The installation and pre-commissioning of oil-immersed transformers require strict adherence to procedures—covering joint point checks, secondary handling, stable installation, handover tests, and pre-power transmission inspections—to ensure equipment safety and operational reliability. Below is a detailed breakdown of each key link.
1. Equipment Joint Point Check
This step is jointly executed by the installation unit, supply unit, and construction unit representatives, with complete records kept for traceability.
Key Check Contents
- Consistency Verification:
- Compare the transformer body, accessories, and spare parts against the equipment list, construction drawings, and technical documents to confirm that specifications, models, and quantities meet design requirements.
- Ensure no missing or damaged parts (e.g., radiators, tap changers, insulating oil drums).
- Body Appearance Inspection:
- Check the transformer tank for no damage, deformation, or paint peeling; ensure the paint surface is intact and smooth.
- Insulation Component Inspection:
- Inspect insulation porcelain bushings (high/low voltage) and epoxy resin castings for no cracks, defects, or damage—any micro-cracks may lead to insulation breakdown during operation.
2. Secondary Handling of the Transformer
Secondary handling requires collaboration between hoisting personnel and electricians, with strict protection of vulnerable components.
Core Requirements
- Hoisting Equipment Selection:
- Priority is given to truck cranes; chain hoists can be used for small-capacity transformers (≤500kVA) in confined spaces.
- Porcelain Bushing Protection:
- Cover high-voltage and low-voltage porcelain bushings with dedicated boxes or cartons to prevent collision damage during handling.
- Shock & Vibration Prevention:
- Avoid severe shocks or vibrations during handling—internal core/winding deformation may occur if impacted.
- When using mechanical traction, ensure the traction force acts below the transformer’s center of gravity to prevent tilting.
- Transportation Tilt Limit:
- The maximum allowable tilt angle during transportation is ≤15° to avoid oil leakage or internal structural damage.
- Direction Confirmation:
- Before handling/loading large transformers, confirm the orientation of the high-voltage and low-voltage sides (align with installation drawings) to avoid repositioning difficulties on-site.
3. Stable Installation & In-Place
The transformer must be accurately positioned to meet operational and maintenance space requirements.
Installation Methods
- Truck Crane Direct Placement:
- For transformers that can be lifted directly into the transformer room (with sufficient door/window space), use a truck crane to hoist and place the transformer directly on the pre-built foundation.
- Temporary Track Pulling:
- For confined spaces (e.g., underground transformer rooms), lay temporary tracks with sleepers. Use a three-point sling (note: “three steps and a sling” in the original text refers to a three-point hoisting method) to lift the transformer onto the track, then pull it to the target position with a winch.
In-Place Requirements
- The transformer’s orientation (high/low voltage side direction) and distance from surrounding walls must match the construction drawings.
- The allowable error for in-place position is ±25mm (to ensure subsequent accessory installation and maintenance space).
4. Accessory Installation & Handover Test
After the transformer is in place, install accessories (e.g., radiators, tap changers, oil conservators) first, then conduct a handover test to verify electrical performance.
Handover Test Contents (Mandatory Items)
- Measure the DC resistance of the winding (together with the bushing) – confirm no open circuits or poor contacts.
- Check the transformation ratio for all taps – ensure the ratio meets design requirements at each tap position.
- Verify the wiring group of three-phase transformers and the polarity of single-phase transformer leads – prevent reverse phase sequence.
- Measure the insulation resistance of the winding (together with the bushing) – use a 2500V megohmmeter; the resistance value must meet the standard (≥100MΩ for new transformers).
- Conduct an AC withstand voltage test on the winding (together with the bushing) – verify insulation withstand capacity (e.g., 35kV for 10kV transformers, 1-minute duration).
5. Pre-Power Transmission Inspection
The transformer can only be commissioned after passing a comprehensive inspection and quality supervision verification.
Key Inspection Items
- Confirm all accessory connections are tight (e.g., busbar connections, grounding wires) with no loose parts.
- Check the insulating oil level (in the oil conservator) is within the normal range (corresponding to ambient temperature).
- Verify that protective devices (e.g., gas relays, temperature controllers) are calibrated and functional.
Mandatory Verification
- Before trial operation, the transformer must pass an inspection by the quality supervision department – only after obtaining a qualification certificate can it be connected to the grid for power transmission.
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