Insulation components made from cellulose-based Transformerboard meet the highest requirements specified for use in power and distribution trans- formers. These components form barriers in the liquid-cellulose (e.g. mineral oil & natural/synthetic ester oils) insulation structure of the transformer. They can be shaped according to the specific electrical field pattern optimizing the amount of insulation material and helping to reduce the size of the apparatus.
Clamping Rings
Clamping Rings, or Press Rings, apply pressing force to the winding of power transformers and are a critical component in the transformer’s mechanical design and strength. They are often designed as a donut-shaped component, compress the winding, and are strong enough to hold the winding tightly in case of a short circuit.
The material used in these components is polyester resin-glued laminated Transformerboard or sometimes laminated pressed wood for smaller units. Compared to wood, Clamping Rings manufactured from laminated board have uniform mechanical characteristics, superior electrical values, and do not re- lease acids during drying.
Material Choice
Laminated Transformerboard and wood, used to make Clamping Rings, is a homogenous base material, and, combined with selected high-quality ad- hesives, ensures the superior mechanical support and clamping structures of transformer windings and cores.
Material selection is based not only on mechanical but also on electrical considerations. Material used for Clamping Rings must meet the following requirements to guarantee long-term performance in the transformer:
- Highest electrical and mechanical strength
- Simple and low-cost machining
- Complete oil impregnation
- Dimensional stability during the process treatment of the transformer
Favorable aging characteristics
The use of solid insulation materials for oil-filled transformers, such as Clamping Rings, is mostly determined by the electrical stress the materials are subjected to. This information is calculated and controlled by the design engineer.
Pressboard Benefits
Material choice in modern transformers is a key consideration to meet stringent IEC/IEEE requirements and in high-voltage and high-stress applications. Transformerboard components have a range of clear advantages over laminated wood, some of which include:
- Slower aging and increased reliability - through reduced insulation degradation, and fewer internal insulation faults which can lead to costly outages or repairs
- Enhanced operational safety - where there is a reduced chance of insulation failure, and enables safer operation at higher field stresses
- Dielectric advantages - pressboard eradicates the need for plywood veneer butt joints, thus reducing the risk of voids which may not impregnate
- Increased stress loads – where Transformerboard components have a higher dielectric puncture and surface (creep) strength and are more robust and reliable
Electrical Characteristics
At higher voltage levels, electrical strength is one of the most important design criteria. Laminated Transformerboard is a high-value material with a very homogenous and stable structure.
A reduction in electrical strength can occur when there are impurities in the material. This increases the probability of transformer test failures. Components manufactured from Weidmann Transformerboard are specifically checked in- line for any metal inclusions to ensure that no conductive particles are present.
Mechanical Characteristics
Reliable data on the mechanical design of insulation components such as Clamping Rings are of great importance to the transformer designer. The mechanical strength requirement for materials is generally measured by two criteria: flexural strength and the modulus of elasticity. The type of adhesive is also an important factor in mechanical strength. Tests to assess mechanical strength should be performed under conditions that conform as closely as possible to real performance in a transformer.
In Conclusion
High-quality laminated Transformerboard components offer transformer designers many electrical and mechanical advantages, including:
- Enhanced mechanical strength – the higher density board has superior compression resistance to withstand higher mechanical and thermal stresses
- Improved dielectric properties – pressboard’s higher dielectric strength make it a safer material option, reducing the risk of partial discharges or electrical breakdown
Weidmann continues to invest in updating its technology to improve product quality and maintain efficiency. State-of-the-art production lines coupled with decades of experience in the machining of laminated board enable Weidmann to meet the increasing demands of the transformer industry.