Scott Barnes, Progress Energy &
William Peterson, Jianlin Chen and Bob Fesmire, ABB Inc.
Locating faults on distribution lines has historically involved information from a variety of sources including customers, 911 emergency calls, and outage predictions from the OMS. Sometimes this information leads directly to the faulted line location. Often, however, the fault location must be found by a time consuming process of patrolling and inspecting the lines of a faulted circuit.
Progress Energy has implemented a real-time fault location system at their Raleigh Distribution Control Center that has helped reduce outage repair time by reducing the time it takes to field crews to locate faults. The system combines real-time fault current measurements with a fault location system in ABB’s outage management system (OMS) to accurately compute the possible locations of a fault on a circuit.
Progress Energy capitalized on a new DSCADA substation monitoring system and fault location system in their OMS to provide real-time fault location information to distribution repair crews. The DSCADA system includes a Feeder Monitoring System (FMS) in their distribution substations to automatically record fault current information. As part of the FMS, engineers at NCSU wrote an interface to the DSCADA system to compute fault current phasor measurements (magnitude and angle), fault type, and faulted phase(s) from real-time sampled current measurements.
Whenever a feeder lock-out occurs, the centrally located FMS automatically calls the substation RTU. Pre-fault and fault current samples are downloaded over the dial-up link by the FMS, and fault current magnitude, fault type, and faulted phases are calculated from the current samples. This information is automatically input to the OMS through an ASCII SCADA interface. The fault location system in the OMS is then automatically triggered, and receives fault current magnitude and phase measurements in real time.
The core processing of the fault location system is comprised of a short circuit analysis run on the faulted circuit to compute the available short circuit current at each node on the circuit. Nodes are points where wires make electrical connections to poles, bus work, or other equipment, and represent the locations where fault current is computed. The program then computes the possible line segments that could produce the measured fault current under fault conditions. A given line is a possible fault location if the measured fault current is numerically between the short circuit fault current available at each end of the line.
Real faults are not limited to electrical connection points and often occur at various locations along a distribution line segment. To compensate for this limitation, the program interpolates the location of the fault along the line based on the actual current measurement and fault current calculated at each line end node. The result is a more specific estimate of the fault location that can then be passed on to field crews.
Integration of the fault location program directly into the OMS distribution network model assures accurate and efficient processing of fault locations and provides for results to be presented directly to distribution network operators on their native graphical network maps. Per-phase circuit models coupled with the actual operational status of devices, along with actual wire size and material, allow fault location to be computed with a high degree of accuracy. To put this in perspective, the average Progress Energy feeder length in the Carolinas is 43 miles and the fault locations are often computed within 0.25 mile of the actual location.
Based on the system’s calculations, the OMS operator is presented with a tabular list of lines where the fault could be located, which are also highlighted on the OMS graphical map. The OMS operator then communicates the possible fault location to field crews that are dispatched to restore the resulting outage.
Progress Energy’s system has been operational for seven months in a fully automated mode, and has met with positive results. According to Richard Rackley, director of Progress Energy’s distribution control center in Raleigh North Carolina, “automated fault location has reduced customer minutes out because of the ability to locate faults faster and begin fault isolation switching sooner.” Consistently accurate results are a key factor in the program’s acceptance by field crews, who are quickly realizing that looking for the fault at the estimated locations is much faster than patrolling the circuit based on reported outage patterns.
Presently the location of faults is only computed for permanent faults that result in feeder lock-out. However, the system has recently been enhanced to compute the location of temporary faults where the feeder does not lock-out. These fault locations can be inspected at a future date for damage that may ultimately lead to a permanent fault condition.
Temporary fault data is downloaded during off-peak periods and fed automatically into the fault location system. The location process is similar to that of permanent faults except that results are not shown to the operator automatically in real time. Instead, the results are stored in the OMS database for later analysis. Changes in network topology can introduce errors to this delayed approach, but given the sheer volume of temporary faults experienced each day, the benefits of delayed processing are expected to outweigh the disadvantages.
Progress Energy’s introduction of fault location into distribution outage restoration shows that real-time network analysis can provide significant benefits in distribution operations. Utilizing dial-up communications was essential for implementing the system in a timely and economical manner.
Barnes is a senior energy management system support specialist at Progress Energy’s Carolina Power & Distribution Control Center.
Peterson is manager of power applications engineering in ABB’s utilities division; he oversees the company’s outage management products.
Chen is a senior power systems engineer in ABB’s utilities division.
Fesmire is a marketing writer in ABB’s utilities division. He can be reached at 405-615-6289 or [email protected].
