The Importance of Power Tubes with an Increased Dielectric Strength

Multi-sector technological developments continue to fuel demand for smaller components with enhanced service life and greater performance.  Joerg-Uwe Wichert, New Business Manager for Morgan Advanced Materials, discusses why specifying power tubes with an increased dielectric strength is becoming increasingly important in high-voltage applications, specifically at elevated temperatures.

High-voltage power tubes form a key component of many thermally and electrically demanding environments and are expected to deliver both dielectric strength and electrical insulation properties that are able to withstand intense electric fields. At present, there is a greater than ever demand for materials specialists and engineers to specify power tubes with a dielectric performance of 15kV/mm for any wall thickness.

Such a shift change towards a greater assured dielectric strength is mainly driven by technical product design. Highly scientific and fast-paced industries demand equipment with enhanced service life, enhanced performance, and an identical or smaller footprint. This ‘better performance, smaller product’ design criterion has necessitated smaller components that can deliver optimised performance for a longer period of time by themselves. Moreover, in the case of power tube manufacturers, higher dielectric strength is mandatory for producing smaller tubes.

An Industry Overview

In essence, higher dielectric strength enables the creation of high-performing, smaller and longer lasting power tubes. Nevertheless, the challenge here is that traditional alumina ceramic materials usually offer a guaranteed dielectric strength value of ~9kV/mm. This value is way short of the 15kV/mm now in demand in sectors such as healthcare, communications, aerospace, defence and oil & gas. In all these sectors, the progressing technical development of high-performance and compact equipment, such as CT scanners, satellite engines, photo-multiplier tubes and aerospace electronic countermeasure systems, is already enjoying the benefits from the design options provided by materials of higher guaranteed dielectric strengths. Moreover, this trend is showing no signs of a slowdown.

The Secret Behind Dielectric Strength

The dielectric strength of a material can be affected by a number of variables such as the way in which the material is processed during manufacture and its raw material quality. Within the application setting of the material, operating temperature, thickness and thermal cycling frequency can all affect the service life and performance of the material. In order to ensure optimised material properties, Morgan adopts to careful process control measures when manufacturing its own raw materials from specially-selected bauxite sources.

When specifying a power tube, care must be taken not only to make sure that the specified material provides a high thermal conductivity but also to guarantee a dielectric strength of 15kV/mm regardless of the wall thickness.

Smaller Components, Longer Lasting

In the case of high-voltage applications, the key advantages of specifying power tubes manufactured using high-purity alumina to provide a guaranteed dielectric strength of 15kV/mm can be summarised in three points: smaller components, optimised performance, and increased lifespan.

Alumina with increased dielectric strength can be employed for manufacturing such all-important smaller parts that can persistently deliver increased or identical performance levels when compared to the larger components. In certain sectors, the size of an individual component can increase more than the physically smaller machines built for aesthetic purposes. For example, in the medical sector, component size proves to be a critical design element for manufacturing equipment in which weight is used as a counterbalance, e.g. CT scanners in which the power tubes turn around 120 times per minute with a force of 20G.

Likewise, the very nature of the application mandates the use of increasingly smaller parts that can operate within an electrically demanding environment for the development of image intensifier tubes in the defence sector. Even when the wall thickness of the power tube used in this product is approximately 1.4mm, it still remains durable enough to endure the high voltage that is needed.

Greater stability and device reliability are behind the upsurge in demand for high dielectric strength products, such as Morgan’s AL300™ power tubes (Figure 1). The outstanding dielectric performance of these tubes enhances the reliability of the brazed assemblies in terms of performance and quality, thereby offering the manufacturers increased mean time between failures (MTBF), which is extremely important.

Morgan’s AL300™ power tubes

Figure 1. Morgan’s AL300™ power tubes

This is specifically important in high-voltage environments which are prone to abrupt electrical breakdowns (usually of the order of nanoseconds), where an electrically conductive path and a disruptive discharge are formed through the material, thus severely destroying or damaging any electrical insulating capabilities. As costly breakdowns are real reasons of concern to both end users and engineers, the introduction of these higher dielectric strength materials to the market is seen as a much sought after alternative to traditional material solutions.

Conclusion

It is a known fact that reduction in the equipment downtime enhances the time and cost efficiencies, which are crucial in sectors demanding highly complex and expensive technical equipment. The smart combination of smaller footprint, increased performance and improved reliability helps in developing products with longer service life, which is an attractive aspect for any key decision maker, and something which can have an added value in all sectors.

This information has been sourced, reviewed and adapted from materials provided by Morgan Advanced Materials.

For more information on this source please visit Morgan Advanced Materials.

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