Identifying Conductor Slap and Mitigating Impact On Distribution Systems

Consumers Energy investigates circuit lockouts that are identified by the line crews as “No Cause Found.” As these events were analyzed, a trend emerged. The majority of these events involved a line-to-line fault, followed shortly by a higher magnitude line-to-line fault on the same two phases. Consumers Energy concluded that these events were caused by conductor slap. Conductor slap could result in customer outages and extended outage times, as line crews patrol for a fault that is no longer on the system. Mitigation options were evaluated to find a solution that could be implemented easily across their system. Mitigation options can include structural changes or changes to protection, including clearing times and reclosing. Consumers Energy revised their reclosing standard to allow their system to recover after a conductor slap.

Consumers Energy’s existing reclosing standard is three trips to lockout (one fast trip and two delayed trips) with reclose time delays of two seconds then two seconds (2 sec, 2 sec). Two second reclose delays can amplify conductor movement and do not allow the conductor swinging to decay before reclosing. Consumers Energy created a new reclosing standard for substation reclosers which includes an additional reclose shot and extended reclosing times. The new reclosing standard is four trips to lockout (one fast trip and three delayed trips) with reclose time delays of five seconds, then fifteen seconds, then twenty seconds (5 sec, 15 sec, 20 sec). Having the substation recloser set with four trips to lockout and line reclosers set with three trips to lockout will help mitigate substation lockouts due to a marching fault.

The extended reclose time delays will allow more time for conductor swinging to settle before reclosing. The reclose time delay after the first trip is set shorter at five seconds because conductor slap is unlikely after a fast trip (there is less conductor movement with a shorter fault duration). The longest reclose time delay was chosen to be twenty seconds because there needed to be a level of comfort and confidence that the line reclosers will not automatically reset. Consumers Energy’s electronic line reclosers will automatically reset after thirty seconds (when the recloser is in the closed position and no current above an overcurrent minimum trip setting is detected).

In conclusion, Consumers Energy’s mitigation solution has greatly enhanced the system’s ability to recover after a conductor slap event. This solution does not prevent conductor slap from occurring on the distribution system, however, this solution was cost-effective and could be implemented system-wide in a short period of time. Consumers Energy has observed a reduction in circuit lockouts due to conductor slap and all types of temporary fault conditions.