Engineering guide
Selecting Ceramics for Electrical Insulation
Dielectric strength is only one of the parameters. Creepage geometry, thermal load and dimensional stability usually decide the material before dielectric strength does.
Parameters
What actually decides the material
| Parameter | Why it decides the material |
|---|---|
| Dielectric strength | Sets the minimum wall thickness for the working voltage |
| Creepage and clearance | A geometry requirement, driven by contamination level |
| Service temperature | Rules out polymers and constrains some ceramics |
| Thermal load through the part | Pushes the choice from alumina to aluminum nitride |
| Mechanical load | Pushes the choice from alumina to zirconia or silicon nitride |
| Tracking resistance | Surface condition and cleanliness rather than bulk material |
The material map
| Material | Selected when |
|---|---|
| Alumina (Al2O3) | General insulation with moderate mechanical load and no heat path requirement |
| Aluminum nitride (AlN) | Heat must pass through the insulator |
| Silicon nitride (Si3N4) | Mechanical load and thermal cycling on the insulator |
| Zirconia (ZrO2) | Impact on the insulator |
| Boron nitride (BN) | Machinable insulation with non-wetting behaviour |
Why wall thickness alone is not the answer
Dielectric performance depends on the assembly, not only on the part.
- Creepage distance along the surface, which contamination reduces
- Clearance through air, which changes with altitude and humidity
- Ribs and grooves, which require radii the drawing must show
- Surface condition after grinding, since contamination reduces performance
- The interface with the conducting element, which is where tracking usually starts
What a ceramic supplier can and cannot provide
Parts from the batch
Frequently asked
Does the part come with a voltage rating?
No. It is supplied to dimension and material specification. The dielectric performance depends on the assembly geometry and contamination level.
Which ceramic for a high-voltage bushing?
Alumina is the usual answer. Aluminum nitride only when heat has to pass through the insulator.
Can the surface be metallised?
The substrate can be supplied with the finish and cleanliness the coating process requires. The metallisation itself is normally applied by a specialist process.
Why does wall thickness not settle the design?
Because creepage along the surface is often the controlling distance, not the thickness through the material.
Have a drawing that this guide applies to?
Send it with the material and the quantities. The review confirms what is achievable before any price is issued.