When a cold wave hits, substations and distribution rooms start acting up. Switchgear discharges, transformer oil levels drop, terminal boxes take on water-these problems tend to surface once the snow starts melting. Low temperatures alone are not the main threat. The real danger is the daily freeze-thaw cycle. Moisture condenses inside cabinets, water droplets form on insulation, and a short circuit is not far behind.
Infrared thermometers should be used on main transformers, circuit breakers, disconnectors, busbar joints, and bushings. Compare readings with previous data and flag any abnormal temperature rise. Check oil and gas pressure values, and look at the main transformer's breather oil level and silica gel. If the silica gel has changed color by more than two-thirds, replace it. If it discolors too quickly, moisture may have entered the oil system. Terminal boxes and mechanism boxes need a close look at sealing. Gaps around incoming and outgoing cables, plus any unsealed holes, let meltwater seep in. That is a common cause of DC grounding and false alarms. Also confirm that anti-condensation heaters inside the cabinets are working.
Condensation is the most frequent cause of switchgear faults in cold weather, but many maintenance teams get the first step wrong. A typical case: a 35 kV substation had frequent discharges from switchgear, traced to condensation. The team bought heaters and installed them inside the cabinets. The discharges got worse. The reason is simple. Heaters raise the internal temperature but do not reduce absolute humidity. When the temperature falls again, moisture condenses even faster. The right approach depends on the space inside the cabinet. Cable compartments are relatively open, so semiconductor condensation dehumidifiers work well. They drain water out, typically 500–580 ml per day, and RS485 models can connect to monitoring systems. Busbar compartments have limited headroom at the top, so condensation units may not fit. For these, use ultrasonic atomization dehumidifiers. They exchange air and maintain slight positive pressure, atomizing moisture and expelling it while dry air flows back in. Heaters should not be the primary solution. They can help maintain a base temperature in extreme cold, but dehumidification requires dedicated equipment.
When buying heaters, match power to cabinet size. Small terminal boxes need 50–150 W. Larger switchgear or ring main units generally need 200–500 W. Operating voltage is usually AC/DC 220 V. Check whether mounting is rail-based or bolt-fixed, and choose compact models if space is tight. Pair heaters with temperature and humidity controllers for automatic start-stop. For dehumidifiers, confirm dehumidification capacity, communication interface, and installation dimensions before ordering.
For transformers, focus on the oil system and breather. Oil levels drop as temperatures fall. If the level is too low, the gas relay may trip incorrectly. During inspections, compare the oil level against the current oil temperature and top up if needed. Check the breather silica gel regularly. Replace it when color change exceeds two-thirds. If discoloration accelerates, investigate whether water has entered the transformer. Clear snow from the transformer body and cooling fins, but avoid sharp tools that could damage the anti-corrosion coating. Remove snow and ice from bushings to prevent conductive water films and flashover during melting.
A few actions are urgent once snow begins or stops. Sweep snow from the tops of switch terminal boxes and mechanism boxes to prevent meltwater from seeping in. Check outdoor contact points for snow coverage or steam. Steam indicates possible overheating, because snow evaporates quickly on a hot contact. Measure temperature on these points closely. Inspect cable trench covers and cable hole sealing. Small animals look for warmth in cold weather and may enter trenches through unsealed openings.
Prepare the following items ahead of time:
Dehumidification: intelligent dehumidifiers (semiconductor condensation type for cable compartments, capacity above 500 ml/day, preferably with RS485), ultrasonic atomization dehumidifiers (for narrow spaces such as busbar compartments), temperature and humidity controllers (rail-mounted, capable of switching heaters and fans automatically).
Heating: comb-shaped aluminum alloy heaters (50–500 W depending on cabinet size, AC/DC 220 V, used with controllers).
Sealing: polymer moisture-proof sealing compound (for cable trench entries and cabinet bottoms; cures into a sealed barrier against moisture and small animals).
Inspection tools: infrared thermometer, clamp meter, insulation resistance tester.
Spare parts: silica gel breathers, sealing strips, industrial petroleum jelly, spare heaters.
Before winter, wipe dust from insulators inside cabinets and apply a thin layer of industrial petroleum jelly to improve moisture resistance. Low temperatures can make operating mechanisms and interlocks on ring main units and switchgear stiff. Check fasteners and apply low-temperature lubricant to rotating parts such as load break switches and earthing switches. If cable trench or terminal box sealing is inadequate, repair it before the cold sets in. Once heavy snow blocks access, the work becomes much harder.