Tightened reliability requirements for the electricity distribution are causing distribution system operators to improve the quality of supply by renovating the network. To achieve a weather-proof distribution network by the end of year 2028, major investments must be made by means of replacing overhead lines with cables and increasing the level of automation in the network. Since the renovation process is rather slow and expensive, DSOs must obtain cost savings in distribution network operation by utilizing existing network automation more efficiently. One of the main solutions is to automatize the fault management and thereby reduce outage duration experienced by the customer.
Traditional fault management comprises the co-operation of the network control center and field crews working along the distribution network. An increasing amount of network automation, such as remote-controlled disconnectors, sectionalizing reclosers and fault detectors, is improving the response time of medium network faults when the operator can isolate the fault remotely from the control center. However, multiple simultaneous faults in major electricity disruption can cause personnel of the control center to be overburdened with fault handling and dispatching field crews. Therefore, automatic Fault Location, Isolation, and supply Restoration (FLIR) functionality is considered as a beneficial tool to assist the network operator. While the FLIR performs the first steps of fault management, operator is freed to conduct the operation of field crews repairing failures.
MicroSCADA Pro is a product family for electricity distribution control and supervisory by ABB. The current version of MicroSCADA Pro DMS600 4.5 already includes functionality for automatic fault isolation and supply restoration, but it is not used by any DSOs due to functional imperfections. The current fault detection, isolation and supply restoration (FDIR) functionality requires an exact fault location inferred by fault current measurements or fault indicator operations and therefore, it can rarely operate due to lack of initial data. To achieve an efficient operation, a trial switching sequence must be introduced as part of the existing functionality. The method of trial switching is normally used by the operator when fault cannot be located according to measurements and indications. A basic principle of the trial switchings is to divide faulty feeder into minor sections and close the substation circuit breaker against the suspected fault. This is continued until the circuit breaker trips and the fault has been located and isolated into a single disconnector zone.
The research for this thesis was carried out by interviews for Finnish DSOs to gather requirements and restrictions for the FLIR functionality. The main objective of the interview process was to familiarize the fault management process of a network control center operator, so as human-like operation of the FLIR could be obtained. Interviews gathered the most important development needs and possible restrictions to ensure the most fluent operation between automation and the network control center operators. For example, automation may not be wanted to restore supply from adjacent feeders during major disturbance, since multiple fault can occur and cause also backup feeder to trip and increase the faulty area. Automatic functionality should not also disturb the operation of network control center, and thus separate fault handling areas should be determined for FLIR to operate
