Different connection form of composite insulator
mechanical load analysis can be found from the current study, the effects of composite insulator mechanical load control key, is the control of metal accessories and plug connection area, we have already analysis of connection form.
Wedge connection form and crimping type USES the same principle, is to plug a prestressed, which between them produce to realize the mechanical load transfer static friction force.
But the wedge wedge under huge pressure with the with the inner cavity of the strong molecular motion, because it is the same kind of material, with a continuation of the time, both as a whole.
And because of the mandrel and hardware have different expansion coefficient, in the case of inconsistent expansion coefficient, the mandrel and the hardware of slip.
Once appear, slip, the mechanical load could be further reduced, at the same time cause the sheath rupture of end sealing area, seal damage caused by water again, created conditions for hydrolysis of mandrel, resulting in further damage, mandrel * cause high voltage insulator in the connection area after fracture.
Wedge inside connection structure using self-locking principle, its shortcomings is the production of mandrel before saw a seam, but also reduces the mechanical strength of the core rod itself.
In the middle of the saw seam into a wedge, has a lot of stress on the mandrel.
In the kerf when its symmetry is not easy to control, stress of the asymmetry of the mandrel is uneven, more easily damaged.
Due to adopt self-locking structure, thus generally do not appear core-pulling phenomenon, but asymmetric half mandrel fracture.
Hardware processing requirement is high, the assembly manual process and more strict, so rarely used.
Type pressure is a common recognition at home and abroad popular connection form, its principle is hardware peripheral pressure evenly and make hardware to produce plastic deformation, to plug a prestressed, thus produce static friction force between the mandrel and hardware, to achieve the connection.
Due to the cavity and core rod is no taper in hardware, around the mandrel is uniform pressure, stress concentration phenomenon well control.
The process operation high mechanization degree, hardware is compact and beautiful, low production cost, has been widely applied.
Composite insulator mandrel brittle fracture belongs to typical brittle material, glass and glass fiber pull rod in vertical fracture with tension stress direction and fracture surface smooth level off, described as brittle fracture or brittle failure.
Glass fiber led stick this class fiber reinforced composite material's normal fracture morphology, usually is to enhance the glass fiber fracture in different position in the core rod, and at the same time companion has a lot of fiber and matrix resin separation of stratification, fracture surface is rough, like broken bamboo or sugar cane, known as the delamination damage.
But the glass fiber pull rods or composite insulator under certain conditions but can happen brittle fracture, fracture surface smooth and flat, as if no fiber, cross section perpendicular to the mandrel axial force direction.
The brittle fracture of composite insulator is particularly concern, is not a unique form of fracture, and mainly in a completely unexpected happen.
So-called surprise, on the one hand, refers to the brittle fracture load is far lower than the normal fracture load, such as in normal damage load less than 30% of the brittle fracture may occur;
On the other hand, the time of brittle fracture is unpredictability.
According to the operation experience, the time of brittle fracture irregular, long can run for several years, short of fracture is only a few months.
Based on the above two points, the brittle fracture of the composite insulator, researchers from the production power to the majority of the users are very importance to brittle fracture.
According to many years of research found that that is caused by stress corrosion, in acidic solution and mechanical load, under the joint action of acid corrosion acid performance is not good glass fiber, the fiber to produce tiny cracks.
If fiber has tiny crack can be prompted further intensify the tiny crack, in the external mechanical stress on average is not high, the tiny crack fiber * * mechanical stress can increase greatly, make the fiber began to break, cause fiber crack expanding, the stress corrosion crack front further intensified, so that the mandrel under low load the fracture.
As for acid solution is generally considered as a result of the composite insulator sheath or end seal failure, lead to moisture into the outside world, water under the action of a strong electric field, or in a local weak discharge.
Can be seen from the above analysis, to improve the way of stress corrosion resistance of the composite insulator has two kinds.
The first is to improve the performance of composite insulator sheath and end seal level, completely prevent the intrusion of water;
Another way is to improve the composite insulator with glass fiber the stress corrosion resistance of pull rod in * good use acid mandrel.
Insulator rupture will cause the wire to the ground, the seriousness of the brittle fracture is self-evident.
But the probability of brittle fracture is extremely low, running in China only a few millions in composite insulator rupture, and composite insulator can be trustworthy products, especially the manufacturers in the production of core rod was adopted, the sheath and the end of the seal has improved dramatically, as long as the production and use of collaboration agreement, will be under control for brittle fracture accident.
From the above analysis can be concluded that the better the connecting way of operating experience, strict production process control, make the protection of mandrel, acid core rod, the corrosion resistance on the mechanical properties of the composite insulator will be reliable.
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