FAQ’s

Unless specifically designed for harsh environments, dry-type distribution transformers typically operate under the following standard service conditions:

• Ambient Temperature: -40°C to +30°C (maximum peak of +40°C)
• Relative Humidity: Less than 70%
• Altitude: Up to 1000 meters (3300 feet) above sea level

To ensure proper operation, avoid installing transformers in environments with excessive moisture, extreme temperatures, or direct sunlight. Maintain recommended clearances and keep all ventilation panels unobstructed.

Dry-type transformers can generally be connected in reverse (backfed), but there are some precautions to consider:

• Compensated Windings: Control transformers and distribution transformers below 3kVA are designed with overvoltage on the secondary side to compensate for voltage regulation. Backfeeding these transformers may result in lower than expected output voltage.
• Inrush Current: Backfeeding a transformer increases inrush current significantly, which may cause nuisance tripping of breakers. Special considerations may be needed.
• Voltage Taps: Typically, secondary windings lack voltage adjustment taps. Therefore, reverse-feeding transformers must operate within their rated voltage to avoid overexcitation and insulation damage.
• Grounding: When the secondary side of a delta-wye transformer is energized, the neutral is not separately derived and should not be grounded. Always consult local codes before backfeeding transformers.

Temperature rise refers to the increase in the temperature of transformer windings above the ambient temperature when operating at full load. In addition to the average temperature rise of the windings, transformers also experience a "hot spot" temperature, which refers to the highest temperature point in the windings.

For example, a transformer with a 220°C insulation system may be designed with a 150°C average winding temperature rise and a 30°C hot spot allowance. This means that the winding temperature can rise by up to 150°C above the ambient temperature, and the hottest spot in the transformer can rise by an additional 30°C. Combined, this gives a maximum winding temperature of 220°C.

Transformers are designed with different insulation classes, each specifying the maximum permissible temperature rise and corresponding insulation life. Below is a table showing the most common insulation ratings:

Benefits of Lower Temperature Rise:

• Longer Transformer Life: Lower temperature rise means the transformer can operate at a lower overall temperature, extending its life expectancy.
• Handling Higher Ambient Temperatures: Transformers with lower temperature rise ratings can operate safely in higher ambient temperatures without exceeding their insulation limits.
• Increased Overload Capacity: These transformers can handle continuous or short-term overloads without overheating, making them ideal for environments where transformers may be subject to occasional overloading.

Lower temperature rise transformers provide greater flexibility, reliability, and longevity, especially in demanding conditions.

The life expectancy of a dry-type transformer is primarily determined by the insulation system and the operating temperature. According to IEEE Std. C57.96, the deterioration of insulation is directly related to the time and temperature the transformer experiences during operation. Insulation materials degrade faster at higher temperatures, so the transformer’s life expectancy is closely tied to how well it is kept within its design temperature limits.

In most transformers, the highest temperature occurs at a specific point in the windings, known as the hot spot. This area undergoes the most significant wear over time, making it the primary factor in determining the transformer's aging process.

All of Transformer Source's dry-type transformers are designed using UL-listed insulation systems with a maximum hot spot temperature that ensures a design life of at least 30 years under standard operating conditions (continuous rated load, typical ambient temperatures, and no sustained overloads). Transformers designed with reduced temperature rise can extend this design life expectancy to over 50 years, as operating at lower temperatures slows the insulation's aging process.

Factors That Affect Life Expectancy:

• Temperature: As discussed, the most significant factor is the operating temperature of the transformer. Operating continuously at higher temperatures reduces the expected lifespan.
• Humidity and Condensation: Humid environments or condensation can affect the insulation material and lead to premature failure. Proper storage and maintenance help mitigate this risk.
• Short Circuit Events: Sudden surges or short circuits can damage internal components and shorten the transformer’s life.
• Overloading: Continuous overloading beyond the transformer’s rated capacity generates excess heat, which accelerates insulation degradation.
• Environmental Conditions: Extreme environments, such as exposure to dust, moisture, or chemicals, can also lead to earlier-than-expected failure.

By following proper installation and maintenance practices, such as avoiding overloading and ensuring the transformer operates within its designed ambient temperature, you can significantly extend its lifespan. Transformer Source’s high-quality transformers are built for durability, ensuring reliable performance for decades under standard conditions.