What factors can cause excessive temperature rise in current transformers?

I. Overload Operation (Current Exceeding Rated Value)
When the primary current consistently exceeds the transformer's rated value, winding copper losses and core losses increase significantly, generating substantial heat.

Especially in high-current surge scenarios (such as a sudden increase in load on 110kV/220kV lines), if the transformer's rated current does not cover the actual operating conditions (e.g., designed only up to 1000A), a short-term temperature rise to 70–80℃ is highly likely.

II. Poor Conductor Connection Contact

Excessive contact resistance is a common cause of temperature rise. For example: Loose primary connector screws or unpressed spring washers result in insufficient contact pressure; Oxidation, corrosion, or surface contamination at copper busbar connections damages microscopic contact points; Cable crimping areas form "conductive bottlenecks," increasing local resistance.

Increased contact resistance makes this area a concentrated heat source, reaching temperatures exceeding 130℃ in severe cases.

III. Design and Selection Mismatch

Rated parameters do not match actual operating conditions: The rated current of the transformer is too low, unable to adapt to large current fluctuations in the field (e.g., 1600A~2600A); The secondary winding design is unreasonable (e.g., too many turns, too thin wire diameter), leading to increased internal resistance and heat generation.

Magnetic circuit structure design defects: Excessive iron loss in the core material or improper magnetic circuit closure easily generates additional hysteresis and eddy current losses.

IV. Poor Heat Dissipation

Poor internal heat dissipation: Traditional single-sided winding technology causes heat to focus and cannot be effectively conducted; The use of epoxy resin potting compound with poor thermal conductivity hinders internal heat dissipation.

External environmental influences: The installation space is enclosed and poorly ventilated; Multiple heat-generating elements are compactly arranged, creating a heat accumulation effect.

V. Internal Faults or Manufacturing Defects

Inter-turn short circuits or multiple core grounding points: Cause local circulating currents, increasing additional losses;

Winding insulation damage: Triggers partial discharge or short circuits, generating high-temperature hotspots;

Manufacturer's components exceeding temperature rise limits: Some products have issues with excessively high DC resistance or insufficient temperature rise margin at the time of manufacture.

VI. Non-standard Installation Process

Excessive or insufficient bolt torque during installation:

Insufficient torque: Insufficient contact pressure, increased contact resistance;

Excessive torque: Damages copper threads, leading to loosening due to thermal expansion and contraction after long-term operation, resulting in increased contact resistance.