How to Deal with Surface Tracking on Bushing?

—Key Considerations for RTV Silicone Coating Application

 

Surface tracking on reactor bushings is a critical cause of power equipment failures. According to the IEEE 1584-2018 standard, 35% of insulation failure cases are directly attributed to tracking phenomena. This article systematically explains solutions for handling surface tracking and details the standardized application process for RTV silicone coatings based on the IEC 62217 international specification.

 

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1. In-Depth Analysis of the Hazards of Surface Tracking

The carbonized conductive channels formed by surface tracking on reactor bushings can trigger a three-level chain reaction of hazards:

● Stepwise Decline in Insulation Performance
The carbonized paths increase leakage current by 50%-300% (based on IEC 60507 test data), reducing surface flashover voltage by over 40%. When leakage current density exceeds 3mA/cm², localized temperature rise can reach over 200°C, accelerating thermal aging of insulation materials.

● Irreversible Structural Damage
Continuous discharge can erode the silicone rubber or porcelain surface of bushings, creating pits deeper than 2mm (see Figure 1). Experiments show that pits deeper than 0.5mm increase electric field distortion by 80%, raising the risk of internal insulation breakdown.

● System-Level Chain Reaction Failures
Single-phase bushing flashover can lead to inter-phase short circuits, generating short-circuit currents exceeding 40kA in 35kV systems (as per the IEC 62271-100 calculation model). This can cause protection device malfunctions, grid oscillations, and other systemic accidents.

Données clé: EPRI research reports indicate that untreated surface tracking increases equipment failure rates by 6.8 times.

 

2. Methods for Handling Surface Tracking on Reactor Bushings

● Conventional Treatment Methods

Méthode	Applicabilité	Avantages et inconvénients
Polissage mécanique	Minor surface tracking	Removes carbonized layers but may damage insulation materials.
Nettoyage chimique	Contamination grave	Cleans pollutants but requires avoiding corrosive solvents.
Réparation localisée	Dommages localisés	Uses insulating paint or epoxy resin for filling, but durability is limited.

● RTV Silicone Coating Protection Technology

RTV silicone coating is one of the most effective anti-tracking measures, offering the following advantages:

(1)Hydrophobicité : Forms water droplets on the surface, reducing wetting area and leakage current.
(2)Autonettoyant:Prevents contamination buildup, minimizing conductive layer formation.
(3)Résistance aux intempéries: UV-resistant and high-temperature tolerant (-50°C to 200°C), suitable for outdoor environments.

 

●Anti-Tracking Mechanism of RTV Coating:

(1)Lowers Surface Energy:Silicone rubber’s hydrophobic properties prevent continuous water film formation, reducing conductive paths.
(2)Suppresses Partial Discharge:High resistivity (>10¹⁴ Ω·cm) reduces leakage current, preventing carbonization.
(3)Elastic Protection:The coating adapts to thermal expansion and contraction of bushings, avoiding cracks.

 

● Key Considerations for RTV Silicone Coating Application

Préparation préalable à la demande

Produit	Norme technique	Étapes clés
Nettoyage de surface	ASTM D3359 Adhesion Grade B	1. Sandblasting: 80-100 mesh quartz sand, 0.6MPa pressure.2. Chemical cleaning: Isopropyl alcohol + deionized water (1:3), wipe 3 times.
Réparation des défauts	IEC 62217 Annex C	Fill pits >0.3mm deep with EP-42 epoxy resin; post-curing surface <0.1mm.
CONTRÔLE DE L'ENVIRONNEMENT	IEEE 1523-2018	Temperature: 5-35°C / Humidity <65% RH, dew point温差 ≥3°C.

● Critical Control Points During Coating Application

(1) Primer Application

Necessity: Porcelain bushing surface energy (~45mN/m) is lower than RTV silicone (>100mN/m), requiring primer for enhanced adhesion.

 Spécifications :

• Use silane-based primer (e.g., Dow Corning 1200).
• Spray thickness: 5-8μm, coverage: 150g/m².
• Drying time: 15min (25°C environment).

(2) RTV Main Coating Application

Spraying Formula:

 

Q: Coating amount (kg)
D: Bushing diameter (m)
L: Spraying length (m)
δ: Design thickness (mm)
ρ: Density (1.2g/cm³)
η: Utilization rate (0.7)

Layered Spraying Process:

Couche	Contrôle d'épaisseur	Temps de séchage
Première couche	0.15 ± 0.02mm	30min (25°C)
Deuxième couche	0.20 ± 0.03mm	45min
Couche finale	0.10 ± 0.02mm	-

Prohibited Conditions:

(1)Wind speed >3m/s prohibits outdoor application.
(2)Relative humidity fluctuations >10%/h require work   suspension.

● Curing Quality Verification

Three-Level Inspection Process:

(1) Visual Inspection (2h post-application)
– Orange peel texture: Wavelength 0.5-1.5mm qualifies.
– No sagging or fish-eye defects.

(2) Electrical Performance Test (24h post-curing)

Article d'essai	Valeur standard	Méthode
La resistance d'isolement	≥5000MΩ	IEC 60243-1
Hydrophobie	HC1-HC2 Level	IEC 62073

(3) Thickness Verification (7 days post-curing)
– Use Elcometer 456 coating thickness gauge.
– Allowable deviation: ±0.05mm.

 

3. Stratégie de maintenance à long terme

● Coating Lifespan Prediction Model

 

L: Predicted lifespan (years)
L₀: Baseline lifespan (15 years)
T: Annual average temperature (°C)
SDD: Equivalent salt density (mg/cm²)

 

● Preventive Maintenance Cycle

Environment Level	Inspection Cycle	Articles clés
Light Contamination	24 mois	Hydrophobicity degradation test.
Heavy Contamination	6 mois	Coating thickness + salt density test.
Zones côtières	3 mois	Chloride ion corrosion scan.

 

 

En résumé

RTV silicone coatings can prevent over 95% of surface tracking on reactor bushings (based on CIGRE 338 report data). By following the standardized process of surface preparation → layered spraying → quantitative testing, along with the formulas and parameters provided in this article, the coating’s effective lifespan can exceed 12 years. Maintenance personnel should monitor the environmental adaptability coefficient (K= T×RH/1000) and initiate special protection measures when K >1.2.

 

 

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