Transformer On-Site Core Lifting Inspection Specifications and Operating Procedures
Transformers are subject to continuous vibration and bump impact during long-distance transportation, which may lead to loose internal structures, displaced components and hidden insulation defects. Therefore, comprehensive on-site body inspection is mandatory after equipment arrival. Transformer body inspection is mainly divided into core lifting inspection and cover lifting inspection, with identical inspection items and standards for both methods. To improve on-site commissioning efficiency, the entire core lifting inspection operation must be completed within one working day.
Basic Technical Specifications for Core Lifting Inspection
1. Environmental Site Requirements
Core lifting operation is preferably carried out in a closed indoor environment. If implemented outdoors, professional rainproof and dustproof tents must be set up in advance. Core lifting inspection is strictly prohibited under severe weather conditions such as rain, snow, dense fog and windy sand to prevent moisture intrusion and dust contamination inside the transformer.
2. Ambient Temperature Requirements
In winter low-temperature environments, the on-site core lifting temperature shall not be lower than 0°C. When the ambient temperature is too low, preheating treatment must be carried out on the transformer to ensure the internal core temperature is 10°C higher than the ambient temperature, avoiding insulation condensation and low-temperature structural embrittlement.
3. Air Exposure Time Limit
To reduce moisture absorption of internal insulation materials, the core air exposure time should be minimized. The statistical timing starts from the completion of oil draining to the end of oil filling. When the ambient relative humidity is ≤65%, the maximum allowable exposure time shall not exceed 16 hours; when the relative humidity is ≤25%, the exposure time shall be controlled within 12 hours. Strictly control the operation cycle to ensure insulation performance stability.
4. Humidity Prohibition Standard
Core lifting inspection is strictly forbidden when the ambient relative humidity exceeds 75%, so as to prevent the internal winding and core insulation from absorbing moisture in large quantities, which would reduce insulation strength and cause potential discharge hazards.
5. On-Site Operation Safety Requirements
During the entire core lifting and inspection process, strict management of parts, tools and auxiliary materials must be implemented. All tools and disassembled accessories shall be counted and kept properly to avoid falling into the oil tank, causing blockage, short circuit and other serious faults.
Standard Operating Steps for Transformer Core Lifting
The on-site core lifting inspection shall be carried out in strict accordance with standardized procedures to ensure operational safety and comprehensive inspection without missing any items. The detailed steps are as follows:
1. Pre-operation preparation: Determine a reasonable core lifting position, and drain the internal transformer oil to below the large cover plate level to create safe operating conditions for disassembly and core lifting.
2. Accessory disassembly: Remove external accessories including explosion-proof cylinder, oil conservator and gas relay in sequence, and keep all disassembled parts intact and properly stored.
3. Fixed disassembly: Loosen and remove all fastening bolts of the transformer large cover, and mark the bolt positions for subsequent accurate reinstallation.
4. Integral core lifting: Adopt balanced iron lifting tools to stably lift the core and winding assembly, and place it flat on a clean special oil pan to avoid structural collision and contamination.
5. Comprehensive internal inspection: Carry out full-item detection and verification for internal components, focusing on the following key items:
① Integrity and dryness of winding insulation without damage, aging or discharge traces;
② Firmness of core lamination and intact core insulation performance;
③ Reliable insulation of core through bolts and clamping bolts without breakdown or aging;
④ Good contact and intact insulation of tap changer contacts without ablation and poor contact;
⑤ Firm connection and intact insulation of high and low voltage leads without displacement or damage;
⑥ Cleanliness inside the oil tank without residual sundries, oil sludge and impurities;
⑦ Unblocked heat dissipation pipes without blockage, deformation or leakage hidden dangers;
⑧ Detection and recording of remote insulation resistance data to ensure compliance with standard values;
⑨ Measurement and verification of winding DC resistance to judge internal circuit connection status.
6. Reset and reinstallation: After all inspection items are confirmed qualified with no abnormal hidden dangers, quickly reset the core assembly and reinstall it into the oil tank to shorten air exposure time.
7. Fixed locking: Install and fasten the large cover bolts in sequence with standard torque to ensure overall tank tightness.
8. Accessory restoration: Reinstall all previously disassembled accessories such as gas relay, oil conservator and explosion-proof cylinder correctly in place.
9. Qualified oil injection: Inject filtered, dried and qualified transformer insulating oil into the tank to the standard oil level.
10. Performance test: Let the transformer stand for 6–10 hours for internal static settlement, then conduct a complete set of withstand voltage tests and electrical performance detection to verify operational reliability.
11. On-site installation and commissioning: After all tests are qualified, complete the final on-site fixed installation and pre-operation debugging.