This is what a falling conductor looks like

Look closely at the waveform captures in Figures 1 and 2. You can easily pick out four distinct fault transients. What is more difficult to see is what happens a slightly more than one second in to the event: current on one phase drops suddenly - 39% of the current on the C-Phase conductor, to be precise. See the zoomed in waveforms in Figures 3 and 4.

Figure 1. Complete falling conductor event current waveform

Figure 2. Complete falling conductor event, RMS current

Figure 3. Sudden loss of partial load on phase C

Figure 4. Sudden loss of partial load on phase C with other phases removed

After 48 cycles the first overcurrent fault occurs. During this 0.8 second time the conductor is in free-fall, finally contacting either the ground or some other conducting material and causing a protective device to operate four times.

Our objective is to take a waveform like this and extract as much insight as possible. In this case the DFA report indicated the following information:

• Possible broken conductor has occurred on Phase C

• Protective devices operated four times, with de-energized time between shots of 1.3, 1.4, and 1.4 seconds

• Total time exposed to fault current (maximum 1610 Amps) was 14.5 cycles

• Fault durations beginning with the initial transient, followed by three additional shots, were 1.5, 2.0, 4.0, and 7.0 cycles.

• We were later able to add that service restoration occurred about 30 minutes later, with a link to a capture and analysis of that event.

Figure 5. Sequence of event

Figure 5 graphically illustrates the sequence of event for this incident, making it easy to understand at-a-glance. Figure 6 shows the condensed summary of the event analysis automatically performed by DFA and presented to the user. This analysis summary delivers a lot of information in a very compact space, clearly calling out the potential of a broken conductor, how much load was lost, and conductor fall time. It also provides phase involvement, general event classification, fault data designed to help the user determine what happened, especially when a non-communicating or older hydraulic recloser is involved.

Figure 6. Condensed event analysis

You can draw additional interesting insight from this event. Each fault transient is different. This may be an indication the fault is "mechanically unstable": moving about as it makes its way toward the ground through any obstructions it encounters.

This is just one of the events DFA classifies every day. If you found it interesting, consider signing up for emails. We'll deliver information like this right to your inbox. If you have any questions please don't hesitate to send them to us at info@powersolutionsllc.us.