Advantages of DC hipot test compare to AC test

DC/AC Hipot, insulation test

What is the difference between and AC and DC hipot? Is DC hipot be considered as insulation resistance test as well?
We are installing a 36kV line (direct buried) and it is being tested by 10kV DC insulation test. Now the other team is requiring HIPOT test (which we dont have any info whether it is DC or AC), which from our experience is only being used with bare coppers and conductors without insulation.

Link to Hengfeng

Advantages of DC hipot test compare to AC test

One of the advantages of using a DC test voltage is that the leakage current trip can be set to a much lower value than that of an AC test voltage. This would allow a manufacturer to filter those products that have marginal insulation, which would have been passed by an AC tester.

When using a dc hipot tester, the capacitors in the circuit could be highly charged and, therefore, a safe-discharge device or setup is needed. However, it is a good practice to always ensure that a product is discharged, regardless of the test voltage or its nature, before it is handled.

It applies the voltage gradually. By monitoring the current flow as voltages increase, an operator can detect a potential insulation breakdown before it occurs. A minor disadvantage of the dc hipot tester is that because dc test voltages are more difficult to generate, the cost of a dc tester may be slightly higher than that of an AC tester.

The main advantage of the DC test is DC Voltage does not produce harmful discharge as readily occur in AC. It can be applied at higher levels without risk or injuring good insulation. This higher potential can literally &#;sweep-out&#; far more local defects.

The simple series circuit path of a local defect is more easily carbonized or reduced in resistance by the dc leakage current than by ac, and the lower the fault path resistance becomes, the more the leakage current increased, thus producing a &#;snow balling&#; effect which leads to the small visible dielectric puncture usually observed. Since the dc is free of capacitive division, it is more effective in picking out mechanical damage as well as inclusions or areas in the dielectric which have lower resistance.

Carrying out High Voltage or High Potential (Hi-Pot) DC testing on XLPE insulated cables has a tendency to 'polarize' the insulation. It can also lead to capacitive space charges within the tiny anomalies in the insulation. These space charges will eventually form water trees which will seek a path to earth. The ideal test would be a frequency (50Hz/60Hz) test but the test equipment is size and weight restrictive, especially on long lengths of cable because of the charging current required. A VLF (Very Low Frequency) test is something of a compromise, a true sine wave (ac) test but low frequency. Therefore none of the destructive qualities of a dc test.

Contact us to discuss your requirements of DC hipot test kit for electrical power cables. Our experienced sales team can help you identify the options that best suit your needs.

Difference Between AC and DC Hi Pot

DC hipot testing measures insulation resistance by applying a high DC voltage to cables and measuring leakage current. This can damage old cables during testing. AC hipot testing applies a high AC voltage and measures a higher leakage current due to cables acting as capacitors, with AC current flowing more easily through capacitors than DC. While AC hipot requires less voltage, more power is needed due to low capacitive reactance at 60 Hz. DC hipot testing is preferred over AC hipot testing for cables since using DC avoids issues with cable capacitance affecting insulation resistance measurements.

It adheres on the tenet "Honest, industrious, enterprising, innovative" to develop new items frequently. It regards buyers, success as its very own success. Let us produce prosperous future hand in hand for ground resistance tester,power factor tester,insulation resistance tester,Dc Hipot Test Kit,Resistance Tester Electric,lightning arrester tester,3 phase leakage current tester,leakage current monitor,dissipation factor tester

Hi,

High voltage test...
We test our products (power supplies) as follows.
Input to ground, output to ground, input to output if necessary, if there is galvanic isolation between the two.
Whereby ground means the housing(earthing point).
As a rule, we test this with DC voltage, which has the advantage that any capacitors against ground (EMC!) are charged once.*
If we were to test with AC, there would be a unwanted constant current flow.
The inputs/outputs are connected together to protect internal components in the event of a breakdown.
The polarity does not play a role in DC tests in the constellation, but generally minus is connected to ground, while plus is connected to the inputs or outputs.
However, we once had a case where a diode was connected in series in the input as reverse polarity protection.
In this case, minus was connected to the input, plus to ground.
Now there was a breakdown against ground and since the reverse voltage of the diode was lower than the test voltage, it broke due to the breakdown, which would not have happened if plus had been connected to the input.
Since then, plus has always been connected to the input and minus to ground.
What to do in the event of a high-voltage breakdown?
Possible causes:
- Test voltage accidentally set too high
- Tripping current set too low for DC, keyword charging of EMC capacitors against ground
- Insulation of installed cables damaged
- Insulation generally too low between the potentials
- Metal chip residue present in the housing
- Wire residues present in the housing/between the potentials due to incorrect insulation of cables.
- Humidity too high during test (creepage distance: 1mm/V)
- Rare: Defective components in the system itself

Repetitions after a failed high voltage test are best carried out with reduced test voltage, as long as this does not fall below the minimum requirement.
Reason:
The components experience a stress phase as a result of a high voltage test, which they should not be subjected to too often (shortening of service life).

For more information, please visit DC hipot test kit for motors.