What does Hi-Pot mean?
Hi-Pot is the abbreviation for High Potential, and generally refers to the high voltages used to test dielectric withstand capability for regulatory agency electrical safety requirements.
The hi-pot test is performed to ensure that there is good isolation between different the live parts and the ground of a power supply, or between the various parts that require an electrical isolation between each other.
A pass in the hi-pot test guarantees that the equipment or system is safe and does not pose any danger such as an electric shock to the operator or someone who touches the equipment. The test uses very high voltages, several times the normal operating voltage of the equipment. The high values simulate a transient such as those that may arise from switching equipment or lightning storms.
DC and AC Hi-pot test voltages
The high potential voltage lever may differ from one equipment and application to the other as well as the stage in a product’s development cycle. The voltage may be DC, AC, or an impulse.
When using the AC voltage, the insulation is subjected to the highest stress during the positive and negative peaks. To ensure that the same level of voltage is applied when using the DC voltage, the equivalent DC test voltage should be 1.414 (√2) times the AC test voltage. For example, if the AC test voltage is 1500V, the equivalent DC voltage will be 2121 V (1500 x 1.414V).
During the hi-pot test of a power supply, one test is carried by applying the high voltage between the primary or the input and the ground of the power supply unit. The other test is carried by applying the high voltage between the primary side and the user accessible parts which are the secondary circuits.
The high voltage can be either DC or AC, however, DC is more commonly used in testing power supplies due to the use of Y capacitors which would allow a current to flow and hence affect the measurement.
Hi pot test – Image Credit
Most of the safety standard bodies such as CSA and UL allow for the use of DC hi-pot voltages, and instead of 1500VAC the test uses 2121 VDC (√2 x 1500). At times, the voltage can be increased by 10% so as to reduce the test time from 1 minute to between 1 and 2 seconds.
Another two commonly used isolation testing voltages are 3kVAC and 4kVAC, however, these are only used for testing the main transformer, which must be removed from the power supply and tested on its own. IT products such as power supplies as well as test and measurement equipment must pass the input-to-output isolation test of 3kVAC. On the other hand, the medical equipment is required to pass the isolation test of a higher voltage of 4kVAC.
When carrying out the test, the DC voltage should be applied gradually to allow the power supply capacitors to charge up without tripping the test equipment’s over-current protection system. The capacitors should be discharged after the test and before handling the equipment.