Judgment Standards for the Quality and Reliability of Insulators
Historically, insulators were primarily used on utility poles. With the advancement of technology, they evolved into strings of disc-shaped units suspended from high-voltage transmission towers. These units, typically made of glass or ceramics, are designed to increase creepage distance.
Insulators play two fundamental roles in overhead transmission lines: supporting the conductors and preventing current from returning to the ground. These functions must be guaranteed under all environmental and electrical load conditions. An insulator must not fail due to mechanical or electrical stresses; otherwise, the operational life and safety of the entire transmission line will be compromised.
1. Standards for Insulation Resistance
The quality...
Root Cause Analysis of Core Rod Fracture During Crimping or Tensile Testing
I. Failure Characteristics
The fracture typically occurs inside the ball-end or socket-end metal fitting. The primary symptom is a tensile failure load that is significantly lower than the rated design value.
II. Root Cause Analysis
Excessive Crimping Force: The pressure applied during the crimping process exceeds the radial compressive strength of the core rod, leading to internal structural damage.
Improper Crimping Position: The crimping dies are not centered; the compression zone should ideally be located in the middle of the fitting's connection area.
Poor Machining Precision of Fittings: Issues such as eccentricity of the inner hole, insufficient cylindricity, or internal tapers can...
Critical Issues During Demolding in Composite Insulator Production
The manufacturing process of composite insulators has evolved significantly, from dry-sleeve assembly to integral injection molding. Simultaneously, core rods have advanced from standard types to high-temperature, acid-resistant, and high-impact-strength versions to meet the demands of modern production techniques.
Currently, the integral injection molding combined with crimped end-fittings is the most recommended structure for suspension insulators. However, a technical contradiction exists: according to polymer characteristics, core rods with higher heat resistance often exhibit lower impact strength. Solving this requires collaboration between core rod and insulator manufacturers to ensure the rod can withstand injection temperatures while maintaining the high impact strength necessary for...
Insulation Resistance and Withstand Voltage Testing of Insulators: An Overview
Insulators are essential components used extensively in power grids. Currently, porcelain insulators are the most widely used, followed by glass insulators. In recent years, organic or composite insulators have also seen increasing application across domestic networks.
1. Classification of Insulators
Insulators come in various shapes and sizes, categorized by their application and structure:
By Application: Line insulators and station insulators; indoor and outdoor types.
By Shape/Structure: Suspension, pin-type, post, long-rod, bushing, and stay (guy) insulators.
Special Types: Anti-pollution (dust-proof) insulators and insulating cross-arms.
The porcelain or glass components provide both electrical insulation and high mechanical strength. To ensure durability, these parts are often...
Measurement of Insulator Insulation Resistance
Insulation resistance measurement is a fundamental method for evaluating the condition of porcelain, tempered glass, and composite insulators. The primary objective is to detect insulation deterioration, dielectric breakdown, and other defects that could compromise grid safety.
1. Equipment and Standards
For overhead transmission lines ranging from 35kV to 220kV, a 5000V Megohmmeter is recommended for accurate measurement.
New Insulators: Insulation resistance should be ≥ 500 MΩ.
In-Service Insulators: Insulation resistance should be ≥ 300 MΩ.
2. Criteria for Insulation Degradation
The state of an insulator is determined based on the following resistance thresholds:
Low-value Insulator: Resistance < 300 MΩ but > 240 MΩ.
Zero-value...
Power Frequency AC Withstand Voltage Test for Insulators
The Power Frequency AC Withstand Voltage Test is the most direct, effective, and authoritative method for assessing the dielectric strength of insulators. It is a mandatory requirement during commissioning (handover) tests.
In preventive maintenance, this test can replace zero-value detection and insulation resistance measurements, or serve as the final judgment for insulators flagged by other methods. For single-unit post insulators, it remains the most efficient and straightforward testing approach.
1. Voltage Standards and Requirements
35kV Pin-type Post Insulators:
For two-part bonded units: 50kV per unit.
For three-part bonded units: 34kV per unit.
Disc Suspension Insulators: For units with a mechanical failing load...
In-Service Testing and Evaluation of Composite Insulators
The primary characteristics of composite insulators during operation are hydrophobicity and hydrophobicity migration, which determine the insulator's anti-pollution flashover performance.
Critical Risk Points in Operation:
Mechanical strength of the connection between the end-fitting and the core rod.
Quality of the epoxy FRP (Fiber Reinforced Plastic) rod.
Quality of the silicone rubber material.
Integrity of the sealing system.
Correct installation of grading (corona) rings.
1. Sampling Principles for In-Service Testing
Based on performance characteristics and potential risks, the following criteria are recommended for selecting test samples from the grid:
Insulators located on towers within a 5km radius downwind of industrial pollution sources.
Insulators in...
Discussion on the Lightning Protection Level of Composite Insulators
Abstract
This article summarizes the operational status of composite insulators (110 kV and above) within the Zhongshan Power Grid. It provides a detailed analysis and discussion on the necessity of auditing whether the Lightning Full-Wave Impulse Withstand Voltage of composite insulators meets the localized lightning protection requirements. The study highlights that maintaining a sufficient effective dry arc distance is the critical factor in achieving the required lightning protection level.
Overview
In recent years, composite insulators have been widely adopted in transmission lines of 110 kV and above due to their superior anti-pollution performance, lack of "zero-value" or "low-value" units, lightweight nature, ease of installation, and minimal maintenance...
Design and Manufacturing of Composite Insulators
1. Dimensional Tolerances
Unless otherwise specified, the dimensional tolerances of composite insulators shall comply with the following regulations (where d is the inspection dimension in mm):
For d ≤ 300 mm: ± (0.04d + 1.5) mm
For d > 300 mm: ± (0.025d + 6) mm (Maximum deviation: ±50 mm)
2. Structural Composition
A composite insulator consists of at least two insulating parts: the core rod and the sheath (with integrated sheds), equipped with metal end-fittings.
3. Composite Insulator Core Rods
The core rod is the internal insulating component of the composite insulator, designed to ensure the specified mechanical strength.
Material: It is manufactured from glass fiber reinforced resin rods (FRP/GRP).
Corrosion Resistance: The rod must...
Taporel’s Criteria for Selecting Resin Materials for Acid-Resistant Composite Core Rods
1. The Critical Role of the Resin Matrix
Resin serves as the matrix material in the core rod, functioning to encapsulate and bind the glass fibers. Although resin accounts for only about 20% of the core rod's total weight, it occupies over 35% of its spatial volume. Its structural properties are vital to the core rod's performance, particularly in providing a protective barrier for E-glass (alkali-free) fibers. The quality of the resin directly determines the long-term stability and acid-corrosion resistance of the core rod.
2. Selection of the Curing Agent (Hardener)
The resin system primarily consists of epoxy resin, a curing agent, an...
Selection Requirements for Glass Fibers in Taporel Insulating Core Rods
1. The Dominant Role of Glass Fiber
Glass fiber is the primary structural material in insulating core rods, serving as the reinforcing "skeleton." In composite insulators used domestically, glass fiber accounts for approximately 80% of the core rod's total weight and about 65% of its volume. Consequently, the properties of the glass fiber dictate the overall performance of the core rod.
2. Advantages of E-Glass (Alkali-Free Glass Fiber)
Composite insulator core rods typically utilize E-glass (Alkali-free glass fiber). E-glass is primarily composed of silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), and boron oxide (B₂O₃). These oxides possess stable molecular structures and exist in a crystalline...
Analysis of Pultrusion Process Parameters for Composite Insulating Core Rods
Process Overview
The pultrusion process for insulating core rods involves non-twisted fiberglass rovings being impregnated with resin in a dip tank at a controlled traction speed. After being pre-formed by specialized equipment, the materials enter the mold cavity. The final product is formed through complex physical and chemical reactions as it passes through specific zones: cooling, preheating, gelation, and curing.
The fundamental solidification of the core rod occurs within the mold cavity. Therefore, the process parameters for each zone must be strategically selected based on the continuous movement and phase transitions of the impregnated fibers inside the mold.
Zone Analysis within the Mold Cavity
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