Key Factors Affecting Anti-Corona Varnish Service Life

What Factors Influence the Service Life of Anti-Corona Varnish?

The service life of anti-corona varnish is influenced by multiple dimensions, including material properties, motor operating conditions, application quality, and maintenance practices. Typically, its lifespan ranges between 5 and 15 years, depending on the actual application scenario.

From a materials perspective, epoxy resin-based varnishes formulated with nanoscale carbon black or metal oxide fillers offer high thermal stability and excellent filler dispersion. Under standard operating conditions, their lifespan can reach 8–15 years. Silicone rubber-based coatings, while known for superior elasticity and aging resistance, are more expensive, and in high-temperature environments, their service life is typically around 10–15 years.

In motors operating above 10 kV, or in applications with frequent starts and stops and strong vibrations, the combination of high electric field strength and mechanical stress accelerates electrical erosion and fatigue cracking of the coating. In these cases, the service life may be reduced to 5–8 years. By contrast, motors operating below 6 kV with stable conditions and minimal vibration often see varnish lifespans extending to 10–15 years.

Long-term exposure to high temperatures or high humidity can cause thermal-oxidative degradation or moisture-induced swelling of the resin matrix. These factors may lead to cracking and delamination of the coating, reducing lifespan by 30–50%. Additionally, insufficient coating thickness, poor uniformity, or low adhesion can create localized field concentrations or early peeling, shortening lifespan by 2–3 years—or, in severe cases, to less than 5 years.

Employing advanced techniques such as electrostatic spraying and vacuum drying ensures uniform thickness and adhesion strength above 3 MPa, significantly improving coating reliability. In typical applications, motors operating in hot and humid climates often see lifespans of 8–12 years, while motors in high-temperature equipment such as dryers achieve around 6–10 years of service.

Utilizing polyimide-based or ceramic-filled composite coatings, combined with gradient resistivity designs, can extend service life beyond 15 years. When the coating develops extensive cracking, delamination, resistivity fluctuations exceeding ±30%, or when the partial discharge inception voltage falls below 1.2 times the operating voltage, these are clear indicators that the service life is approaching its end. Timely repair or replacement is essential to prevent severe failures such as winding breakdown.

Therefore, motor operators should assess real-world conditions and schedule appropriate maintenance. Maintenance teams should avoid limiting their efforts to bearing systems alone and should implement necessary repairs and reinforcement of the motor winding insulation system.