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The 75 kVA pad mounted transformer is a three-phase, oil-immersed distribution unit for small commercial and residential subdivision loads. Installed on a concrete pad with underground cabling in and out, it serves strip malls, medical clinics, small motels, telecom cabinets, water booster stations and the laterals of a growing residential area. Because the primary is fully underground, the installation stays clear of pedestrian and vehicle routes.
Oil temperature, oil level and pressure gauges are fitted so the unit can be checked without opening a door, and the sealed tank removes the need for routine oil top up. Off-circuit taps give two 2.5% steps above and below rated voltage, and every 75 kVA pad mounted transformer is routine tested before it leaves the works. The tank is filled with mineral oil or FR3 ester where fire or environmental rules require it.
| Electrical & Standards | Rated Capacity | 75 kVA |
Rated Primary Voltage | 2.4/4.16/7.2/12.47/13.2/13.8/24.9/34.5 kV or Customized | |
Secondary Voltage | Customized | |
Frequency | 50/60 Hz | |
Vector Group | Dyn11, Yyn1 or customized | |
HV Tap Changer | No-load / off-circuit ± 2×2.5% | |
Efficiency | DOE / NEMA TP-1 | |
Temperature rise | 55/65 °C | |
Impedance Voltage | 4-6% | |
Cooling Method | ONAN/ KNAN | |
Operation | Step Down & Step Up | |
Standards/Certificate | IEEE/ANSI, UL / cUL/ CSA/ DOE /NEMA | |
Application | Residential communities, Commercial centers, Industrial plants, Airports and railway stations, Schools and hospitals, Data centers, Solar / wind farm step-up applications, Temporary power supply | |
Altitude | ≤1,000 m, 1000–2000 m, 2000–3000 m, >3000 m | |
| Material & Structure | Transformer Oil | Mineral Oil or FR3 |
Winding Material | Aluminum / Copper | |
Core Material | CRGO Silicon Steel / Amorphous Alloy | |
Color | Customized | |
Tank Material | Mild Steel / Stainless Steel | |
Sealing | Nitrogen / inert gas blanket | |
Feed type | Radial feed / Loop feed | |
HV termination | Dead-front / Live-front | |
Elbow connectors | Load-break / Dead-break | |
Enclosure | One-piece steel housing with separate HV / LV / transformer compartments | |
Enclosure rating | NEMA 3R, etc. | |
Mounting | On concrete pad | |
Cooling structure | Sealed oil tank with exposed radiators | |
| Protection & Accessories | HV Protection | Bayonet fuse (Bay-o-net, dual-sensitive: temperature + current, field replaceable); backup current-limiting fuse (ELSP) |
Switching | Oil-immersed load-break switch (2-position terminal / 4-position loop feed); vacuum interrupter optional | |
Pressure Protection | Pressure relief valve | |
Monitoring | Oil temperature gauge, oil level gauge, pressure / vacuum gauge (contacts optional) | |
Maintenance Ports | Drain valve, sampling valve, Schrader valve | |
Enclosure Accessories | Lifting lugs, hinged doors, flip-top cover, tamper-proof channel, ground strap / pads, nameplate, brass plug, 15 kV inserts with dust caps, CEA ground bracket | |
Optional | Lightning arresters, viewing windows, key interlocks, sudden pressure relay, electrostatic shielding, K-factor design, vacuum circuit breaker |
It sits at the centre of the active part, stacked from cold-rolled grain-oriented silicon steel or amorphous alloy to form a closed magnetic circuit. Mitered 45° joints, core clamps and a single-point ground keep no-load loss, noise and circulating current low.
The winding nearest the core limbs. Because the low-voltage side carries the highest current, it is normally wound as copper or aluminium foil, giving a uniform distribution of ampere-turns and a high short-circuit withstand capability.
The outer winding, placed concentrically with the LV winding. It is built as a multilayer cylinder with oil ducts between layers, so the dielectric strength required by the primary voltage is achieved together with effective cooling of the conductor.
The tank is filled with mineral oil or a natural ester such as FR3. The fluid insulates the windings, carries heat from the active part to the tank walls and radiators, and excludes moisture from the paper insulation to slow its ageing.
A sealed mild steel or stainless steel tank with exposed radiators dissipates the heat of the loaded transformer by natural convection. The oil space is blanketed with nitrogen or an inert gas, so the fluid never meets outside air and remains maintenance free.
The primary compartment is arranged for either radial or loop feed. Dead-front or live-front terminations are mated with load-break or dead-break elbow connectors, allowing the incoming cable to be isolated and the loop to be extended without exposing live parts.
A separate low-voltage compartment brings the secondary leads out to underground service cables. Keeping the LV terminations in their own locked section means service work on the secondary side can be carried out without entering the primary compartment.
Primary protection is provided by a Bay-o-net bayonet fuse that senses both temperature and current and is replaceable in the field, backed up by an ELSP current-limiting fuse. An oil-immersed load-break switch handles two-position or four-position loop operation.
A one-piece steel housing divides the unit into separate HV, LV and transformer compartments, each with its own hinged door and tamper-proof channel. The enclosure is rated NEMA 3R, with lifting lugs, ground pads, a nameplate and viewing windows available.
The complete unit is mounted on a concrete pad, so no vault or fenced compound is needed and the transformer sits directly at the point of load. A pressure relief valve, drain valve, sampling valve and gauges are fitted for safe operation over its service life.
Every pad mounted transformer is tested before shipment against the applicable standards and customer requirements — from the first batch of raw material to the final routine test on the factory floor.
Quality begins with the materials we bring in. Every batch of tank steel, core lamination, winding conductor and insulating fluid is inspected against approved specifications before production, with supplier qualification and traceability records maintained for each shipment.
Progress tests are conducted at key stages of the manufacturing process to verify that every 75kVA three-phase pad mounted transformer meets design and quality requirements before final assembly.
Before leaving the factory, each transformer undergoes routine testing — conducted in accordance with IEEE/ANSI, UL / cUL and CSA requirements for pad mounted distribution transformers — covering key parameters such as insulation resistance, winding DC resistance, voltage ratio and vector group, no-load loss and current, load loss and short-circuit impedance, applied and induced voltage withstand, and pressure tightness of the sealed tank.
Upon successful completion of all tests, the unit is shipped with a factory test report and a certificate of conformity, ensuring that every delivered product meets its rated performance and safety specifications.
75kVA Pad Mounted Transformers are available with a range of configurable options to meet different electrical and environmental requirements. Customers can select the appropriate insulating fluid, voltage configuration, feed arrangement, protection devices and accessories according to their specific project conditions.
For projects with higher environmental and fire-safety requirements, a natural ester such as FR3 can be selected instead of conventional mineral oil. These fluids offer a higher fire point and good biodegradability, making them suitable where environmental protection and installation safety are important considerations.
The primary compartment can be configured for radial or loop feed, with dead-front or live-front terminations and load-break or dead-break elbow connectors. Protection options include bayonet fuses with current-limiting backup, oil-immersed load-break switches, lightning arresters, sudden pressure relays and oil temperature monitoring.
The enclosure can be supplied in mild steel or stainless steel with a customized finish, together with viewing windows, key interlocks, electrostatic shielding, K-factor designs for harmonic-rich loads, and vacuum circuit breakers where switching duty demands them.
We ensure every three-phase pad mounted transformer is safely packed, securely transported, and ready for installation.
Secure Packaging: Weather-resistant wooden crates or steel containers protect against moisture, vibration, and impact.
Complete Accessories: Fuses, elbow connectors, gauges and standard accessories are factory-installed and tested, while optional components are packed separately.
Reliable Transport: Road, rail, or sea shipping is arranged according to project requirements.
Complete Documentation: Test reports, certificates, manuals, and shipping documents are provided.
Installation Support: Siting on the concrete pad, cable termination and commissioning guidance is available for smooth project delivery.
A pad mounted transformer is a three-phase distribution transformer installed outdoors at ground level on a concrete pad, with its enclosure sitting directly at the point of load. Both the primary and the secondary cables are routed underground, so no overhead line or fenced substation is visible from the street.
An oil-immersed load-break switch handles primary switching, and its configuration follows the feed arrangement of the network.
The feed arrangement decides how many primary cables enter the unit and whether the loop can be continued to a neighbouring transformer.
