The Gradient Coating Systems for Electrical Field Control in High-Voltage Generator Stator Windings

In various industry documents and standards, these coatings are referred as endturns corona protection (ECP), the gradient coating, stress control coating, others self-explanatory names are also in use.

There are multiple variations in design and properties of the materials to smoothly grade voltage from the ground potential to the full operational voltage. This paper focuses on the development, validation, and long-term field performance of a specific epoxy-based surface coating filled with silicon carbide powder.

This paper combines theory, laboratory validation, and operational insights into a single technical framework. The performance of the gradient coating is assessed from theoretical aspects and from actual experimental data collected in controlled lab environments and under full-scale generator operations.

The key topics addressed include:

1. Material Chemistry and Electrical Functionality

• Review of the chemical formulation of the gradient coating

• Purpose of silicon carbide fillers and epoxy matrix for the gradient coating

• Surface resistance properties of the gradient coating 2. Operational Reliability and Life Extension

• Field data from installed machines with over 20 years of operation

• Case studies where life extension was achieved through local repair and re-coating

The paper merges extensive R&D testing with global operational experience into a unified knowledge base for OEMs, service providers, and utilities. The methodology and findings can significantly improve predictive maintenance and insulation design strategies for high-voltage rotating machines.