As multi-sector technological developments continue to demand smaller parts with higher performance and improved longevity, Joerg-Uwe Wichert, explores why specifying power tubes with an increased dielectric strength is becoming increasingly important in high-voltage applications, particularly at high temperatures
As a key component for many electrically and thermally demanding environments, high-voltage power tubes are required to deliver both electrical insulation properties and a dielectric strength great enough to withstand intense electric fields. Now, more than ever before, there is a need for engineers and materials specialists to guarantee the dielectric performance of the power tubes they specify to 15kV/mm for any wall thickness; something which many materials manufacturers are struggling to deliver.
This shift change towards higher guaranteed dielectric strength is largely being driven by technical product design. Fast-paced and highly scientific industries are moving towards equipment with increased performance, improved lifespan and a typically smaller or identical footprint.
This ‘better performance, smaller product’ design criterion has created a requirement for smaller components which themselves deliver optimised performance for longer; and for power tube manufacturers, higher dielectric strength is a must in order to produce smaller tubes.
An industry overview
In short, higher dielectric strength allows for the creation of smaller, high-performing and longer-lasting power tubes. The challenge, however, is that conventional alumina ceramic materials typically offer a dielectric strength guaranteed value of ~9kV/mm, which falls short of the 15kV/mm now demanded by sectors such as healthcare, communications, aerospace, defence and oil and gas.
Throughout these sectors the ongoing technical development of compact, high-performance equipment like CT scanners, photo-multiplier tubes, satellite engines and aerospace electronic countermeasure systems is already benefitting from the design possibilities provided by materials with higher guaranteed dielectric strengths – and it is a trend which shows no signs of slowing.
The secret behind dielectric strength
There are a number of variables that can affect the dielectric strength of a material, inlcuding the raw material quality and the way in which it is processed during manufacture. Within its application setting, thickness, operating temperature and thermal cycling frequency can all impact on performance and service life. Morgan manufactures its own raw materials from specially selected bauxite sources with careful process control to ensure optimised material properties.
When specifying a power tube, it is therefore vital to ensure that the material in question offers high thermal conductivity, as well as guaranteeing a dielectric strength of 15kV/mm - regardless of the wall thickness.
Smaller components, longer lasting
For high-voltage applications, the key benefits to specifying power tubes which have been manufactured using high-purity alumina to deliver a guaranteed dielectric strength of 15kV/mm can be summarised in three points; smaller components, optimised performance and increased lifespan.
Alumina with an increased dielectric strength can be used to manufacture those all-important smaller parts, which remain capable of delivering identical or increased performance levels when compared with their larger counterparts. In some environments, the size of each individual component goes above and beyond building physically smaller machines for aesthetic purposes. In the medical sector for example, component size is a critical design element for creating equipment in which weight is used as a counterbalance, such as in CT scanners where the power tubes turn around 120 times per minute with a force of 20G.
Similarly, due to the very nature of the application, the development of image intensifier tubes in the defence sector requires increasingly smaller parts capable of operating within an electrically demanding environment. The power tube used in this product has a wall thickness around 1.4mm, yet remains durable enough to withstand the high voltage required.
Enhancement of stability and equipment reliability is the other key industry driver for the development of high dielectric strength products, like Morgan’s AL300TM power tubes. The outstanding dielectric performance of this material makes brazed assemblies more dependable in quality and performance, which importantly, offers manufacturers increased Mean Time Between Failures (MTBF).
This is especially important for high-voltage environments, where electrical breakdowns happen so abruptly (typically in nanoseconds), that they can form an electrically conductive path and a disruptive discharge through the material, severely damaging or destroying any electrical insulating capabilities. With costly breakdowns a real concern to both engineers and end users, the introduction of higher dielectric strength materials to the market has been received as a welcome alternative to conventional material solutions.
It goes without saying that minimising equipment downtime equates to cost and time efficiencies, which are magnified in sectors that rely on expensive and highly complex technical equipment.
The intelligent combination of increased performance, smaller footprint and improved reliability aids in the development of products which ultimately last longer – a real selling point for any key decision maker and something which can command increased value in all industries.
Joerg-Uwe Wichert is Manager of New Business for Morgan Advanced Materials.
