Fault Location, Isolation and Network Restoration as a Self-Healing function

One of the main emphasis of the smart grid is the interaction of power supply and power customer in order to provide a reliable supply of power as well as to improve the flexibility of the network. Along with this, the increased energy demand, coupled with strict regulations on the quality and reliability of supply intensifies the pressure on distribution network operators to maintain the integrity of the network in its faultless operation mode. Additionally, regardless of the huge investments already made in replacing aging infrastructure and translating “the old-fashioned grid” in a “Smart Grid” to minimize the probability for equipment failure, the chances of failure cannot be completely eliminated. In accordance, in the event of faults in the network, apart from the high penalty costs in which network operators may incur, certain safety factors must be taken into consideration for particular customers (for example, hospitals). In view of that, there is a necessity to minimize the impact on customers without supply and maintain outages times as brief as possible. Within this scenario comes the concept of self-healing grid as one of the key-technologies in the smart grid environment which is partly due to the rapid development of distribution automation. Self-healing refers to the capacity of the smart grid to restore efficiently and automatically power after an outage. Self-healing main goals comprise supply maximum load affected by the fault, take the shortest time period possible for restoration of the load, minimizing the number of switching operations and keeping the network capacity within its operating limits. This research has explored insights into the smart grid in terms of the self-healing functionality within the distribution network with main emphasis on self-healing implementation types and its applicability. Initially a detailed review of the conception of the smart grid in order to integrate the self-healing and thus fault location, isolation and service restoration capabilities was conducted. This was complemented with a detailed discussion about the electricity distribution system automatic fault management in order to create a framework around which the aim of the research is based. Finally the self-healing problem coupled with current practical implementation cases was addressed with the objective of exploring the means of improvement and evolution in the automation level in the distribution network using Fault Location Isolation and Service Restoration (FLISR) applicability as a medium

Wide-Area Backup Protection Against Asymmetrical Faults Using Available Phasor Measurements

This paper proposes a robust and computationally efficient wide-area backup protection (WABP) scheme against asymmetrical faults on transmission systems using available synchronized/unsynchronized phasor measurements. Based on the substitution theorem, the proposed scheme replaces the faulted line with two suitable current sources. This results in a linear system of equations for WABP, with no need of full system observability by measurement devices. The identification of the faulted line is attributed to the sum of squared residuals (SoSR) of the developed system of equations. To preserve accuracy, the scheme limits the calculations to the assessment of the negative-sequence circuit of the gird. Relevant practical aspects that have not been properly addressed in the literature, namely the non-simultaneous opening of circuit breakers (CBs) and their single-pole tripping for single-phase to ground faults are investigated. The linearity of the formulations derived removes concerns over convergence speed and potential time-synchronization challenges. The proposed scheme is able to identify the faulted line and retain this capability for hundreds of milliseconds following the fault inception. More than 20 000 simulations conducted on the IEEE 39-bus test system verify the effectiveness of the proposed WABP scheme

Improving reliability on distribution systems by network reconfiguration and optimal device placement.

Masters Degree. University of KwaZulu-Natal, Durban.A distribution system without reliable networks impacts production; hinders economy and affects day to day activities of its customers who demand uninterrupted supply of high quality. All power utilities try to minimize costs but simultaneously strive to provide reliable supply and achieve customer satisfaction. This research has focused on predicting and thereafter improving the South African distribution network reliability. Predictive reliability modelling ensures that utilities are better informed to make decisions which will improve supply to customers. An algorithm based on Binary Particle Swarm Optimization (BPSO) was implemented to optimize distribution network configuration as well as supplemental device placement on the system. The effects on reliability, network performance and system efficiency were considered. The methodology was applied to three distribution networks in KwaZulu-Natal, each with diverse topology, environmental exposure and causes of failure. The radial operation of distribution networks as well as the practical equipment limitations was considered when determining the optimal configuration. The failure rates and repair duration calculated unique to each network was used to model the performance of each component type. Historical performance data of the networks was used as a comparison to the key performance indicators obtained from DigSILENT PowerFactory simulations to ensure accuracy and evaluate any improvement on the system. The results of a case study display improvements in System Average Interruption Duration Index (SAIDI) of up to 20% and improvements in System Average Interruption Frequency Index (SAIFI) of up to 24% after reconfiguration. The reconfiguration also reduced the system losses in some cases. Network reconfiguration provides improved reliable supply without the need for capital investment and expenditure by the utility. The BPSO algorithm is further used to optimally place and locate switches and reclosers on the networks to achieve maximum improvement in reliability for minimal cost. The results show that the discounted future benefit of adding additional protection devices to a network is approximately R27 million over a twenty-five-year period. The maximum SAIDI improvement from adding reclosers to a network was 21%, proving that additional device placement is a cost-effective means to improve system reliability

Development Needs in Automatic Fault Location, Isolation and Supply Restoration of MicroSCADA Pro DMS600

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

Progress on protection strategies to mitigate the impact of renewable distributed generation on distribution systems

The benefits of distributed generation (DG) based on renewable energy sources leads to its high integration in the distribution network (DN). Despite its well-known benefits, mainly in improving the distribution system reliability and security, there are challenges encountered from a protection system perspective. Traditionally, the design and operation of the protection system are based on a unidirectional power flow in the distribution network. However, the integration of distributed generation causes multidirectional power flows in the system. Therefore, the existing protection systems require some improvement or modification to address this new feature. Various protection strategies for distribution system have been proposed so that the benefits of distributed generation can be fully utilized. This paper reviews the current progress in protection strategies to mitigate the impact of distributed generation in the distribution network. In general, the reviewed strategies in this paper are divided into: (1) conventional protection systems and (2) modifications of the protection systems. A comparative study is presented in terms of the respective benefits, shortcomings and implementation cost. Future directions for research in this area are also presented

Model-based dynamic relaying for power system protection under uncertainty

Several major cascading outages have involved mis-operation or mis-coordination of protective relays during stressed system conditions that resulted in a vulnerable network. Such stressed conditions include concurrent high load demand, changes in circuit topology, equipment outages, and short-circuit faults. With levels of wind and photovoltaic (PV) generation projected to increase in the future, large-scale variable generation also presents an additional point of vulnerability to the existing protection system. In this work, a new framework is introduced that is built on model-based distributed relay intelligence. The framework integrates real-time measurements from adjacent buses and predictive circuit models embedded in relays. The data collected by the relay is input to circuit simulations in order to accurately predict possible fault conditions at the relay location. Settings can then be adapted in real-time based on prevailing system conditions. Several scenarios are evaluated to demonstrate the effectiveness of this approach. This work further develops a probabilistic formulation of optimal relay characteristics that adapts to the randomness and uncertainty introduced by renewable generation. In this framework, the calculation of relay operating times is formulated as a stochastic optimization problem. In addition, at the system level, a mixed-integer linear program is developed for protective device and switch allocation considering intentional islanding with distributed generation in distribution systems.Electrical and Computer Engineerin

A Review of Active Management for Distribution Networks: Current Status and Future Development Trends

Driven by smart distribution technologies, by the widespread use of distributed generation sources, and by the injection of new loads, such as electric vehicles, distribution networks are evolving from passive to active. The integration of distributed generation, including renewable distributed generation changes the power flow of a distribution network from unidirectional to bi-directional. The adoption of electric vehicles makes the management of distribution networks even more challenging. As such, an active network management has to be fulfilled by taking advantage of the emerging techniques of control, monitoring, protection, and communication to assist distribution network operators in an optimal manner. This article presents a short review of recent advancements and identifies emerging technologies and future development trends to support active management of distribution networks