Switchgear Overhaul Maintenance in Korea: Gas Recovery to Mechanism Overhaul

Switchgear overhaul maintenance in Korea means taking switchgear out of service and dismantling it to inspect the interrupting and operating mechanisms in detail, replace auxiliary relays and parts, and run a full set of tests to restore performance. The interrupting section includes all conductors, insulation and arc-quenching parts inside breakers, disconnectors and earthing switches. Moisture and contamination control starts the moment SF6 is recovered and the tank is opened, so the order of gas work and dismantling matters. This guide covers four stages: gas recovery and vacuum, interrupter overhaul, mechanism overhaul and detailed testing.

Contents

• Common Pre-Work Review
• 1. Gas Recovery and Vacuum
• 2. Interrupter Overhaul
• Key Interrupter Overhaul Items
• 3. Mechanism Overhaul
• 4. Detailed Testing
• FAQ
• Reference Standards
• Summary

Common Pre-Work Review

Overhaul timing weighs joint outages, age, fault history, overload periods and ease of outage. Keep safe clearance from anything live, and confirm earthing and barrier ropes on the outage section. Work to the manufacturer’s maintenance manual and installation procedure and KEPCO’s GIS installation standard. Prepare an SF6 recovery unit, vacuum pump, vacuum gauge, electronic borescope, timing analyzer, contact resistance meter, SF6 analyzer, dry-air generator and mobile crane, plus conductive grease, O-rings and desiccant.

1. Gas Recovery and Vacuum

1. Identify the GIS gas compartments.
2. Check rated gas pressure for each device and analyze gas quality.
3. Check recovery piping and recover SF6 with the recovery unit.
4. Connect the vacuum pump and high-pressure hoses and pull vacuum.
5. Check enclosure and joint tightness, including during vacuum.
6. Inspect barrier and support spacers for cracks.
7. Refill each compartment to its rated pressure.
8. Measure and record the SF6 supplied and used on the job.

2. Interrupter Overhaul

1. Inspect the inside of breakers and disconnectors with an electronic borescope.
2. Measure contact gaps to confirm insulation distance.
3. Measure wear and depth of fixed and moving arcing contacts, and condition and depth of fixed and moving main contacts.
4. Inspect the insulating nozzle and cover for wear, the puffer cylinder and grading capacitors.
5. Inspect disconnector and earthing switch contacts.
6. Inspect conductors, shields, insulating supports and enclosures.
7. Remove old grease from contacts and apply new conductive grease.
8. Replace inspection covers, O-rings and desiccant.

Key Interrupter Overhaul Items

Part	What to check
Arcing contacts (fixed and moving)	Wear and contact depth
Main contacts (fixed and moving)	Contact condition and depth
Insulating nozzle and cover	Wear
Puffer cylinder	Damage or abnormality
Grading capacitors	Appearance and abnormality
Disconnector and earthing switch contacts	Contact condition
Conductors, shields, supports, enclosure	Contamination, cracks, discharge marks
Consumables	Fresh conductive grease; new cover gaskets, O-rings and desiccant

Acceptance values follow the manufacturer’s manual. The NCS calls for calibrated instruments and gas analysis at 0–40 °C and 80% humidity or less.

3. Mechanism Overhaul

1. Check that breakers, disconnectors and earthing switches operate smoothly by hand.
2. Measure mechanism stroke.
3. Check closing and opening coils for open circuits and aging.
4. Check piston rings for sticking and rust.
5. Inspect and replace solenoid valves, and inspect the main and other valves and operating cylinder.
6. Check and adjust operating angles of the close hook, links and levers.
7. Inspect the oil dashpot, closing spring, auxiliary contacts, buffers and mechanism housing.
8. Inspect the compressed-air or hydraulic system.

4. Detailed Testing

1. Measure GIS and GCB operating characteristics and test interlocking with related equipment.
2. Measure CT saturation and ratio, and main circuit insulation and contact resistance.
3. Measure gas and air tightness, air valve leakage, and SO₂ and moisture in SF6.
4. Measure opening and closing times per phase, pole discrepancy, breaker stroke and contact depth.
5. Measure pressure gauge and auxiliary relay characteristics, drive operating pressures, auxiliary circuit insulation and resistor values.
6. Test interlocks, trip-free operation, emergency opening and every device’s operation.

If a cascading fault is possible during measurement, stop, restore the equipment and record why. If gas pressure is well below rated, do not measure — top up slowly at low pressure first.

FAQ

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 Switchgear Overhaul Maintenance (개폐장치 정밀유지보수공사, 1901070311_22v2; NCS is Korea’s National Competency Standards) — ncs.go.kr

Summary

The most common mistakes are not recording gas recovery and reusing O-rings or desiccant after dismantling. Gas work depends on compartment identification, tightness and usage records; the interrupter on contact depth and nozzle wear; the mechanism on stroke and operating angles; and testing on timing and interlocks. Related guides: Switchgear Routine Maintenance, Substation Switchgear Installation, Substation Switchgear Removal. A Korean version of this guide is available here.

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This article restructures the Korean NCS competency unit ‘Switchgear Overhaul Maintenance’ (개폐장치 정밀유지보수공사, code 1901070311_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