Problematibus et Remediis pro Connexionibus Cabilis Unitatis Cycli Principalis Communi Tela SF₆ 10kV (Stilo Europaeo)
Problema et Solutio pro 10kV SF₆ Gas-Insulata Communis Tank Ring Main Unit (Stilo Europaeo) Nexus Cabellicus
Cum usu extenso lineis cabelleis in urbibus rete distributionis, 10kV SF₆ gas-insulata communis tank Ring Main Units (RMUs) (stilo Europaeo) ad nodos rete propter characteres insulati integri, clausi completi, operationis sine cura, magnitudinis compactae, et installationis flexibilis. Hae RMUs stilo Europaeo ad regiones litorales humidas, nebulae salinae aptae sunt et offerunt operabilitatem fidelem.
Recentes casus operationis RMUs indicant plerosque problemata a nexus inter RMU bushings et 10kV cables provenire. Hoc maxime verum est pro RMUs internis et externis quae magnas currentes et magnas sectiones cables habent. Cum casu fit, tota RMU de-energizari et substitui debet, et T-body connector eius cable rursum installari debet. Hoc significanter impactum facit in fidebilitate supply electrici et damna economici gravis incurrendo.
Nexus inter RMU bushings et 10kV cables est punctus infirmus operationis criticus. Haec articulus analysat problemata existentia et proponit solutio.
1. Problemata cum RMUs Communis Tank et Nexus Triplex Cabellicus
Praesentiter, 10kV SF₆ communis tank RMUs (stilo Europaeo) et eorum associatis T-body connectors praedominanter marcas Europaeas sunt. Haec primarie pro unico-core cables designata sunt, quae facilius fixari et installari possunt, nullam torsionem torque ad bushings imponunt, bonam contactum inter terminalem et bushing assecurant, et minuant probabilitatem fault thermalium. In contrarium, installatio triplex cables multo complexior est, ducens ad varios problemata absentes in installatione unicicore:
- Nexus triplex cables fixare punctus est sheath externus: Phases individuales non independenti fixari possunt. Etiam post nexus, pondus proprium sive vires externae torsionem torque ad bushing sections transmittunt.
- Alignment phase sequenti requirit torque: Durante installatione triplex cables, alignment phase sequenti saepe necessitat applicare torque ante fixationem. Post installationem, stress internus ab hoc torsione gradualiter relinquitur, generans restituendo torque qui agit in bushings.
- Altura chamber cable limitata: Altura compacta chamber cable RMUs (designata pro unicicore cables) restricta est longitudine disponibili singulis core phase individualibus.
- Adjustment limitatum post termination: Postquam cable lug crimpatur, longitudo installationis fixa est. Cum brevioribus core individualibus (propter restrictiones spatiales) difficilis flexibilis, forzando T-body connector in positionem saepe requiret applicationem excessivam push, pull, vel levering forces. Hoc periculum bushings laedi vel contactum malum facere.
2. Solutio
Ad problema haec, solutio implementari possunt concernente RMU ipsa, T-body connectors, practicae installationis, et fundamentum civile RMU.
2.1 Ring Main Unit (RMU)
2.1.1 Adequate Incrementum Altura Chamber Cable:
SF₆ communis tank RMU chamber cables saepe parva sunt (circa H: 600mm, W: 350mm). Hoc unicicore cables bene convenit sed facit installationem T-body connectors, praesertim in magnis sectionibus cables (240mm² vel 300mm²), multo difficile pro triplex cables. T-body connector trifurcating sleeve quoque spatium requirit, relicta circa 400mm pro core cables. Magnae sectiones cores rigidae sunt, et cum restrictionibus loci, correctam T-body positionem assequi arduum est.
- Solutio: Licet RMUs communis tank standard sint, altitudinem installationis posse incrementari per extensionem base. Elevando altitudinem chamber ad circa 800mm et assecurando verticalis distantiam a clamp cable a centro bushing HV ≥750mm permittit core longitudines circa 600mm. Hoc facilitat correctam T-body installationem. Essentialiter, extensio base longitudinem separatas single-phase cores post split triplex cable elongat, similem connectionem unicicore cables efficiens.
- Beneficia: (1) Significanter reducit torsionem torque in bushings; (2) Incrementat tolerationem installationis, minimizat necessitatem vis; minuit periculum leakage gas; (3) Facilitat correctam positionem lugs et stress cones.
2.1.2 Considera Conductivity Bushing Durante Selectio RMU:
Standard 630A RMUs saepe habent bushings bolt-type cum diametro tubi cupri externi 25mm et foramen internum threadatum pro M16 bolts (area conductiva ~289.6mm²). Area contactus actualis saepe minor est propter tolerationes fit. Quando bolts stainless steel utuntur (propter cuprum molle), conduction tantum dependet ex hoc contactus extremi. Intra insulatio clausa, dissipatio caloris mala est. Si contactus lug-to-bushing malus est sub magnis currentibus (>400A), fault thermalia eveniunt.
- Solutio: Pro RMUs utentibus 240mm² vel 300mm² cables currunt >400A, selectio modelli cum bushings 800A-rated (cupri externi Ø 32mm) ad minuendum periculum fault thermalium.
2.1.3 Enhance RMU Bushing Temperature Monitoring:
Communis tank RMUs clausi non possunt aperi pro inspectione. Standard IR thermography non potest mensurare temperatures juncturae. Addendo portas inspectionis compromittit rating IP.
- Solutio:
- Inspectiones routine: Manu sentire temperature panel frontis chamber cable ad detectandum overheating T-body.
- Unitates criticae: De-energizare periodicam post initialis operationis high-current ad inspectandum nexus pro signis overheating.
- Best practice (Technologia): Installare sensors temperature directe in RMU bushings vel T-body connectors pro monitoring real-time temperature.
2.2 Cable T-Body Connector
2.2.1 Ensure Quality of Conductive Components:
Switching to stainless steel bolts makes conduction solely dependent on end contact, increasing demands on lug structure/material quality. Common issues found:
Lug contact surface too narrow/hole too large → reduced contact area.
Poor lug material quality, uneven plating.
Mismatch between lug hole taper and double-ended bolt → lug cannot contact bushing properly → conduction only via bolt.
Copper washer too thin/small → cannot ensure parallel lug-to-bushing contact.
All lead to reduced current capacity and thermal fault risk.
- Solution: Specify T-body connector conductive components clearly:
- Lug contact surface width: 25mm or 32mm (match bushing conductive area).
- Lug material: T2 copper (>99.9% Cu, electrolytic, molded, annealed). Tin or silver plating.
- Washer: Large surface, ≥3mm thick to ensure good pressure contact.
2.2.2 Select Soft-Material T-Body Connectors to Ease Installation:
EPDM or rigid plastic/rubber T-bodies are hard/brittle, difficult to adjust during installation (especially large cores/stress cones/insulation), and hard to verify positioning. Poor elasticity/radial force risks long-term interface separation and tracking.
- Solution: Choose Silicone Rubber T-body connectors for common tank RMUs. Benefits: Soft, elastic → easy positioning adjustment; Excellent radial force and uniformity → good sealing, prevents tracking; Sufficient mechanical strength for RMU chambers.
2.3 Site Installation Practices
2.3.1 Secure Cable Entry Point:
Secure the three-core cable entering the RMU directly below the HV bushings using a cable clamp. Avoid tilting or unsupported cable entry. Unsecured cables impose torsional/pulling forces, potentially compromising bushing/seal integrity → SF₆ leakage, bushing cracks, HV faults.
- Position cores vertically and symmetrically; minimize twisting.
- Place the branch glove and cable clamp as low as possible (≥750mm vertical distance from bushings).
- Site Process: After pulling cable through foundation into chamber, cut off any damaged cable end. Verify phase sequence. Align cable entry angle so cores are straight towards bushings. If angle is excessive, retract cable to trench/pit, correct angle, then re-insert and clamp firmly. Double-fixing: Where possible, add a second clamp point (e.g., fixing beam in cable pit below) to secure the outer sheath further.
2.3.2 Cable Phase Separation and Preparation:
- Fix cable branch glove using clamp before trimming core lengths.
- Align B phase with B bushing.
- Slightly bend A/C phases outward at the root before vertically aligning them with their bushings.
- Place termination bolt into bushing, hang lug loosely on it.
- Cut core ends to exact required length after verifying alignment.
- Crucial: Fix cable before final trimming. Failure to do so results in inconsistent core lengths → bushing stress and poor contact.
- Peeling/Cleaning Process:
- Follow T-body manufacturer's peeling dimensions exactly.
- Avoid damaging inner layers while peeling outer layers.
- Absolutely prevent longitudinal scratches on core insulation → prevents internal tracking.
- Use manufacturer-supplied cleaning paper. Avoid other solvents like industrial alcohol.
- Use polyfluoroether-based lubricant (compatible with silicone rubber). Avoid silicone grease → mutual dissolution → interface drying → tracking risk.
2.3.3 Stress Cone Installation:
- Ensure stress cone matches cable size → correct interference fit. Too tight: hard install, risk splitting. Too loose: poor sealing, risk surface discharge.
- Position strictly per T-body manufacturer’s instructions (positions relative to insulation and cable core affect stress control/sealing). Minimal tolerance.
- Position stress cone on the vertical section of the cable if possible → ensures best seal.
- Prevent sharp objects from scratching silicone rubber surfaces.
- Apply uniform coating of compatible lubricant on interference fit surfaces.
2.3.4 Ensure Sufficient Conductor Contact Area:
Conductor connection inside the insulation sleeve is invisible/hard to check. Must ensure:
- Lug surface is parallel to bushing conductive surface → minimized stress on bushing.
- Excellent contact to prevent heating.
- Crimping: Crimp lug to core per procedure. Ensure lug face orientation is parallel to bushing plane. After crimp dies close fully, hold pressure for 10-15 seconds. Deburr surfaces. Clean lug and core insulation.
- Connection: Place lug onto bolt, push T-body into bushing → ensure parallel lug-to-bushing contact before tightening.
2.3.5 Ensure Reliable Grounding:
Shielded T-body connectors must be properly earthed using dedicated grounding rings/wires connected to the RMU ground grid. Failure risks:Static charge build-up on surface → shock hazard.
Surface discharge to nearby ground → material electrical erosion.
2.4 Requirements for RMU Civil Foundation
- RMU base typically 300-500mm above ground level.
- Cable pit depth below base should be ≥800mm; strive for 1000mm if site permits.
- Purpose: Provides adequate bending radius for cable entry (especially large sections), allowing near-vertical entry → reduces stress on cable/connection.
