66kV Series 630KVA-63000KVA Oil-immersed Main transformer
Overview
The 66kV main transformer is a core power equipment in the power system that connects the medium-voltage distribution network (66kV) to distribution networks of lower voltage levels (such as 10kV and 35kV). It mainly undertakes the key functions of voltage transformation, electric energy transmission and distribution, and is widely used in regional substations, power supply systems of industrial parks, and self-owned power stations of large enterprises. It is a “hub equipment” that ensures efficient and safe connection of electricity from the power transmission link to the distribution link.
Brief introduction
Ⅰ.Brief introduction
1.Standards: IEC 60076, GB 1094
2.Power Rating: 630KVA-63000 kVA
3.Primary Voltage: 66KV
4.Secondary Voltage: 6.3KV-10.5KV
5.Voltage regulation mode: OLTC tap-changing or off-excitation tap changing
6.Frequency: 50HZ or 60HZ
7.Type: 3 Phase Electric Power Transformer
8.Connection Type: Yd11 or YNd11
9.Cooling method: ONAN, ONAF
Ⅱ.Working conditions
1.Ambient Temperature: No more than +40℃ No less than -25℃, The monthly average temperature is no more than +30℃, The yearly average temperature is no more than +20℃
2.Altitude: No more than 1000m.
3.Relative air humidity:≤90%
4.installation site: no corrosion gas, No obvious dirt
5.Scope of application: The 66kV main transformer is mainly suitable for regional power grid hubs, large-scale industrial/energy bases, places with high fire protection requirements, remote industrial parks, and rural power supply.
Ⅲ.The tests for oil-immersed transformer
The tests for 66kV main transformers are divided into three stages: factory test, commissioning test, and preventive test. They mainly focus on insulation, electrical performance, oil quality (for oil-immersed type) and safety functions, as detailed below:
1. Insulation Performance Tests (Prevent Breakdown)
①Measurement of insulation resistance/absorption ratio/polarization index: Determine if insulation is damp or aged.
②AC withstand voltage test: Apply a voltage higher than the rated voltage (e.g., 95kV on the 66kV side) to verify insulation’s resistance to overvoltage.
③Lightning impulse withstand voltage test: Simulate lightning strikes (e.g., 750kV peak on the 66kV side) to check transient voltage resistance.
2. Electrical Performance Tests (Ensure Accuracy)
①Turns ratio test: Measure the voltage ratio between high-voltage and low-voltage sides; the deviation shall be ≤±0.5% to avoid abnormal output voltage.
②DC resistance measurement: Check for broken winding strands and loose joints; the deviation within the same phase shall be ≤2% and between phases ≤4%.
③No-load test: Measure no-load current/loss to verify core performance and tap changer position.
④Load test: Measure load loss/impedance voltage to ensure stable parallel operation.
⑤Winding connection group test: Confirm the winding connection mode (e.g., Yd11) and phase to prevent circulation.
3.Oil Quality Tests (Oil-Immersed Type Only, Ensure Insulation & Cooling)
①Breakdown voltage test: The breakdown voltage of oil shall be ≥35kV to prevent insulation failure caused by moisture and impurities.
②Dissolved Gas Analysis (DGA) in oil: Measure hydrogen, acetylene, etc., to determine winding overheating or arc faults.
③Moisture/dielectric loss measurement: Moisture content shall be ≤15ppm, and dielectric loss at 90℃ shall be ≤0.5% to reduce loss and prevent insulation deterioration.
4. Safety & Structural Tests
①Gas protection test: Simulate gas/oil flow impact to verify the operation of the gas relay (light alarm, heavy trip).
②Temperature rise test: Measure temperature under rated load; for oil-immersed type, the oil surface temperature rise shall be ≤55K and winding temperature rise ≤65K to verify heat dissipation.
③Partial discharge test: Measure partial discharge quantity (≤100pC) to prevent insulation aging due to long-term discharge.
Ⅳ.Component inspection of oil-immersed transformer
1.Iron Core: Measure no-load loss/current to check for lamination short circuits and magnetic circuit abnormalities.
2.Windings: Measure DC resistance (to detect broken strands/loose joints), insulation resistance (to check for moisture/aging), and partial discharge (to identify insulation deterioration).
3.Insulating Components (Bushings, Separators, etc.): Measure dielectric loss and conduct AC withstand voltage tests to prevent insulation breakdown.
4.Insulating Oil (for Oil-Immersed Type): Test breakdown voltage, moisture content, and dissolved gases (DGA) to ensure insulation and cooling performance.
5.Tap Changer: Verify turns ratio and measure contact resistance to ensure accurate voltage regulation and no poor contact.
6.Protection Devices (Gas Relay, Temperature Controller): Test gas relay operation (light alarm/heavy trip) and temperature controller accuracy.
7.Cooling System (Radiators/Fans): Conduct temperature rise tests to check heat dissipation capacity and ensure oil/winding temperatures do not exceed limits.
Ⅴ.Certificate: CE, UL, ISO, SGS, CCC
Structural Features
Ⅰ.Product features
1.Voltage Adaptability: The high-voltage side is compatible with the 66kV power grid, while the low-voltage side can output 10kV/35kV, meeting the power transmission and distribution needs of medium-to-low voltage conversion.
2.Capacity Flexibility: The rated capacity ranges from 5MVA to 120MVA, which can be matched to regional/industrial loads as required.
3.Safety and Reliability: It has insulation and voltage withstand capabilities (resistant to lightning/overvoltage) and electrical isolation function to prevent high-voltage intrusion.
4.Diversity of Cooling Methods: Oil-immersed type (natural oil cooling/forced oil-air cooling, suitable for large-capacity applications) and dry type (epoxy resin casting, suitable for fire-proof scenarios).
Ⅱ.Product Advantages
1.High Efficiency & Energy Saving: The rated efficiency ranges from 98% to 99.5%, with low no-load/load losses, resulting in less energy consumption during long-term operation.
2.Stable Power Supply: It features high voltage conversion accuracy, adapts to power grid fluctuations, and ensures stable voltage for downstream equipment.
3.Strong Scene Adaptability: The oil-immersed type is suitable for outdoor large-capacity scenarios, while the dry type meets fire protection requirements in urban core areas, hospitals, and other places.
4.Long Service Life: The oil-immersed type has a service life of 20-30 years; its insulation system is stable, and it can operate reliably for a long time with proper maintenance.
Product structure
The production of 66kV main transformers requires strict control over insulation, electromagnetic performance, and structural stability. The core process consists of 6 key stages:
1.Core Manufacturing
High-magnetic-permeability silicon steel sheets are cut according to design dimensions. During lamination, the joint gap is controlled (to reduce losses). After being clamped as a whole, the core undergoes vacuum drying to ensure uniform magnetic circuit and up-to-standard insulation.
2.Winding Winding
Copper wires/aluminum wires (selected based on capacity) are wound around insulation cylinders. A segmented winding method is adopted, with interlayer insulation (paper/film) applied. For oil-immersed transformers, the windings are impregnated with insulating oil to enhance insulation and mechanical strength.
3.Core Assembly
The iron core and windings are assembled coaxially. The windings are fixed to prevent displacement, and a tap changer (for voltage regulation) is installed. The entire assembly undergoes vacuum drying (to remove moisture and avoid insulation degradation).
4.Oil Tank/Housing Fabrication
Steel plates are welded to form the oil tank, which is then subjected to anti-corrosion treatment (painting/galvanizing). Interfaces for radiators and gas relays are pre-installed.
5.Overall Assembly and Oil Filling/Encapsulation
The core assembly is placed into the oil tank (for oil-immersed transformers), and insulating oil is injected under vacuum (to eliminate air bubbles and ensure insulation performance).
6.Factory Testing
Each transformer undergoes insulation resistance testing, turns ratio testing, withstand voltage testing, loss testing, and oil quality analysis. Only those that meet national standards are allowed to leave the factory.
Specification
66kV series OLTC oil-immersed main transformer
| Rated Capacity | High-Voltage Tap Range | L.V. | Connection symbol | No-load loss(kw) | On-load loss(kw) | No-Load Current% | Short circuit impedance% |
|---|---|---|---|---|---|---|---|
| 6300 | 63±8*1.25% 66±8*1.25% 69±8*1.25% |
6.3 6.6 10.5 |
YNd11 | 8.00 | 34.20 | 0.60 | 9~11 |
| 8000 | 9.60 | 40.50 | 0.60 | ||||
| 10000 | 11.3 | 47.8 | 0.56 | ||||
| 12500 | 13.4 | 56.8 | 0.56 | ||||
| 16000 | 16.1 | 69.8 | 0.52 | ||||
| 20000 | 19.2 | 84.6 | 0.52 | ||||
| 25000 | 22.7 | 100 | 0.48 | ||||
| 31500 | 26.9 | 120 | 0.44 | ||||
| 40000 | 32.2 | 141 | 0.44 | ||||
| 50000 | 38.0 | 167 | 0.40 | 10~12 | |||
| 63000 | 44.9 | 198 | 0.36 |
66kv series no-load tap changing oil-immersed main transformer
| Rated Capacity | High-Voltage Tap Range | L.V. | Connection symbol | No-load loss(kw) | On-load loss(kw) | No-Load Current% | Short circuit impedance% |
|---|---|---|---|---|---|---|---|
| 630 | 63±5 66±5 69±5 |
6.3 6.6 10.5 |
Yd11 | 1.20 | 7.10 | 1.10 | 8 |
| 800 | 1.50 | 8.50 | 1.00 | ||||
| 1000 | 1.70 | 9.80 | 1.00 | ||||
| 1250 | 2.00 | 11.90 | 1.00 | ||||
| 1600 | 2.40 | 14.00 | 1.00 | ||||
| 2000 | 2.80 | 16.60 | 0.96 | ||||
| 2500 | 3.40 | 19.60 | 0.88 | ||||
| 3150 | YNd11 | 4.00 | 23.00 | 0.84 | |||
| 4000 | 4.80 | 27.30 | 0.80 | ||||
| 5000 | 5.70 | 30.70 | 0.68 | ||||
| 6300 | 63±2*2.5 66±2*2.5 69±2*2.5 |
6.3 6.6 10.5 |
7.30 | 34.20 | 0.60 | 9 | |
| 8000 | 8.90 | 40.50 | 0.60 | ||||
| 10000 | 10.5 | 47.8 | 0.56 | ||||
| 12500 | 12.4 | 56.8 | 0.56 | ||||
| 16000 | 15.0 | 69.8 | 0.52 | ||||
| 20000 | 17.6 | 84.6 | 0.52 | ||||
| 25000 | 20.8 | 100 | 0.48 | ||||
| 31500 | 24.6 | 120 | 0.44 | ||||
| 40000 | 29.4 | 141 | 0.44 | ||||
| 50000 | 35.2 | 167 | 0.40 | ||||
| 63000 | 41.6 | 198 | 0.36 |
FAQs
Ⅰ.Basic Maintenance Service
1. What are the main cooling methods of Kete 66kV oil-immersed main transformers?
The cooling methods of 66kV oil-immersed main transformers are designed around “transformer oil circulation for heat dissipation”, mainly including the following two types:
①Oil-Immersed Natural Cooling (O.N.A.N.)
·Principle: Rely on the natural convection of transformer oil (rising when heated, falling when cooled) to transfer the heat generated by the iron core/windings to the tank wall, and then dissipate the heat to the air naturally through the tank surface.
·Characteristics: No additional cooling equipment, simple structure, high reliability, and low noise; however, the heat dissipation efficiency is relatively low. It is suitable for scenarios with small capacity (usually ≤31.5MVA) and stable load (such as rural substations and small-scale industrial power distribution).
②Oil-Immersed Forced Air Cooling (O.N.A.F.)
·Principle: Radiators (to increase heat dissipation area) are installed outside the oil tank, and cooling fans are equipped; at low load, heat is dissipated through natural oil circulation. When the load increases (e.g., ≥60% of rated capacity), the fans start automatically to force air to flow through the radiators, accelerating the cooling of the oil.
·Characteristics: Its heat dissipation capacity is 30%~50% higher than that of O.N.A.N. It is suitable for scenarios with larger capacity (usually 50~120MVA) and fluctuating load (such as regional power grid hubs and large-scale industrial parks); the fans need regular maintenance to prevent heat dissipation failure due to fan malfunction.
2. What aspects should be paid attention to in the daily maintenance of Kete oil-immersed main transformers?
①Oil Level & Color Check: Ensure oil level in the conservator is within the normal range; check oil color (should be light yellow, no darkening or turbidity).
②Leakage Inspection: Check seals (e.g., tank joints, bushing bases) for oil leakage.
③Gas Relay Maintenance: Regularly discharge accumulated gas; ensure no alarm/trip malfunction.
④Cooling System Check: Verify radiators are clean (no blockage); confirm forced cooling fans (if equipped) operate normally.
⑤Insulation & Protection: Inspect bushings for no damage/oil contamination; ensure temperature controller displays normally (oil temperature ≤ 85℃ generally).
⑥Abnormal Response: Immediately shut down and inspect if oil temperature surges, gas relay trips, or heavy leakage occurs; do not restart blindly.
3.How to select different types of 66kV main transformers based on climatic conditions and pollution conditions?
①Climatic conditions:
·In hot and humid areas, “moisture-proof radiators” shall be selected, and the oil tank sealing shall be enhanced.
·In extremely cold areas, oil temperature heating devices (such as electric heating rods) shall be equipped to prevent oil solidification or deterioration of insulating oil fluidity.
②Pollution level:
In industrial zones and coastal areas, “anti-pollution bushings” (such as silicone rubber bushings) shall be adopted, and the creepage distance of bushings shall be increased (e.g., the creepage distance in grade IV pollution areas shall be ≥ 31mm/kV) to avoid creepage breakdown.
4.Which components of a 66kV oil-immersed on-load tap-changing main transformer can be customized?
①Iron Core: Select high-magnetic-conductivity silicon steel sheet models based on loss and cost requirements. The clamping structure can be optimized to enhance stability and short-circuit resistance.
②Winding: The conductor material can be copper wire (including oxygen-free copper, etc.), and the structure can be customized to balance performance and loss.
③Voltage Regulating Switch: Different brands and models (such as imported MR switches) are available, with adjustable gears and precision customizable; the operating mechanism can be manual or electric, and the electric type can be equipped with remote control.
④Oil Tank: The structure can be chosen as bell-jar type (easy for maintenance) or barrel type (excellent sealing performance); high-quality steel plates are used as the material, and the surface can be customized with anti-corrosion treatment (such as three-bottom and one-top coating, hot-dip galvanizing).
⑤Insulating Bushing: Select types (such as pure ceramic, oil-filled ceramic, etc.) based on voltage, current, and environment, and customize the size and shape to fit the installation and wiring.
⑥Cooling Device: The cooling method can be oil-immersed self-cooling/air cooling, forced oil circulation air cooling/water cooling; for air cooling, the number and power of fans can be customized, and for forced oil circulation, the specifications of oil pumps and oil flow relays can be customized.
⑦Protection Device: The type and quantity of protection devices (such as gas relays, pressure relief valves, etc.) can be customized, and temperature alarm and trip functions for oil and windings can be added; the monitoring and control system can be mechanical or intelligent, and the intelligent type supports real-time monitoring and remote control.
Ⅱ.After-sales maintenance
1.What is included in Kete's warranty coverage during the warranty period? And how are the costs borne?
Our company’s warranty coverage includes performance failures caused by material defects or manufacturing process issues, such as cabinet water leakage, insulation failure, abnormal switch operation, etc.
We provide spare parts for maintenance free of charge, and will dispatch technical personnel for on-site inspection and repair if necessary, with travel expenses borne by the supplier.
2.Will Kete provide guidance documents for installation?
For large transformers that require the removal of some accessories to fit into containers, we will provide an installation video and an electronic version of the installation instructions.
3.If maintenance is required and spare parts are purchased from Kete, how long will it take for the spare parts to arrive?
If the customer needs to purchase spare parts from our company, the goods can generally be shipped within 2-7 days.
4.How to handle emergency maintenance requests, and what is the typical response time?
24/7 technical support hotline, ensuring a fault time of ≤ 2 hours.
5.What kind of after-sales support can Kete provide, including troubleshooting and maintenance services?
During the warranty period, regular return visits (once every 3 months) will be conducted to provide operation status testing and maintenance recommendations.
After the warranty period expires, lifelong maintenance services at cost price and spare parts supply can be provided.
6.Can Kete provide options for service contracts or extended warranty periods?
Yes, we can. Generally, the warranty period for our products is one year. If an extension of the warranty period is required, we will increase the price by a certain profit margin based on the existing price accordingly.
Ⅲ.Delivery and Payment
1.What is the manufacturing and delivery lead time for Kete oil-immersed transformers?
Generally speaking, if the customer provides detailed design drawings and specification requirements, transformers below 2500KVA can be completed within approximately 20 days; transformers above 2500KVA usually take about 30 to 40 days. The specific lead time depends on the complexity of the transformer.
2.What is the packaging for Kete oil-immersed transformers?
For bulk cargo, we will use wooden cases for packaging; for full containers, we will use wooden pallets to reinforce the packaging.
If you have legally registered patent, we can pack the goods in your branded boxes after getting your authorization letters.
3.What are the payment terms for Kete transformers?
①T/T 30% as deposit, and 70% before delivery.
②LC at sight
③DP at sight
4.What are the delivery terms for the bulk shipment of Kete transformers?
EXW, FOB, CFR, CIF or some other delivery terms inquired by customers.
Ⅳ.Systems and Certifications
1.Does the design of Kete oil-immersed transformers comply with specific industry standards and certifications?
Kete Oil-Immersed Transformers Meet Various International Standards, National Standards, and Core Certification Systems
①General Standards: IEC 60076, GB 1094
②Key Certification Systems
·Chinese Certifications: CCC Certification, ISO System Certification
·EU Certification: CE Certification
·US Certification: UL Certification
·Canadian Certification: GSA Certification
·Russian Certification: Gost Certification
·African Certification: COC Certification
Why Choose us ？
Built to last, engineered to perform.
Kete Transformer is a key national-level manufacturer specializing in transformers, recognized as a “Contract-Honoring and Promise-Keeping” enterprise, a high-tech enterprise, and a national-level enterprise technology center. It is recommended in the national directory for rural and urban power grid construction and renovation, as well as a recommended supplier of major electromechanical equipment for hydropower projects. Its products have been awarded the title of “National Quality Inspection Qualified Product – Quality Trustworthy Product” and “Nationally Recognized Product for Mechanical Industry Users.
Our Project
Our products not only dominate the domestic market but are also exported to more than 30 countries and regions, including Russia, Southeast Asia, Africa, and the Americas, serving industries such as power, municipal engineering, metallurgy, and petrochemicals.
