Stress Control Tube vs Stress Cone: Which Fits?
Both components grade the field where a cable screen ends. One does it with a material property, the other with a shape. Which one belongs in your termination follows from the cable and the voltage class, not from preference.
Two ways to grade a field
A stress control tube grades by material. It is co-extruded from a semiconductive grading layer and an insulating layer, cross-linked and expanded. The grading layer has a controlled impedance that redistributes the field along the tube, so the peak at the screen end is spread out. It recovers with the same hot air process as the rest of the kit and conforms to the prepared core. Heat shrinkable stress control tube is supplied as a kit component or as a standalone replacement.
A stress cone grades by geometry. The insulating body is shaped so the field is spread over a longer path through a thicker dielectric, and the screen continues over the cone. It builds a controlled profile exactly where the stress is highest. The cone is a larger, more deliberate assembly, and its fit depends on the cable insulation diameter.
Side by side
| Dimension | Stress control tube | Stress cone |
|---|---|---|
| Grading method | Material, capacitive | Geometry, shaped profile |
| Component count | One tube plus the kit tubes | A shaped body built on site |
| Space needed | Low | Higher, radial and axial room |
| Voltage classes in use | 0.6/1 kV, 8.7/15 kV, 26/35 kV | Common on 8.7/15 kV and 26/35 kV |
| Insulation diameter sensitivity | Medium | High, the profile is built to the cable |
| Installation time | Short, one hot air pass | Longer, layer by layer |
| Re-work | Cut away and replace | Rebuild the cone |
| Void tolerance at the cut | Low | Higher in a careful build up |
How to decide
- Start with the kit. If the accessory kit is a heat shrink kit, the tube is its grading component.
- Check the voltage class. At 0.6/1 kV the grading requirement is small. The difference between designs matters most at 26/35 kV.
- Measure the prepared insulation diameter. The cone depends on it, and the tube does too, except a tube can be re-sized from stock.
- Count the space. A cone has to be built in place. A tube needs room to be recovered with a swept heat source.
- Confirm the re-work policy. Tubes are cut away and replaced, a cone is rebuilt on site.
Where they meet
Both routes rely on the same interface. A smooth semicon cut, a clean insulation surface and no air void matter more than the choice of grading design. MV termination partial discharge prevention covers the interface, and heat shrink vs cold shrink cable accessories covers the system choice around it.
What to send
Send the cable voltage class, cross-section, prepared insulation diameter, the kit type and the space in the enclosure. We return the tube and the installation dimension for it.
Frequently asked questions
Which design do I use at 26/35 kV?
It follows the accessory kit you are installing. Where the kit is a heat shrink kit, the stress control tube is its grading component and the position dimension comes from the kit drawing.
Can I replace a stress cone with a tube?
Not inside a designed kit. The grading design is part of the kit's type approval, and substituting a component changes the design you are installing.
Does the cone work better on irregular cables?
A cone built in place can accommodate a profile more easily, and it is more tolerant of a small amount of contamination in the build up. A tube is less forgiving of a void at the cut.
How much space does each need?
A tube needs room to recover with a swept heat source. A cone needs radial and axial room to be built layer by layer, which is often the deciding factor in a crowded enclosure.
Which one is faster to install?
The tube, because it recovers in one pass. A cone is built up in layers and takes longer, and it is also longer to re-do if something is wrong.