Winter Challenges for UK Substations: Essential Electrical and Maintenance Checks
A UK winter brings more than just frost and fog - for substations, it brings a unique set of electrical, mechanical, and environmental challenges. Cold, wet, and windy conditions can trigger insulation breakdowns, moisture ingress, sluggish circuit breakers, and even full outages if not properly managed.
To keep substations reliable through the harsh months, here are ten essential electrical and maintenance checks every operator should perform before and during winter.
🦺 Safety Notice
All electrical testing and inspection work shall be carried out only by competent, trained personnel. Appropriate personal protective equipment (PPE) must be worn at all times, and safe isolation procedures, along with the company’s own procedures, must be strictly followed.
1. Electrical Connections and Joint Integrity
Inspect all high-voltage terminations, cable joints, and busbar connections using thermal imaging. Temperature cycling can loosen connections, while snow or ice can bridge conductors. Even minor resistance increases can cause local overheating under heavy winter loads. (IEC 60894, ISO 18434-1).
2. Insulator and Bushing Condition
Visually inspect all outdoor insulators and bushings for dirt, salt, or industrial contamination combined with moisture or ice. Damp pollution layers can form conductive paths and cause flashovers. (ENA TS 41-36, National Grid STP 09-2).
3. Transformer and Switchgear Oil Quality
Measure oil levels and perform Dissolved Gas Analysis (DGA) and moisture content testing. Temperature fluctuations can draw in moisture and reduce oil dielectric strength, increasing the risk of internal arcing. (IEC 60296).
4. Heating, Ventilation, and Anti-Condensation Systems
Confirm that anti-condensation heaters in cubicles, control rooms, and relay panels are operational. Check ventilation filters and thermostats. These heaters protect sensitive electronics and relays from condensation and corrosion. (BS EN 62271-200).
5. Circuit Breaker Operation
Inspect operating mechanisms and test a representative sample for timing and responsiveness. Hydraulic oils and greases thicken in low temperatures, causing sluggish operation or failures during faults. (IEC 62271-100).
6. DC Battery Bank and Control Supply
Measure electrolyte levels, string voltage, and internal resistance. Cold weather reduces battery capacity by up to 20%. A weak DC supply can prevent protective systems from tripping or closing switchgear in emergencies. (IEEE Std 450).
7. Protection Relay and Control System Testing
Perform functional testing of critical protection relays and trip logic. Temperature and humidity fluctuations can affect relay contacts and calibration. (IEC 60255).
8. Drainage and Flood Prevention
Clear gullies, cable trenches, and culverts. Inspect sump pumps and any flood barriers. Heavy rainfall and snowmelt can lead to local flooding — one of the most common causes of winter substation outages. (Environment Agency, 2021).
9. Earthing System Integrity
Inspect accessible earth conductors for corrosion and verify continuity and resistance. Frozen ground increases soil resistivity, potentially weakening fault current dissipation. (IEEE Std 80, ENA ER S34).
10. Site Access and Safety
Ensure access roads are clear, walkways gritted, and external lighting and CCTV systems operational. Limited daylight and icy conditions increase safety risks for maintenance staff and first responders. (HSE INDG244).
🦺 Safety Tip: Personnel and Asset Safety
The importance of partial discharge testing before substation entry
Carrying out partial discharge (PD) testing before entering a substation is an essential first step for utility technicians. Using EA Technology’s UltraTEV Detector2 or UltraTEV Plus2, technicians can assess the condition of high-voltage equipment safely and non-intrusively.
Why partial discharge testing matters:
- Partial discharge is an early sign of insulation deterioration.
- Undetected PD can lead to equipment failure, arc flash, or unplanned outages.
- PD activity is often present long before visible damage occurs.
Benefits of using UltraTEV instruments before entry:
- Detect PD using TEV and ultrasonic measurements without opening panels.
- Allow surveys to be completed while equipment remains energized.
- Identify high-risk assets before technicians are exposed to danger.
Why it should be the first step in condition-based maintenance:
- Improves personal safety by highlighting potential hazards early.
- Enables proactive maintenance instead of reactive repairs.
- Supports data-driven decisions and long-term asset reliability.
Top 10 Electrical Checks for UK Substations in Winter
| # |
Essential Electrical Check |
Why It Matters in Winter |
Recommended Test Instrument / Equipment |
Example Popular Brand |
| 1 |
Thermal Inspection of Connections & Joints |
Hotspots from poor connections are more visible but more dangerous under high load. |
Thermal Imaging Camera (Infrared) |
FLIR, Fluke |
| 2 |
Insulator & Bushing Condition Assessment |
Damp or salt-contaminated surfaces create conductive paths that can cause flashovers. |
Visual Inspection, Leakage Current Monitor |
Megger |
| 3 |
Transformer/Switchgear Oil & Moisture Analysis |
Cold weather increases moisture ingress, reducing oil dielectric strength. |
Oil Analysis Kit, Oil Dielectric Test Set |
Megger |
| 4 |
Verification of Anti-Condensation Heaters |
Prevents condensation on sensitive electronics and relays, reducing corrosion. |
Clamp Meter, Thermometer |
Fluke, Chauvin Arnoux |
| 5 |
Circuit Breaker Timing Test |
Low temperatures cause oils/greases to thicken, slowing operation. |
Circuit Breaker Timer / Analyser |
OMICRON, Megger |
| 6 |
DC Battery Bank Integrity Check |
Cold reduces battery capacity; a weak DC system can prevent fault tripping. |
Battery Impedance Tester, Digital Multimeter |
Megger (BITE), Fluke |
| 7 |
Earthing System Continuity & Resistance Check |
Frozen ground raises soil resistivity; poor connections compromise safety. |
Earth Resistance Tester, DLRO |
Megger |
| 8 |
Protective Relay System Functional Test |
Ensures relays operate correctly during faults — vital for asset protection. |
Protection Relay Test Set |
OMICRON |
| 9 |
Condition of HV Disconnectors & Mechanisms |
Ice or snow can freeze mechanisms or cause conductive bridges. |
Visual Inspection, Thermal Camera, Torque Wrench |
FLIR |
| 10 |
Integrity of Building Seals & Cable Glands |
Prevents moisture and pests entering control and relay areas. |
Visual Inspection, Smoke Pencil, Thermal Camera |
FLIR |
References and Standards
- IEC 60894 / ISO 18434-1 – Thermography for Electrical Maintenance
- ENA TS 41-36 – Distribution Substation Equipment Standards
- IEC 60296 – Transformer Oil Quality
- BS EN 62271-200 – Metal-Enclosed Switchgear
- IEEE Std 450 – Maintenance of Lead-Acid Batteries
- IEC 60255 – Protection Relay Standards
- IEEE Std 80 – Earthing Safety in AC Substations
- HSE INDG244 – Preventing Slips and Trips at Work
- Environment Agency (2021) – Flood Resilience for Electricity Substations