Testing of cables with high voltage (2023)

What is a "hipot" test?

Many people are familiar with a continuity test. A continuity test checks for "good connections," meaning current is flowing from one point to its destination point. If the current flows easily enough, the dots are connected. Many people are less familiar with a hipot test. "Hipot" is short for high potential (high voltage).

A Hipot test checks for "good insulation". A hipot test checks that no current flows between points where no current should flow. In a way, a hipot test is the opposite of a continuity test.

Continuity test: "Ensures current flows smoothly from one point to another."

Hipot test: "Ensures no current flows between points where no current should flow (using high voltage to ensure no current flows)."

A hipot test takes two conductors that should be isolated and applies a very high voltage between the conductors. The flowing stream is observed. If too much current flows, the points are not well insulated and will fail the test.

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Why high voltage testing?

A hipot test verifies good insulation between parts of a circuit. Good insulation helps ensure the safety and quality of electrical circuits. Hipot tests are helpful in the search

(Video) High Voltage Testing of Cables by Dr. Jitendra Jamnani

  • nicked or pinched insulation
  • Stray wires or braided shields
  • conductive or corrosive contaminants around conductors
  • Problems with the terminal spacing
  • Tolerance error in IDC cables

All of these conditions can cause a device to fail.

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What types of high-voltage tests are there?

There are three common high voltage tests.

  • Dielectric breakdown test
  • Dielectric Resistance Test
  • insulation resistance test

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What is "dielectric breakdown test"?

Dielectric breakdown testing answers the question, "How much voltage can I apply between wires before the insulation fails?" The test increases the voltage until the current increases. This method finds the highest voltage that the cable can withstand before it fails. Once the cable fails, it is usually damaged or destroyed.

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What is "Dielectric Strength Test" (DW)?

Dielectric strength testing answers the question, "Will this cable withstand a required voltage for a required time?" The test applies the required voltage for the specified amount of time and monitors the current flow. Ideally, no current flows and the cable is not damaged.

(Video) Hipot Test for medium voltage cable part 1

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What is "Insulation Resistance Testing" (IR)?

The insulation resistance test tries to answer the question: "Is the resistance of the insulation high enough?" The test applies a voltage and measures the current. It then calculates the insulation resistance according to Ohm's law (R = V/I).

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How do these "hipot" tests affect quality?

All of these tests are tools used to understand how a cable works and to monitor changes in the cable's performance.

Dielectric breakdown testing is used in the product design and qualification phase. It helps set the maximum tension of the design. It can also be used on a sample basis to verify that the maximum voltage does not change. A breakdown test may be required during the development of assemblies used in critical applications.

Many test specifications require a dielectric withstand test for each cable manufactured. The test is typically performed at around 75% of typical breakdown voltage and serves as a safety net. The test is sensitive to arcing or corona, so it often finds problems with terminal spacing, overmolds, tolerance errors in IDC cables, or other problems that could create arcing. This test does not significantly degrade the cable.

The insulation resistance test is typically performed on each cable tested and is typically performed at 300 to 500 VDC with a resistance of 100 to 500 megohms. The test is very sensitive to contamination in the assembly process. Solder flux, oils, mold release agents, and skin oil can cause problems. This test is excellent for identifying insulation that conducts in the presence of moisture. By performing this test on each cable, you can see pollution changes in the manufacturing process.


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What about safety with all the high voltage being used?

Products being developed today should comply with product safety regulations. Some of these regulations reduce the chance of receiving a harmful electric shock. You may be at some risk during a hipot test. The risk can be reduced by following the manufacturer's instructions. When it comes to Hipot Charge, Energy and Voltage, choose the “safest” device that meets your cable testing needs.

To minimize your risk of injury from electrocution, make sure your hipot gear meets these guidelines:

  • The total charge you can sustain from a shock should not exceed 45 uC.
  • The total hipot energy should not exceed 350 mJ.
  • The total current should not exceed 5 mA peak (3.5 mA rms).
  • The fault current should not last longer than 10 ms.
  • If the tester does not meet these requirements, make sure it has a safety interlock system that guarantees you cannot touch the cable during the high voltage test.

These guidelines originate from the test standard EN61010-1, safety requirements for electrical measuring, control, regulating and laboratory equipment, April 1993,CENELEC.In the last decade, many of the safety regulations have been harmonized (standardized) and EN61010-1 is similar to UL 61010A-1 (formerly UL3101-1).

While testing cables, there are several things you can do to reduce risk even further:

  • With each calibration, verify the correct operation of the safety circuits in the device.
  • Follow all manufacturer instructions and safety guidelines.
  • Do not touch the cable during the hipot test.
  • Wait for the hipot test to complete before removing the cable.
  • Wear insulating gloves.
  • If you have a health condition that can be made worse by being startled, do not use the device.
  • Do not allow children to use the device.
  • If you have electronic implants, do not use the devices.

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Where is the high voltage applied?

To understand how hipot testing works, you need to understand where the high voltage supply connects. Hipot testers typically connect one side of the supply to safety earth (ground). The other side of the supply is connected to the conductor that is powered up. With the supply hooked up like this, there are two places a particular conductor can be connected: high voltage or ground.

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If you have more than two contacts to high voltage test, connect one contact to high voltage and connect all other contacts to ground. Testing a contact in this way ensures that it is isolated from all other contacts.

What happens when you test something more complicated than just contacts? A set of contacts connected to wires, resistors, capacitors, diodes, and other components is called a "network" of connections (or "mesh"). To test a net, connect all contacts in the net to high voltage and connect all other contacts in the device to ground. For example, if you have a wire connecting two pins, the high voltage will be applied to both pins at the same time, increasing the voltage of the entire wire. All other wires and pins are held to ground. If you have a resistor connecting two pins, the voltage on both pins will be increased and the voltage drop across the resistor will always be zero. All resistance is raised in tension. In short, all pins on a component see the same voltage at all times. Applying the voltage in this way ensures that the body of the component is isolated from the rest of the device.

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Where is the current measured?

The high voltage test measures the current flowing from the high voltage power supply.

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What causes current to flow through an insulator?

Insulation "does not conduct". But if you use enough voltage, even the best insulation will allow some current to flow. There are several reasons why current flows through the insulation during a hipot test. Resistance, capacitance, arcing, electrochemical effects, and corona are all effects that describe current flow. All of these effects taken together during a hipot test shape the results.

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Which Cirris testers are suitable for high-voltage tests?

Cirris manufactures industry leading high voltage cable testers. Information about these analyzers can be found on ourProduct page cable tester.

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