A hi-pot for locating shorts????
Wrong tool for the job.
1) Hi-pot testing is considered destructive testing. It is entirely possible to damage the cable under the test.
2) Destructive testing is falling by the wayside. Non destructive tests are taking it's place. Time domain reflectivity and ELF tests are now dominating the avante guard testing market.
3) Hi-pot testing is not a one shot deal. Since the test is designed to measure insulation integrity, not as a troubleshooting means, each test consists of varying voltages and measuring the leakage over time in order to create a graph that is illustrative of the integrity of the insulation. The first test after installation is the base for further tests as time goes by to monitor the degradation of the insulation.
4) Hi-pot testing is dangerous. A 15kV cable should be tested at around 75kV with the exact test voltage dictated by the engineering department of the cable manufacturer. For instance, I tested an 18kv iso-phase conductor at 63.5kV based upon the engineering standards. Rule of thumb would have been too high, but still, when the tester is doing it's thing, hundreds of feet of conductor is charged to several times it's nominal rating with a possibly fatal amount of electricity.
5) Hi-pot tests leave residual charges sometimes lasting for several minutes, even when a drain is connected. We had one long run of high voltage DC cable that still had several hundred volts in it after a 15 minute drain. Remember, shielded cable is not just wire, it is a HUGE capacitor.
That being said, you should use something else to locate the short. A megger would be better and I have a DVM that measures down to 2 meghoms that works great and is over half as accurate as a hi-pot and uses far less voltage, reducing the chances of damaging the insulation.
Once the short is located and repaired, THEN it's time to use the hi-pot if and only if the maker of the cable is in favor of it and gives you the proper test voltage and plotting parameters. The biggest problem would be that if you don't have access to the original test results, the results you get may have little or no value. If all you are looking for is a pass or fail, a megger may indeed be a better tool.
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When it comes to high voltage (HV) cables testing, HiPot testing is a widely used methodology. HiPot tests help to detect any insulation faults or weaknesses that could later impact the performance and safety of the cable. Two commonly used tests are the High Voltage AC and DC Hipot test.
The main difference between the two tests is that High Voltage AC Hipot test applies an alternating voltage to the cable at a frequency between 50 to 60 Hz. On the other hand, a High Voltage DC Hipot test applies a direct voltage to the cable.
When compared, High Voltage DC Hipot test is known to be a more effective test for HV cables as a DC voltage test can help detect more faults in the system due to its ability to penetrate deeper into the insulation. AC voltage, on the other hand, may clear some corona or partial discharges than with DC voltage, thus may not show up all the time.
One advantage of the AC Hipot testing is that it is less likely to cause irreversible dielectric breakdown in the cable insulation. This is because the sinusoidal waveform of AC voltage allows for charge to be dissipated along the cable insulation, minimizing the formation of any potential voids or weak areas which may lead to dielectric failure. AC voltage also has the added benefit of being able to test both the insulation and the cable's shield and/or jacket simultaneously.
On the other hand, one downside of AC Hipot testing is the limited ability to detect certain types of cable defects. For example, AC Hipot testing is not able to reveal small pinholes in the insulation or impurities in the cable material.
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In terms of DC Hipot testing, one of its major advantages is its ability to detect and reveal such defect types as pinholes, voids, impurities, and other types of gas inclusions which may be present in the cable insulation. DC voltage also readily penetrates through the insulation and reaches the conductor, making it useful for detecting surface contamination on the conductor.
However, one disadvantage of DC Hipot testing is that it may cause irreversible damage to the cable insulation if care is not taken. This is because DC voltage does not easily dissipate through the insulation as it does in AC voltage, and thus has the increased potential to cause partial discharges and dielectric breakdown if proper precautions are not taken. Additionally, DC Hipot testing cannot test the cable's shield or jacket insulation.
Leakage current is another important consideration for both AC and DC Hipot testing. With AC Hipot testing, the cable capacitance and the test voltage frequency interact to produce a capacitive current that is typically measured to assess insulation performance. However, leakage current measurement becomes more critical with DC Hipot testing due to the constant high voltage applied.
DC Hipot testing cables must be monitored closely for leakage current as this method stresses the insulation material much more than AC Hipot testing. The insulation resistance and its variation over time are also measured. The measurement of leakage current is critical in determining the overall insulation health and determining whether any repairs or replacements are necessary.
In conclusion, while both AC and DC hipot testing methods have their pros and cons, and Phenix Technologies stands out as a reliable manufacturer of both systems. We have years of experience and expertise in both AC and DC HV cable testing. Our AC and DC hipot testing systems are designed to be safe and effective in detecting and locating various types of cable defects.
We understand that choosing between AC and DC HV cable testing can be a tough decision. In addition, you may find yourself confused when selecting the appropriate testing equipment for your needs. That's why we're here to help! We can even offer a combination of AC/DC testing units. This versatile equipment is universal and can be used up to the range of 100 kV AC/ 120 kV DC cable testing. By combining these two types of testing, we can offer you a much broader range of testing capabilities, ensuring that all your needs are met.
The company is the world’s best DC hipot tester for insulators supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.