Leakage tracking (CTI) - electrical performance test

Date：2021-10-29 17:41:12Views：2146

The process that the surface of solid insulating material gradually forms a conductive path under the combined action of electric field and electrolyte is called leakage marking. The ability of insulating material surface to resist leakage scratch is called resistance to leakage scratch.

Purpose of leakage marking test

The leakage resistance and scratch test is mainly to simulate whether the conductive substances deposited on the surface of insulating materials by live parts of different polarity in the actual use of household electrical appliances cause creepage, breakdown, short circuit and fire hazards on the surface of insulating materials. During the use of electrical products, there is dirt and moisture on the surface of insulating materials due to environmental pollution, resulting in electric leakage, resulting in corrosion and damage to the insulation performance. The test specified in this standard is an accelerated test simulating extremely harsh conditions to test whether the insulating materials will form leakage traces, so as to distinguish the anti leakage and marking ability of solid insulating materials in a short time and ensure the use safety of products under specific environmental conditions.

Scope of application of leakage marking

It is applicable to the research, production and quality inspection departments of lighting equipment, low-voltage appliances, household appliances, machine tool appliances, motors, electric tools, electronic instruments, electrical instruments and information technology equipment, as well as the industries of insulating materials, engineering plastics, electrical connectors and accessories.

Standard for leakage trace test

The leakage trace tester is a simulation test item specified in iec60112:2003 measurement method of electric trace resistance index and comparative electric trace resistance index of solid insulating materials.

The leakage trace tester is on the surface of solid insulating material with the specified size (2mm × Apply a certain voltage between the platinum electrodes of 5mm) and drip the contaminated liquid (0.1% NH 4CL) with the specified droplet volume at a fixed height (35mm) at a fixed time (30s) to evaluate the resistance of the surface of solid insulating material under the combined action of electric field and contaminated medium, and measure its relative electric trace index (CT1) and electric trace resistance index (pT1).

Analysis of leakage trace test

The factors affecting the test mainly include the following aspects:

① Pretreatment of samples

As the standard requires that the surface of the sample should be clean, and the sample will inevitably have mold release agent, oil, dust and other dirt after manufacturing, transportation, transmission and other links to the final test. Therefore, the sample surface must be cleaned. At present, there are several cleaning methods used for this test in China:

a. Distilled water B. dry cotton ball C eraser D anhydrous alcohol. And the cleaning procedures are different. Using distilled water will change the humidity of the sample surface. It is difficult to remove the grease by wiping with a dry cotton ball. Wiping with an eraser will change the real condition of the sample. Anhydrous alcohol can not only clean the grease, but also volatilize by itself, which is ideal. Improper cleaning methods have a great impact on the test results.

② Test surface flatness, test size and thickness

If the test surface is uneven or scarred, it will affect the test results and make the test results deviate. Sample size does not meet 15mm × 15mm × When the thickness is less than 3mm, the heat capacity of the material becomes smaller, the heat dissipation is faster, and the test results are affected.

③ Resistivity and purity of electrolyte

The resistivity and purity of electrolyte are two important factors in leakage trace test. Due to the conductivity meter commonly used for platinum black conductivity electrode, its platinum black conductivity electrode is easy to be inerted, resulting in inaccurate resistivity test. Therefore, how to use a simple method to determine the good and accurate performance of platinum black conductivity electrode

The resistivity of the test solution is the key I, and the problem that the solution contains impurities is usually easy to be ignored, which is mainly due to the impure distilled water used to prepare the electrolyte.

Relative leakage initiation index and leakage initiation index

Relative leakage initiation index (CTI): the maximum voltage value of five test samples that can withstand the test process of 50 drops without leakage initiation failure and continuous flame. It also includes a description of the characteristics of the material when subjected to a 100 drop test.

(PTI): the test voltage value of five test samples that can withstand the test process of 50 drops without leakage, marking failure and continuous flame.

Precautions for leakage trace test:

1) Do not open the sample box or contact the electrode during the test to avoid electric shock.

2) Special reminder: 2.1 When doing 100-200v voltage test, be sure to put the current fine adjustment at the low position to avoid excessive current due to voltage rise and burning the current fuse and internal resistance. 2.2 reset the three buttons of "voltage selection", "current regulation" and "voltage regulation" to zero before the equipment is powered on.

3) After each test, the electrode, test glass platform and micropump shall be cleaned in time. The method is to replace the solution in the solution cup with 2-3 times of the test solution, pull out the needle, place a solution cup on the glass platform, turn on the power supply, turn on the handle switch in the box and press the "drip adjustment" button on the lower board, turn the stroke length adjustment button on the micropump panel to the maximum (100), and turn the stroke frequency selection switch to 100%, Until all the water in the lower solution cup is discharged from the needle seat. If the electrode edge is corroded, it shall be reground.

4) The solution cup shall be placed carefully to avoid dumping and causing corrosion and short circuit of surrounding electrical and metal parts.

5) During the above "(drop check)", the scale of the liquid cup given above may not meet the requirements due to the bending degree of the liquid duct and whether the air in the duct is exhausted. In this case, it is necessary to adjust the height of the liquid in the liquid cup.

6) The drip tube shall not be bent.

7) The internal parameters of the instrument of this test device have been set at the factory. Please do not change them except for the preset parameters required for the test.