Pourquoi les isolateurs composites supplantent les types traditionnels

By the time the failed unit from pole 21C reached the dissecting bench in 2022, its breaking force measured far below the 1.5 N/mm2 minimum that Swedish specifications demand. Investigators found a completely adhesive fracture where the silicone housing should have bonded to the fiberglass core. That result, from a composite insulator installed in 2007, fed straight into a national restriction on composite line insulators. It says more about the composite insulator vs traditional question than any catalog comparison ever will.

The 170+ specialists at RaxPower have manufactured pole line and overhead line hardware since 2003, supplying composite, glass, and porcelain insulators together with the link fittings around them. Two decades of export work keep returning one observation: the switch away from ceramic strings rarely follows a laboratory verdict. It follows paperwork — purchasing policies, stop orders, specification revisions — and the timing of those documents is the real replacement story.

Replacement Decisions Live in Purchasing Policies

Ask a German transmission operator when composite insulators won, and the answer is a date on a document, not a test report. Amprion has run composite line insulators since 1967, through three housing generations. Since 2008, the utility has specified composite units exclusively for every new construction and refurbishment project.

The clause that dates the transition precisely: up until 2019, Amprion’s tower designs still kept a formal option to revert to ceramic strings. That provision is now gone, and a new tower family was developed around composite insulation instead. In composite insulator vs traditional terms, the decision closed when the paperwork stopped hedging.

• 1967: first composite installations; Generation 1 housings (1967–1975) fought erosion, brittle coatings, and porous seals.
• 1975–1980: Generation 2 introduced HTV silicone rubber, but brittle fractures traced to cap construction still surfaced.
• 2008: composite became the exclusive specification for new construction and refurbishment.
• 2019: the revert-to-ceramic clause was removed, and a composite-oriented tower family took its place.

Uprating Projects Open the First Window

Working ceramic strings rarely come down for their own sake. They come down when the line around them is already being rebuilt, and the biggest rebuild window is an uprating. Sweden’s first regional composite long-rod lines arrived exactly that way in 2014.

E.ON uprated the VKA–FLD route from 50 kV to 130 kV and uprated Strömsund–Hoting (line L144) from 40/50 kV to 130 kV, replacing wooden poles with tubular steel. Two more 130 kV lines followed in 2016 and 2018, plus Nysäter–Jenåsen in 2018. Vattenfall’s first composite line had already landed in the mid-1990s, riding the 145 kV sub-transmission expansion.

The engineering logic is structural, not cosmetic. Amprion notes that composite strings carry higher conductor tensions in double-string configurations, while porcelain reaches its limits even in triple strings. The swap pattern works the way you re-roof a house only when the scaffolding is already up: rebuilds absorb the marginal cost. Sweden’s TSO has now scheduled about 4,800 km of new lines and 100 substations over 20 years — precisely the scale of window where defaults get rewritten.

Interface Failures Froze the Swedish Rollout

The same country that opened the uprating window also proved how fast the door can slam shut. In 2016, two years after installation, the VKA–FLD lines failed — the root cause was weak adhesion between the fiberglass rod and the silicone housing. About 150 insulators were replaced, and every replacement batch faced extra adhesion testing before installation.

Line L144 followed in 2017 with a flashunder and the same root cause. An infrared survey then covered the entire route, and several more units came down for raised temperature and surface damage. At Nysäter–Jenåsen in 2018, two sample batches failed adhesion tests outright before a third went up.

The regulatory response hardened from there. E.ON stopped specifying composite line insulators at 130 kV, allowing them case by case until updated internal requirements arrive. Svenska kraftnät went further: no composite line insulators on transmission lines at all, except special structures such as transposition towers. Damaged composite station supports are being replaced with porcelain ones.

In our view, the Swedish freeze was a supplier-verification failure, not a materials verdict. The failing interfaces traced to batch quality that acceptance testing at the time could not see. The 2022 pole 21C dissection — breaking force far below the required 1.5 N/mm2, a completely adhesive fracture — closed the argument.

Specifications Moved Before the Standard Did

Vattenfall Eldistribution reported no major service problems with its composite fleet, and it still tightened procurement. Specification VTR05 18E, issued in 2023, requires a calculated maximum electric field at the end fittings plus a pull-off adhesion test on factory acceptance samples.

That was two years before the third edition of IEC 61109 landed in February 2025 with exactly those concerns — electric field limits and interface verification — folded in. Svenska kraftnät now demands compliance with IEC 61109:2025, including its limits on electric field, for any composite use it still permits.

No composite line insulators are allowed on transmission lines, except for specific applications — and any permitted use must comply with IEC 61109:2025, including limits on electric field. — Svenska kraftnät’s summarized position, as reported in the joint Swedish utilities review

The lesson for buyers: specification revisions lead standard editions. When a utility rewrites an insulator spec, the market follows within one purchasing cycle, whatever the catalog says.

Inspection Data Sets the Replacement Rhythm

Once fleets mix, inspection cadence decides which strings get touched. E.ON’s field experience ranks infrared thermography — from the ground and from drones — as the most effective method for catching poor adhesion and interface heating. Visual inspection catches external damage; partial discharge and ultraviolet cameras complement them for corona issues.

Svenska kraftnät formalized the regime: grading rings on all composite line units, infrared and ultraviolet follow-up, seal checks whenever a line is de-energized, and dissections of selected units. Replacement follows evidence — a unit exchanged for raised temperature today is a data point that shapes next year’s batch specifications.

The L144 case shows the method working end to end. One flashunder triggered a full-route infrared sweep, and the units with raised temperature or surface damage came down on inspection evidence rather than on age alone. Fleets managed this way swap strings before failures accumulate, which is why inspection budgets now shape insulator demand as much as construction schedules do.

None of this resembles a property contest between materials. It is a measurement program, and the composite insulator vs traditional decision moves at the speed of its data.

Outfitting a Rebuild or Uprating?

Line up composite long rods, glass strings, and batch test evidence before the construction window opens — lead times follow the paperwork, not the pole schedule.

Parcourir les Isolateurs pour Lignes Aériennes

Condition Testing Decides Whole-Line Swaps

Picture the asset engineer at FortisBC in British Columbia reading the 2021 lab report on a 230 kV corridor. The line’s composite insulators were mid-1980s vintage, roughly 30 years in service, and had never recorded a single failure. The report said the fleet was dying anyway.

Back in 2016, dye-penetration testing had already failed on two of three sampled units, yet overall condition kept them in service with a retest ordered within three years. The 2021 campaign sampled 27 insulators: only two of ten passed dye penetration, one unit read HC7 hydrophobicity on its bottom sheds, and cracking was visible.

Out of 774 insulators on the line, 38 were sacrificed to destructive testing — about five percent — because destructive tests remain more conclusive than any live-line indicator. The replacement that followed is staged by mechanical duty: dead-ends and heavy angles first in 2025, remaining suspension units in 2032, post insulators in 2040.

The deeper shift is historical. When wood poles died younger than the ceramic insulators bolted to them, swaps simply rode pole renewals. Polymer units on steel structures broke that synchronization, and, as the utility put it, what once seemed a relatively straightforward decision has become complex.

Six Decades Behind One Exclusive Policy

Exclusivity like Amprion’s is earned, not announced. Generation 1 housings from 1967 to 1975 fought severe erosion, brittle coatings, and porous seals. Generation 2 brought HTV silicone rubber between 1975 and 1980, only to surface brittle fractures traced to cap construction.

Generation 3, after 1980, finally stabilized the formula, and the utility now reports no known failures to date across the fleet. Damage still occurs — bird pecking, biological growth, paint splashes. The maintenance guide Amprion co-wrote with 11 European TSOs and DSOs separates damage from failure using CIGRE TB 481’s traffic-light rating.

That is why the 2008 exclusivity clause and the 2019 removal of the revert option read as evidence milestones rather than marketing. Six decades of inspection data, three housing generations, and one shared European maintenance playbook sit behind a single line in a purchasing policy.

Where Traditional Insulators Keep the Specification

Replacement enthusiasm has a geography, and Sweden marks its edge. Pollution there is very light, with creepage targets around 25 mm/kV, so the classic hydrophobic argument for composite barely applies. Line design life runs to 80 years, and the first 220 kV porcelain strings date to the 1930s.

The consequences sit in the specifications. E.ON states that glass cap-and-pin insulators remain the main choice for overhead lines at higher voltage levels. Svenska kraftnät keeps glass strings standard across its 220 and 400 kV transmission network of roughly 17,500 km. Even substations split the vote — Swedish engineers chose composite station posts for safety during explosive failures, not for economy.

The Swedish record is not an argument against composite technology in polluted or coastal service. It is an argument against defaulting to any single insulator technology across an entire national network, whatever the brochure comparison concludes.

For a buyer, that split is the composite insulator vs traditional question in its honest form: the answer tracks network position, pollution climate, and inspection regime, not any absolute ranking. The équipements d'isolateurs ecosystem around both technologies — pins, caps, and link hardware — keeps both supply chains alive.

Reading the Triggers Before the Next Tender

Pull the cases together and the replacement wave stops looking like a product migration and starts looking like a calendar. Four trigger types decide when the composite insulator vs traditional balance actually tips on a given network.

None of these triggers asks whether composite insulators are better in the abstract. Each asks whether the evidence, the window, and the paperwork have aligned — and utilities that wait for all three replace fleets without drama.

The Transition Question Has Moved On

The same class of evidence produced opposite policies in Germany and Sweden, and both look rational on their own ledgers. Amprion locked in composites after six decades of data; the Swedish utilities gated them behind interface testing and electric field limits.

That is what maturity looks like in the composite insulator vs traditional debate: not a winner, but a managed transition with dated decision points. RaxPower has supplied composite, glass, and porcelain insulators since 2003, along with the link fittings that string them together. Its customers keep ordering all three, on different schedules — which is exactly what a managed transition predicts.

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