Retrofit of the KRU-2-10 roll-out element involves replacing the connection trolley (VE) in 6–10 kV cells for currents of 2000–3150 A with the installation of a modern circuit breaker and updated interface units while retaining the KRU cabinet: busbars, cable connections, main metal structures, and switchgear layout. Unlike “universal” solutions for 630–1600 A, the KRU-2-10 retrofit in the 2000–3150 A range places increased demands on the contact system and thermal regime: repeatability of adjustment, contact force, contact surface quality, and coordination of current-carrying parts with the existing busbar are critical. Therefore, a correct design begins with an inspection of a specific cell and confirmation of the main circuit parameters by measurements (including micro-ohmmetry) and heating calculations.

Page content

• When is a KRU-2-10 retrofit most appropriate?
• KRU-2-10 withdrawable unit: what exactly is being replaced
• Features of 2000–3150 A currents: contacts, heating, adjustment
• Compatibility with the cell: mechanics, curtains, secondary interface
• Technical data (typical)
• Work stages and downtime minimization
• Testing and acceptance criteria
• Options: arc protection, relay protection, monitoring, and telemechanics

When is retrofitting KRU-2-10 most appropriate?

• Input and sectional connections with currents of 2000–3150 A, where downtime is unacceptable and the service life of the circuit breaker/trolley already limits the reliability of the switchgear.
• Overheating of the plug-in unit and traces of thermal impact on contact parts: this is a typical “trigger” for replacing the switchgear in a high-current design.
• Worn adjustment and fixation: failure to adjust at high currents quickly leads to an increase in contact resistance and accelerated aging of the contacts.
• Inability to maintain old equipment: shortage of spare parts, lengthy repairs, lack of factory regulations for the actual condition.
• Transition to modern relay protection and automation and requirements for event recording/remote control without reconstructing the entire switchgear.

KRU-2-10 withdrawable unit: what exactly is being replaced

The withdrawable unit in the KRU-2-10 is a functional connection module that combines power switching and safe cell maintenance. During retrofitting, as a rule, the entire withdrawal unit is replaced, not just the circuit breaker, since at currents of 2000–3150 A, “interfaces” and mechanics play a significant role:

• Trolley (frame) with bases for the circuit breaker, guides/rollers, fixing and adjustment assemblies.
• 6–10 kV switch of the vacuum type (or SF6 according to the technical specifications) with a drive and a set of contact blocks.
• Primary plug-in contacts for high current loads with adapters for fixed contacts of a specific KRU-2-10 cell.
• Current-carrying jumpers/buses on the trolley (if available in the design), rated for 2000–3150 A in terms of heating and short-circuit dynamics.
• Curtain mechanism and elements to protect against access to current-carrying parts when the trolley is rolled out.
• Locks and limit switches for the “repair/test/operating” positions, prohibiting erroneous operations.
• Secondary interface (connector/terminal module) for control, signaling, and relay protection circuits.

Features of 2000–3150 A currents: contacts, heating, adjustment

High main circuit currents in KRU-2-10 place increased demands on each element of the plug-in connection. The following points are essential for retrofitting in the 2000–3150 A range:

• Contact force and geometry: the pressure must be reproducible with each insertion cycle. Any misalignment at these currents quickly manifests itself in overheating and increased contact resistance.
• Quality of contact surfaces: the material, coating, condition of the contact lamellas/fingers, and absence of local defects are critical for stable thermal conditions.
• Thermal decoupling and heat dissipation: the design takes into account the heating of the contact area, the location of current-carrying parts relative to screens/partitions, as well as the ventilation conditions in the compartment (depending on the cabinet design).
• Mechanical rigidity of the trolley: skewing of the trolley during rolling in can result in uneven contact between phases — this is a direct path to local overheating of one phase and accelerated wear.
• Resistance to dynamics during short circuit: the current-carrying parts of the switchgear, fastenings, and contact assembly must withstand electrodynamic forces without “opening” the contact and without residual deformation.

That is why, when retrofitting KRU-2-10 2000–3150 A, it is recommended to set measurable quality criteria: micro-ohm measurement of the main circuit, verification of repeatability of adjustment, and control of trolley position locking.

Compatibility with the cell: mechanics, curtains, secondary interface

The correct replacement of the KRU-2-10 roll-out element must be carried out without “rearranging” the cabinet. To do this, the following interfaces must be compatible:

1. Mechanical: guides, stops, fasteners, kinematics of adjustment, access to controls, stability of the trolley in extreme positions.
2. Power: mating of plug-in contacts with fixed contacts of the cell, compliance with height marks and insertion depth, dielectric distances.
3. Curtain: automatic closure of current-carrying part openings when rolling out, no jamming, access blocking in case of incorrect position.
4. Secondary: connection via a compatible “1:1” connector, via an adapter or by replacing the mating part of the connector (in case of contact wear or function upgrade).

If a grounding device is available, the “trolley-switch-grounding device” interlocks are coordinated to eliminate conflicting positions and ensure a safe sequence of operations.

Technical data (typical)

Work stages and downtime minimization

For KRU-2-10 at currents of 2000–3150 A, downtime is usually critical, so a work plan is recommended where the main complexity is shifted to factory preparation:

1. Inspection: fixing the contact system, guides/adjustments, curtains, secondary connector, condition of fixed contacts.
2. Binding project: contact adapters, kinematics of adjustment, list of interlocks, table of secondary circuit correspondence.
3. Manufacturing and assembly of VE: adjustment of the adjustment, verification of interlocks, functional runs of secondary circuits.
4. Installation in the control room: installation of the trolley, connection of the secondary interface, control measurements of the main circuit.
5. PNR: checking interaction with RZA, correctness of shutdown and signaling, drawing up protocols.

Tests and acceptance criteria

For high-current KRU-2-10 switchgear, it is recommended to accept the product based on criteria directly related to reliability and heating:

• Micro-ohmmetry of the transition resistance of the main circuit after several roll-in/roll-out cycles (assessment of contact repeatability).
• Finishing check: position fixation, absence of backlash, correctness of limit switches and permissions for switching on.
• Shutters and interlocks: guaranteed closure, no jamming, unambiguous interlocks.
• Secondary circuits: functional checks of switching on/off, position signals, locking circuits, disconnection from RZA.
• Switch: checks according to RE (drive readiness, coil power supply, if necessary — control of operation times).

Based on the results, a set of protocols and a list of settings are drawn up: limit switches, interlock parameters, connector/adapter pinout, and a list of changes made.

Options: arc protection, relay protection, monitoring, and telemechanics

• arc protection (optics + current criterion) with circuit breaker tripping and event logging;
• RZA modernization: terminals, UROV/APV according to the project, expansion of oscillography and event archive;
• monitoring: operation counter, resource control, control of operating circuit voltage and “drive ready” signal;
• integration into ACS/SCADA: remote signaling of positions and alarms, exchange protocols according to the project (if a terminal/gateway is available).

We offer you documentation for replacing the KRU-2-10 roll-out element (retrofit):

- Preliminary technical documentation for participation in tenders for the replacement of the KRU-2-10 withdrawable unit (6–10 kV, 2000–3150 A). 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-2-10 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:

- Focus on high currents of 2000–3150 A: the contact system, adjustment, and thermal regime are confirmed by measurements and protocols.
- Link to your specific KRU-2-10 cell without interfering with busbars and cable connections.
- Possibility of phased modernization: first, reliable VE, then arc protection/RZA/telematic according to the project.

For more information on replacing the KRU-2-10 roll-out element (retrofit), please contact: inbox@proekt-energo.com

PDF - Download technical information on replacing the KRU-2-10 withdrawable unit