What is the Comparative Tracking Index? Why do the tracking test?

What is the Comparative Tracking Index? Why do the tracking test?

What is the Comparative Tracking Index?

Comparative Tracking Index is an index used to measure the electrical breakdown (tracking damage) performance of insulating materials.

Tracking occurs on the surface of isolating materials. Due to the existence of dielectric loss, the solid dielectric will gradually heat up in the electric field. However, the increase in temperature will lead to a decrease in the resistance of the solid dielectric, which will further increase the current, so the loss and heating will also increase. While the dielectric continues to heat up, there is a process of continuous heat dissipation through electrodes and other media. If the heat generation exceeds the heat dissipation at the same time, the temperature of the medium will continue to rise, which will cause the decomposition and carbonizaion of the dielectric. The carbonized material has better electrical conductivity than the original insulating material, the discharge current is further increased, and more heat is generated to expand the carbonized part, which eventually extends to the electrode and causes a short circuit.

Why do the tracking test?

The tracking resistance test is mainly to simulate whether the conductive substances deposited on the surface of the insulating material by the live parts of different polarities in the actual use of the household electrical appliance products will cause creepage, breakdown short circuit and fire danger on the surface of the insulating material. During the use of electrical products, due to environmental pollution, there is dirt and moisture on the surface of the insulating material, resulting in tracking, which causes corrosion and damages the insulation performance.

The test specified in GB/T 4207 & IEC 60112 is an accelerated test simulating extremely harsh conditions to check whether the insulating material will form tracking, so as to distinguish the ability of solid insulating materials to resist tracking in a short time, ensuring that the product is safe to use under specific environmental conditions.

Comparative Tracking Index and Proof Tracking Index

Comparative tracking index (CTI): The highest voltage value at which the surface of the material can withstand 50 drops of electrolyte (0.1% ammonium chloride aqueous solution) without forming a tracking trace. (Unit: V)

Proof tracking index (PTI): Apply a voltage value to the material to test, check whether it can not cause tracking failure. (Unit: V)

The difference between them is: PTI is to apply a voltage value to check whether it can not cause tracking failure. CTI is used to test the maximum voltage value that the material can withstand.

Requirements of Sample preparation

The sample size is at least 15*15*3mm, and 5 Pcs is provided. If the thickness is less than 3mm, the superposition method is adopted, and than the test is carried out.

Factors Affecting CTI Test Results

a. Sample thickness;

b. Resistivity of distilled water;

c. Sample short-circuit current;

d. The size of the droplet;

e. Cleanliness of electrodes;

f. Cleanliness of sample surface

Our tracking index tester can fully meet the test requirements of IEC 60112, welcome to contact about the relevant information!

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