In the operation of power systems, the oil-immersed transformer is a core piece of equipment. Its safety and stability directly affect the power supply reliability of the entire grid. Among all faults, “sudden short circuit” is a common cause of damage or even burnout of oil-immersed transformers. Understanding the causes of sudden short circuit in oil-immersed transformers not only helps maintenance personnel take preventive measures in advance but also provides a scientific basis for selecting high-quality transformers. As a professional brand deeply engaged in the power equipment industry, Xinhong Electrical, based on years of manufacturing and application experience, systematically summarizes several key factors leading to such faults.
During the operation of an oil-immersed transformer, if an outlet short circuit occurs on the low‑voltage or high‑voltage side (e.g., due to lightning strikes, tree contact, animal intrusion, or human misoperation), the short‑circuit current can reach tens of times the rated current. Such a huge short‑circuit current generates extremely strong electromagnetic forces between the transformer windings. These mechanical forces increase with the square of the current, which can lead to:
Axial and radial instability of windings, resulting in bulging or distortion;
Loosening of insulating spacers and failure of the clamping structure;
In severe cases, direct inter‑turn or phase‑to‑phase short circuits.
Xinhong Electrical optimizes the ampere‑turn distribution of windings through finite element simulation and adopts a high‑strength clamping structure, significantly improving the product’s short‑circuit withstand capability and effectively reducing the risk of damage caused by such external faults.
After long‑term operation, the oil‑paper insulation system of an oil‑immersed transformer gradually deteriorates due to heat, oxygen, moisture, and other factors. Insulation aging reduces dielectric strength. Under slight overvoltage or current fluctuations, partial discharge is easily initiated and can evolve into a sudden short circuit. Common causes include:
Increased acid value and decreased interfacial tension of the transformer oil;
Reduced degree of polymerization of the insulating paper, leading to mechanical embrittlement;
Seal failure allowing moisture ingress.
To address this pain point, Xinhong Electrical adopts a fully sealed structural design, equipped with high‑performance desiccants and online monitoring interfaces. This significantly slows down insulation aging and moisture ingress, eliminating the hidden danger of sudden short circuits at the source.
Lightning strikes, switching overvoltages, or resonance overvoltages can instantaneously damage the main or longitudinal insulation of the transformer. Even if the short‑circuit current itself does not form immediately, insulation breakdown caused by overvoltage often becomes the trigger for a sudden short circuit. This is especially true for oil‑immersed transformers, where the internal electric field distribution is complex. If the inter‑turn insulation margin is insufficient, overvoltage can easily cause an inter‑turn short circuit.
To address this, Xinhong Electrical designs its oil‑immersed transformers with an insulation margin higher than national standards and equips them with zinc‑oxide arresters or RC snubbers, enhancing the overall overvoltage withstand capability.
Some sudden short‑circuit accidents are not entirely caused by operating conditions but originate from hidden defects in manufacturing or assembly, such as:
Damaged inter‑turn insulation or residual metal burrs during winding;
Improper position of the core grounding piece causing multi‑point grounding;
Poorly welded leads that disconnect under high current impact;
Incomplete drying of the active part, leaving residual moisture or bubbles.
Xinhong Electrical implements a strict ISO9001 quality management system. Before delivery, each oil‑immersed transformer undergoes induction withstand voltage tests, partial discharge tests, and short‑circuit withstand capability verification, ensuring extremely high process consistency.
The on‑load or off‑circuit tap changer is a weak point often overlooked in oil‑immersed transformers. When the tap changer contacts oxidize, spring pressure weakens, or switching is incomplete, the contact resistance increases abnormally. Once a slight disturbance occurs in the system, high‑temperature arcing at the contacts will carbonize the insulating oil and cause a short circuit between adjacent taps, eventually evolving into a full winding short circuit.
Regular DC resistance measurement of the tap changer is recommended. Xinhong Electricaloffers maintenance‑free off‑circuit tap changer options to further reduce this risk.
If residual welding slag, iron filings, or metal powder (often introduced during assembly or repair) remain inside the transformer, these conductive particles can align under the electric field to form “small bridges,” distorting the local electric field. When voltage or current fluctuates, a low‑energy short circuit easily occurs and rapidly escalates into a high‑energy arc.
Xinhong Electrical uses a fully enclosed clean assembly workshop and performs multiple vacuum washing and filtration processes on the active part, ensuring internal cleanliness far exceeds industry standards, completely eliminating the possibility of short circuits caused by foreign matter.
It is particularly important to note that a sudden short circuit in an oil‑immersed transformer is often not caused by a single high‑current impact but by multiple small short‑circuit shocks. Each shock gradually deforms the winding and increasingly abrades the insulation, until a minor disturbance finally triggers a sudden failure. This cumulative effect is very difficult to detect during routine inspections.
Therefore, it is recommended that important transformers undergo regular winding deformation tests (frequency response analysis or low‑voltage short‑circuit impedance method). Xinhong Electrical provides full life‑cycle technical support to help users develop condition‑based preventive maintenance strategies.
In summary, the causes of sudden short circuit in oil‑immersed transformers can be classified into seven major categories: external short‑circuit electrodynamic forces, insulation aging, overvoltage, manufacturing defects, tap changer issues, foreign particle contamination, and cumulative winding deformation. To fundamentally reduce the accident rate of sudden short circuits, both standardized operation & maintenance and high‑quality equipment are essential.
Xinhong Electrical focuses on the R&D and manufacturing of oil‑immersed transformers. By optimizing electromagnetic structures, strengthening clamping systems, increasing insulation margins, and performing rigorous factory verification, we deliver products with excellent short‑circuit withstand capability. Choosing Xinhong Electrical means lower failure risk, longer service life, and professional pre‑sales and after‑sales support.
For more information on the causes of sudden short circuit in oil‑immersed transformers or selection advice, please visit the Xinhong Electrical official website or contact our technical team.
