TDR Tutorial and Riser Bond TDR Product Review
Applications
POWER
A TDR can be used on any metallic two conductor cable, including power cable. Power cable presents some unusual challenges for a TDR.
Working with high power cable can be dangerous and even fatal. Exercise extreme caution when working with high power cable. Make sure all power is removed from the cable before proceeding.
There are two major problems when finding fault in powered cable: correct VOP and a quality connection. Power cable is seldom, if ever, required to carry high frequency signals, therefore VOP is not specified. The VOP between two power conductors and the VOP between conductor and concentric neutral will be different . Therefore, determine VOP by the same techniques used to find the fault.
Test the cable from both ends. Change the VOP setting until the two measured distances equal the total length of the cable. You now have the correct VOP and the location of the fault. The second way is to measure the full length of two of the good conductors and adjust the VOP setting until the right length is shown on the TDR. Then measure the bad conductors with this same VOP setting and find the distance to the fault.
Power cable is physically very large and obtaining a good connection can be difficult. Making a good connection requires the technician to pay close attention to detail. It is best to keep the conductors as close together as possible to ensure a quality test.
Power cable can actually be tested in two different ways; one power conductor against another power conductor (twisted pair concept) or power conductor as one conductor and concentric neutral as the other conductor. The latter technique allows the testing of the quality and integrity of the concentric neutral.
A lot of time and energy is spent testing power cable with high voltage breakdown testers. This is time consuming, expensive for the equipment, and can actually damage the cable. Many times, simply testing with a TDR in the first place will find many power cable faults. The TDR is a simple, fast, and inexpensive way for finding many faults.
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