For encapsulated explosion-proof electrical equipment, all tests are conducted for the purpose of assessing various performance indicators of the encapsulating compound. The encapsulating compound meets the requirements. In principle, the explosion-proof safety performance of this explosion-proof type can be guaranteed.
The potting compound used in potting type explosion-proof electrical equipment should withstand the following tests.
- Encapsulated compound sample test
(1) Water absorption test
When the encapsulated explosion-proof electrical equipment is used in a humid environment, the encapsulating compound should be tested for water absorption.
The test sample of the encapsulating compound is a cylinder with a diameter of (50±1) min and a height of (3±0.2) min.
During the test, the tester should first weigh the 3 dry test samples, and then put them in water at (23+2)℃ for 24h. then, take the test samples out of the water and dry and weigh them again.
After the test, the weight of the test sample should not exceed 1% of the weight of the dry sample.
(2) Dielectric strength test
The Encapsulated compound used in encapsulated type explosion-proof electrical equipment should withstand the dielectric strength test.
The test sample of the encapsulating compound is a cylinder with a diameter of (50±1) min and a height of (3±0.2) min.
During the test, the tester should symmetrically place the test sample on two circular electrodes with a diameter of (30 ± 1) min, and the electrodes are made of brass. The surface contacting the test sample should be flat and smooth (R. ≤ 0.8). The prepared test sample should be placed in an environment at a high temperature point in the continuous operating temperature (COT) range of the encapsulating compound for 24 hours for pretreatment.
Then, the tester applies a charging voltage of 4kV (error 0-5%, effective value) at a frequency of 48-52 Hz (or 58-62 Hz) between the two electrodes of such a test sample for at least 5 minutes.
During the test, no flashover or breakdown should occur at the test site.
- Heat and cold resistance test
The heat and cold resistance test of encapsulated explosion-proof electrical equipment should be carried out in accordance with the general test requirements for explosion-proof and explosion-proof electrical equipment.
However, the temperature used in the heat resistance test should be:
1) For "ma" class equipment and "mb" class equipment
- The highest external surface temperature of the test sample when it runs under fault conditions.
- The maximum temperature of the surface of the components encapsulated in the encapsulating compound when the test sample is running under the rated operating conditions.
2) For "mc" class equipment
The highest surface temperature of the test sample when it is operated under rated operating conditions plus the temperature value of at least 20K.
In the test of "ma" class equipment and "mb" class equipment, if the temperature of the former is used as the test temperature in the heat resistance test, the test sample should also withstand the following thermal cycle test.
- Thermal cycle test
When conducting thermal cycle test for encapsulated explosion-proof electrical equipment, the tester should place multiple temperature sensors in the test sample.
The sensor can be placed on the outer surface of the test sample, and it should also be placed at the hottest possible position inside the test sample.
During the test, the tester should place the test sample in an environment with a temperature of (21±2)oC for 24h without electricity; then, place it in an environment of (t...+10-1-2)°C until The temperature difference between the inside and outside of the sample is less than 2K; the test sample is energized (the voltage is the upper limit of the rated voltage) to produce a temperature not greater than 2K on the thermal protection device (the internal thermal protection device can be Bridged together).
Here, t represents the maximum operating ambient temperature of the encapsulated explosion-proof electrical equipment.
This test state is maintained until the internal temperature of the test sample is stable (the temperature change is not more than 2K/h).
At this time, the tester cuts off the power of the test sample, removes the test sample from the environment of (t±10)℃ and cools it to (21±2)℃; then, place it in an environment with a temperature of (t±5)℃, Until the temperature inside and outside the test sample is not greater than 2K; then, the test sample is energized again (the voltage is the upper limit of the rated voltage) to generate a temperature not greater than the protection temperature of 2K in the thermal protection device (the internal temperature during the test) Thermal protection devices can be bridged together).
Here, t represents the minimum operating ambient temperature of the encapsulated explosion-proof electrical equipment.
This test state is maintained until the internal temperature of the test sample is stable (the temperature change is not more than 2K/h).
The above test process is a cycle. The thermal cycle test should be carried out for 3 cycles.
After the end of the heat resistance test, cold resistance test or (and) thermal cycle test, the encapsulating compound must not crack, fall off, shrink, expand, soften and other signs that affect safety performance.