” connector — the type and pinout are preserved; installation is reduced to connecting the standard harness and functional testing.
2. Transitional pinout — an adapter (transitional plate/frame) with a circuit correspondence table is installed, while the marking and signaling logic are retained.
3. Replacement of the mating part of the connector — performed when the contacts are worn or when functions are expanded (addition of control circuits, arc protection, telemechanics).

In any case, it is recommended to draw up a “secondary interface passport”: pinout, list of circuits, control measurement points, and list of limit switches/block contacts involved in the interlock logic.

Interlocks, curtains, and safe operations

The safety of the K-33 retrofit is determined by the correct sequence of operations. A typical set of implemented functions:

• prohibition of trolley movement when the switch is on;
• prohibition of switching on the switch outside the “test/operating” positions (with confirmation of trolley fixation);
• locks with a grounding device (if available): exclusion of simultaneous “operating position of the electrical equipment” and “grounding device turned on”;
• correct operation of curtains when switching between positions, blocking access to openings when the position is incorrect;
• position indication and sealing capability (as required by operating conditions).

Quality control and acceptance: measurable criteria

To reduce technological risks, it is recommended to accept the K-33 retrofit based on measurable parameters rather than “visual compliance.” . Typical list:

• Kinematic: no misalignment or jamming, repeatability of position fixing, correct operation of curtains and locks.
• Main circuit: micro-ohmmetry of the contact node transition resistance after several roll-in/roll-out cycles; quality control of contact surfaces.
• Secondary part: functional check of switching on/off, position signaling, locking circuits, disconnection circuits from the relay protection and automation system (including backup disconnection circuits, if any).
• Circuit breaker and drive: electrical checks (drive readiness, coil correctness, power supply control, if necessary — switching on/off time measurements).

The result of the acceptance test is a set of protocols, a list of settings (limit switches, interlocks, pinouts), and a list of changes relative to the original diagram.

Standard work plan and downtime minimization

For facilities where deadlines are critical, it is advisable to organize the K-33 retrofit as a sequence of “inspection → factory assembly and testing → short installation window → PNR” . When a new assembled switchgear is delivered, the main labor intensity is transferred to the factory: adjustment of fine-tuning and interlocks, checking of secondary circuits, preparation of marking kits. The following remain at the facility: installation of switchgear, control measurements, checking of relay protection and automation/signaling logic, and commissioning according to an agreed program.

We offer you documentation for replacing the KRU K-33 roll-out element (retrofit):

- Preliminary technical documentation for participation in tenders for the replacement of the KRU K-33 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 manufacturing the KRU K-33 roll-out element at your enterprise. If you do not plan to manufacture the product's 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:

- You receive a technical solution (contacts, fine-tuning, interlocks, secondary interface) linked to a specific K-33 modification with controlled quality criteria.
- The main volume of work is transferred to factory assembly and testing, which reduces risks and downtime at the facility.
- Your specialists receive advice on critical power equipment components: plug-in contacts, repeatability of fine-tuning, curtains, interlocks, and test measurements.

For more information on replacing the K-33 switchgear roll-out element (retrofit), please contact: inbox@proekt-energo.com

PDF - Download technical information on replacing the K-33 roll-out element