Model: SCHST
Semi-Conductive Heat Shrink Tube (SCHST) for Medium Voltage Cable Joints
Semi-Conductive Heat Shrink Tube (SCHST) is engineered from thermally stabilized, radiation cross-linked semi-conductive polymeric material. It is specifically designed for use in medium voltage cable joints (up to 36kV) to provide an insulation screen and smooth out electrical stress over connectors and build-up insulation.
By equalizing the electric field around irregularities in cable splices, the SCHST prevents localized electrical stress concentrations, significantly reducing the risk of partial discharge and ensuring the long-term reliability of high-voltage terminations and joints.
Key Features & Benefits
- Electrical Stress Control: Semi-conductive properties (10² to 10³ Ω·cm) effectively smooth electrical stress and equalize the electric field at cable joints.
- Thermally Stable: Manufactured from cross-linked polymers that maintain mechanical and electrical integrity in harsh thermal environments.
- High Mechanical Strength: Excellent tensile strength and elongation ensure the tube resists tearing and provides robust mechanical protection.
- Low Water Absorption: Highly resistant to moisture ingress, ensuring stable performance in underground or damp environments.
- Easy Installation: Starts shrinking at 110°C and fully recovers at 130°C, allowing for quick and secure application using standard heat guns or propane torches.
Common Applications
- Insulation screen build-up over connectors in medium voltage (up to 36kV) cable joints
- Electrical stress control on cable splices and terminations
- Shielding irregularities in high-voltage equipment maintenance
- Substation and switchgear cable joint protection
- Wind turbine and solar farm medium voltage cable splicing
Product Specifications
- Material: Radiation Cross-Linked Semi-Conductive Polymer
- Color: Black
- Operating Temperature: -40°C to 100°C
- Shrink Temperature: Starts at 110°C, fully shrinks at 130°C
- Volume Resistivity: 10² to 10³ Ω·cm
Technical Properties
| Item | Test Method | Value |
|---|---|---|
| Operating Temperature | IEC 60216 | -40°C to +100°C |
| Tensile Strength | ASTM D638 | ≥ 14 MPa |
| Elongation at Break | ASTM D638 | ≥ 300% |
| Tensile Strength After Aging (120°C, 168 hrs) | ASTM D2671 | ≥ 11 MPa |
| Elongation at Break After Aging (120°C, 168 hrs) | ASTM D2671 | ≥ 240% |
| Volume Resistivity | ASTM D257 | 1×102 to 1×103 Ω·cm |
| Longitudinal Shrinkage | – | ≤ 15% |
| Eccentricity | ASTM D2671 | ≤ 30% |
| Water Absorption | ISO 62 | ≤ 0.1% |
Dimensions & Specifications
| Part No. | As Supplied ID (Min) (mm) |
After Recovery ID (Max) (mm) |
Recovered Wall Thickness (mm) |
Standard Length (mm) |
|---|---|---|---|---|
| SCHST-45/18 | 45 | 18 | 2.4 ± 0.1 | 400-1200 |
| SCHST-50/20 | 50 | 20 | 2.4 ± 0.1 | 400-1200 |
| SCHST-55/23 | 55 | 23 | 2.4 ± 0.1 | 400-1200 |
| SCHST-65/26 | 65 | 26 | 2.4 ± 0.1 | 400-1200 |
| SCHST-100/30 | 100 | 30 | 2.9 ± 0.1 | 400-1200 |
| SCHST-120/35 | 120 | 35 | 2.9 ± 0.1 | 400-1200 |
Frequently Asked Questions (FAQ)
Q: What is the main purpose of the SCHST semi-conductive tube in cable joints?
A: Its primary function is to provide an insulation screen and smooth out electrical stress over connectors. By equalizing the electric field, it prevents localized stress concentrations that could lead to partial discharge. It is typically used in conjunction with an outer insulating layer, such as our Anti-Tracking Heat Shrinkable Tube, to provide complete protection for medium voltage splices.
Q: Can this semi-conductive tube be used for insulating bus bars or standard wire joints?
A: No. Because it is specifically designed to be semi-conductive (with a volume resistivity of 10² to 10³ Ω·cm), it will not provide electrical insulation. For standard insulation and protection of bus bars or low-voltage connections, you should use our fully insulating Heat Shrink Bus Bar Protection Tubing.
Q: Is there a solution that combines both the semi-conductive layer and the outer insulation in one product?
A: Yes, to simplify the installation process for complex cable joints, we offer a Semi-Conducting Two Layers Heat Shrink Tube. It features an inner semi-conductive layer for stress control and an outer insulating layer for environmental protection, saving you time and labor on site.
Q: What is the significance of the volume resistivity range (10² to 10³ Ω·cm)?
A: This specific resistivity range classifies the material as “semi-conductive.” It is high enough to prevent electrical current from flowing through the tube (which would cause a short circuit) but low enough to dissipate static charges and equalize the electric field around irregularities in cable joints, ensuring optimal electrical performance.
Q: What are the shrink temperature requirements for this tubing?
A: The SCHST tube begins to shrink at 110°C and will fully recover and conform tightly to the substrate when heated to 130°C. It is recommended to use a propane torch or a high-temperature heat gun, starting from the center and working outwards to avoid trapping air.
Q: What is the maximum operating temperature for this semi-conductive tubing?
A: The continuous operating temperature range is -40°C to 100°C. The cross-linked polymer formulation ensures long-term thermal stability and reliable mechanical performance even in demanding industrial and utility environments.