Why Are Dry Type Transformers Preferred in High-Humidity Environments?

1. What Specific Risks Does High Humidity Create for Oil-Filled Transformers?

An oil-filled transformer relies on mineral oil for two functions: insulation and cooling. In a high-humidity environment, both functions are compromised. The first risk is moisture ingress into the oil. Even with a sealed tank, breathing action caused by thermal cycling can draw moist air into the conservator tank. Over time, the oil absorbs water, which reduces its dielectric strength. A water content of just 30 ppm can reduce the breakdown voltage of mineral oil by 30 percent. The second risk is condensation on the windings. When the transformer cools, moisture in the air inside the tank can condense on the winding surfaces. This creates a path for partial discharge and eventual flashover. The third risk is external corrosion. The tank, cooling fins, and bushings are all exposed to humid air. Rust and pitting can lead to oil leaks and structural failure. In our factory, we have inspected oil-filled transformers from coastal installations that required oil replacement every 2 to 3 years because of moisture contamination.

Lugao Power Co.,Ltd. manufactures Dry Type Transformer units that are specifically designed for high-humidity environments. Our transformers use cast resin insulation and a sealed winding structure that prevents moisture from reaching the conductive parts. We have supplied these transformers to coastal substations, offshore platforms, and underground metro stations.

2. How Does the Insulation System of a Dry Type Transformer Resist Moisture?

The insulation system of a Dry Type Transformer is based on solid dielectric materials rather than liquid. The most common type is cast resin, in which the windings are encapsulated in an epoxy resin that is cured under vacuum. The vacuum casting process eliminates air voids and creates a hermetic seal around the winding. Moisture cannot penetrate the resin, and condensation cannot form on the winding surface because there is no air gap. The table below compares the moisture resistance of different transformer insulation systems.

Cast resin insulation provides the highest level of moisture resistance. The epoxy resin is hydrophobic, meaning it repels water. Even if the transformer is exposed to direct water spray, the insulation maintains its dielectric strength. Our factory tests every cast resin Dry Type Transformer with a water spray test per IEC 60076-11. The transformer must maintain full dielectric strength after the test.

3. What Are the Key Parameters to Verify When Selecting a Dry Type Transformer for High Humidity?

When selecting a Dry Type Transformer for a high-humidity environment, there are five key parameters to verify. The first is the insulation class. Class F (155°C) or Class H (180°C) insulation provides a higher temperature margin, which is important because high humidity can reduce the cooling efficiency of the air. The second is the ingress protection rating. An IP54 rating ensures that the enclosure is protected against dust and water splashes. The third is the anti-condensation heater. Even a dry type transformer can benefit from a heater to prevent condensation on the enclosure and the terminals during rapid temperature changes. The fourth is the winding material. Copper windings are preferred over aluminum because copper has lower resistance and better thermal conductivity. The fifth is the temperature rise. A lower temperature rise (e.g., 80K instead of 100K) reduces the thermal stress on the insulation and extends the service life. The table below shows the specifications of our standard dry type transformer models for high-humidity applications.

Lugao Power Co.,Ltd. manufactures Dry Type Transformer units with these specifications. Our factory uses vacuum casting for the windings and a corrosion-resistant enclosure for the humid environment. We also offer a stainless steel enclosure for coastal installations.

4. What Maintenance Practices Extend the Life of a Dry Type Transformer in Humid Conditions?

Although a Dry Type Transformer requires less maintenance than an oil-filled unit, it still requires periodic attention to ensure reliable operation in a humid environment. The most important maintenance task is cleaning. Dust and moisture can combine to form a conductive film on the insulation surface, which can lead to tracking. We recommend cleaning the windings and the enclosure every 12 months using a vacuum cleaner and a dry cloth. Do not use water or solvents. The second task is checking the anti-condensation heater. The heater should be operational whenever the transformer is de-energized. The third task is inspecting the terminals for corrosion. If corrosion is found, clean the terminals and apply a protective coating. The fourth task is checking the tightness of the electrical connections. Thermal cycling can cause connections to loosen over time. We recommend retorquing the connections annually to the specified torque values. In our factory, we provide a maintenance manual with every Dry Type Transformer that includes a checklist for humid environment installations.

Summary for Electrical Design Engineers

Dry Type Transformer units are the preferred choice for high-humidity environments because they eliminate the moisture-related failure modes of oil-filled transformers. The cast resin insulation system is hermetic and hydrophobic, so it does not absorb moisture or allow condensation on the windings. The key parameters to verify are the insulation class, the ingress protection rating, the anti-condensation heater, and the winding material. With proper maintenance, a dry type transformer can provide decades of reliable service in the most demanding humid environments. Lugao Power Co.,Ltd. has been manufacturing Dry Type Transformer units for over 15 years and supplies to projects in more than 30 countries.

Lugao Power Co.,Ltd. manufactures cast resin Dry Type Transformer units with IP54 or IP55 enclosures, copper windings, and anti-condensation heaters. We provide full test reports and installation support for high-humidity applications.