Mike Howell
Technical Support Specialist
Electrical Apparatus Service Association

The paper "Insulation Technology Improvements and the Repair Market" by Mike Howell, presented at the EASA Convention 2018, explores advancements in insulation technology and their implications for the repair market. The primary function of stator winding insulation systems is to transfer heat away from conductors, provide electrical insulation, withstand environmental conditions, and minimize vibration. Insulation materials are classified based on their resistivity, with conductors having low resistivity and insulators having high resistivity.

Insulation systems are categorized by their thermal ratings, with modern machines typically using Class B, F, or H insulation. These classifications indicate the maximum temperature the insulation can withstand, with higher classes offering better thermal life. For instance, a Class F insulation system can significantly extend the thermal life of a winding compared to a Class B system.

The paper details the components of insulation systems, including conductor strand insulation, turn insulation, and ground insulation. Conductor strand insulation, often made of polyester-based film, separates parallel strands within a turn to reduce electrical losses and increase mechanical flexibility. Turn insulation, which may be the same as strand insulation in some machines, separates turns that experience high voltages during transient events. Ground insulation separates coil turns from the stator core and is critical for preventing ground failures.

Advancements in insulation technology have led to the development of materials with improved thermal and electrical properties. For example, the use of nanoparticles in magnet wire insulation and varnishes has enhanced partial discharge inception voltage (PDIV) and thermal endurance without increasing insulation thickness. This is particularly beneficial for inverter duty applications, where voltage transients can be severe.

The paper also discusses the importance of proper winding treatment processes, such as Dip & Bake and Vacuum Pressure Impregnation (VPI). VPI, which involves impregnating the winding with resin under vacuum and pressure, results in a homogeneous structure with excellent thermal, electrical, and mechanical properties. This process is widely used for form-wound stators and is increasingly being applied to random-wound stators.

Technological advancements in mica tapes, such as the use of boron nitride fillers and flat glass yarns, have improved the thermal conductivity and electrical stress handling of ground insulation. These innovations allow for higher electrical loading without additional temperature rise, enhancing the performance and reliability of insulation systems.

The paper emphasizes the need for service centers to stay abreast of these advancements to effectively repair and maintain modern machines. Understanding the latest insulation technologies and their applications can help service centers improve the reliability and efficiency of rewound motors, ensuring they meet or exceed original equipment manufacturer (OEM) specifications.

Key Points Covered:

• Functions and classifications of insulation systems
• Components of insulation systems: conductor strand insulation, turn insulation, and ground insulation
• Advancements in insulation materials, including the use of nanoparticles
• Importance of proper winding treatment processes like Dip & Bake and VPI
• Technological improvements in mica tapes for ground insulation
• Implications of insulation technology advancements for the repair market

Key Takeaways:

• Higher thermal class insulation systems offer better thermal life for windings.
• Advancements in insulation materials, such as nanoparticle-enhanced films, improve performance without increasing thickness.
• Proper winding treatment processes are crucial for the longevity and reliability of stator windings.
• Technological improvements in mica tapes enhance thermal conductivity and electrical stress handling.
• Service centers must stay updated on insulation technology advancements to ensure effective repairs and maintenance of modern machines.