1250kVA Three Phase Pad Mounted Transformer
NPC ELECTRIC's 1250kVA Three Phase Pad Mounted Transformer is a high-performance, oil-immersed distribution transformer engineered for reliable underground power distribution in demanding environments. It delivers exceptional efficiency (up to 99.2% or higher), low no-load and load losses, and a 65°C average winding rise for extended service life exceeding 30-40 years. Key components include high-grade silicon steel core, aluminum or copper windings, 5-position tap changer (±2x2.5%), pressure relief valve, oil level gauge, and tamper-resistant enclosure in Munsell green finish.
- Primary Voltage Ratings 34.5-19.92/13.8-7.957/13.2-7.62/12.47-7.2 or others
- Secondary Voltage Ratings 208GrdY/120;416GrdY/240 or Customized
- H.V. Tap Range ± 2×2.5% HV taps or others
- Type Loop Feed or Radial Feed
- BIL 30/95kV
- Standards IEEE, ANSI, NEMA, ASTM
- Application step-up systems, EV charging stations, and data center
- Power Rating 1250kVA
- Certificate UL
- Cooling Method ONAN, ONAN/ONAF, KNAN, KNAN/KNAF
- Oil Mineral Oil or FR3
- Opeartion Step Down & Step Up
Technical Specifications
Customization Optional
Packing and Shipping
Manufacturer Test
Routine Testing
Application
Technical Specifications
1250kVA Three Phase Pad Mounted Transformer
Technical Specifications
Accessories
| Rated Power | 1250kVA |
| Rating Primary Voltage | 4.16-34.5kV or customized |
| Secondary Voltage | 480GrdY/277 208GrdY/120 400GrdY/230 Customized（208Y/120 V to 4,160 V） |
| Frequency | 50/60Hz |
| Vector Group | Dyn1/Yyn0/Dyn11/Dyn5 |
| Winding Material | Aluminum/Copper |
| Efficiency | As IEEE,Doe 2016,CAS Std or Customized |
| Impedance Voltage | Nominal 3.5% or Customized 1.1-5.75% |
| Altitude | ≤1,000m or Customized |
| Color | ANSI 70 Light gray/Munsell 7GY3.29/1.5 or customized etc |
| Tank material | Mild Steel, 304 Stainless Steel |
| Insulating Oil Weight | 3500 kg |
| Total Weight | 9700 kg |
| Outline Dimensions（L×W×H）in. | 2880×2200×2100（mm） |
| Lifting Lug | ELSP Fuse |
| Hinged Door | BAY-O-NET Fuse |
| Parking Bracket | Tap Changer |
| Tank Cover | Oil Level Gauge |
| L.V Bushing (4-Hole ) | Pressure Relief Valve |
| Two/Four Position Load break Switch | Vacuum Pressure Gauge |
| HV Grounding Copper Bar | Terminal Block |
| Temperature Indicator | Door Handle |
| H.V Bushing Well(15kV) | Ground Strap |
| Grounding Copper Bar | Nameplate |
| 1"'Drain Valve With 3/8" Sampler | IR Window |
| 1" Upper Fill Valve Filter Press Connection | Terminal Box |
| Non-PCB decal | High Voltage Warning Signs |
Customization Optional
1250kVA Three Phase Pad Mounted Transformer
NPC Electric 1250kVA three-phase pad mounted transformer supports extensive customization to match specific project requirements, ensuring optimal performance across diverse electrical grids and applications. Voltage configurations are highly flexible, with primary ratings from 2.4kV to 34.5kV (including common options like 12.47kV, 13.8kV, 24.94kV, or 34.5kV grounded wye/delta) and secondary voltages such as 208Y/120V, 480Y/277V, 600V, or custom low-voltage outputs. Feed types include radial or loop configurations, with dead-front (200A bushing wells) or live-front bushings for enhanced safety and accessibility. Winding materials can be selected as high-conductivity aluminum for cost efficiency or premium copper for superior thermal performance and reduced losses. Tap changers offer 5-position (±2x2.5% or wider ranges) for precise voltage regulation under varying loads.
Optional upgrades include FR3 natural ester fluid for improved fire resistance (meeting NEC less-flammable requirements), K-factor ratings for harmonic-heavy loads (e.g., data centers or EV charging), vacuum fault interrupters (VFI), or differential protection relays. Enclosure enhancements feature stainless steel hinges, reinforced tamper-proof doors, seismic bracing for high-risk zones, or specialized coatings for corrosive environments like coastal or industrial sites. Accessories such as gauges (liquid level, pressure, temperature), sampling valves, surge arresters, and remote monitoring provisions can be integrated. All customizations adhere to IEEE, ANSI, DOE, and CSA standards, with full factory testing to verify compliance. This versatility allows seamless integration into utility networks, renewable energy setups, or heavy-duty commercial projects, delivering tailored solutions that maximize efficiency, safety, and longevity while minimizing installation footprint and operational costs.
Packing and Shipping
1250kVA Three Phase Pad Mounted Transformer
The 1250kVA three-phase pad mounted transformer is securely packaged to withstand international transportation demands, ensuring it arrives undamaged and ready for installation. The complete unit—tank, cabinet, bushings, and accessories—is typically shipped as a fully assembled transformer mounted on a reinforced wooden pallet base for easy handling via forklift or crane. The enclosure is wrapped in protective plastic film to shield against moisture, dust, and minor impacts, with all external bushings, gauges, and valves covered by temporary caps or padded guards to prevent damage during transit.
Wooden crates or heavy-duty wooden cases enclose the transformer for ocean freight or long-haul trucking, constructed from fumigated, export-grade timber compliant with ISPM-15 standards to meet global phytosanitary regulations. Internal bracing, foam padding, and shock-absorbing materials secure the unit against vibrations, tilting, or rough handling. Sensitive components like tap changers, pressure relief devices, and oil level indicators receive additional shockproof packaging. For oil-filled units, the transformer is shipped with factory-filled dielectric oil (or dry-type equivalent), sealed under vacuum or nitrogen blanket to maintain insulation integrity and prevent oxidation. Oil drums for any supplementary fluid are packed separately in sturdy crates with absorbent materials.
Shipping methods prioritize safety and efficiency. For domestic North American deliveries, flatbed trucks or lowboy trailers with specialized securing straps and chains transport the transformer directly to the site, often with escort vehicles for oversized loads exceeding standard dimensions (typical weight ~3750-4500kg, dimensions approx. 2.2-2.5m length/width/height). International shipments utilize 20ft or 40ft open-top or flat-rack containers for RoRo vessels, with lashings and blocking to IMO standards for sea stability. Air-ride suspension trailers minimize road vibrations during inland transport. All shipments include comprehensive insurance coverage, real-time tracking via GPS, and detailed documentation (packing list, bill of lading, test reports, and customs declarations).
Upon arrival, the transformer undergoes visual inspection for transit damage, with any issues reported immediately for resolution under warranty. Proper packing and shipping practices extend the transformer's service life by preventing mechanical stress or contamination, ensuring reliable performance from day one in utility, commercial, or industrial installations.
Wooden crates or heavy-duty wooden cases enclose the transformer for ocean freight or long-haul trucking, constructed from fumigated, export-grade timber compliant with ISPM-15 standards to meet global phytosanitary regulations. Internal bracing, foam padding, and shock-absorbing materials secure the unit against vibrations, tilting, or rough handling. Sensitive components like tap changers, pressure relief devices, and oil level indicators receive additional shockproof packaging. For oil-filled units, the transformer is shipped with factory-filled dielectric oil (or dry-type equivalent), sealed under vacuum or nitrogen blanket to maintain insulation integrity and prevent oxidation. Oil drums for any supplementary fluid are packed separately in sturdy crates with absorbent materials.
Shipping methods prioritize safety and efficiency. For domestic North American deliveries, flatbed trucks or lowboy trailers with specialized securing straps and chains transport the transformer directly to the site, often with escort vehicles for oversized loads exceeding standard dimensions (typical weight ~3750-4500kg, dimensions approx. 2.2-2.5m length/width/height). International shipments utilize 20ft or 40ft open-top or flat-rack containers for RoRo vessels, with lashings and blocking to IMO standards for sea stability. Air-ride suspension trailers minimize road vibrations during inland transport. All shipments include comprehensive insurance coverage, real-time tracking via GPS, and detailed documentation (packing list, bill of lading, test reports, and customs declarations).
Upon arrival, the transformer undergoes visual inspection for transit damage, with any issues reported immediately for resolution under warranty. Proper packing and shipping practices extend the transformer's service life by preventing mechanical stress or contamination, ensuring reliable performance from day one in utility, commercial, or industrial installations.
32
32 years of industry experience
Manufacturer Test
1250kVA Three Phase Pad Mounted Transformer
Progress test
The first set of progress tests (routine factory acceptance tests per IEEE C57.12.90 and ANSI standards) for the 1250kVA three-phase pad mounted transformer verifies core electrical integrity and performance before final assembly stages.
- Winding Resistance Measurement: DC resistance of all windings (high-voltage and low-voltage) is measured at ambient temperature using a bridge or voltage drop method. Values are corrected to 75°C reference and compared to design tolerances to confirm uniform connections, no open/short circuits, and proper conductor sizing.
- Turns Ratio Test (TTR): Voltage ratio is tested across all tap positions using a precision turns ratio meter. Results must match nameplate specifications within ±0.5% to ensure accurate voltage transformation and phase alignment.
- Polarity and Phase Relation Test: Polarity (additive/subtractive) and phase sequence are verified at rated voltage to confirm correct winding orientation and vector group (e.g., Dyn11).
Design Tests
All transformers will be tested after finishing the production, test items as follows:
♦ Insulation Power Factor
♦ Ratio, Polarity, and Phase Relation
♦ Winding Resistance
♦ Impulse Tests
♦ On load Loss Test
♦ No Load Loss Test
♦ Leak Test
♦ DC Insulation Resistance Test
♦ Polarity, 1-Ph / Phase Relation, 3-Ph (Rated Voltage)
♦ Excitation & No-Load Loss (Rated Voltage)
♦ Applied Voltage
♦ Induced Voltage
♦ Lightning Impulse
♦ Insulation Resistance (Rated Voltage)
♦ Temperature Rise
♦ Dielectric Withstand (Hipot)
Transformer Factory Acceptance Test
The Factory Acceptance Test (FAT) for the 1250kVA three-phase pad-mounted transformer is a comprehensive series of routine tests performed on every unit prior to shipment, in full compliance with IEEE C57.12.90-2021 (Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers), IEEE C57.12.00 (General Requirements), and IEEE C57.12.34 (specific requirements for pad-mounted compartmental-type distribution transformers). These tests verify electrical integrity, insulation quality, performance parameters, efficiency, and mechanical sealing to ensure reliable operation in underground distribution systems, while confirming adherence to DOE efficiency standards and UL-listing criteria.
Routine Test - Applied Voltage
Purpose of Testing
The purpose of testing the applied voltage is to verify the insulation strength of the transformer by applying a voltage higher than its normal operating level, ensuring it can withstand potential electrical stresses. This test helps identify any weaknesses or defects in the insulation system before the transformer is put into service.
Testing Equipment
Test equipment: High voltage tester (e.g. TTR, Hipot, etc.)
Voltage source: usually 1 kV, 5 kV, 10 kV, or customized according to customer needs
Temperature and humidity meter: used to record environmental conditions
Voltage source: usually 1 kV, 5 kV, 10 kV, or customized according to customer needs
Temperature and humidity meter: used to record environmental conditions
Pre-Test Preparation
Disconnect the device from the power supply and make sure it is properly grounded and discharged.
Check the connection terminals and wiring to ensure that they are not loose or contaminated.
Test under suitable environmental conditions: relative humidity below 75% and no rain (recommended temperature: 20-30°C).
Check the connection terminals and wiring to ensure that they are not loose or contaminated.
Test under suitable environmental conditions: relative humidity below 75% and no rain (recommended temperature: 20-30°C).
Test Progress
Connect the Test Instrument:
Properly connect the test equipment to the bushings or terminals of the device under test and ensure that all connection points are properly grounded.
Selecting the test voltage:
Select the appropriate applied voltage based on the rated voltage of the equipment.
Properly connect the test equipment to the bushings or terminals of the device under test and ensure that all connection points are properly grounded.
Selecting the test voltage:
Select the appropriate applied voltage based on the rated voltage of the equipment.
Measure and Record
Start the test and record the following parameters:
Measuring leakage current
Applied voltage
Current stability
Any possible voltage fluctuations
Measuring leakage current
Applied voltage
Current stability
Any possible voltage fluctuations
Temperature Correction
If necessary, the measured data is temperature corrected to ensure that it corresponds to standard temperature conditions (usually 20°C).
Repeat Testing (if necessary)
Multiple tests were conducted on different windings (high voltage, medium voltage, low voltage) and bushings, and comparative analysis was performed.
Evaluation Criteria (Reference)
The test was normal and the equipment performed well (qualified)
The current value exceeded the allowable range and the equipment needs to be inspected or maintained (pending repair)
There was a serious fault or instability and the equipment could not continue to operate (unqualified)
The current value exceeded the allowable range and the equipment needs to be inspected or maintained (pending repair)
There was a serious fault or instability and the equipment could not continue to operate (unqualified)
Observing electrical behavior
Observe the electrical behavior of the device under test to ensure that there are no abnormal currents, arcing, noise, or electrical faults.
*These comprehensive tests ensure that each transformer meets performance standards and operates
reliably under various conditions.
Application
This 1250kVA three-phase pad mounted transformer excels in utility distribution networks, commercial complexes like shopping centers and office buildings, and light industrial facilities. It combines with renewable setups such as solar farms or wind turbine step-up systems, EV charging stations, and data center backup power for reliable, underground medium-voltage supply in urban and suburban environments requiring high capacity and minimal visual impact.
Technical Advantages
● 30+ years of manufacturing experience
● ISO and UL certified production
● Customized cable and transformer solutions
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What is a Transformer?A transformer is an electrical device used to change the voltage of alternating current (AC). It works on the principle of electromagnetic induction, converting high-voltage current into low-voltage current or low-voltage current into high-voltage current. Transformers are widely used in power transmission, distribution systems, and various electronic devices.
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What are the main uses of a transformer?The main use of a transformer is voltage conversion. Transformers are used in power transmission systems to help transfer electricity from power plants to consumers. In addition, transformers are also used in electronic devices such as chargers, televisions, power adapters, etc., to adjust the voltage to meet the requirements of different devices.
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Do you have UL listed?Yes, our transformer has UL listed. We have exported to America many pad mounted transformer,substation transformer and HV.
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