Advantages and disadvantages of glass insulators and composite insulators

Glass insulators have excellent performance

Glass insulators play two fundamental roles in overhead transmission lines, supporting the conductors and preventing current from returning to the ground. During the operational life of the entire line (usually 40 years), these two functions must be guaranteed and the insulators should not fail due to various electromechanical stresses caused by changes in environmental and electrical load conditions. In addition to the weight of the wires and metal fittings, the mechanical load on the insulator must withstand the wind load, snow load, wire galloping under severe weather conditions, and the impact load caused by improper operation during transportation and installation. From an electrical point of view, the insulator must not only insulate the conductor from the ground, but must also withstand the overvoltage surge caused by lightning and switching operations. Local overheating caused by flashover due to voltage surges should not cause bursting of the insulator tempered glass body. . All external factors have an effect on the performance of the insulator, and therefore, higher requirements are placed on the design of the insulator.

Excellent dielectric properties and no aging

Dielectric properties refer to the electrical properties exhibited by an electric medium under the action of an electric field. The insulation performance of the insulator has a great relationship with the internal molecular structure of the insulating material. The glass belongs to an amorphous structure and is a silicate compound having no fixed melting point. The structure is dense and the texture is uniform, resulting from an easy-to-control continuous production process. SiO2 is a skeleton constituting glass. Other oxides are filled in the skeleton and are connected by chemical bonds. The interaction is large, and it is not easily polarized by an electric field. It exhibits good inertness and is an ideal insulating material. The tempered glass insulator utilizes this characteristic, and its lightning impulse voltage value is 3.8 times that of the porcelain insulator. The term "aging" as used herein refers to the aging of electrical properties, that is, under the action of the electric field for a long time, certain physical and chemical changes will gradually occur to cause irreversible deterioration of the medium, and finally the medium is broken down. The tempered glass insulator has good anti-aging performance. According to the tracking test of the insulators operated by the French Seddyville Company on the 132kV transmission line in Malaysia for 27 years, the mechanical and electrical properties have not changed significantly. The porcelain insulators used in the same period, after running for a period of time, their electromechanical performance decreased significantly.

The tempered glass insulator has the characteristics of self-breaking zero value and easy detection. It can fully demonstrate good performance advantages and perform well functions and functions in actual use. The tempered glass insulator has the characteristics of zero value self-breaking. As long as it is observed on the ground or on a helicopter, there is no need for on-the-spot inspection, which reduces the labor intensity of workers. The insulator is a product introduced into the production line. The annual self-breaking rate is 0.02-0.04%, which can save the maintenance cost of the line, and has the performance of good arc resistance and vibration resistance. It plays an important role and value in the power industry.

The new surface of the glass insulator subjected to lightning burns during operation is still a smooth vitreous body and has a tempered internal stress protective layer, so it still maintains sufficient insulation and mechanical strength. On the 500kv line, the lightning caused by the wire skating occurred many times, and the glass insulator after the wire was tested was tested, and the electromechanical performance was not attenuated. Types of tempered glass insulators: standard, stain-resistant, DC-type, spherical, aerodynamic, ground-type, electrified railway contact nets, different types of types show important role and value in actual use.

Advantages of glass insulators: If there are various defects in the glass body of the insulator, the glass body will be broken automatically, which is called “self-breaking”. After the insulator is broken, the iron cap residual hammer still maintains a certain mechanical strength to hang on the line, and the line can continue to operate. When the line patrol personnel patrol the line, it is easy to find the self-breaking insulator and replace the new insulator in time. Since the glass insulator has such a "self-breaking" feature, it is not necessary to perform a preventive test on the insulator during the operation of the line, thereby bringing great convenience to the operation.

Composite insulator advantages and disadvantages

The composite insulator is a high voltage insulator made of a composite of a silicone rubber material. The main products are rod and cross-arm type, which are used as suspension and tensile load insulation on 35kV, 110kV and 220kV lines. There are also insulator products for 10kV lines.

The composite insulator has an outer structure of approximately suspended insulators, and is composed of end fittings, insulated umbrella corrugations, sheaths, and sleeves.

It has the following advantages:

(1) Excellent mechanical properties: Since the mandrel is made of epoxy glass fiber, its expansion strength is 1.5 times that of ordinary steel, 3 to 4 times that of high-strength porcelain, the axial tensile force is particularly strong, and it has strong vibration absorption capacity. The seismic damping performance is very high, 1/7 to 1/10 of the porcelain insulator.

(2) The composite insulator string has good anti-soil flash performance: the composite insulator has water repellency. When it rains, the umbrella-shaped corrugated surface of the composite insulator will not wet to form a water film, but will drop in the form of water droplets, which is not easy to form a conductive channel. The pollution flash voltage is higher, which is 3 times that of the same voltage grade porcelain insulator.

(3) Excellent resistance to electric corrosion: The surface of the insulator leaks and flashes to form an irreversible deterioration. The general standard is not less than 4.5 (ie 4.5 kV), and the composite insulator is 6 to 7.

(4) Good anti-aging performance: After ten years of practice test, the composite insulator has no deeper color and slightly increased dielectric constant and dielectric loss angle, and has no surface wettability and corrosion resistance. Change indicates that the anti-aging performance is good.

(5) Good structural stability: the general porcelain suspension insulator is an inner rubber assembly structure. Due to galvanic corrosion, a low-zero insulation resistance is generated during operation, and the composite insulator is an external rubber assembly structure, and the inner core is a solid rod insulation material. There is no degradation and breakdown, and zero-value insulators do not appear.

(6) High efficiency of line operation: Since the composite insulator has good self-cleaning performance and no zero-value insulator, the cleaning inspection work can be changed every 4 to 5 years, thus shortening the time for maintenance and power failure.

(7) Light weight: The weight of the insulator is light. In transportation and construction work, the labor intensity of the staff can be greatly reduced.

But things are divided into two, and composite insulators also have some disadvantages:

(1) The price of composite insulators is high.

(2) The radial resistance (perpendicular to the center line) of the composite insulator is very small. Therefore, the high-voltage insulator used for the tensile rod is strictly prohibited from being stepped on, or any form of radial load, otherwise it will cause breakage.

(3) The composite insulator is strictly prohibited from falling and rubbing during construction or normal operation. Because the umbrella part is made of silicone rubber, the texture is soft and tender, and it is easy to damage and damage the sealing performance, resulting in a decrease in insulation performance.