Hi-Pot Testing : What, Why and How

The electrical grid network is oftentimes classified as critical infrastructure. For electrical utilities, any disruption which leads to major downtime is a major source of revenue loss. Furthermore, policymakers today expect network operators to deliver 24/7 electricity to the retail consumers. As a result, it is important that electrical equipment have the highest standards of quality and reliability while also ensuring user safety. As a leading manufacturer of electrical test and measurement equipment in India, SCOPE takes great pleasure in providing our customers with products with the above-mentioned criteria. 

In this blog, we will discuss the technique of Hipot testing, a commonly used safety test which ensures the safety of the user and the insulation healthiness of the test object.

What is Hi-pot Test?

Hipot test, shorthand for high-potential test, is also known as the Dielectric-Withstand test. The test is used to evaluate the insulation condition of the test object (such as transformers, switch-gear, relays, generators lightning arresters, bus-bar, cables, DC high voltage capacitors, etc).  The Hipot test ensures that current will not flow from one point to another and indicates the ability of the insulation to withstand high voltage and over voltage transient. Therefore, the Hipot test is an excellent method to detect any defect in an electrical product on account of poor workmanship.

In order to prevent the breakdown of the insulation of electrical products during operation potentially causing catastrophic damage to man and machine, this test is usually performed during the manufacturing process and during installation, acceptance, routine repair and maintenance activities. Through such evaluations, managers can decide on corrective action to be taken to ensure quality of electrical equipment.

Hipot tests are useful in determining:

  1. Nicked or Crushed Insulation
  2. Stray wire stands or braided shielding
  3. Conductive or corrosive contaminants
  4. Terminal spacing problems
  5. Reduction in creepage and clearance
  6. Improper cable joints and terminations

How is Hipot Testing Done?

Hipot tests involve the application of overvoltage to a device under test (DUT) for a short duration to verify the dielectric integrity of the system. Hipot testing can be done using AC, DC or Very Low Frequency (VLF) test voltage. In this blog, we will discuss AC & DC Hipot testing and the parameters that need to be considered while selecting the ideal AC/DC Hipot test kit for a particular test object.

Fig 1 : Hipot Testing

Guidelines for Hipot Testing

IEC 60590 is the applicable standard for Hipot testing. As per this standard:

Sr.noParametersStandard
1Basic test voltage2*(operating voltage) + 1 kV
2Test duration1 minute

Furthermore:

  • As a thumb rule, if DC Hipot test is used on AC circuit, Hipot voltage should be two times the peak (2 * 1.4 * RMS) + 1kV
  • Extra 1 kV voltage is to be applied to check whether the DUT insulation is able to withstand daily transient overvoltage
  • DUT is considered to have passed the test if either the leakage current measured is less than the maximum allowable current or no breakdown occurs, i.e., there is no sudden and uncontrolled flow of current

Pre-Testing Arrangements for Hipot Testing

  • Ensure that the body of the instrument is grounded properly
  • Collect previous testing data, logs for reference
  • Ensure the test location / area has sufficient light / illumination
  • Wooden bench / table to place the instrument
  • Mains power supply with proper earthing
  • Instrument with proper test lead set without any wear and tear
  • Multimeter should be available for continuity testing of test Leads
  • Discharge rod must be used before physically touching the test object
  • Wear HV Gloves, safety glasses, helmet and safety shoes for personal safety
  • Operator should be standing on HV insulated rubber mat while operating the kit
  • Ensure proper earthing, earth spikes required for additional earthing
  • Maintain safe distance from the HV Terminals while applying HV
  • Audio- visual indications and barricades can be used for warning people while injecting HV

Steps of Hipot Testing

  • Step -1 : open circuit breakers or switches to isolate the DUT from both the ends
  • Step -2: discharge all the conductors using a discharge rod
  • Step -3: put CAUTION labels / Barricades around the HV testing area
  • Step -4: connect Master Earthing Terminal of Hipot to a proper System Earthing
  • Step-5: connect Operational Earthing Terminal (LV terminal of the kit) to safety ground (Body Earth)
  • Step -6: ensure proper connection
  • Step -7: the HV terminal of the kit should be connected to the conductive part of the test obejct
  • Step-8: test all circuit phase conductors testing each phase to ground as per pre-determined voltage, time and current setting

Once these steps are followed, the below points are to be ensured:

  1. As a result of the voltage difference between the conductors, current flow would be observed. No breakdown of either the air insulation or the solid insulation should take place
  2. Furthermore, current should not be more than 5mA peak (3.5mA rms)
  3. To PASS the test, the test object must be exposed to a minimum stress of pre-decided Voltage for 1 minute (or other test duration depending on the DUT and its test standard) without any indication of breakdown
Fig 2 : Connection of Hi-pot to the Device Under Test (DUT)

Conclusion

In this manner, Hipot testing can ensure the safety, quality and reliability of critical electrical equipment. The parameters which should be considered while selecting the ideal Hipot test kit are:

  • Application: AC/DC/AC-DC depending on the DUT
  • Combined or separate control unit as per the voltage level
  • Required output voltage of the Hipot test kit as per the DUT’s rated voltage
  • Required leakage current range of the Hipot test kit as per the DUT’s recommended current range 
  • Timers
  • Trip current settings
  • Volt-meters & Amp-meters for output parameters
  • Add on safety features include external interlocks, beacon/buzzer

Hipot test kits provided by SCOPE are fit for purpose and the features mentioned above make our test kits stand apart from kits offered by our competitors

To know more about SCOPE Hipot testing capabilities, please visit https://www.scopetnm.com/test-and-measurements/other-products/hi-pot-series or write to us at marketing@scopetnm.com.

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