Restoring & Refilling 11kV 33kV Cable Boxes | Replacing Legacy Compounds & Resins

Published 22 May 2026

Restoring transformer termination integrity with LoviSil

A Modern Solution for Ageing PILC Networks

UK DNO Approved For 25 Years+

When a major site recently experienced a fault on an 11kV transformer termination, the challenge was clear: restore the system quickly and safely without the expense/disruption of full PILC cable replacement.

Upon investigation, engineers discovered that a void had formed within the pitch insulation of the termination box: an all-too-common issue in legacy installations. Although the termination assembly had failed, the underlying PILC cable remained structurally sound and fully capable of continued service.

Instead of replacing the cable, the team opted for a smarter, more efficient approach: upgrade only the insulation system using the proven LoviSil liquid-silicone technology.

Thorne & Derrick are the UK’s specialist distributors for Lovink Enertech: LoviSil, PILC cable jointing solutions and MV termination systems; supporting utilities, DNOs, industrial sites and contractors with market-leading products.

Lovisil has been approved for use by NGED for more than 25 years and is also widely used by UKPN. It provides a dielectric strength greater than 21 kV/mm and remains fluid in service, allowing for natural movement without creating voids.

Lovisil has been been specified by National Grid Company Directive as a Standard Technique for Making 33kV Cable Terminations; download copy here.

National Grid Approved MV HV Cable Box Filled Compounds

Advantages of Lovisil v Resin & Compound Type Box Filling Compounds 11/33kV

•      Cost-effective alternative to full switchgear replacement, enabling refurbishment and continued operation of existing assets.
•      Supports asset life extension strategies by improving insulation performance and long-term reliability of ageing infrastructure.
•      Minimum dielectric strength of 21 kV/mm, replicating and exceeding the performance of XLPE primary cable insulation.
•      Fluid insulation technology continuously backfills any developing voids, eliminating trapped air pockets and reducing the risk of partial discharge.
•      No air void formation during installation or service life, supporting long-term insulation reliability.
•      The fluid medium allows natural cable core movement under thermal and load cycling without creating insulation gaps or stress points.
•      More tolerant to harmonic loading and thermal cycling due to the absence of rigid insulation interfaces and void formation.
•      Fluid insulation supports improved heat circulation and thermal dissipation around the conductors.
•      Compatible with legacy cable materials and compounds, including G38 and bitumen-based systems.
•      Simple single-part pour application with no mixing ratios, curing compounds, or complex preparation required.
•      No requirement to grease or prepare the enclosure prior to installation, reducing installation time and contamination risk.
•      Fast and straightforward installation process with minimal additional training or specialist skills required.
•      Re-entry is simple and non-destructive — open and drain the fluid without cutting.
•      No shelf-life limitations, removing concerns around expired materials or stock rotation.
•      Ergonomically designed packaging developed specifically for field operatives, enabling controlled handling and pouring on site.

LoviSil Solution

Upgrading Without Replacing

1. Removing the Old Pitch/Bitumen/resin Medium

All degraded insulation compound was safely extracted by extensive time-consuming and careful cutting of the existing insulating medium from the termination box, exposing a clean cavity ready for refurbishment. Lovisil is directly compatible with traces or remnants of other compounds and resins so once most of the existing box-filling compound or resin has been removed the Lovisil can be used to re-fill the cable box.

2. Introducing LoviSil Liquid Silicone

The housing was refilled using LoviSil, a premium liquid-silicone medium designed for high-integrity insulation in MV applications up to 33kV.

Performance Advantages of LoviSil

Enhanced Insulation Performance

LoviSil delivers superior dielectric strength, helping reduce the likelihood of future failure.

Full Void-Free Insulation

The silicone compound flows into every internal space, eliminating air gaps that can lead to partial discharge (PD) and premature breakdown.

Compatible with Legacy PILC Installations

Because the system works seamlessly with the paper insulation of PILC cables, engineers avoided a costly and disruptive network decommissioning.

Long-Term Breakdown Resistance

LoviSil maintains integrity under thermal and electrical stress, offering a modern, robust alternative to historical insulation materials.

Why This Matters for Utilities & Network Operators

This project highlights an increasingly important theme in today’s power networks: extending the life of legacy infrastructure using modern materials and smarter engineering choices.

By retaining the original PILC cable and upgrading only the termination insulation, the client achieved:

• Significant cost savings

• Reduced downtime and site disruption

• Improved long-term network reliability

• A future-proofed termination assembly

Lovink

Reliable & Resilient Cable Jointing, Connection & Sealing Solutions for MV Networks

Cable Joints for Medium & High Voltage Cables | the Lovink range of cable joints provide high-performance for high-challenge applications including configurations for straight, transition, trifurcating-transition, branch and loop jointing of cables typically distributing electricity at 11kV, 24kV and 33kV; this includes connection joints for extensions and repairs for MV HV cables with XLPE, PILC & EPR insulation.

Lovink Enertech products are proven in service worldwide for network resilience, ease of installation, and long-term reliability.

Authorised Stockists & Distributors for Leading HV Cable Accessory Manufacturers

LV-HV Jointing, Termination, Substation & Electrical Eqpt Distributors 600V to 66kV 

Further Reading

• Lovink – Cable Joints MV 11kV 24kV 33kV Catalogue Size: 1.77 MB
• National Grid Company Directive as a Standard Technique for Making 33kV Cable Terminations Size: 5.10 MB