50kVA-3000kVA Power Oil Immersed Test Distribution Transformers

Ⅰ. Product Features

1.As the core equipment for insulation performance testing in power systems, the product features of test transformers focus on four dimensions: high-voltage output capability, precise control accuracy, safety and reliability, and environmental adaptability, while integrating material innovation and intelligent technology. The following is a systematic analysis of its core features:

①Ultimate Balance between High-Voltage Output and Insulation Performance

Test transformers can provide a single-unit output voltage ranging from 10kV to 750kV, and higher voltage requirements can be achieved through a series-excited structure (e.g., 3 units of 150kV in series to reach 450kV). The insulated cylinder type test transformer adopts an epoxy cast cylinder shell and full insulation design, with a maximum single-unit voltage of 750kV, meeting the testing needs of ultra-high voltage equipment.

②Medium Innovation: Gas-insulated test transformers use SF6 gas insulation, with insulation strength 2.5 times that of air, partial discharge amount ≤ 5pC, and maintenance-free.

③Low Impedance and High Stability: The system impedance of the insulated cylinder type test transformer is ≤ 5%, meeting the low-impedance requirements of AC pollution tests; the impedance voltage of the oil-immersed test transformer is ≤ 10%, ensuring that the voltage waveform distortion rate during testing is < 1%.

2.Precise Control and Intelligent Testing Capability

①5Automated Testing: Computer-controlled test transformers support automatic voltage boosting, withstand voltage timing, voltage reduction to zero, and have built-in overcurrent (high-voltage/low-voltage) and overvoltage protection, and can display parameters such as voltage, current, and time in real time.

②Data Recording and Analysis: Equipped with a high-speed thermal printer and RS232 interface, it can generate test reports and upload them to the Internet of Things platform to realize remote diagnosis and data analysis.

③Multiple Grounding: The transformer shell, high-voltage tail end, and operation box must be reliably grounded. During series tests, the shell of the secondary transformer is isolated by an insulating bracket.

④Rapid Protection: The insulated cylinder type test transformer adopts a rapid electronic protection device, which cuts off the power supply within 0.1 seconds when the test object breaks down, and its response speed is 5 times faster than that of traditional mechanical protection.

3.Modular Design and Portability Breakthrough

①Series Structure: Multiple single-unit test transformers (e.g., 3 units of 100kV) can be flexibly combined into a 300kV test system, meeting the withstand voltage requirements of large-capacity test objects (such as cables and GIS equipment).

②Multi-Voltage Compatibility: Lightweight test transformers realize rapid switching of three voltage grades (10kV/35kV/50kV) through tap windings and external copper bar switching, without the need for disassembly and adjustment.

③Gas-insulated Design: SF6 gas insulation reduces the volume and weight by 40%-65% compared with oil-immersed transformers of the same grade. For example, a 100kV gas-insulated test transformer weighs only 80kg and can be carried by a single person.

④Dry-type Structure: The dry-type test transformer with epoxy vacuum casting insulation weighs ≤ 150kg, supports vehicle-mounted transportation, and is suitable for field on-site testing.

Ⅱ. Product Advantages

1.Environmental Adaptability and Adaptation to Complex Scenarios

①High-Altitude Derating Design: For every 1000 meters increase in altitude, the capacity is derated by 5%-8%, while the insulation distance is increased by 20%, and the power-frequency withstand voltage test voltage is increased by 10%.

②Wide Temperature Range Operation: Standard test transformers can operate at -10℃ ~ +40℃, and wide-temperature type ( -40℃ ~ +50℃) is suitable for extremely cold or high-temperature environments.

2.Anti-Interference and Anti-Corrosion Properties

①Electromagnetic Compatibility: Computer-controlled test transformers adopt software and hardware anti-interference design, which can work stably in a strong electromagnetic environment, with a voltage measurement accuracy of 0.5 class.

②Pollution and Moisture Resistance: The insulated cylinder type test transformer is treated with a special coating, with a creepage ratio distance of 3.1cm/kV, suitable for pollution level IV environments.

3.In-depth Integration of Intelligent and Green Technologies

①SF6 Recovery System: Gas-insulated test transformers are equipped with gas recovery devices, with a leakage rate ≤ 0.5% per year, complying with the EU RoHS Directive.

②Energy-Saving Design: High-efficiency silicon steel sheet iron core and low-loss winding design, no-load loss ≤ 0.35%, 20% lower than traditional products.

③Real-Time Monitoring: Through high-precision sensors and 14-bit AD acquisition chips, it can display parameters such as high-voltage voltage, current, and insulation resistance in real time, with a resolution of 0.1%.

④Data Analysis: Automatically generate test reports, support historical data query and trend analysis, and help locate equipment aging laws.

4.Professional Expansion of Application Fields

①Series Resonance Test: For capacitive test objects such as cables and GIS equipment, high-voltage output under low-voltage excitation is realized by adjusting the frequency (30-300Hz), reducing the capacity requirement of test equipment.

②AC-DC Superposition Test: Complete the power-frequency withstand voltage and DC leakage tests of the equipment at one time, improving efficiency by 50%.

③Commissioning Test: Conduct power-frequency withstand voltage (10kV ~ 750kV) and DC leakage (0 ~ 280kV) tests on transformers, cables, insulators, etc.

④Preventive Test: Detect hidden dangers such as inter-turn short circuits in windings in advance through partial discharge detection (sensitivity ≤ 10pC) and insulation resistance testing.

Ⅲ. Production Process

1.Raw Material Selection and Pretreatment Process

The performance of raw materials directly determines the insulation level and stability of the test transformer, which needs to go through multi-dimensional selection and pretreatment:

①Magnetic Conductive Material: High magnetic induction and low-loss silicon steel sheets (such as 35W250, 30W1300) are selected, with iron loss ≤ 2.5W/kg (50Hz, 1.7T), ensuring that the no-load loss of the iron core is reduced by 15%-20%; the lamination factor ≥ 0.96, reducing the magnetic circuit air gap.

②Conductive Material: The winding adopts high-purity oxygen-free copper wire (oxygen content ≤ 0.003%) or copper foil, with a conductivity ≥ 97% IACS. The surface is treated with tin plating or insulating paint to prevent oxidation and partial discharge.

③Insulating Material: Select suitable materials according to the type ——

Dry-type/Insulated cylinder type: Class H epoxy glass cloth board (temperature resistance 180℃), Nomex paper (breakdown strength ≥ 40kV/mm), vacuum-cast epoxy resin (volume resistivity ≥ 10¹⁴Ω・cm) are selected.

Oil-immersed type: Karamay 25# transformer oil (breakdown voltage ≥ 40kV/2.5mm), cable paper (thickness 0.08-0.12mm, tensile strength ≥ 2.5kN/m) are used.

2.Iron Core Manufacturing Process

①The iron core is the magnetic circuit core of the test transformer, and its manufacturing accuracy directly affects the no-load loss, noise and magnetic field distribution:

After lamination, vacuum curing is performed (0.1MPa vacuum degree, 120℃ × 6h) to enhance integrity; the insulation resistance of the iron core to the ground is tested to be ≥ 1000MΩ, and the no-load current deviation is ≤ ±5%.

②The cross-lamination method is adopted (the direction of each layer of laminations is alternated by 90°), fixed by positioning pins and insulating adhesive, with a lamination factor ≥ 0.95.

③For large iron cores, the segmented lamination + integral fastening process is adopted, bound by epoxy glass cloth tape (tension 50-80N) and fixed by clamps, ensuring that the overall flatness of the iron core is ≤ 0.5mm/m and reducing vibration noise (≤ 65dB).

④A CNC precision shearing machine (accuracy ±0.05mm) is used for cutting according to the design size to avoid burrs (≤ 0.03mm) and prevent partial electric field concentration from causing partial discharge.

⑤A stepped joint design (joint stagger angle 30°-45°) is adopted to reduce the magnetic circuit joint loss, which is 8%-10% lower than the traditional flat joint in terms of no-load loss.

3.Winding Winding and Insulation Treatment Process

The winding is the voltage conversion core of the test transformer, which needs to meet the requirements of high voltage withstand, low partial discharge and mechanical strength:

①Interlayer Insulation Treatment: After winding each layer of the winding, epoxy glass cloth or cable paper is laid, and hot-press curing (100-120℃, pressure 0.2MPa) is adopted to make the insulation layer fit closely and avoid air bubble residue.

②Overall Vacuum Drying: After winding, the winding is subjected to vacuum drying treatment (vacuum degree ≤ 10Pa, 130℃ × 12h) to remove moisture inside the insulation layer (moisture content ≤ 0.1%) and reduce dielectric loss.

4.Classification Assembly and Insulation Impregnation Process

The assembly and insulation processes of different types of test transformers are significantly different and need to be handled in a targeted manner:

①Sealed Shell Welding: The aluminum alloy shell is welded by argon arc welding (weld flatness ≤ 0.3mm). After welding, helium mass spectrometry leak detection is performed (leakage rate ≤ 1×10⁻⁹ Pa・m³/s).

②Insulated Cylinder Assembly: Insulating spacers are filled between the epoxy glass cloth cylinder (wall thickness ≥ 10mm) and the winding, and fastened by bolts to ensure uniform radial gap (deviation ≤ 1mm) and creepage ratio distance ≥ 3.1cm/kV.

③Oil Tank Assembly: The oil tank is welded with low-carbon steel plates (thickness 6-10mm) and undergoes a water pressure test (0.3MPa × 30min without leakage); heat dissipation tubes or fins are arranged inside (heat dissipation area ≥ 0.1m²/kVA) to ensure that the temperature rise is ≤ 65K.

5.Final Assembly and Electrical Accessory Integration Process

①Iron Core and Winding Assembly: Positioning shafts are used for positioning (coaxiality deviation ≤ 0.2mm). After assembly, insulation pressure plates and screws are used for fastening to ensure uniform axial pressing force (10-15kN/m) and avoid winding loosening.

②High-Voltage Bushing Assembly: Bushings (porcelain or silicone rubber) are installed after partial discharge testing (≤ 5pC @ 1.1 times the rated voltage). Nitrile rubber sealing rings (compression amount 20%-30%) are used for flange sealing to ensure reliable sealing.

③Tap Changer and Control Module:

The tap changer (no-load/on-load) undergoes mechanical life testing (≥ 10,000 operations), with a contact resistance ≤ 50μΩ.