What are the common faults in the cooling system of dry-type transformers?

The cooling system of dry-type transformers is based on air as the core cooling medium, which is divided into two categories: natural air cooling (AN) and forced air cooling (AF), and the faults are mainly concentrated in the ventilation channels, forced air cooling components and temperature control monitoring systems, and the specific common faults are as follows:
1. Blocked air ducts or poor ventilation
Fault performance: The operating temperature of the transformer is abnormally high, the load capacity is reduced, and the over-temperature alarm will be triggered in severe cases.
Cause of failure: Dust, cotton, fiber and other debris in the installation environment accumulate on the surface of the winding, core gaps and shell inlet/outlet; Surrounding obstacles obstruct the air ducts, or the ventilation system fails during indoor installation, resulting in obstruction of air circulation.
Typical scenarios: textile factories, cement factories, mines and other industrial sites with a lot of dust, or distribution rooms with debris piled around transformers.
2. Forced air cooling fan failure

Fault performance: after the thermostat reaches the starting temperature, the fan does not respond; Or the fan makes an abnormal noise and trips immediately after starting.
Causes of failure: fan bearing wear, rust and jamming; motor coil burnout; The fan power wiring is loose, falling off or short-circuited; Clogged dust mesh leads to overload of fans.

Fault performance: The fan is running normally, but the transformer cooling effect is poor, and the temperature is continuously high.
Causes of failure: fan blades are deformed and dust accumulates seriously; abnormal fan motor speed (such as capacitor aging leading to a decrease in single-phase motor speed); Some fans are not started synchronously (when multiple fans are configured).

Fault performance: The fan emits sharp noises or violent vibrations during operation, affecting the stability of the equipment.
Causes of failure: unbalanced and loose fan blades; bearings lack oil and serious wear; The fan installation fixing bolt is loose.
3. Temperature control and control loop failure

Fault performance: The temperature displayed by the thermostat is too deviated from the actual temperature; Disruption of fan start/stop temperature threshold (such as low temperature start, high temperature not start); The thermostat does not show or the alarm is triggered incorrectly.
Cause of failure: Damaged, loose or poor contact of the temperature sensor (thermistor or thermocouple): Aging of the internal electronic components of the thermostat, short circuit; Thermostat calibration fails.

Fault performance: the fan cannot be controlled by the thermostat and needs to be manually started and stopped; or control loop tripping, fuse fuse.
Fault causes: loose and oxidized control loop wiring; ablative adhesion of intermediate relay and AC contactor contacts; Improper selection or aging of overload protection components.
4. Damage to the heat dissipation structure of the shell (for natural air cooling type)
Fault performance: Under natural air cooling, the temperature rise of the transformer accelerates and the heat dissipation efficiency decreases.
Fault causes: deformation and damage to the heat dissipation fins of the transformer shell; The poorly sealed shell causes a large amount of dust to enter the interior and adhere to the winding surface, affecting radiant heat dissipation and air convection.