Overhaul Preparation Work and Project Introduction of Oil-immersed Transformers
Overhaul Preparation Work and Project Introduction of Oil-immersed Transformers
An oil-immersed transformer is a static electrical device for voltage conversion. Based on the principle of electromagnetic induction, it serves as a power transmission device that converts a voltage of a certain frequency into one or more voltages of the same frequency but different values.Due to various factors, oil-immersed transformers may also have potential safety hazards that can easily lead to malfunctions. It is crucial to implement effective prevention and periodic overhauls, and correctly determine the nature of faults, so as to take prompt and accurate countermeasures.
I. Inspection and Maintenance Cycles of Oil-immersed Transformers
1. Major Overhaul Cycles
- Conduct a major overhaul once every 10 years after putting into operation.
- If abnormal conditions are detected during operation or internal faults are identified through tests, schedule an early major overhaul.
- Consider an early major overhaul after the transformer withstands an outlet short circuit.
- Clean the accident oil drain pool once every 5 years.
2. Minor Overhaul Cycles (to be scheduled during spring and autumn inspections each year or when the line is out of service)
- Conduct a minor overhaul on the main oil-immersed transformer of a power station once a year.
3. Maintenance Cycles of Auxiliary Devices
- Calibrate protection devices and temperature measurement devices once a year.
- Disassemble and maintain cooling fan motors once a year.
- Calibrate, inspect, and clean automatic devices and control circuits once a year.
4. Maintenance Cycles of On-load Tap Changers
- If the oil quality is found to be below the standard during sampling, replace or filter the oil. Replace the oil with new oil once a year even if the oil breakdown voltage exceeds 30 kV.
- For a newly commissioned on-load tap changer, lift out the switching part for inspection after 5,000 switching operations, or after 1 year of operation even if the number of operations does not reach 5,000.
- Overhaul the switching switch after 50,000 operations; overhaul the tap changer after 5 years of operation even if the number of operations does not reach 50,000.
5. Capacitor Bushings
- Determine the maintenance cycle based on electrical test results and the aging condition of sealing materials.
II. Preparations Before Inspection and Maintenance of Oil-immersed Transformers
1. Before a major overhaul, first understand the operation status of the transformer, including the following key points:
- Learn about defects and abnormal (accident) conditions detected during operation, as well as the frequency and details of outlet short circuits.
- Review technical data and archives from the previous major overhaul of the transformer.
- Understand the transformer’s operation status (load, temperature, number of switching operations of the on-load tap changer, and operation conditions of other auxiliary devices).
- Check the original test records of the transformer (including simplified oil analysis and chromatography) to assess the insulation condition of the transformer.
- Identify oil leakage points (and mark them) and external defects.
- Conduct analysis tests on the transformer body and oil before the major overhaul to determine additional maintenance items (such as drying, oil treatment, etc.).
2. Compile a technical and organizational measure plan for the major overhaul project, covering the following contents:
- Personnel organization and division of labor.
- Verify maintenance items and formulate a construction schedule.
- Construction plans for special projects, technical measures to ensure construction safety and quality, and on-site fire prevention measures.
- List of main construction tools and equipment, and list of main materials.
- Draw necessary construction sketches and blueprints.
- Prepare technical record forms and determine the drawings of spare parts to be drawn and verified.
- Secure materials required for the major overhaul.
3. Arrange the construction site
- For the maintenance of large power transformers carried out directly on-site, take adequate measures for rain protection, moistureproofing, dust prevention, and fire prevention.
- At the same time, pay attention to the safe distance from live equipment, and properly arrange the power supply capacity, the location of oil storage containers, the placement area for disassembled accessories, and the layout of fire-fighting equipment.
4. Complete the following material preparations
- Materials (including spare parts, common tools, special tools, common materials, and special materials, etc.).
- Hoisting devices, handling tools, bushing racks, sealing plates, sleepers, etc.
- Vacuum oil filters, oil tanks, supplementary new insulating oil, etc. (oil filters, oil tanks, and oil pipes must be free of moisture and dirt).
- Safety gear and equipment (including safety bumpers, special work clothes, shoes, rainproof and dustproof tarpaulins for lighting, and fire-fighting equipment, etc.).
- Test instruments and meters.
- Moisture drying equipment.
III. Inspection and Maintenance Items of Oil-immersed Transformers
1. Major Overhaul Items
- Formulate a major overhaul plan and prepare equipment and materials before the overhaul.
- Lift the core or cover to inspect the transformer body.
- Overhaul windings (coils), leads, and on-load (off-load) tap changers.
- Overhaul the iron core, through-core screws, yoke frames, compression nails, and grounding plates, etc.
- Overhaul the oil tank and accessories, including bushings, conservators (including capsules and diaphragms), pressure relief valves, breathers, etc.
- Reassemble the transformer, replace sealing gaskets of all parts, and conduct leak tests.
- Inspect and test gas relays, protection devices, temperature measurement devices, and operation control cabinets.
- Overhaul auxiliary cooling equipment such as fan motors, oil flow relays, valves, pipelines, and oil purifiers.
- Perform necessary insulation drying treatment if required.
- Treat or replace transformer oil (adopt vacuum oil filling for transformers of 110 kV and above voltage classes).
- Clean the outer casing, remove rust, and apply paint.
- Conduct post-overhaul tests and trial operation.
Supplementary Notes
- Terminology Standardization
- On-load tap changer: Standard industry translation, consistent with international power equipment terminology.
- Vacuum oil filling: Professional term for transformer oil injection process, highlighting the technical requirement for high-voltage transformers.
- Gas relay: Special protection device for transformers, the translation is accurate and unambiguous.
- Sentence Structure Optimization
- The original Chinese text contains many imperative sentences; the English translation uses modal verbs such as 'conduct, consider, determine' to conform to the rigorous style of technical documents.
- For cyclic requirements, adverbials such as 'once every 10 years, once a year' are placed at the end of sentences to meet English expression habits.
Foshan Chanxingte Transformer Co., Ltd.
Address: No. 8, Zhongyou Avenue, Leping Town, Sanshui District, Foshan City
