Understanding Transformer Safety Protection Devices: Oil Cushion, Moisture Absorbers, and More

Transformer Main Body Construction and Safety Protection Devices

A power transformer is equipped with several critical safety protection devices to ensure reliable and safe operation. These components play essential roles in monitoring, protecting, and maintaining the integrity of the transformer under varying operating conditions.

1. Oil Cushion (Conservator Tank)

The oil cushion, also known as the conservator tank, typically has a capacity of approximately 8–10% of the total transformer oil volume. Its primary functions are to accommodate the expansion and contraction of insulating oil due to temperature fluctuations, minimize direct contact between the oil and ambient air, and thereby reduce oil degradation caused by moisture absorption and oxidation. To further enhance protection, moisture absorbers (breathers) are installed on the oil cushion to prevent unfiltered air from entering the transformer during oil volume changes.

2. Moisture Absorber (Breather) and Oil Purifier (Filter)

• The moisture absorber, commonly referred to as a breather, is filled with desiccants such as silica gel or activated alumina. In many designs, color-changing silica gel is used—appearing blue when dry and turning pink or red when saturated with moisture—providing a visual indication for maintenance, such as drying or replacement of the adsorbent.

• The oil purifier, also known as a filter or reclaimer, contains similar adsorbent materials (e.g., silica gel, activated alumina) within a cylindrical chamber. As the transformer oil circulates through this unit, the adsorbents remove moisture, organic acids, and oxidation byproducts, helping to maintain oil purity, dielectric strength, and overall longevity.

3. Explosion-Proof Tube (Safety Duct) / Pressure Relief Device

The explosion-proof tube, or safety duct, is mounted on the transformer tank cover and serves to release excessive internal pressure rapidly in the event of a severe internal fault, such as an arc or short circuit, thereby preventing catastrophic tank rupture. In modern large power transformers, this device has largely been replaced by pressure relief valves. These valves are designed to activate automatically when internal pressure exceeds a safe threshold. Upon operation, they not only relieve pressure but also trigger alarm contacts or trip signals to alert operators or initiate circuit breaker tripping, enhancing system protection.

4.Additional Safety and Monitoring Devices

In addition to the above, transformers are also fitted with various other protective and monitoring components, including:

• Gas protection (Buchholz relay) for detecting internal faults such as arcing or insulation breakdown that generate gas;

• Temperature gauges to monitor winding and oil temperature;

• Oil level indicators to provide real-time visualization of oil levels in the conservator.

Together, these safety devices ensure the transformer operates efficiently, reliably, and safely throughout its service life.