18 June 2024

Optimize Transformer Insulation Systems: A Q&A with Brad Greaves, Laboratory Services Manager at Weidmann

In this article, we explore with Brad how Transformer manufacturers can optimize the insulation system to reduce cost, optimize design, and improve the supply chain.

Q1. Please provide an overview of a few key insulation design concepts that can contribute to a more optimized insulation system.

Three key concepts that can improve the design of liquid-immersed core form power transformers are:

– Milled spacers

– Calendered crepe conductor insulation

– Low-density pressboard barriers

Q2. Explain the benefits of milled spacers as a substitute for un-milled board.

There are multiple benefits of substituting un-milled board with milled spacers, such as:

– Reduced thickness variation allows for a more precise and consistent winding height

– Predictable shrinkage after the drying process due to consistent material thickness and moisture compensation during the milling process

– Improved compressibility characteristics; reduced and consistent compressibility across all thicknesses

Q3. Why choose Calendered Crepe paper to wrap the conductors

The benefits of using Calendered Crepe paper as conductor insulation include:

– High dielectric strength – determined by thickness and number of layers

– High tensile strength & high elongation – allowing the paper to be wrapped as tightly as possible (controlling turn-to-turn thickness)

– Enhanced moisture resistance – the calendering process reduces the porosity of the paper, decreasing moisture absorption & improving performance with insulating fluids

Q4. How do Low-Density Pressboard barriers contribute to optimizing transformer design?

Low-density pressboard, manufactured from cellulose materials and impregnated with mineral oil, typically displays the following values:

– Dielectric stress distribution is inversely proportional to the material permittivity for better operational efficiency

– Using a Low-Density Board (instead of a High-Density Board) brings the relative permittivity of the solid closer to the relative permittivity of the liquid – reducing the stress in the liquid & improving insulation performance

– Replacing Hi-Lo barriers from High-Density Pressboard (T4) to Low-Density Pressboard (Hi-Val) results in a shift of the dielectric stress away from the liquid and an increase in the percent margin during the Insulation Design Analysis.

Q5. How would you summarize this topic?

As part of the global Weidmann Technical Engineering Services team, we utilize these concepts, among many others, to provide Optimized Insulation Design Analysis Services.

Some of the primary insulation design concepts that contribute to a more optimized insulation system are:

– By utilizing milled spacers, windings can be manufactured with improved sizing control and have improved compression characteristics

– By creping and then calendaring conductor insulation, the strength, and elongation are significantly improved, allowing for high tension during the wrapping process, which provides an improved space factor

– Utilizing pressboard barriers with lower relative permittivity (closer to that of the liquid) lowers the dielectric stress in the liquid, allowing for smaller oil gaps

Get more insights from Brad Greaves by watching his presentation at the IEEE PES Expo.