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The box type transformer is a compact outdoor unit that encloses the transformer and its switching equipment in a steel box for direct connection to an overhead or cable network. It suits commercial buildings, apartment blocks, warehouses, logistics yards and light manufacturing plants. The unit is assembled and routine tested in the factory, which shortens the site programme to foundation work, cable termination and commissioning.
The box type transformer is built around a welded steel enclosure with a galvanised finish and a sandwich panel roof, and the cable compartment is sealed against dust and water. The incoming side takes a load switch or a vacuum circuit breaker, and the low voltage side provides busbar distribution with moulded case circuit breakers. The unit is supplied for 10 kV, 12 kV, 35 kV or 40.5 kV networks.
| Electrical & Standards | Rated HV voltage | 10 kV / 12 kV / 35 kV / 40.5 kV (IEC 1 -52 kV) |
Rated LV voltage | 0.4 kV (three-phase, 4/5-wire) or Customized | |
Rated capacity | 50–2500 kVA or Customized | |
Rated frequency | 50 Hz / 60 Hz (IEC 62271-202 covers up to 60 Hz) | |
Transformer type | Oil-immersed/ dry-type | |
HV switchgear | Ring main unit (RMU), load switch + current-limiting fuse, vacuum circuit breaker (VCB), or gas-insulated switchgear (GIS/SF6) | |
LV switchgear | Moulded-case circuit breakers (MCCB), air circuit breakers (ACB), high-breaking capacity | |
Enclosure protection | IP33 / IP44 / IP54 / IP65 | |
Ambient temperature | −45 °C to +50 °C (extreme-cold variants lower) | |
Seismic resistance | Horizontal acceleration ≈ 0.4 m/s² | |
Noise level | Controllable below 45 dB | |
Supply modes | Ring, radial (terminal), dual-source | |
Standards | IEC/ASTM/UL/IEEE/GB | |
| Structure & Materials | Type | European-style/US-style/Chinese-style/Mobile substation |
Enclosure — outer skin | aluminum alloy / stainless steel | |
Enclosure — insulation core | high-density rock wool or polyurethane foam | |
Enclosure — inner skin | galvanized steel sheet or fire-resistant panel | |
Anti-corrosion coating | Epoxy zinc-rich primer + polyurethane topcoat (double-layer) | |
Enclosure fabrication | CNC bending, welding → pickling & phosphating → multi-layer painting | |
Transformer core | CRGO Silicon Steel / Amorphous Alloy | |
Transformer windings | Copper windings (or aluminum); epoxy cast-resin insulation for dry-type | |
Transformer insulation/cooling | Mineral transformer oil / epoxy resin / air | |
HV/LV busbars | Copper or aluminum busbar, armored busway | |
Switchgear enclosures | Coated steel sheet (e.g., aluzinc/galvanized) | |
Foundation / base | Welded steel platform + concrete base | |
| Application | Urban distribution | Urban network renovation, old-residential upgrading, road lighting, commercial complexes, schools, hospitals, municipal pumping stations |
Rural electrification | Rural grid upgrading, township supply | |
Renewable energy | Wind farms , PV plants, distributed storage integration | |
EV charging | EV charging-station substations, battery-swap stations | |
Industrial & mining | Factories, mines, oil & gas fields, large construction sites | |
Temporary & emergency | Site temporary power, emergency rescue, mobile rental units | |
Special environments | Severe cold, high altitude, seismic zones, coastal saline areas | |
Municipal landscaping | Parks, scenic areas, urban landscape belts | |
| Accessories | Metering | Energy meters, current/voltage transformers, metering compartment |
Power factor correction | Automatic low-voltage reactive power compensation (capacitor bank, controller, switching devices) | |
DC supply | DC panel (DC 220V / 110V) for control, protection and signaling | |
Protection | Relay protection (overcurrent, earth fault, gas, temperature), fuses, surge arresters, interlocking | |
Climate control | Anti-condensation heater, intelligent temperature controller, axial fans, temperature/humidity sensors | |
Monitoring & communication | Smart monitoring system, remote data acquisition, fault diagnosis, SCADA / telecontrol, IEC 61850 communication | |
Lighting | Independent lighting per compartment (explosion-proof optional) | |
Ventilation | Natural vents, forced exhaust fans, louvered vents | |
Lightning & earthing | Surge arresters, earthing busbar, earth electrodes, earthing grid | |
Fire protection | Fire alarm system, extinguishers; oil pit / oil drain for oil-immersed transformers | |
Cable & busway | Incoming/outgoing cables, cable terminations, busway/bus duct | |
General | Safety locks (anti-misoperation), lifting lugs, nameplate, warning signs, tool kit |
The enclosure is a double-layer sandwich construction: aluminium alloy or stainless steel outer skin, galvanised steel or a fire-resistant panel inside, and a core of high-density rock wool or polyurethane foam. Panels are CNC bent and welded, then pickled, phosphated and painted in multiple layers with an epoxy zinc-rich primer and a polyurethane topcoat.
The unit is divided into separate high voltage, transformer and low voltage rooms, each with its own access door. Separating the rooms keeps operation of the switchgear independent of work on the transformer, and the layout follows the type selected for the project - European, US, Chinese or mobile.
The transformer is oil-immersed or dry-type, as the project requires. It is built on a CRGO silicon steel or amorphous alloy core with copper windings (aluminium on request), and dry-type units use epoxy cast-resin insulation so that no oil is present in the room.
The high voltage room accepts a ring main unit, a load switch with current-limiting fuse, a vacuum circuit breaker, or gas-insulated switchgear, selected against the rated HV voltage of 10 kV, 12 kV, 35 kV or 40.5 kV and the supply mode of the network.
The low voltage room carries moulded-case or air circuit breakers with high breaking capacity, together with copper or aluminium busbars and, where required, an armoured busway for the outgoing circuits.
A dedicated metering compartment houses the energy meters and current and voltage transformers. Automatic low voltage reactive power compensation, with capacitor bank, controller and switching devices, can be fitted in the same room.
A DC panel at 220 V or 110 V supplies control, protection and signalling. Relay protection covers overcurrent, earth fault, gas and temperature, backed by fuses and surge arresters on the incoming and outgoing circuits.
An anti-condensation heater and an intelligent temperature controller keep the interior dry, with axial fans for forced cooling when the load demands it. Natural vents, louvered openings and exhaust fans maintain air movement through the rooms in service.
A smart monitoring system collects operating data for remote acquisition and fault diagnosis, and can report to a SCADA or telecontrol system where the operator requires remote supervision of the substation.
The enclosure stands on a welded steel platform over a concrete base. Earthing is provided by a busbar, earth electrodes and an earthing grid, while fire protection covers alarms, extinguishers and an oil pit with oil drain below oil-immersed transformers.
Every prefabricated substation is checked as a complete assembly — enclosure, switchgear and transformer — before it is released for shipment.
Enclosure panels, switchgear, busbar and the transformer active part are inspected against the approved specification on receipt, and the records are kept so that each batch of material can be traced to the assembled substation it was used in.
The enclosure is checked after fabrication and painting, and the wiring, busbar and protection settings are verified during assembly, so that every box type transformer is confirmed against its design before final testing.
Before shipment the transformer goes through its routine tests to IEC 60076, and the complete assembly is function tested to IEC 62271-202 practice, covering ratio, losses, impedance, dielectric withstand, insulation resistance, circuit breaker and switch operation, interlocking, and the sealing of the enclosure.
The substation is delivered with the test reports, protection settings and a certificate of conformity, together with final inspection photographs where the project requires them.
Box Type Transformers are built to the network they will serve. Rated HV voltage, rated LV voltage, capacity, supply mode and the transformer type are fixed first, and the switchgear, enclosure and accessories are then configured around them.
High voltage is selected from 10 kV, 12 kV, 35 kV or 40.5 kV, the low voltage side from 0.4 kV in three-phase four or five wire arrangement, and the capacity from 50 kVA to 2500 kVA, or to a customized value. Ring, radial and dual-source supply modes are available, and the enclosure is offered in European, US, Chinese or mobile form.
The enclosure can be supplied with aluminium alloy or stainless steel skin and the insulation core, coating system and ingress protection are matched to the site — coastal, severe cold, high altitude or seismic zones — as described in the project specification.
On the equipment side, the high voltage room is configured with a ring main unit, load switch with fuse, vacuum circuit breaker or gas-insulated switchgear; the low voltage room with the breakers, busbar and power factor correction the load requires; and metering, DC supply, relay protection, climate control and remote monitoring are added where the operator needs them.
Prefabricated substations are shipped as tested assemblies, packed so that the enclosure, switchgear and transformer arrive ready for site installation.
Secure Packaging: Panels and bushings are protected against moisture, vibration and impact, and openings are sealed for the journey.
Factory Assembly: Internal wiring, busbar and protection settings are completed and verified in the factory, which keeps site work to foundation, connection and commissioning.
Reliable Transport: Road, rail or sea freight is arranged to the project schedule, with lifting points marked on the enclosure for the crane or forklift.
Complete Documentation: Drawings, test reports, protection settings, manuals and shipping documents travel with the unit.
Installation Support: Guidance on foundation levelling, cable termination, earthing and energisation is available for commissioning.
The enclosure is a double-layer sandwich panel construction, fabricated in the factory and finished for outdoor service.
The low voltage room carries the outgoing protection and distribution equipment for the load.
Yes. A smart monitoring system collects operating data for remote acquisition and fault diagnosis, and can report to a control centre.
