Cable Testing Comes of Age – One Cycle at a Time

By By Craig Goodwin, President: HV Diagnostics Inc

Field Testing of MV and HV cables has come a long way in recent decades. Gone are the days of old, when the traditional DC (Direct Voltage/Current) hipot was the recommended method for testing these modern cables that form the critical backbone of the distribution electrical power network. Extensive research, often rooted in the hard lessons learned through negative experiences in the field, has brought about changes to and improvements in the approaches and methods used when testing MV and HV cables.
The traditional high voltage “DC Hipot” and/or the routine insulation resistance measurement may still be a viable and useful technique for testing various types of electrical apparatus. However, when it comes to shielded MV and HV cables, this approach has been found to be seriously lacking and, in some cases, potentially damaging to the cables themselves. The latest IEEE400 clearly states that high voltage DC should not be used on extruded cables. Critically significant research around the world and focused studies like the CDFI project led by the National Electric Energy Testing Research and Applications Center (NEETRAC) at Georgia Tech has allowed International Standard bodies, such as the IEEE, to lead the way in prescribing better testing and diagnostic methods and guidelines for detecting abnormalities in MV and HV cables and/or their accessories.
AC (Alternating Voltage/Current) has effectively replaced the DC method for testing these cables. While technically beneficial to the test engineer in evaluating the true condition of these cables, this change also introduced some practical challenges to the test equipment and users involved. This is mainly because shielded MV and HV Cables are effectively very large capacitors, capable of storing large amounts of electrical charge – their capacitances getting larger with the length of the cable. Energizing the cable’s capacitor, while relatively easy with DC, is not as simple with AC due to the excessive and continuous reactive power demands AC requires. These power demands increase with cable length, frequency of AC and applied voltage.

Read full article in the SPECIAL HV Electrical Testing ISSUE.

HV Diagnostics Inc advertisement in the issue:
“Find Weak Cables… BEFORE They Fail!”

SOURCESPECIAL HV Electrical Testing ISSUE. Electricity Today Magazine. 2020 Volume 33, No.1
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Craig Goodwin is President of HV Diagnostics Inc – a worldwide leader in developing, training, servicing and supplying cable testing and diagnostic equipment for the industrial, utility and the power generation industries. Craig holds a BSc in Electrical Engineering and has spent the last 30 years working in the fields of cable testing, fault location and cable diagnostics both in field application and research environments. Craig has worked on cable research projects with organizations such as EPRI, NEETRAC-GA Tech, and Department of Energy (DOE). Craig is a member of the working group committees for the IEEE400, IEEE400.2, IEEE400.3, IEEE1234, and other standards covering the field testing of medium voltage shielded power cables. Craig has also worked with and presented at several of the NETA technical conferences. Craig has authored several technical presentations and papers and is an active member of the IEEE, ASTM and ICC standards committees.