• Fault Detection

    Fault Detection, Isolation and service restoration

    Fault Detection Identification and Restoration (FDIR) is a class of technologies whose goal is to identify the occurrence of a fault, record the occurrence, determine the fault location, and aid in the restoration process. It is a combination of advanced DMS & OMS systems, as well as a close integration of feeder level assets with the DMS. FDIR systems can also use automated switching, e.g. reclosers, sectionalizers and switches, to help minimize the number of customers affected by a fault.

    The FDIR system is tightly integrated with the DMS so that measured values from the shunt capacitors, reclosers, and sectionalizers are available for determining the location of the fault. Additionally, the capability exists to automatically reclose switches, reclosers, and sectionalizers, which further reduce the length of the outage. The net result is that the system operates with reclosers and sectionalizers and when a fault does occur, the time required to identify and locate the fault is reduced by 30%.

    From the analysis of FDIR the following conclusions and observations can be made:

    1) The primary benefit of the implemented FDIR is increasing reliability; it does not affect the peak load or annual energy consumption except by the isolation of system faults.

    2) When coordinated with reclosers, sectionalizers, and the DMS & OMS, the FDIR system is one of the most effective ways to increase the reliability of a distribution feeder.

    3) Because of the significant amount of equipment that must be deployed, a fully coordinated FDIR system is only necessary on systems with low reliability.

    Broadly, two technology components are required to provide FDIR capabilities. These are field devices and algorithms.

    • Field devices consist of sensors and switches - Sensors detect issues on the network, while switches are used to control the power flow in the network .

    • Algorithms are the mathematical logic that guides the switching activities when isolating equipment on the network. Switching actions proposed by software algorithms could be applied by a system and/or human operator.

     

    Figure 1 shows a typical 11 kV distribution network. When there is a fault on the network
    at the location shown, the over-current protection element in IED1 detects the fault and opens CB1. This will result in an outage at loads L1 to L5. Since there are no automated components in the network, supply restoration for a part of the network requires human intervention (crew members). Supply restoration is normally initiated by phone calls from one or more customers (in the area where outage occurred) reporting a loss of supply to the electricity supplier. Upon receiving these calls a restoration crew is dispatched to the area. It will take some time for the team to locate the fault and manually isolate it by opening SD3 and SD4. Then CB1 is closed to restore the supply to L1, L2 and L3. The normally open point (NOP) is closed to restore the supply to L5. Load L4 will be without supply until the fault is repaired.

     

    A simple method to reduce the restoration time of loads L1, L2, L3 and L4 is using a pole-mounted recloser and sectionalizer as shown in Figure 2. When a fault occurs, the recloser trips. Upon detecting the interruption, the sectionalizer, S, increments its counter by 1. After a short time delay, the recloser closes and if the fault persists, it will trip again. The counter of S increments again and it is then opened. The recloser then closes successfully. The operation of the sectionalizer facilitates restoration of supply to L1, L2, L3 and L4 within a couple of minutes. However, the restoration of supply to L5 requires the intervention of the crew. As this method does not need any communication infrastructure, it is reliable and relatively inexpensive.

     

    A greater degree of automation may be introduced by using reclosers with RTUs, with communication infrastructure between them (see Figure 3). In this scheme, an agent is employed that gathers data from all the intelligent devices in the system. During normal operation, the Agent polls all the RTUs and IEDs to establish the system status. When there is a fault at the location shown, IED1 detects the fault current, opens the CB and informs the Agent. The Agent sends commands to RTU1 to RTU4 (remote terminal units up to the normally open point) to open them and requests current and voltage data from them in real time. A possible automatic restoration method is:

    1.  Send a command to IED1 to close CB1.

    2.  Send a command to RTU1 to reclose R1. If the fault current prevails, initiate a trip but as there is no fault current, R1 remains closed. Similarly send commands to RTU2, 3 and 4 to reclose R2, R3 and R4. When R3 is closed, fault current flows, thus causing R3 to trip and lock-out.

    3.  Then send a command to RTU9 to close the normally open point.

    4. Finally, send a command to RTU4 to close R4. As the fault current flows, a trip command is initiated for R4. R3 and R4 thus isolate the fault and supply is restored to loads L1, L2, L3 and L5.