The reason for using 2 as a factor is that the line leakage current is generated by a Y capacitor, but the leakage current generated by the hipot test is generated by the capacitance of each line at the same time. By deriving the equation I (hipot), you can predict the hipot test current. Therefore, the hipot tester current limit should be set high enough to avoid false positives due to the presence of leakage currents, but not so high that a true insulation breakdown cannot be detected.
Most safety standards allow hipot testing using either AC or DC voltages. When AC voltage is used for testing, the insulation under test is subjected to a peak voltage. So, if you decide to test with DC voltage, you must make sure that the dc test voltage is 2 (or 1.414) times the AC test voltage, so that the dc voltage value is equal to the peak AC voltage. For example, for 1500 Vac, the equivalent dc voltage for insulation testing would be 1500 x 1.414 or 2121 Vdc.
One advantage of using a DC test voltage is that the leakage current limit can be set to a lower value than with an AC test voltage. This gives the manufacturer a better chance of checking for products that are on the verge of insulation failure, which may pass when tested with AC voltage. It is important to note that when using a DC hipot tester, the capacitors in the circuit are highly charged, so a safety discharge device or setting is necessary. However, regardless of the test voltage, it is good practice to discharge the product before it is touched.
Another benefit of the DC hipot tester is its gradual increase in voltage. By monitoring the change in current as the voltage increases, operators can see potential insulation failures before they occur. A minor disadvantage of using a DC hipot tester is that DC test voltages are more difficult to generate, and DC hipot testers may cost slightly more than AC testers.
A minor disadvantage of AC hipot testers is that if the circuit under test has a large Y-capacitor, the hipot tester's current-limit settings may cause the AC tester to indicate a test failure when the insulation has not actually broken down. Most safety standards allow the user to test with the Y-capacitor disconnected, or alternatively use a DC hipot tester. A DC hipot tester will not indicate a failure due to the presence of a large Y-capacitor because the Y-capacitor will not pass current through itself in response to a DC voltage.
These tests are equally applicable to Class I and Class II equipment. For Class II equipment, accessible conductive parts and the enclosure (a 10x20cm metal film is used to contact the surface of the enclosure) are tested. This film simulates a human hand.8 r3 o- l/ {/ ^9 a. g! }Safety.com www.angui.org
This test also needs to be performed under any conditions, such as normal, switch on or off, and power polarity alignment. Equipment designed with multiple power inputs, where only one power supply is required to be connected at a time (e.g., backup power), must be tested with only one power supply connected. While most standards do not require 100% leakage current testing of production lines, there are some standards, such as medical devices, that do require 100% testing.