Technical Specification for Cable Accessories, Terminations, and Joints (Up to 33 kV)

The integrity of an underground electrical power network depends heavily on the quality and reliability of its cable accessories. For systems operating at voltages up to 33 kV, cable joints and terminations are critical components that must withstand electrical, thermal, and mechanical stresses equal to or greater than the cables they connect. This document outlines the general technical requirements for these accessories.

1. Scope of Application

This specification covers the design, manufacture, testing, and supply of heat-shrinkable, cold-shrinkable, or pre-molded accessories for XLPE and PILC insulated power cables. These components are intended for use in distribution networks operating at voltages of 11 kV, 22 kV, and 33 kV.

2. Design and Construction Requirements

Accessories must be designed to maintain the electrical field integrity of the cable. The following criteria are mandatory:

• Stress Control: All terminations and joints must include high-dielectric constant stress-control tubing or mastic to manage electrical stress at the screen cutback point.
• Moisture Sealing: Components must be equipped with hot-melt adhesive or mastic sealants to prevent the ingress of water, humidity, and pollutants.
• Tracking Resistance: Outdoor termination kits must utilize materials with high anti-tracking properties to withstand exposure to UV radiation, salt spray, and industrial pollution.
• Compatibility: Accessories must be fully compatible with the cable insulation, semi-conductive layers, and metallic screens.

3. Jointing and Termination Components

A standard kit for 33 kV applications must include the following components:

• Mechanical Connectors: Shear-bolt connectors are preferred for their ease of installation and ability to provide a reliable electrical connection without the need for specialized hydraulic crimping tools.
• Stress Control Mastic: To fill voids and reduce electrical stress intensity at the conductor connector interface.
• Semi-conductive Layers: Essential for restoring the cables semi-conductive shield continuity across a joint.
• Insulating Tubes: High-quality, cross-linked polymeric materials providing the primary dielectric insulation.
• Earth Continuity Kits: Tinned copper braids and constant force springs to maintain the integrity of the metallic sheath or wire armor.

4. Electrical and Physical Performance

Accessories must comply with international standards such as IEC 60502-4, CENELEC HD 629, or equivalent national standards. Key performance benchmarks include:

• AC Withstand Voltage: The accessory must withstand specified power frequency voltage tests for a duration of at least one minute without puncture or flashover.
• Partial Discharge Testing: Accessories must demonstrate low partial discharge levels (typically < 10 pC at 1.73 Uo) to ensure long-term insulation health.
• Impulse Voltage Withstand: The system must be capable of surviving lightning impulse voltage tests, reflecting typical network surges.
• Short-Circuit Rating: Joints must be capable of carrying the same short-circuit current as the host cable without thermal degradation.

5. Installation Guidelines

Proper installation is paramount for the longevity of 33 kV joints. The following practices are mandatory:

• Environmental Control: Installation should ideally occur in clean, dry environments. In wet conditions, a temporary shelter is required to prevent moisture contamination.
• Surface Preparation: Cable surfaces must be cleaned using non-conductive solvents. Abrasives must be used carefully to ensure a smooth transition without damaging the insulation.
• Workmanship: Only certified cable jointers should be authorized to install accessories for voltages exceeding 11 kV.

6. Quality Assurance and Testing

Suppliers are required to provide comprehensive type-test reports from recognized independent laboratories. Routine tests must be performed on every production batch to verify material quality, dimensions, and electrical functionality. Documentation must include serial numbers for traceability and shelf-life instructions for chemical components (sealants/mastics).

7. Environmental and Storage Conditions

All kit components must be stored in their original packaging, away from direct sunlight and extreme temperatures. Chemical components with limited shelf lives must be clearly marked with expiry dates. Products must be resistant to environmental aging, including ozone, UV radiation, and general chemical exposure found in industrial underground environments.