Here is an in-depth analysis on the comparison of Geometric Stress Control vs Dielectric Stress Control, used in LV MV HV 3M Cold Shrink Cable Terminations. High Dielectric Stress Control (also known as Refractive Stress Control) is used in all 3M Electrical Cold Shrink Cable Terminations, whereas Geometric Stress Control is commonly used due to ease of manufacturing processes, but faces a number of disadvantages.
Electrical Stress Control is known as a potential voltage difference across a distance, typically being reported as kV/mm (or v/mil). In the scenario of a larger voltage difference of a distance results in a higher electrical stress to be controlled.
The insulation shield on cable terminations provides uniform electrical stress in the cable insulation. In the event of insulation shield removal from the cable termination, the electrical stress will concentrate at the end of the insulation shield (as shown in the image example). The equipotential lines being close together at the end of the insulation shield, results in very high electrical stress.
Cable termination failure will occur with no Electrical Stress Control.
3M Cold Shrink Cable Termination With No Electrical Stress Control
The process of Geometric Stress Control, is the use of extra insulation to overcome high electrical stress. As seen in the example image, the insulation is gradually increase in a ramp formation, with the insulation shield being extended to the top of the ramp. Similar to cable terminations with no stress control, the equipotential lines are still very close together at the end of the extended insulation.
High electrical stress determines that the cable terminations using this level of Electrical Stress Control will have higher surface stress, which requires a longer termination to meet standards and can also cause more tracking in highly contaminated areas. Longer cable termination lengths lead to geometric cable terminations have a long creepage distance, which may not translate to better performance because of the high surface stress on geometric terminations.
3M Cold Shrink Cable Termination With Geometric Stress Control
The other method of Electrical Stress Control is through the use of high Dielectric Stress Control (or Refractive Stress Control), used for 3M Cold Shrink Cable Terminations LV MV HV. The material used offers a high dielectric constant, meaning the material is not an ideal electrical insulator in comparison to materials with lower dielectric constants.
The following table provides further insight on dielectric constants of varied insulating materials, ultimately determining that Electrical Stress Control materials require a significantly higher dielectric constant than the table insulation due to the cause of equipotential lines bending or refracting:
| Stress Control Material | Typical Dielectric Constant |
| Air | 1.0 |
| XLPE | 2.5 – 3.0 |
| EPR | 3.0 – 3.5 |
| Silicone | 3.5 |
| Stress Control Tubes | 14 – 25 |
| Stress Control Mastic | 25 – 30 |
After refracting the equipotential lines, high Dielectric Stress Control spreads out the equipotential lines, resulting in significantly less surface stress than on a Geometric Stress Control 3M Cold Shrink Cable Termination. The image below demonstrates the process of high Dielectric Stress Control spreading out the equipotential stress lines. In this case, the equipotential lines are much further apart at the end of the cable insulation shield for Dielectric Stress Control vs Geometric Stress Control.
3M Cold Shrink Cable Termination With Dielectric Stress Control
The following table highlights the advantages/pros for both Geometric Stress Control & Dielectric Stress Control:
|
Advantages Geometric Stress Control vs Dielectric Stress Control |
|
| Geometric Stress Control | Dielectric Stress Control |
| Easier to design and manufacture, making it more cost-effective. | Lower surface stress on cable terminations, allowing for shorter and more efficient cable terminations that still perform well at higher voltage (HV) levels. |
| Widely used in cold shrink and push-on cable terminations, ensuring familiarity and availability. | Better performance in contaminated environments with reduced tracking due to lower surface stress. |
| Performs well in low voltage (LV) & medium voltage (MV) applications. | Higher position tolerance with more flexibility in design, as the dielectric tube overlaps the insulation shield. |
| Less susceptible to dielectric losses as it doesn’t rely on high dielectric materials. | Developed and reliably used for over 45 years by 3M, demonstrating proven reliability and performance. |
The following table highlights the disadvantages/cons for both Geometric Stress Control & Dielectric Stress Control:
|
Disadvantages Geometric Stress Control vs Dielectric Stress Control |
|
| Geometric Stress Control | Dielectric Stress Control |
| Not as effective for higher voltage systems (e.g., 25 kV), where it tends to fail under testing. | More complex and difficult to design and manufacture, which can increase costs. |
| More prone to higher surface stress on terminations, which can affect long-term performance. | Material has higher dielectric losses, leading to minor temperature increases (2 to 5 degrees Celsius) at the semicon step of the cable. |
| Can have issues in contaminated environments due to higher surface stress, leading to potential tracking. | Slightly higher dielectric heating, though typically not impacting performance at normal operating voltages. |
| Requires longer termination lengths compared to dielectric stress control. | The dielectric stress control design, especially with the overlapping high dielectric tube, might add more bulk or weight to the termination |
Systems up to 69kV, high Dielectric Stress Control cable terminations perform better than Geometric Stress Control terminations. Offering better results due to widespread equipotential lines, ultimately creating a lower surface stress on the Cable Joints & Terminations. The lower surface stress reduces the chances of tracking and allows a shorter termination to perform better than a longer Geometric Stress Control termination. Some of 3M’s Cold Shrink high Dielectric Stress Control terminations have been in service sine 1977, concluding a long and reliable history.
Thorne & Derrick distribute the most extensive range of MV HV Medium & High Voltage Cable Joints, Terminations & Connectors from manufacturers including 3M, Prysmian, Nexans Euromold, Elastimold, Pfisterer CONNEX & SEANEX and Shrink Polymer Systems.
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Aiden | Welcome To The Team
“Where do I start? Well, first things first, I’m a Geordie through and through. Now we’ve got the important stuff out of the way… I’m a 23-year-old easy-going lad from Chester-le-Street of all places. Little did I know, my marketing career would take to the next level, right around the corner at Thorne & Derrick.
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