Préparation des terminaisons de câbles MT est l'enlèvement et le nettoyage contrôlés des couches de câbles avant l'installation d'une terminaison moyenne tension. Les points critiques sont le retrait de la gaine, traitement d'armure, réduction d'écran métallique, préparation de l'écran isolant, état de la surface de l'isolation, préparation du conducteur, et ajustement des accessoires. Une terminaison peut échouer même lorsque le câble lui-même est correct si le bord de l'écran est rugueux, l'isolation est rayée, l'accessoire ne correspond pas au diamètre réel du câble, ou le chemin de mise à la terre est incomplet.
L'extrémité du câble devient partie intégrante du système d'isolation
A l'usine, un câble moyenne tension est réalisé avec un système d'isolation et d'écran continu. À la fin, cette géométrie contrôlée est ouverte et reconstruite grâce à un accessoire. L'extrémité du câble préparée doit donc supporter le même objectif électrique que la construction d'origine.: contrôler le champ électrique, protéger la surface isolante, connecter l'écran métallique, et maintenir la continuité de la gaine ou de l'armure si nécessaire.
C'est pourquoi la préparation des terminaisons doit être revue avec la construction du câble., non traité comme une opération générale du site. Pour Câble d'alimentation MT, des détails tels que la taille du conducteur, diamètre d'isolation, ruban de cuivre ou écran en fil de cuivre, type d'armure, matériau de la gaine, et la classe de tension affectent tous la sélection des accessoires et la méthode de préparation. Une classe de tension supérieure telle que 33Câble kV rend généralement le contrôle dimensionnel et l’état de surface plus importants.
La réduction de l'écran est le point de rencontre des risques électriques et mécaniques
La zone de réduction d'écran est l'une des parties les plus sensibles d'une terminaison. L'écran isolant ou la couche semi-conductrice doit avoir une forme contrôlée afin que l'accessoire puisse gérer le stress électrique.. Un bord rugueux, isolation entaillée, résidu semi-conducteur restant, ou une réduction inégale peut créer une concentration locale de stress. Le défaut peut ne pas être visible une fois la terminaison assemblée, mais cela peut devenir une décharge partielle ou un risque de suivi pendant le service.
L'écran métallique a également besoin d'un traitement correct. Ruban de cuivre, fil de cuivre, ou les conceptions d'écrans combinées ne se terminent pas de la même manière. La connexion à la terre, continuité de l'écran, et les composants de mise à la terre des accessoires doivent s'adapter à la conception réelle du câble. Article précédent de XWA sur Types d'écrans de câbles MT explains why this construction detail matters before accessory preparation starts.
| Preparation area | But | Risk if poorly controlled |
|---|---|---|
| Gaine extérieure | Provides mechanical and environmental protection. | Water path, sheath cracking, or poor sealing surface. |
| Armure | Provides mechanical protection and may require bonding. | Sharp edges, poor continuity, or difficult accessory closure. |
| Écran métallique | Provides electric field control and earth-fault path. | Incomplete grounding, loose wires, or screen damage. |
| Écran d'isolation | Creates controlled interface around the insulation. | Stress concentration, tracking, or partial discharge risk. |
| Isolation XLPE | Maintains the main dielectric strength. | Surface scratch, contamination, or moisture path. |
| Conducteur | Connects to lug or connector. | Poor contact, surchauffe, or mechanical looseness. |
Accessory fit starts with the approved cable drawing
Termination accessories are designed for a range of cable dimensions and construction details. The accessory kit must match the actual insulation diameter, taille du conducteur, type d'écran, armor arrangement, sheath diameter, et classe de tension. A cable name is not enough. Two MV cables with the same voltage and conductor size can still have different insulation diameter, conception d'écran, armure, or oversheath thickness.
Factory drawings and datasheets help prevent mismatch. The approved drawing should provide the dimensions and construction details needed for accessory selection. Published accessory test frameworks such as IEEE 404 show why terminations and joints are treated as tested cable-system components rather than simple end fittings. The visible link is used only as a neutral standards reference, not as a product or supplier recommendation.
Surface condition is more important than appearance
A prepared cable end can look clean from a distance and still contain defects that matter electrically. Scratches on XLPE insulation, residue from the insulation screen, uneven sanding, poussière, humidité, or oil can weaken the interface between cable and accessory. The prepared surface should be clean, dry, smooth, and compatible with the accessory manufacturer’s procedure.
Over-preparation can also be a problem. Excessive scraping or sanding may reduce insulation thickness or create uneven areas. The goal is not to make the cable end look polished; the goal is to create the correct surface and geometry for electric stress control. For higher MV classes, the margin for careless preparation becomes smaller.
Factory information that should be available before termination work
XWA normally supports termination planning by making cable construction data clear before shipment. The termination team should not need to guess the screen type, classe de chef d'orchestre, conception d'armure, épaisseur de la gaine, or voltage designation after the cable arrives. Documentation reduces accessory mismatch and avoids late site decisions.
| Information item | Why it matters for termination | Typical source |
|---|---|---|
| Rated voltage U0/U(Un) | Defines the voltage class of the accessory system. | Approved cable datasheet. |
| Taille et classe du conducteur | Controls lug or connector selection. | Datasheet and conductor standard reference. |
| Diamètre d'isolation | Controls stress cone or termination body fit. | Factory drawing. |
| Type d'écran métallique | Controls grounding and screen termination method. | Construction drawing. |
| Armor and sheath design | Controls gland, scellage, et arrangement de cautionnement. | Cable drawing and packing documents. |
| Test and release documents | Confirm the cable supplied matches the approved design. | Factory inspection records. |
Common failure paths linked to preparation errors
Termination problems are often described as accessory failures, but the root cause can be preparation quality or mismatch. A lug may overheat because conductor preparation or crimping was poor. A stress-control area may discharge because the insulation surface was scratched. A sheath seal may fail because the sheath cut was rough or the cable was contaminated before assembly.
- Screen cutback edge is rough, uneven, or left with semiconductive residue.
- XLPE insulation is scratched during sheath or screen removal.
- Accessory kit does not match actual insulation diameter or sheath diameter.
- Metallic screen wires or tapes are damaged before grounding connection.
- Armor bonding is not coordinated with the termination design.
- Moisture, poussière, or oil remains on the prepared insulation surface.
- Phase identification and drum records are unclear after cable cutting.
The practical factory view
Good termination work starts before the cable reaches the site. The factory must supply a cable that matches the approved drawing, clear markings, dossiers de tests, and construction data. The installation side must use an accessory that matches that exact cable design and follow the accessory procedure. These two parts are connected; neither side can solve the problem alone after dimensions or construction details are wrong.
The practical conclusion is simple: MV termination preparation is not only cutting and stripping. It is the controlled rebuilding of the cable’s insulation and screen system at the end of the route. Clean geometry, correct accessory fit, reliable grounding, dry surfaces, and traceable cable data are the items that make the termination ready for testing and service.
FAQ
Why is screen cutback important in MV cable termination?
Screen cutback controls where the semiconductive screen ends and where the accessory begins to manage electric stress. Poor cutback can create local stress concentration and partial discharge risk.
Can one termination kit fit all MV cables of the same voltage?
Non. The kit must match actual insulation diameter, taille du conducteur, type d'écran, sheath diameter, armor arrangement, et classe de tension. The same voltage name does not guarantee the same dimensions.
What cable data is most important before termination accessory selection?
Tension nominale, taille du conducteur, diamètre d'isolation, metallic screen type, sheath diameter, conception d'armure, and cable standard are the most important data points.
Does factory testing guarantee termination reliability?
Non. Factory testing confirms the cable supplied against the approved design. Termination reliability also depends on accessory match, preparation quality, propreté, mise à la terre, and installation procedure.
Why should the insulation surface be kept clean and smooth?
The insulation surface becomes part of the accessory interface. Scratches, residue, humidité, or contamination can disturb stress control and reduce long-term reliability.