EN
Wall Bushing
Wall bushing is an epoxy resin insulation component engineered for 12kV medium voltage switchgear, designed for busbar penetration between adjacent compartments. Manufactured using APG casting technology, this wall-through bushing features a hollow channel that allows solid busbar feed-through, deep alternating creepage skirts for high flashover resistance, and an integrated central mounting flange for secure cabinet installation. Available in round and oval profiles with comprehensive size options, this wall bushing seals and isolates busbars passing through metal compartment walls, maintaining insulation integrity across compartment boundaries while providing mechanical support and dielectric isolation for busbar systems.
- Overview
- Applications
- Technical Data
- Services
- Quality Control
- Recommended Products
Epoxy Wall-Through Bushing - 12kV / 24kV Busbar Penetration
A wall-through bushing carries a live busbar through an earthed metal barrier while maintaining both the insulation and the compartment seal. In metal-clad switchgear this is what allows the busbar to pass from the busbar compartment into the breaker compartment, and from panel to panel along a lineup, without compromising the compartmentalisation that defines metal-clad construction. MOLDVOLT manufactures 12kV and 24kV bushings using APG casting.
THE COMPARTMENT SEAL IS THE POINT
Metal-clad switchgear works because its compartments are separated. An internal arc in the breaker compartment must not propagate into the busbar compartment, and pressure from an arc must vent through the designed relief path rather than through a gap around a busbar penetration. The bushing is what maintains that separation at every point where a conductor crosses a barrier.
A poorly made or incorrectly fitted bushing undermines the entire internal arc classification of the panel. This is not a component where dimensional approximation is acceptable, which is why our critical fit dimensions are 100% inspected rather than sampled.
APG CASTING AND PARTIAL DISCHARGE
Automatic Pressure Gelation produces a void-free epoxy matrix. Voids inside cast epoxy sit in regions of concentrated electrical stress and discharge internally at operating voltage, progressively eroding the resin until the bushing punctures to earth - typically years after installation and long after any acceptance test would have caught it. Every bushing is partial-discharge tested to below 10 pC at 1.1 times rated voltage.
CYCLOALIPHATIC EPOXY FOR HARSH CLIMATES
Cycloaliphatic resin resists surface tracking and UV degradation far better than general-purpose bisphenol formulations, giving a -40 C to +105 C service range that covers both Gulf switchroom temperatures and CIS winter conditions. Extended creepage is available for coastal and heavily polluted environments.
TYPES AND RATINGS
Wall-through bushings for busbar penetration between compartments, rated 630A to 3150A. GIS insulating sleeves, including the 202 type bushing, for RMU and gas-insulated switchgear cable elbow connections. Current ratings and conductor bar dimensions are matched to the panel busbar system, and both cast-in conductor and clearance-hole configurations are available.
SUPPLY
Available as OEM production to customer drawings and as direct-replacement spares for KYN28, HXGN, RMU and GIS panels. Where the original part is obsolete, send a sample, drawing or dimensioned photograph and we will produce an equivalent.
PRIMARY APPLICATIONS
- Busbar penetration between the busbar and breaker compartments in KYN28-12 and KYN28-24 metal-clad switchgear.
- Panel-to-panel busbar continuity through side walls along a switchgear lineup.
- Cable compartment conductor penetrations.
- GIS and RMU cable elbow connection interfaces, including 202-type insulating sleeves.
- Transformer and reactor terminal bushings within enclosures.
- Penetrations in fixed-type switchgear and compact substation cabinets.
- LV distribution board busbar penetrations, using the appropriate LV rating.
- Replacement spares for aged switchgear across the installed base in Africa, CIS and the Middle East.
- Panel builder and switchgear workshop production stock.
WHY BUSHINGS FAIL AND WHY THEY MATTER
Bushings degrade from three causes: internal partial discharge from casting voids, surface tracking from pollution and condensation, and mechanical cracking from busbar thermal expansion or short-circuit forces. All three progress invisibly. A failed bushing is a phase-to-earth fault at the compartment barrier, which is among the more destructive failures a panel can suffer because it occurs precisely where the compartmentalisation is supposed to contain damage.
SELECTION GUIDANCE
Specify by rated voltage and BIL, rated current and conductor cross-section, barrier plate thickness and mounting hole pattern, and pollution level of the installation environment. For coastal Gulf and West African sites, specify extended creepage. Confirm whether the conductor is cast in or passes through a clearance hole, as this affects both the thermal path and the sealing arrangement.
REGIONAL FIT
- Middle East: high ambient temperature and coastal salt fog; extended creepage and verified elevated-temperature performance are the relevant specifications.
- Africa: humid and industrially polluted environments, with high replacement demand across an aged installed base.
- Russia and CIS: verified low-temperature performance to -40 C, since epoxy embrittles as temperature falls and busbar thermal cycling is severe.
- Eastern Europe: standard IEC service in temperate switchrooms.
NOT SUITABLE FOR
Outdoor unprotected installation unless specified with outdoor creepage and UV-stabilised formulation. Current ratings above the selected type. Applications requiring an oil-filled or gas-filled bushing.
| Category | Parameter | 12 kV Type | 24 kV Type |
| Standards | Compliance | IEC 60137, IEC 60168, IEC 62217 | IEC 60137, IEC 60168, IEC 62217 |
| Electrical Ratings | Rated Voltage | 12 kV | 24 kV |
| Rated Current | 630 / 1250 / 1600 / 2000 / 2500 / 3150 A | 630 / 1250 / 1600 / 2000 A | |
| Power-Frequency Withstand Voltage (1 min) | 42 kV | 50 kV | |
| Lightning Impulse Withstand Voltage (BIL) | 75 kV peak | 125 kV peak | |
| Partial Discharge | < 10 pC at 1.1 × Uₙ | < 10 pC at 1.1 × Uₙ | |
| Short-Circuit | Short-Time Withstand Current | 25 kA / 31.5 kA for 4 s (matched to panel rating) | 25 kA / 31.5 kA for 4 s (matched to panel rating) |
| Peak Withstand Current | 63 kA / 80 kA | 63 kA / 80 kA | |
| Material & Construction | Material | Cycloaliphatic epoxy resin, APG cast | Cycloaliphatic epoxy resin, APG cast |
| Filler | Silica, controlled ratio for thermal & mechanical stability | Silica, controlled ratio for thermal & mechanical stability | |
| Colour | RAL 7035 light grey (standard) | RAL 7035 light grey (standard) | |
| Conductor | Cast-in copper bar, or clearance hole for customer busbar | Cast-in copper bar, or clearance hole for customer busbar | |
| Conductor Plating | Silver or tin plated where cast in | Silver or tin plated where cast in | |
| Inserts | Brass or steel threaded inserts, cast in | Brass or steel threaded inserts, cast in | |
| Mounting | Flange with bolt pattern to customer specification | Flange with bolt pattern to customer specification | |
| Barrier Plate Thickness | To customer specification | To customer specification | |
| Creepage | Standard Creepage Distance | ≥ 16 mm/kV | ≥ 16 mm/kV |
| Extended Creepage | 20 mm/kV / 25 mm/kV (medium & heavy pollution, coastal & industrial) | 20 mm/kV / 25 mm/kV (medium & heavy pollution, coastal & industrial) | |
| Service Conditions | Operating Temperature | −40 °C to +105 °C | −40 °C to +105 °C |
| Altitude | Up to 1000 m standard; up to 2000 m on request | Up to 1000 m standard; up to 2000 m on request | |
| Humidity | Suitable for tropical & high-humidity service | Suitable for tropical & high-humidity service | |
| Temperature Rise | Within 70 K per IEC 62271-1 at rated current | Within 70 K per IEC 62271-1 at rated current | |
| Flame Retardancy | UL94 V-0 grade available | UL94 V-0 grade available |
TESTING - EVERY PIECE OR EVERY BATCH
Partial discharge test | power-frequency withstand voltage test | dimensional inspection with critical fit dimensions 100% checked | visual inspection for cracks, voids and surface defects | contact resistance measurement on cast-in conductor types | thermal cycling on type samples | salt-spray testing for coastal-service parts
OPTIONS
Extended creepage for coastal and heavy-pollution sites | cast-in conductor or clearance-hole configuration | custom flange, length and mounting to customer drawing | customer part numbering and packaging | flame-retardant UL94 V-0 formulation | low-temperature verified formulation for GOST 15150 service | GIS 202-type insulating sleeve | reverse engineering from sample for obsolete parts
SPECIFICATION AND SOURCING
- Send a drawing, a sample or a photograph with the existing part number and we will identify the equivalent and confirm fit before you commit to an order.
- Reverse engineering from a physical sample where the original part is obsolete or the OEM no longer supplies it - common for aged KYN28, HXGN and imported panels still in service across Africa, CIS and the Middle East.
- OEM and private-label production to your drawings, with your part numbering and packaging.
- Material and plating selected for the destination environment: silver plating for lowest contact resistance indoors, tin plating for coastal and industrial atmospheres where salt fog and sulphides attack silver.
WHY THIS MATTERS COMMERCIALLY
Limited local technical expertise and difficult spare parts supply are consistently identified as the main barriers in Middle East and African electrical markets. A panel is out of service for as long as it takes the part to arrive. We hold consumable items in stock and quote fleet spares lists against your installed base so the part is on the shelf before it is needed.
QUANTITY AND LEAD TIME
- Stock items dispatched from inventory; typical production lead time 15-25 days for standard specifications.
- Low minimum order quantities on standard parts - we supply single-piece emergency replacements as well as bulk production volumes.
- Air freight for breakdown situations, sea freight consolidation for planned restocking.
TESTING AND DOCUMENTATION
- Routine testing per applicable IEC standard with results supplied per batch.
- Material certificates, plating thickness reports and dimensional inspection records available on request.
- Certification support for SONCAP, KEBS PVoC, SABER and GOST R submissions where the component ships as a standalone consignment.
AFTER-SALES
- Technical response within 24 hours; application engineering support for fit, assembly torque and maintenance intervals.
- Warranty against manufacturing and material defects: 12 months from delivery.
- Framework and call-off agreements available for panel builders, utilities and switchgear service workshops.
MATERIAL CONTROL
- Copper verified as T2 grade electrolytic copper or specified copper-silver alloy, with mill certificates retained per batch.
- Epoxy resin verified as cycloaliphatic grade with documented gel time, viscosity and filler ratio; general-purpose bisphenol resin is not accepted for outdoor or high-humidity service because of its poorer tracking and UV resistance.
- Plating thickness measured by X-ray fluorescence and recorded per batch - typically 8-12 microns of silver on contact surfaces. Under-plating is invisible on delivery and only shows up years later as a thermal fault, so this is measured rather than assumed.
PROCESS CONTROL
- APG (Automatic Pressure Gelation) casting under controlled mould temperature, injection pressure and gel time, producing a void-free matrix. Voids initiate partial discharge, and partial discharge is what eventually punctures an insulator in service.
- Vacuum degassing of resin before injection to eliminate entrapped air.
- Controlled post-cure cycle to relieve internal stress and stabilise dimensions.
- Contact finger spring force calibrated and verified against specification, ensuring uniform current sharing across all fingers.
ROUTINE TESTING - EVERY PIECE OR EVERY BATCH
- Partial discharge test on insulation components, typically below 10 pC at 1.1 times rated voltage.
- Power-frequency withstand voltage test.
- Contact resistance measurement on current-carrying parts.
- Dimensional inspection against drawing, with critical fit dimensions 100% checked.
- Visual inspection for cracks, voids, plating defects and surface finish.
- Mechanical load testing on insulators against rated cantilever strength.
TYPE TESTING
- Insulators verified to IEC 60168 and IEC 62217; contacts and conductive parts verified for temperature rise within the 70K limit of IEC 62271-1 at rated current.
- Thermal cycling and, for parts destined for coastal service, salt-spray corrosion testing.
TRACEABILITY AND SYSTEM
- ISO 9001 quality management system.
- Batch numbering linking finished parts back to raw material certificate and process records.
- Certificates of conformity, material certificates and test reports issued with each shipment.
- Retained samples held per production batch for future reference in the event of a field query.
