33kV Oil Immersed Transformer
33kV Oil Immersed Transformer is a high-voltage, three-phase power distribution and step-down unit engineered for reliable operation in 50/60Hz AC transmission and distribution networks with primary voltages up to 33kV (or 30-38.5kV range). It features a hermetically sealed or conservator-type tank with corrugated radiators or detachable coolers for superior thermal management and oil expansion compensation, providing excellent moisture barrier, oxidation resistance, and service life exceeding 35 years. Utilizing premium cold-rolled grain-oriented silicon steel cores with optimized step-lap joints and low-loss designs (S11/S13 series equivalents), it achieves substantial reductions in no-load losses (often 20-40% below older models), paired with high-conductivity copper windings.
- Primary Voltage Ratings 34.5-19.92/13.8-7.957, 24.94, 26.25, 33 or others
- Secondary Voltage Ratings 480/277V, 400/230V, 380/220V or customized
- H.V. Tap Range ± 2×2.5% HV taps or others
- Type Oil immersed distribution transformer
- BIL 33kV
- Standards IEEE, ANSI, NEMA, IEC, CE
- Application industrial heavy factories and mines
- Power Rating 30kVA - 5000kVA
- Certificate UL, CESI, IEEE
- 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
33kV Oil Immersed Transformer
Technical Specifications
Accessories
| Rated Power | 30kVA - 5000kVA | |
| Rating Primary Voltage | 2.4 - 34.5kV | |
| Secondary Voltage | 480/277V 400/230V 380/220V 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 | |
| Insulating Oil Weight | 850 kg | |
| Total Weight | 5000 kg | |
| Outline Dimensions（L×W×H）in. | 2650 × 1650 × 2450（mm) | |
| 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
33kV Oil Immersed Transformer
Our 33kV oil immersed transformers provide extensive configurability to address specific voltage classes, load profiles, environmental challenges, and regulatory needs. Standard rated powers range from 50kVA to 10MVA (or higher for substation applications), with primary voltages 33kV (options for 30kV, 35kV, 36kV), and secondary voltages customizable to 0.4kV, 0.415kV, 0.69kV, 11kV (step-up variants), or project-specific outputs. Voltage regulation options include multi-position off-circuit tap changers (±2×2.5% or ±5%) for stable operation or on-load tap changers (OLTC) with up to 17-21 steps for dynamic control in fluctuating networks like renewables. Core materials offer high-permeability grain-oriented silicon steel for standard low losses or advanced amorphous metal for dramatic no-load reductions (up to 70%). Winding choices span high-grade copper for optimal conductivity and longevity or aluminum for economical high-capacity designs.
Further tailoring encompasses cooling upgrades (ONAN to ONAF with fans/pumps for extreme ambients -40°C to +50°C or high overloads), insulating fluids (conventional mineral, natural ester/bio-based for fire safety and eco-compliance per IEC 61099), and tank enhancements including full hermetic sealing, conservator with breather, anti-corrosion coatings (C5-M marine grade), seismic-resistant bases, or elevated IP protections for coastal/polluted sites. Accessories integration covers online DGA sensors, fiber-optic winding temperature monitors, SCADA-compatible RTUs, surge arresters, conservators, gas relays, and smart metering. Impedance (6-12%), vector groups (Dyn11, YNd1, etc.), BIL levels (170-200kV), frequency (50/60Hz), noise attenuation, and adherence to IEC 60076, GB1094, ANSI, or local efficiency tiers are fully adjustable. Our specialists partner on bespoke engineering for utility substations, wind/solar farms, mining operations, or industrial plants, optimizing for lifecycle savings through superior efficiency, reduced maintenance, and seamless grid compatibility.
Packing and Shipping
33kV Oil Immersed Transformer
Transporting 33kV oil immersed transformers requires stringent protective measures to maintain factory-calibrated performance and prevent transit-induced damage to core, windings, or oil system. Each unit undergoes final pre-packing inspections including pressure/leak tests on the tank, torque verification on connections, oil dielectric sampling (>60kV), and accessory functionality checks. Smaller distribution models (<5MVA) typically ship oil-filled under positive nitrogen pressure (0.02-0.05MPa) to exclude air/moisture; larger power units often partially drain oil into dedicated sealed ISO-grade tanks or drums, accompanied by vacuum filling equipment and high-purity oil reserves for on-site restoration per IEC guidelines.
Component-specific safeguards include radiators detached and crated with anti-vibration padding, high-voltage bushings (porcelain or RIP) individually shock-mounted in reinforced boxes, OLTC mechanisms locked and protected, and control cubicles sealed with desiccants. The main body mounts on heavy steel skids or ISPM-15 compliant wooden/steel frames with custom blocking, lateral braces, and energy-absorbing materials rated for 3-5g impacts. Packaging incorporates multi-layer weatherproof covers, VCI corrosion inhibitors, humidity/temperature indicators, and electronic shock/tilt recorders fortraceability.
Ocean freight—predominant for export—utilizes flat-rack, open-top, or break-bulk vessels with IMO-compliant lashing, salt-mist barriers, and protective sheeting; road/rail segments employ specialized low-loader trailers with weight-distributed cradles and marked lifting points. Full export documentation package comprises commercial invoices, packing lists, certificates of origin/conformity, detailed test reports (routine/type), dimensional/lifting drawings, oil SDS, handling/installation manuals, and HS code declarations (8504.23 for >650kVA).
We manage comprehensive logistics from factory to destination, including FOB/CIF terms, customs facilitation, insurance coordination, and value-added services like third-party inspections, on-site unloading supervision by certified riggers, oil filtration/degassing, erection oversight, and commissioning support. This integrated approach minimizes risks, upholds transformer integrity, complies with international regulations, and guarantees punctual, damage-free delivery for worldwide utility, industrial, and renewable projects.
Component-specific safeguards include radiators detached and crated with anti-vibration padding, high-voltage bushings (porcelain or RIP) individually shock-mounted in reinforced boxes, OLTC mechanisms locked and protected, and control cubicles sealed with desiccants. The main body mounts on heavy steel skids or ISPM-15 compliant wooden/steel frames with custom blocking, lateral braces, and energy-absorbing materials rated for 3-5g impacts. Packaging incorporates multi-layer weatherproof covers, VCI corrosion inhibitors, humidity/temperature indicators, and electronic shock/tilt recorders fortraceability.
Ocean freight—predominant for export—utilizes flat-rack, open-top, or break-bulk vessels with IMO-compliant lashing, salt-mist barriers, and protective sheeting; road/rail segments employ specialized low-loader trailers with weight-distributed cradles and marked lifting points. Full export documentation package comprises commercial invoices, packing lists, certificates of origin/conformity, detailed test reports (routine/type), dimensional/lifting drawings, oil SDS, handling/installation manuals, and HS code declarations (8504.23 for >650kVA).
We manage comprehensive logistics from factory to destination, including FOB/CIF terms, customs facilitation, insurance coordination, and value-added services like third-party inspections, on-site unloading supervision by certified riggers, oil filtration/degassing, erection oversight, and commissioning support. This integrated approach minimizes risks, upholds transformer integrity, complies with international regulations, and guarantees punctual, damage-free delivery for worldwide utility, industrial, and renewable projects.
32
32 years of industry experience
Manufacturer Test
33kV Oil Immersed Transformer
Progress Test
Insulating oil incoming progress test evaluates dielectric breakdown voltage moisture acidity tan-delta and gas content per IEC 60296 with multi-stage filtration/dehydration to achieve <10ppm water and zero contaminants. Core-coil vacuum drying progress tracks oven temperature cycles residual moisture extraction and dew point attainment below -50°C for Class A insulation integrity. Final tanking progress monitors vacuum oil impregnation hot oil circulation degassing nitrogen sealing and extended pressure hold/leak detection tests. Protection device progress verifies Buchholz relay operation gas accumulation tripping oil temperature/pressure gauge calibration relief valve setpoint and OLTC drive mechanism sequencing smoothness.
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)
♦ Insulation Resistance (Rated Voltage)
♦ Temperature Rise
♦ Dielectric Withstand (Hipot)
Transformer Factory Acceptance Test
Load loss short-circuit impedance and temperature rise tests short secondary apply reduced voltage compute copper losses impedance (6-10%) efficiency at full load and simulate thermal performance (top-oil <60K windings <65K). Oil quality routine includes breakdown voltage (>60kV/2.5mm) water content (<20ppm) acidity DGA baseline zero acetylene. Functional verification covers pressure relief device activation Buchholz/gas relay tripping temperature indicator alarms OLTC full-range operation and sound power level (<60dB). Mechanical integrity confirms tank overpressure withstand leak-free seals bushing flashover margins and accessory wiring. Detailed FAT protocol yields traceable reports calibration certificates optional client/third-party witnessing ensuring IEC 60076 full compliance type/routine test certification prior to release.
Routine Test - Induced Voltage
Purpose of Testing
The purpose of the Induced Voltage test is to simulate the electrical stress that the equipment may encounter under actual working conditions by applying an induced voltage, thereby evaluating the tolerance and stability of the equipment's insulation system. This test helps to detect the insulation performance of the equipment under high voltage conditions and ensure its safety and reliability in operation.
Testing Equipment
Induced Voltage Tester (e.g. OMICRON, Megger, HioKI, etc.)
AC voltage source, commonly 2 kV, 5 kV, 10 kV, or customized according to test requirements.
Environmental thermometer and hygrometer, used to record the temperature and humidity of the environment for appropriate test evaluation.
AC voltage source, commonly 2 kV, 5 kV, 10 kV, or customized according to test requirements.
Environmental thermometer and hygrometer, used to record the temperature and humidity of the environment for appropriate test evaluation.
Pre-Test Preparation
Disconnect all relevant power supplies and ensure that the equipment is properly grounded and discharged.
Check the connection wires and terminals to ensure they are secure and free of contamination.
Test under suitable environmental conditions: relative humidity below 75%, no rain (recommended temperature: 20-30°C).
Check the connection wires and terminals to ensure they are secure and free of contamination.
Test under suitable environmental conditions: relative humidity below 75%, no rain (recommended temperature: 20-30°C).
Test Progress
Connect the Test Instrument:
Connect the test equipment to the appropriate terminals or bushings of the device under test, ensuring that the connections are secure and properly grounded.
Apply Test Voltage:
Select the appropriate induction voltage according to the rated voltage and standard of the equipment.
Connect the test equipment to the appropriate terminals or bushings of the device under test, ensuring that the connections are secure and properly grounded.
Apply Test Voltage:
Select the appropriate induction voltage according to the rated voltage and standard of the equipment.
Measure and Record
Start the test and record the following parameters:
Induced Voltage
Applied Current
Voltage peak, stability and waveform (waveform analysis)
Any abnormal current or voltage changes during the measurement process.
Induced Voltage
Applied Current
Voltage peak, stability and waveform (waveform analysis)
Any abnormal current or voltage changes during the measurement process.
Temperature Correction
The measured induced voltage data is corrected to the reference temperature (usually 20°C) to ensure the accuracy of the test results.
Repeat Testing (if necessary)
If necessary, test different windings (HV, MV, LV) and bushings separately and compare the results at different test points.
Evaluation Criteria (Reference)
Inductive voltage ≤ 1% (Excellent): normally and meets safety standards.
1% < Inductive voltage ≤ 3% (Good): still within acceptable range.
Inductive voltage > 3% : faulty or not meet safety requirements and requires further analysis and repair.
1% < Inductive voltage ≤ 3% (Good): still within acceptable range.
Inductive voltage > 3% : faulty or not meet safety requirements and requires further analysis and repair.
*These comprehensive tests ensure that each transformer meets performance standards and operates
reliably under various conditions.
Application
It is suitable for various combined scenarios such as voltage reduction in high-voltage substations, voltage boosting in wind and solar power plants, power supply for industrial heavy factories and mines, urban ring network power distribution, port and mining power, metallurgical and chemical load centers, and railway hub substations, providing reliable 33kV medium-high voltage conversion and efficient low-loss operation.
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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