DC Hipot Test Methods

Dec. 02, 2024

DC Hipot Test Methods

IC'Capacitive

Capacitive, often referred to as inrush current, occurs when the windings possess capacitance and require current to raise their voltage potential. Typically, this current diminishes to zero shortly after the motor tester stabilizes the test voltage.

Link to Hengfeng

IA'Absorption

Absorption current represents the current during the atomic and molecular polarization of the insulation and is crucial during a polarization index (PI) test. The duration for this current to drop to zero varies depending on the motor, taking anywhere from seconds to as long as 10 minutes or more.

IG'Volume Conduction

Volume conduction current flows through the entire insulation between the ground and conductors. In optimal windings, this current is typically zero or nearly zero and varies based on the insulation's composition and condition. While often thought of as leakage current, this is distinct from surface conduction current (IL), which is the primary leakage source in used motors.

IL'Surface Conduction

Surface conduction, commonly termed surface leakage current, traverses the insulation's outer surfaces.

Surface conduction arises due to contamination, dirt, and moisture present on the windings grounded.
Heightened contamination levels reduce the resistance of the contaminants, resulting in increased current flow.
Current flows generally increase in proportion to the applied voltage from the motor tester.
In properly used motors, this current overshadows absorption and volume conduction currents due to the lower resistance of surface contaminants.
Conversely, clean and dry new motors should exhibit minimal to zero surface conduction current.

Hi-Pot Testing : What, Why and How – SCOPE Corporate Blog

The electrical grid is often considered critical infrastructure. For electrical utilities, any disruptions can cause significant revenue losses. Additionally, today’s policymakers expect network operators to maintain a constant supply of electricity. Thus, ensuring that electrical equipment meets the highest quality and safety standards is essential. As a distinguished manufacturer of electrical test and measurement equipment in India, SCOPE is committed to providing products that meet these criteria.

This blog will explore the method of Hipot testing, a vital safety evaluation that ensures user safety and assesses the insulation integrity of test objects.

What is Hi-pot Test?

The Hipot test, short for high-potential test, is also known as the Dielectric-Withstand test. This evaluation is critical for assessing the insulation condition of various test objects, including transformers, switch-gear, relays, generators, lightning arresters, bus-bar, cables, and DC high voltage capacitors. The Hipot test ensures that no current flows between points and gauges the insulation's ability to endure high voltage and over-voltage transients. Consequently, the Hipot test is a potent tool for identifying defects caused by substandard workmanship in electrical products.

To avert insulation breakdown during operation—which could lead to disastrous consequences for both personnel and machinery—this test is generally performed during manufacturing, installation, acceptance, routine maintenance, and repair activities. By conducting these assessments, managers can make informed decisions regarding quality control of electrical equipment.

Hipot tests serve the purpose of identifying:

Nicked or Crushed Insulation
Stray wire stands or braided shielding
Conductive or corrosive contaminants
Terminal spacing issues
Reductions in creepage and clearance
Improper cable joints and terminations

How is Hipot Testing Done?

Hipot tests involve applying overvoltage to a device under test (DUT) for a limited time, verifying the dielectric integrity of the system. This testing can utilize AC, DC, or Very Low Frequency (VLF) test voltages. This blog elaborates on both AC and DC Hipot testing, outlining the parameters essential for selecting the appropriate test kit for a specific test object.

Guidelines for Hipot Testing

IEC serves as the standard applicable to Hipot testing. According to this standard:

Basic test voltage: 2*(operating voltage) + 1 kV
Test duration: 1 minute

Additionally:

For more 160KV DC hipot tester information, please contact us for professional assistance.

As a general rule, if the DC Hipot test is conducted on an AC circuit, the Hipot voltage should be two times the peak (2 * 1.4 * RMS) + 1kV.
An additional 1 kV is applied to ensure the DUT insulation can withstand daily transient overvoltage.
A DUT passes the test if either the measured leakage current is below the maximum allowed or if no breakdown, denoting uncontrolled current flow, occurs.

Pre-Testing Arrangements for Hipot Testing

Ensure proper grounding of the instrument's body.
Gather previous test data and logs for reference.
Ensure the testing area has adequate lighting.
Use a wooden bench or table to position the equipment.
Ensure a properly earthed mains power supply.
Inspect the instrument's test lead set for wear and tear.
Have a Multimeter available for continuity tests of test leads.
Utilize a discharge rod before physically handling the test object.
Wear HV gloves, safety glasses, a helmet, and safety shoes for personal protection.
Operators should stand on a high-voltage insulated rubber mat during operations.
Verify proper earthing; additional earth spikes may be needed.
Maintain a safe distance from HV terminals while applying high voltage.
Use audio-visual warnings and barricades to alert individuals when injecting high voltage.

Steps of Hipot Testing

Step 1: Open circuit breakers or switches to isolate the DUT from both ends.
Step 2: Use a discharge rod to discharge all conductors.
Step 3: Place CAUTION labels/barricades around the high voltage testing area.
Step 4: Connect the Master Earthing Terminal of the Hipot to an appropriate System Earthing.
Step 5: Connect the Operational Earthing Terminal (LV terminal of the kit) to safety ground (Body Earth).
Step 6: Confirm proper connections.
Step 7: Attach the HV terminal of the kit to the conductive part of the test object.
Step 8: Conduct testing of all circuit phase conductors against the ground based on established voltage, duration, and current settings.

When these steps are complete, ensure the following:

The voltage difference between conductors should produce observed current flow without breakdown in air or solid insulation.
Furthermore, current should not exceed 5mA peak (3.5mA RMS).
To PASS the test, the test object must endure a minimum predetermined voltage stress for 1 minute (or other duration per DUT standards) without signs of breakdown.

Conclusion

Through these processes, Hipot testing guarantees the safety, quality, and reliability of essential electrical equipment. When selecting the optimal Hipot test kit, consider the following parameters:

Application: AC/DC/AC-DC based on the DUT.
Combined or separate control unit depending on voltage levels.
Output voltage requirements of the Hipot test kit per the DUT's rated voltage.
Leakage current range benchmarks of the Hipot test kit in line with DUT recommendations.
Timers.
Trip current settings.
Volt-meters & Amp-meters for output parameters.
Safety features like external interlocks, beacons, or buzzers.

SCOPE's Hipot test kits are purpose-built, and our feature set distinguishes our offerings from our competitors.

For more information on SCOPE Hipot testing capabilities, visit https://www.scopetnm.com/test-and-measurements/other-products/hi-pot-series or reach out to us.

DC Hipot Test Methods