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.

Content

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.

Key Data: 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

● RTV Silicone Coating Protection Technology

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

(1)Hydrophobicity: Forms water droplets on the surface, reducing wetting area and leakage current.
(2)Self-Cleaning:Prevents contamination buildup, minimizing conductive layer formation.
(3)Weather Resistance: 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

Pre-Application Preparation

● 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.

 Specifications:

• 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:

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)

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

3. Long-Term Maintenance Strategy

● 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

In Summary

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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LuShan, est.1975, is a Chinese professional manufacturer specializing in power transformers and reactors for50+ years. Leading products are single-phase transformer, three-phase isolation transformers,electrical transformer,distribution transformer, step down and step up transformer, low voltage transformer, high voltage transformer, control transformer, toroidal transformer, R-core transformer;DC inductors, AC reactors, filtering reactor, line and load reactor, chokes, filtering reactor, and intermediate,high-frequency products.

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