Transformer Insulation Coordination: What Buyers Should Specify
Pressboard, paper and oil work as a system. Specifying them separately without a coordination plan creates gaps at the design and inspection stages.
Insulation coordination is often treated as a design task that happens after the core and windings are fixed. In practice, the material choices — pressboard density, paper thickness, oil quality — set the limits of what the design can achieve.
Define the voltage stresses first
List the lightning impulse, switching impulse and power-frequency test levels. These determine the required clearances and the insulation thicknesses, which in turn determine the pressboard and paper specification.
Specify material properties, not just dimensions
For pressboard, density, moisture content and compressibility matter as much as thickness. For paper, thickness tolerance and conductivity matter. A dimension-only specification leaves the supplier free to choose the cheapest material that fits.
Treat oil as part of the insulation system
Oil breakdown voltage, moisture and particle count affect the same clearances. A high-quality pressboard in contaminated oil will not perform as designed. Require oil certificates with the same discipline as steel certificates.
Inspect the assembly, not only the components
Clearances, lead support and barrier placement are visible at inspection. Add them to the pre-shipment checklist so the insulation system is verified as built, not only as designed.
Need this applied to a project?
Send the product, standard and destination. We will translate the general guidance into a specification and quotation basis.
Request a quote