Comparison of Glass Insulators, Ceramic Insulators and Composite Insulators

Glass Insulators VS Ceramic Insulators

Ceramic insulators are, as the name implies, insulators made of electrical ceramics. Electrical ceramics are made of quartz, feldspar and clay baked as raw materials. The surface of porcelain insulators is usually covered with porcelain enamel to improve its mechanical strength, waterproof infiltration and increase the smoothness of the surface.

Glass insulators are insulators made of tempered glass.

1、Mechanical strength: Through the electromechanical performance comparison test on porcelain insulators and glass insulators with different years of operation on the line, it is found that some porcelain insulators have lower test values than the factory test standard values after l5-2O years of operation, and the failure rate increases with years of operation. The stability and dispersion of glass are better than porcelain. The results of the high-frequency vibration fatigue test on porcelain and glass insulators show that the electromechanical strength of glass insulators decreases significantly after high-frequency vibration. The reason: on the one hand, because of the domestic porcelain insulator material and manufacturing process and other factors, resulting in a large dispersion of quality.

2, anti-aging performance: porcelain insulators have nearly one hundred years of operating experience, and their anti-aging ability is strong. In a period of time after the commissioning. Through testing means, a few deteriorated insulators can be replaced. However, with the growth of operation time, its aging will become more and more serious. Glass by tempering treatment, the surface of the formation of compressive stress, if the glass surface emblematic cracks exist, but also solid stress effect so that micro-cracks are compressed and do not expand. The electrical strength of glass generally remains unchanged throughout the operation, and its aging process is much slower than porcelain.

3, electrical properties: glass medium in the standard shock wave, the electric breakdown strength of 1350 ~ 1700 kV / cm, about 3.8 times the porcelain. At home and abroad have repeatedly used the wave head steepness of the shock wave for testing. The results are atmospheric flashover, and the glass body was not penetrated, operating experience has also proved that the glass insulator will not be struck by lightning.

4、Voltage distribution: Due to the large dielectric constant of glass, the glass insulator has a large main capacitance, the voltage distribution of the string is more uniform, the voltage of the glass insulator string piece is lower than the voltage of the porcelain piece, thus reducing the step radio interference, reducing corona loss, extending the life of the glass insulator, and also increasing the flashover voltage of the glass insulator string.

5, size, weight: Because the core bar has high tensile strength, thus the synthetic insulator can be made very light, only 1O of the weight of the porcelain insulator string. Due to the glass dielectric constant of 7 to 8. 6 to 6 5 than porcelain, in the case of mechanical strength and breakdown voltage is the same. Its thickness is smaller, thus the glass insulator is lighter than the porcelain insulator.

6、Later maintenance problem: Ceramic insulators have many years of operating experience and reliable operation but have zero value detection problems and poor anti-fouling performance. Glass insulators have a good effect and easy operation and maintenance.

7. Applications. Ceramic insulators are widely used in lines of various voltage levels. Disc type porcelain insulators are of breakdown type, which is made up of porcelain parts with different physical and chemical properties glued with metal parts by using cement, and will gradually deteriorate when subjected to an electric field, mechanical load and nature's sunlight, wind, rain, snow, fog, etc. for a long time, posing a threat to the safe operation of the power grid. Especially when the insulator string containing deteriorated insulators flash (due to lightning strike or foul flash, etc.), it may make the head of the deteriorated insulator instantly heat up and explode, causing the accident of the wire falling to the ground. Comparison of advantages and disadvantages of glass insulators and porcelain insulators can be used according to the line design using specific use of glass insulators and porcelain insulators.

Glass Insulator VS Composite Insulator

Glass insulators play two basic roles in overhead transmission lines, namely supporting the conductor and preventing the current from returning to the ground. These two roles must be ensured throughout the operational life of the line (usually 40 years) and the insulator should not fail due to various electromechanical stresses caused by changes in environmental and electrical load conditions. The mechanical loads to which the insulators are subjected must, in addition to the weight of the conductors and metal accessories, also withstand wind loads in adverse weather conditions, snow loads, conductor dances, and shock loads caused by improper handling during transport and installation. From an electrical point of view, the insulator must not only insulate the conductor from the ground, but also must withstand lightning and over-voltage shocks caused by switching operations, and the local overheating caused when flashover occurs due to voltage shocks should not lead to the bursting of the insulator's tempered glass body. All external factors will have an impact on the performance of the insulator and, therefore, also place higher requirements on the design of the insulator.

Excellent dielectric properties and no aging phenomenon

Dielectric properties are the electrical properties of a dielectric under the action of an electric field. The insulator insulation performance is highly related to the internal molecular structure of the insulating material. Glass belongs to the non-crystalline structure, is no fixed melting point of silicate compounds, dense structure, uniform texture, produced in a continuous production process easy to control. siO2 is the skeleton of the composition of the glass, other oxides filled in the skeleton, and connected by a chemical bond, the interaction is large, not easily polarized by the electric field, showing good inertia, is the ideal insulating material. Tempered glass insulators take advantage of this characteristic, and their lightning shock voltage resistance value is 3.8 times that of porcelain insulators. The aging mentioned here refers to the aging of electrical properties, i.e., the medium will gradually undergo some physical and chemical changes under the action of electric field for a long time, resulting in irreversible deterioration of the medium, which eventually leads to the breakdown of the medium. Tempered glass insulators have excellent anti-aging properties, and according to the tracking test of insulators after 27 years of operation on 132kV transmission lines in Malaysia by France Sedivel, their mechanical and electrical properties have not changed significantly. The porcelain insulators used in the same period, on the other hand, showed a significant decline in their electromechanical properties after a period of operation.

The tempered glass insulator has the characteristics of zero value self-breakage and easy detection, which can fully demonstrate good performance advantages and perform good functions and roles in the actual use of tempered glass insulators. Just observe on the ground or in the helicopter, no need to board the pole to detect piece by piece, reducing the labor intensity of workers. The insulator is a product of the introduced production line, with an annual operating self-breakage rate of 0.02 to 0.04%, which can save the maintenance cost of the line, and has the performance of good arc resistance and vibration resistance, giving full play to its important role and value in the electric power industry.

The new surface of the glass insulator suffering from lightning burns in operation is still a smooth glass body with a toughened internal stress protection layer, so it still maintains sufficient insulation parts energy and mechanical strength. In the 500kv line, many times the wire track ice was caused by the dance of the disaster, subject to the wire dance after the glass insulator by the test, electromechanical performance did not decay. Types of tempered glass insulators: standard, fouling resistant, DC, spherical, aerodynamic, ground, for electrified railway contact network, different kinds of types show important roles and values in actual use.

Advantages of glass insulator: If the glass body of the insulator has various defects, the glass body will break automatically, which is called "self-breaking". After the insulator is broken, the hammer remains on the line with a certain mechanical strength, and the line can continue to run. When inspecting the line, it is easy to find the self-broken insulator and replace it with a new insulator in time. Since the glass insulator has this "self-breaking" feature, it is not necessary to conduct preventive tests on the insulator during line operation, thus bringing great convenience to the operation.

Advantages and disadvantages of composite insulators

The composite insulator is a high voltage insulator made of silicone rubber material. The main products are bar type and crossbar type, which are used as overhanging and tension bearing insulators in 35kV, 110kV, and 220kV lines. Currently, there are also insulators for 10kV lines.

The composite insulator is similar to the suspension insulator in shape and structure, with end fittings, insulation umbrella corrugation, sheath and insulating core bar.

It has the following advantages.

(1) Superior mechanical properties: As the heart bar is made of epoxy glass fiber, its expansion strength is 1.5 times that of ordinary steel and 3 to 4 times that of high-strength porcelain, and the axial tension is particularly strong, and it has strong vibration absorption ability and high seismic damping performance, which is 1/7 to 1/10 of porcelain insulators.

(2)Good anti-fouling and flashing performance of composite insulator string: the composite insulator has water repellent, when it rains, the umbrella corrugated surface of the composite insulator will not be wet to form a water film, but bead-like drops, not easy to constitute a conductive channel, and its fouling and flashing voltage is high, 3 times that of porcelain insulators of the same voltage level.

(3) Excellent electric corrosion resistance: the insulator surface leakage flash forms irreversible degradation start phenomenon, the general standard is not less than 4.5 level (i.e. 4.5kV), while the composite insulator is 6-7 level.

(4) Good anti-aging performance: Ten years of practical testing shows that the composite insulator has no change in surface non-staining and corrosion resistance, except for a slight darkening of color and a slight increase in dielectric constant and dielectric loss angle, indicating good anti-aging performance.

(5) Good structural stability: general porcelain suspension insulator is the inner glue assembly structure, due to galvanic corrosion, the operation will produce low zero value insulation resistance, and composite insulators for the outer glue assembly structure, its inner solid rod insulation material, there is no deterioration of the combined breakdown, there will be no zero value insulator.

(6) High efficiency of line operation: Since the weather self-cleaning of the composite insulators is good and does not produce zero-value insulators, the cleaning, and inspection work can be changed to once every 4 to 5 years, thus shortening the time of maintenance and power outage.

(7) Lightweight: Containing into insulators' own lightweight in transportation, construction work, can greatly reduce the labor intensity of staff.

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

(1)High price of composite insulator.

(2) The radial (perpendicular to the centerline) stress that composite insulators bear is very small, therefore, it is strictly forbidden to step on the high-voltage insulators used in tension-bearing poles, or any kind of radial load, otherwise, it will lead to breakage.

(3) Compound insulators are strictly forbidden to be dropped or touched by hard objects during construction or usual operation because their umbrella is silicone rubber, which is relatively soft in texture and easily damaged to break the seal and lead to the degradation of insulation performance.