Operating Challenges of Oil-Immersed Transformers in Extremely Cold Regions and a Protection-Configuration Guide

1. Key Problems in Extremely Cold Regions

At very low temperatures, the insulation, cooling and mechanical construction of an oil-immersed transformer all face severe challenges, primarily in the following four areas:

• Deteriorated oil fluidity and solidification risk: at low temperatures the viscosity of transformer oil rises sharply, fluidity weakens, and natural-convection cooling efficiency falls substantially. If the temperature drops below the pour point of the insulation oil, the oil may even solidify, stalling oil circulation and causing local overheating inside the transformer.
• Abnormal oil level and degraded insulation: thermal contraction causes the oil level to drop noticeably, which can trigger a low-oil-level alarm or even expose the windings to air, seriously jeopardizing insulation performance. In addition, moisture dissolved in the oil may precipitate as suspended ice crystals at low temperature, increasing the risk of partial discharge and flashover.
• Mechanical sticking and embrittlement: in extreme cold, the spring materials of operating mechanisms in devices such as circuit breakers and disconnectors can become brittle, and lubricating oil may thicken or solidify — readily causing sluggish operation, sticking or even refusal to operate.
• Seal failure, condensation and icing: large day/night temperature swings repeatedly expand and contract the metal parts of the tank, bushings and flanges, accelerating seal gasket aging and leading to oil seepage. Meanwhile, cold, damp conditions readily cause condensation and icing on equipment surfaces, damaging insulation and accelerating corrosion of metal parts.

2. Key Equipment and Measures Required

To guarantee safe, stable operation of the transformer in severe cold, the following protection equipment and measures must be deployed in a targeted manner:

Select a low-temperature insulating oil: the transformer oil used must have a pour point below the locally recorded minimum temperature. In extreme-cold regions, a low-pour-point transformer oil (e.g., grade No. 45, with a pour point of −45 ℃) or a synthetic ester oil should be used.

Oil selection should not only consider the pour point, but must also ensure that its lowest cold-start energization temperature (LCSET) is below the locally recorded extreme minimum temperature, so that viscosity at low temperature still satisfies circulation requirements.

Install automatic heating and thermal-insulation devices:

• Electric heat tracing and heaters: fit electric heat tracing at the bottom of the tank, or install heaters in the mechanism boxes and terminal boxes. Automatic startup occurs when the oil temperature falls below the equipment's specified safe energization threshold, maintaining oil temperature within the safe operating range.
• Thermal insulation layer: add thermal-insulation padding (e.g., insulation batting) to the outdoor transformer enclosure, protecting control components from freezing and slowing heat loss.
• Low-frequency heating technology: for large oil-immersed transformers, on-site low-frequency heating can be applied, effectively resolving the hot-oil circulation and insulation-recovery difficulties encountered in extreme cold.

Retrofit the intelligent temperature-control and cooling system:

• Independent control circuits: control the oil pump and radiator fans separately. Under low-temperature, low-load conditions, achieve "oil circulation without cooling" — the oil pump continues to run to maintain oil flow while the radiator fans are switched off, avoiding excessively low oil temperature.
• Automatic start/stop control: configure temperature sensors for automatic switching of the cooling fans and oil pump; the exact start/stop thresholds must be set strictly in accordance with the equipment manufacturer's technical manual and the local grid dispatch regulations.

Deploy high-precision condition-monitoring devices:

• Digital instrumentation: fit digital dial-type oil level gauges, digital gas (Buchholz) relays and other instruments that operate reliably in extreme cold, to monitor oil level, pressure and gas condition in real time and transmit the data remotely.
• Broadband dielectric response monitoring: to close the sensing blind spots in extreme cold, broadband (frequency-domain) dielectric response technology is recommended, establishing a dielectric-spectroscopy database spanning an ultra-wide temperature range to precisely identify internal moisture ingress or insulation defects and provide early warning of latent faults.

Equip cold-resistant accessories: select transformer valves, panel-type radiators and a smart maintenance-free breather (which also resolves the problem of LCD displays failing at low temperature) designed specifically for extreme-cold regions, ensuring the reliability of all components at low temperature.

Strengthen mechanical lubrication: for operating mechanisms, the use of low-temperature grease/lubricant designed for extreme cold is mandatory, and the mechanism boxes must be fitted with anti-condensation heaters to prevent mechanical sticking.

Summary

Safe operation of oil-immersed transformers in extreme-cold regions is a systematic undertaking. The oil solidification, falling oil level, mechanical sticking and seal failure caused by severe cold directly threaten grid stability.

Both equipment selection and operation & maintenance must therefore adopt a "prevention-first" integrated strategy: on the physical side, select low-pour-point insulating oil, install automatic heating and thermal-insulation equipment, and retrofit the intelligent temperature-control system to keep the equipment operating normally.

on the monitoring side, rely on high-precision online monitoring devices and cold-resistant accessories to achieve real-time status awareness and accurate early warning. Only by deeply integrating hardware protection with intelligent monitoring can the challenges of extreme climates be effectively countered and the long-term safe and stable operation of power equipment in severe-cold regions be secured.

Edited From：Echo