Substation auxiliary power installation in Korea covers the station service transformer, battery bank and charger that supply normal and backup power to equipment inside the substation, sized to the type and capacity of the loads. Auxiliary power provides AC 380/220 V for lighting and building services and DC 125 V for protection and control. Breakers must still operate and relays must still trip during an outage, so the reliability of this system is the reliability of the whole substation. This guide covers three stages: station transformer, batteries and charger.
Contents
- Common Pre-Work Review
- 1. Station Service Transformer
- 2. Battery Bank
- 3. Battery Charger
- Auxiliary Power Components and Installation Points
- FAQ
- Reference Standards
- Summary
Common Pre-Work Review
Review installation and manufacturer drawings, the auxiliary power installation work standard and the inspection body’s rules. Clear any interferences first, assign enough people for the size and weight of each item, and give workers manual handling training. Prepare electric and manual chain blocks, hydraulic jacks and electric or air winches, and hire a mobile crane and forklift. Test instruments are a multimeter and insulation resistance tester.
1. Station Service Transformer
- Check the unit against manufacturer drawings and the packing list, and inspect the exterior and parts.
- Check earth leads and install the foundation and stand to the drawings, specification and manufacturer guidance.
- Confirm whether it is ground- or stand-mounted, fix it firmly and level, and keep phase clearances.
- Check HV and LV bushing terminals and connect them for the specified vector group (delta or star).
- Test insulation resistance, voltage ratio, oil breakdown, excitation current and phase angle.
- Before energizing, make a final check by eye, ear and smell.
Sequence: delivery and storage → preparation → exterior and parts check → foundation and stand → main body → HV/LV connections → inspection and tests → final check and energization.
2. Battery Bank
- Check ventilation, lighting, mounting height and access in the battery room.
- Keep the specified clearances for cubicle-mounted batteries, and from walls and doors for rack-mounted ones.
- Check batteries for internal and external defects and confirm components are correct before installing.
- Store batteries kept for long periods clean, dry and at the specified temperature.
- Plan rack layout and polarity and install batteries level.
- Confirm the installation meets domestic and international rules, client rules and site conditions such as hazardous areas.
- Install breakers and protective relays to protect the batteries and cables as specified.
Sequence: unpack and inspect → assemble racks → place cells → connect → check connections → check electrolyte → fill electrolyte → charge and commission → finish.
3. Battery Charger
- Confirm the charger’s capacity to charge the battery while supplying remote control, operating power, communications, emergency lighting and the UPS.
- Unpack and check for damaged meters and parts, loose terminals and dust, and vacuum-clean the inside.
- Use full-wave rectification for both single- and three-phase units for smooth output voltage.
- Install in a clean, dry place separate from the battery room, and keep it upright during handling.
- Check internal wiring for loose terminals, earth faults and shorts, and confirm insulation resistance meets the requirement.
- Confirm AC supply voltage matches the charger, and connect AC and DC circuits only with switches open and dead.
- Check charger and battery polarity and terminal tightness after connection.
- Confirm primary and secondary voltages and currents and that input and output voltages are normal.
Sequence: unpack and inspect → install → check circuits → connect → pre-energization checks → tests and inspection.
Auxiliary Power Components and Installation Points
| Equipment | Role | NCS installation point |
|---|---|---|
| Station service transformer | AC 380/220 V for lighting and services | Correct vector group; level with phase clearances |
| Battery bank | Operates equipment, indicators and emergency power during outages | Ventilation, lighting, access; clearances by mounting type |
| Charger | Converts AC to DC to charge batteries and supply DC 125 V | Separate from battery room; ambient max 40 °C |
| UPS | Constant-voltage, constant-frequency AC from batteries during outages | Correct DC connection to the battery |
Modern chargers often use IGBT rectifiers. Specific clearances and storage temperatures follow manufacturer guidance and client standards.
FAQ
What voltages does substation auxiliary power use?
The NCS describes AC 380 V and 220 V for lighting and services, and DC 125 V from the charger and battery for equipment control.
Can the charger go in the battery room?
The NCS says to install it in a clean, dry place separate from the battery room, with ambient temperature not exceeding 40 °C.
What should I watch when connecting AC and DC circuits?
Open the relevant switches so the circuit is dead before connecting, and always confirm charger and battery polarity.
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 Substation Auxiliary Power Supply Installation (소내전원장치 설치공사, 1901070313_22v2; NCS is Korea’s National Competency Standards) — ncs.go.kr
Summary
The most common mistakes are connecting without checking charger and battery polarity and skipping battery room ventilation checks. The station transformer depends on vector group and a final pre-energization check; batteries on room conditions and protection; and the charger on location, dead-circuit connection and polarity. Related guides: Substation Switchboard Installation, Substation Ancillary Facilities, Condition Monitoring System Installation. A Korean version of this guide is available here.
This article restructures the Korean NCS competency unit ‘Substation Auxiliary Power Supply Installation’ (소내전원장치 설치공사, code 1901070313_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