Main transformer removal in Korea covers disconnecting and removing a transformer from the supply circuit, either to replace it with a larger unit or because it has reached the end of its service life. Removed transformers and accessories are often reused at another substation or their oil is reprocessed, so the goal is not just to dismantle but to separate and store everything in reusable condition. This guide covers three stages: oil draining, accessory removal and main tank removal.
Contents
- Common Pre-Work Review
- 1. Draining Insulating Oil
- 2. Removing Accessories
- 3. Removing the Main Tank
- NCS Criteria for Storing Removed Equipment
- FAQ
- Reference Standards
- Summary
Common Pre-Work Review
Review the removal conditions in the general and particular specifications and the method statement (quality, environmental and safety plans). Prepare an oil storage tank, purifier, vacuum pump, dry-air generator, oxygen meter and oil dielectric tester, and hire a mobile crane and oil tanker. Confirm the crane is rated for each accessory’s weight. Workers wear insulated helmets, flame-resistant clothing, insulated boots and harnesses, and verify de-energization with a voltage detector and earthing sets.
1. Draining Insulating Oil
- Confirm the transformer is out of service and safe to work on.
- Prepare suitable draining equipment.
- Open all transformer valves so oil can drain.
- Open the top of the tank and run the draining equipment while supplying dry air.
- After draining, fill with nitrogen to keep outside air out.
Record the dielectric strength, moisture content and volume of recovered oil so you can decide whether it is reused or disposed of.
2. Removing Accessories
- Prepare protective covers for openings and wooden crates for storing accessories.
- Remove the radiators.
- Remove the bushings and surge arresters.
- Separate the OLTC conservator from the main tank.
- Remove the OLTC drive rod and oil-seal tank.
- Pack removed accessories and materials for transport and storage.
Check bushing porcelain for cracks or damage during removal, and store oil-filled bushings with the top raised at least 7°.
3. Removing the Main Tank
- Photograph the transformer’s exterior before removal.
- Disconnect power and control cables from the control cabinet.
- Disconnect bushing leads and remove the earthing terminals.
- Plan the route for moving the tank out of the substation.
- Check risk points with a substation risk checklist before work.
NCS Criteria for Storing Removed Equipment
| Item | Criterion |
|---|---|
| Pre-storage inspection | Structure and exterior of tank, bushings, radiators, cooling and OLTC parts |
| Oil-filled bushings | Stored with the top raised at least 7° |
| Bushing porcelain | Checked for cracks and damage during removal |
| Tank for reuse | Nitrogen pressure held at 0.2–0.5 kg/cm² |
| Insulating oil | Dielectric strength, moisture and volume recorded |
These values come from the considerations in the NCS competency unit. Follow the client’s instructions on reuse and storage.
FAQ
Why fill with nitrogen after draining?
If air and moisture enter the empty tank, the internal insulation absorbs moisture. Sealing with nitrogen keeps the unit reusable.
How is a tank stored for reuse?
The NCS gives an internal nitrogen pressure of 0.2–0.5 kg/cm². If pressure drops, check for leaks and top up.
What needs most care when removing accessories?
Bushing porcelain damage and contamination of openings. Cover openings immediately and store bushings at the specified angle.
Reference Standards
- Electricity Business Act (전기사업법) — law.go.kr
- Electrical Safety Management Act (전기안전관리법) — law.go.kr
- Electric Technology Management Act (전력기술관리법) — law.go.kr
- Electrical Construction Business Act (전기공사업법) — law.go.kr
- Occupational Safety and Health Act (산업안전보건법) — law.go.kr
- Korea Electro-technical Code (KEC, 한국전기설비규정) — law.go.kr
- Technical Standards for Electrical Equipment (전기설비기술기준) — law.go.kr
- KEPCO design standards and substation construction practice; Korean Industrial Standards (KS)
- NCS competency unit Main Transformer Removal (주변압기 철거공사, 1901070306_22v2; NCS is Korea’s National Competency Standards) — ncs.go.kr
Summary
The most common mistakes are treating removal as demolition — leaving openings uncovered or laying bushings flat. Draining depends on dry air and nitrogen filling; accessories on covers and packing; and the main tank on disconnecting cables and earths and planning the exit route. Related guides: Main Transformer Installation, Main Transformer Maintenance, Substation Switchgear Removal. A Korean version of this guide is available here.
This article restructures the Korean NCS competency unit ‘Main Transformer Removal’ (주변압기 철거공사, code 1901070306_22v2) as a practical reference. Actual work must follow applicable standards and the judgment of qualified professionals; always confirm specific values, deadlines and criteria against the latest regulations and client standards.
Written/reviewed by VOLT · Last updated 2026-10-26