What is Hipot Testing (Dielectric Withstand Test)?

Hipot testing, also called dielectric withstand test, is the direct application of high voltage to a device under test (DUT). This is to ensure that the electrical device is standard.

During the test, the insulator passes through a very high voltage, for a specific time more than they will encounter during use.

For the device under test (DUT) to be safe for use, it must withstand the test voltage without defect or breakdown.

Secondly, it must not allow excessive leakage current to flow out of the product surface.

What is Hipot Used for?

Hipot is used to verify the reliability of electrical insulation in finished appliances, cables, or other wired assemblies, electric motors, printed circuit boards, and transformers.

Is Hipot Testing Necessary?

Hipot test is necessary because it helps to check the strength of an electronic device for safety and quality purposes. Under high voltage, the test ensures there is no breakdown or perforation of product insulation, and that insulation distances on the line and in the air are normal.

What is the voltage,of High Potential Testing?

  • It helps to determine if the insulation of a product can withstand over-voltage without defect.
  • It helps to detect nicked or crushed insulation, tolerance errors in cables, stray wire strands, and conductive or corrosive contaminants around the conductors.
  • Helps protect users from the electric shock that may arise from poor insulation.
  • It also detects scrapes, pinholes, spacing, poor creepage, and clearance distances made during production.
  • In the production line, hi-potential testing helps to check whether the construction of a production unit is the same as the construction of the unit under testing.

Some failures that may be detected by a production line hipot test include a transformer wound in such a way that the creepage and clearance have been reduced.

Such failures are usually because of a new operator in the winding department.

What is the test voltage and formular for hipot testing?

The formula for the voltage withstand test is twice the normal operating voltage plus 1000 volt. The reason for adding 1000V is that of the various degrees of high power surges the insulator will pass during use.

Example, For a working voltage of 220 V, the formular will be (220 × 2 + 1000) = 1440 V. The common hipot test voltage will be 1500 V.

High-potential test voltage, which one to use, AC or DC?

You can use an AC or DC power supply for the test. Both have an advantage and drawback. But to be on the safer side, always check the voltage of the appliance you want to test.

If you are using AC current, use an AC tester. Else, use a direct-current tester.

When using an AC or alternating current, the insulation will experience the highest stress when the voltage is at its peak, either positive or negative peak of the sine wave.

Note: When using DC current, make sure that the test voltage is below 2 root (1.414) times the AC test voltage. This will make the DC voltage equal to the AC voltage peak.

Dielectric withstand test equipment

This test is done with hipot insulation testers. There are different brands, some from fluke, megger and other companies. You can buy a quality tester here on Amazon.

High-potential Testing Procedure

  • Isolate the circuit or cable you want to test by opening the circuit breakers or switches.
  • Place a 5ft barrier away from the equipment you want to test to prevent unqualified persons from coming close.
  • Connect the ground lead of the tester to the earth electrode terminal.
  • Connect the high-voltage lead to one of the isolated circuit phases.
  • Switch ON the analyzer and set the meter to 1000V. Press the “test button” on the meter and record the resistance reading after one minute.
  • Switch the HIPOT tester from high potential test mood to voltage measuring mode to ensure that the circuit phase conductor and the voltage of the tester correspond to zero volts.
  • Repeat the above test for all the circuit phase conductors you want to test.
  • Once you are through, disconnect the tester and reconnect the circuits.

To pass the test, the appliance must withstand the stress test unaffected.

Safety Precautions

During high potential testing, you may likely be exposed to some risk. To prevent electrical shock and other hazards, ensure your testing equipment adheres to these tips.

  • The total hipot energy should not be above 350 MJ.
  • The total current should not pass the 5 mA peak (3.5 mA RMS).
  • Fault current should not stay above 10 MS.
  • When testing the cable, don’t touch it during the test
  • Do not remove the cable while testing is ON.
  • Always wear insulating gloves
  • Never allow children to use testing equipment.
  • A qualified electrician should carry out the test

Advantages and disadvantages of using AC voltage for dielectric withstand test

Advantages

  • It does not require ramping of voltage since the polarity changes
  • Discharging the device under testing (DUT) is not needed
  • Measures both reactive and real current
  • It stresses insulation in both polarities
  • Generally accepted by safety agencies

Disadvantage

If the circuit under test has a large value of Y capacitor, the AC tester may show a failure depending on the current trip setting.

Advantages and disadvantages of using DC voltage.

Advantages

  • The leakage current measurement is purely real
  • Requires lower current level with less risk to the operator
  • Usually easier to perform on capacitive DUTs

Disadvantage

DC tester is more expensive because generating DC voltage is hard.

Difference between Hi-potential and continuity test

Hipot is the opposite of a continuity test.

Continuity tester checks to ensure that current flows from one point to another along the circuit, while Hipot checks to make sure the current did not flow to the surface of the insulator.

High potential testing duration

According to the IEC 60950 standard, the test time for the product should be one minute.

Difference between dielectric withstand test and insulation resistance test

The difference between insulation resistance and dielectric withstand test lies in their measurement. The insulation resistance test measures the amount of current that flows through an insulator. The current is usually less than 1000V and is measured in ohm.

While a hipot detector measures about 5000 to 6000V depending on the requirement and also returns values in milliampere.

Difference between Megger and Hi-potential testing?

The difference between megger and hipot is that megger is a megohmeter that measures insulation resistance, while hipot tester measures leakage current.

Is hipot testing destructive?

No, it is a non-destructive test. It is a safety test that measures the insulation of a product to make sure it is safe for consumer use.