5MVA / 6.3MVA 35kV Three-Phase Oil-Immersed Step-Down Power Transformer
The 5MVA / 6.3MVA 35kV Three-Phase Oil-Immersed Step-Down Power Transformer is designed for reliable voltage reduction in medium-voltage power distribution systems. Built with high-grade silicon-steel cores, premium copper windings, and advanced oil-immersed cooling, it delivers low losses, strong short-circuit resistance, and stable thermal performance. The transformer features robust insulation, durable tank construction, and precision-engineered components to ensure long operational life. Suitable for industrial plants, utility substations, renewable energy facilities, and commercial power distribution, it supports both on-load and off-load tap changers for accurate voltage regulation. Engineered in compliance with IEC standards, this 35kV step-down transformer ensures high efficiency, dependable performance, and safe power delivery under various environmental and load conditions.
- Primary Voltage Ratings 35kV, 34.5kV, 33kV, 46kV or others
- Secondary Voltage Ratings 13.8kV 6kV 10kV or others
- H.V. Tap Range ±8×1.25% or others
- Type Oil-immersed power transformer
- BIL 35kV
- Standards IEEE, ANSI, NEMA, IEC, CE
- Application utility substations, industrial power plants, mining sites, renewable energy stations
- Power Rating 5MVA - 6.3MVA
- Certificate UL, CESI, IEEE
- Cooling Method ONAN/ONAF
- Oil Mineral Oil or FR3
- Opeartion Step Down & Step Up
Technical Specifications
Customization Optional
Packing and Shipping
Manufacturer Test
Routine Testing
Application
Technical Specifications
5MVA / 6.3MVA 35kV Three-Phase Oil-Immersed Step-Down Power Transformer
Technical Specifications
Accessories
| Rated Power | 5MVA - 6.3MVA | |
| Rating Primary Voltage | 35 kV | |
| Secondary Voltage |
6.6kV 10kV 13.8kV Customized |
|
| Frequency | 50/60Hz | |
| Vector Group | Dyn11, Yyn0, Dyn5 | |
| Winding Material | Aluminum/Copper | |
| Efficiency | As IEEE, Doe 2016, CAS Std or Customized | |
| Impedance Voltage | Nominal 2% 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 | |
| HV Bushing |
| LV Bushing |
| Tap changer |
| Oil level gauge |
| Oil temperature indicator |
| Pressure relief device |
| Pressure vacuum gauge |
| Lifting hook for complete transformer |
| Name plate |
| Radiators |
| Oil upper filtering valve |
| Oil drain valve with 3/8" sampler |
Customization Optional
5MVA / 6.3MVA 35kV Three-Phase Oil-Immersed Step-Down Power Transformer
The 5MVA / 6.3MVA 35kV Three-Phase Oil-Immersed Step-Down Power Transformer offers comprehensive customization to match specific grid standards and operating conditions. Customers may select custom voltage ratios, impedance levels, vector groups, and tapping ranges based on site requirements. Both on-load and off-load tap changers can be configured to support precise voltage adjustment. Options for upgraded insulation classes, low-loss core materials, and high-conductivity copper windings enhance efficiency and reliability.
Environmental customization includes high-altitude designs, coastal anti-corrosion coatings, low-temperature oil systems, and strengthened mechanical structures. Advanced monitoring functions—such as online gas monitoring, temperature controllers, and digital protection relays—can be integrated for real-time performance tracking. Tank configurations can be specified as hermetically sealed or conservator-type, with radiator styles adapted to heat dissipation needs. These flexible options ensure the transformer performs optimally in diverse utility, industrial, and renewable energy applications.
Packing and Shipping
5MVA / 6.3MVA 35kV Three-Phase Oil-Immersed Step-Down Power Transformer
The 5MVA / 6.3MVA 35kV Three-Phase Oil-Immersed Step-Down Power Transformer is packed and shipped using strict international standards to ensure equipment safety and integrity. Before packaging, the transformer undergoes a final inspection, including tank sealing, oil processing, surface cleaning, and moisture protection. All terminals, bushings, valves, and radiators are covered with protective caps. Detachable parts—such as conservators, radiators, tap changers, and monitoring devices—are individually wrapped with shock-proof and moisture-resistant materials and placed into reinforced wooden crates.
The main transformer body is fixed to a heavy-duty steel or wooden pallet using industrial-grade bolts, steel straps, and anti-slip blocks. Vibration-damping pads, corner protectors, and steel framing are added depending on the unit’s size and weight. A complete set of documentation—including test reports, operation manuals, nameplate data, and packing lists—is stored in a waterproof envelope attached securely to the transformer.
Transport options include sea freight, land trucking, and rail transport. The transformer can be shipped using flat racks, open-top containers, or specialized heavy-load equipment depending on dimensions. Lifting lugs and forklift channels are clearly marked for safe loading and unloading. All logistics processes comply with IEC, ISO, and export regulations, ensuring the 35kV step-down transformer arrives at its destination safely and ready for installation.
The main transformer body is fixed to a heavy-duty steel or wooden pallet using industrial-grade bolts, steel straps, and anti-slip blocks. Vibration-damping pads, corner protectors, and steel framing are added depending on the unit’s size and weight. A complete set of documentation—including test reports, operation manuals, nameplate data, and packing lists—is stored in a waterproof envelope attached securely to the transformer.
Transport options include sea freight, land trucking, and rail transport. The transformer can be shipped using flat racks, open-top containers, or specialized heavy-load equipment depending on dimensions. Lifting lugs and forklift channels are clearly marked for safe loading and unloading. All logistics processes comply with IEC, ISO, and export regulations, ensuring the 35kV step-down transformer arrives at its destination safely and ready for installation.
32
32 years of industry experience
Manufacturer Test
5MVA / 6.3MVA 35kV Three-Phase Oil-Immersed Step-Down Power Transformer
Progress Test
During manufacturing, the 5MVA / 6.3MVA 35kV Three-Phase Oil-Immersed Step-Down Power Transformer undergoes continuous Progress Testing to verify each production stage. Inspections include material quality checks, core lamination accuracy, winding tension and alignment verification, and insulation evaluation. Intermediate electrical tests—such as DC resistance measurement, turns ratio verification, insulation resistance, and partial discharge testing—identify early deviations. Mechanical inspections ensure tank strength, structural integrity, and assembly precision. Oil processing tests confirm moisture removal and dielectric strength. This step-by-step testing system ensures product consistency, reliability, and compliance prior to final assembly and acceptance testing.
Design Tests
All transformer will be test after finished the production, test items as below:
♦ 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
♦ Transformer Turns Ratio/TTR (All Tap Voltages)
♦ Impedance Voltage & Load Loss (Rated Voltage)
♦ 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
Before delivery, the 5MVA / 6.3MVA 35kV Three-Phase Oil-Immersed Step-Down Power Transformer undergoes a full Factory Acceptance Test (FAT) following IEC 60076 standards. Key tests include winding resistance measurement, voltage ratio and vector group verification, no-load and load loss measurement, insulation resistance evaluation, induced overvoltage test, and applied high-voltage withstand test. Partial discharge and dielectric tests confirm insulation strength. Mechanical inspections validate tank pressure performance, protection devices, and accessory functionality. Oil quality analysis, terminal checks, and safety device calibration ensure operational readiness. The FAT guarantees that the transformer meets performance, safety, and customer specifications before shipment.
Routine Test - Insulation Power Factor
Purpose of Testing
The purpose of testing the insulation power factor is to evaluate the dielectric loss of the insulation system in electrical equipment, and to determine whether issues such as moisture ingress, aging, or contamination are present. A high power factor value usually indicates insulation deterioration.
Testing Equipment
Insulation power factor tester (e.g., brands like Doble, Megger) Voltage source (typically 1 kV, 2.5 kV, or 10 kV or as the customer request standard) Temperature and humidity meter (for recording environmental conditions)
Pre-Test Preparation
De-energize tap changer the equipment and ensure it has been properly grounded and discharged. Make sure the bushings and terminal connections to prevent surface contamination from affecting test results. Perform the test under suitable environmental conditions: relative humidity below 75% and no rain (recommended temperature: 20–30°C).
Test Progress
Connect the Test Instrument: Connect the test equipment to the bushings or terminals of the equipment under test and ensure proper grounding. Apply Test Voltage: Select the appropriate test voltage according to the rated voltage of the equipment (e.g., 25 kV for high-voltage windings or as the request of the pad mounted transformer).
Measure and Record
Start the test and record the following parameters: Capacitive current (IC) Power current (IW) Power factor (PF) or dissipation factor (Tanδ) Capacitance Ambient temperature and humidity at the time of testing
Temperature Correction
Correct the measured power factor to the reference temperature (typically 20°C) for accurate evaluation.
Repeat Testing (if necessary)
Measure different windings (high-voltage, medium-voltage, low-voltage) and bushings separately for comparative analysis.
Evaluation Criteria (Reference)
Insulation power factor ≤ 0.5% (Excellent) 0.5% < Power factor ≤ 1% (Good) 1% (Further inspection or corrective action required)
*These comprehensive tests ensure that each transformer meets performance standards and operates
reliably under various conditions.
Application
It efficiently reduces medium-voltage power to usable distribution levels, supporting heavy machinery, manufacturing systems, and large-scale facility loads. Its stable performance and strong insulation design ensure reliable operation in demanding environments.
Technical Advantages
● 30+ years of manufacturing experience
● ISO and UL certified production
● Customized cable and transformer solutions
Product Packaging
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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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