High Tension Cables and its types; HT cables

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High Tension (HT) Cables: Types, Components, and Insulation Levels

High Tension (HT) cables are the backbone of modern electrical power systems. Electricity is transmitted and distributed over long distances using HT cables or conductors, making them an indispensable part of power networks.



The most commonly used HT cables are XLPE (Cross-Linked Polyethylene) cables, which offer high insulation strength, thermal stability, and longer service life compared to traditional PVC cables.

🔹 Types of HT Cables

HT cables are classified mainly into two types:

  1. Single Conductor HT Cable

    • Contains a single conductor per cable.

    • For a three-phase system, three separate cables are required.

  2. Three Conductor HT Cable

    • Contains three conductors within a common jacket.

    • Compact design, often used where space is limited.

🔹 Components of HT Cables

Although HT cables may look different externally, they all share five essential parts:

  1. Conductor (Copper or Aluminum)

  2. Strand Shield

  3. Insulation

  4. Insulation Shield System (Semi-conductive & Metallic)

  5. Outer Jacket

Let’s explore each component in detail:

1. Conductor

The current-carrying element of the cable, made of copper or aluminum. Conductor designs include:

  • Concentric Stranding (Class B): Rarely used in modern shielded cables.

  • Compressed Stranding: Most common; prevents shield penetration, easy to strip.

  • Compact Stranding: Reduced size, same ampacity; used in molded devices.

  • Solid Wire: Not common in industrial shielded cables.

2. Strand Shielding

A semi-conductive layer applied over the conductor to eliminate air voids between conductor and insulation.

  • Prevents partial discharges (corona effect).

  • Protects insulation from ozone deterioration.

  • Modern HT cables use extruded strand shielding.

3. Insulation

The main dielectric material of HT cables. Common insulation types:

  • Polyethylene (PE)

  • Cross-linked Polyethylene (XLPE)

  • Ethylene Propylene Rubber (EPR)

👉 Each material is chosen for strength, flexibility, temperature resistance, or cost-effectiveness.

Insulation Levels (as per system grounding):

  • 100% Level: Used in grounded systems with fast fault clearance (<1 minute).

  • 133% Level: For ungrounded or systems with delayed fault clearance (≤1 hour).

  • 173% Level: For systems where fault clearance time is indefinite (resonant grounded).

4. Insulation Shield System

Consists of:

  • Semi-conductive layer (inner)

  • Metallic layer (outer)

Functions of insulation shield:

  1. Confines the dielectric field within the cable

  2. Ensures symmetrical voltage stress distribution

  3. Protects cable from induced potentials

  4. Reduces radio interference & shock hazards

  5. Provides ground path for leakage & fault currents

👉 Must be grounded for safe operation. Without grounding, shields operate at dangerous voltages due to capacitive charging currents (~1 mA/ft), causing hazards and jacket degradation.

5. Outer Jacket

The protective sheath that shields the cable against:

  • Mechanical stress

  • Moisture ingress

  • Chemical attack

  • Environmental degradation

📌 Key Takeaways

  • HT cables are critical for safe and efficient power transmission.

  • XLPE insulation is the most widely used due to durability and performance.

  • Proper grounding of insulation shield is mandatory for reliability.

  • Cable selection depends on system voltage, grounding method, and fault clearance time.


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