Fault Current Limiters

At this time, the management of fault current in the modern transmission and distribution (T&D) systems is considered as a challenging issue within researchers and government and private electric utilities. Since some of the existing systems and most of the future systems would face with high fault current level. The potential world economic growth in recent decades and consequently the demand for electric energy are the main reasons for this problem. It is evident that the electricity utilities should be continuously upgraded their systems to handle the demand. The construction of new power plants, the interconnection of the networks, the application of distributed generations (DGs), and the utilization of parallel transmission lines and flexible AC transmission system (FACTS) are some of the upgrading programs. In addition to demand response, these activities pursue the important power system facets such as higher efficiency and reliability, longer service availability, and dwindling power loss, maintenance and development costs, environmental effects, and dependency on fossil fuels.

In the attempts to develop an FCL that satisfies the requirements of the power system, a large number of FCL technologies have been proposed by researchers and companies. Proposing novel topologies or improving the previous structures based on depth computer analysis, laboratory experimental tests, and live-grid deployment are the consequence of these activities. Several categories have been proposed in papers, standard, and technical reports to classify FCL structures [1, 2, 8, 11, 12]. IEEE standard divides FCLs into two sets consisting of Type A and Type B. The FCL capability to the current interruption is the distinct property between Type A and Type B. The former is only capable to limit fault current, whereas the latter is able to interrupt fault current as well as current limiting. In other words, Type B plays the role of FCL and CB. In a more detailed classification, they individually have two subsets namely Type A1, Type A2, Type B1, and Type B2. The insertion impedance by Type A1 and Type B1 into the system is linear during fault conditions, whereas the nonlinear impedance is provided by Type A2 and Type B2 FCLs. This issue can be graphically illustrated with the help of Fig. 2.1. It should be noted that the experimental waveforms have more distortion.

The power system has generally three main sections including power generation, transmission systems, and distribution systems. The high short circuit level will threaten all three parts of the future power system. Hence, all sections of the power system can be equipped with FCL in terms of short circuit level. In order to achieve the benefits offered by FCL in the power system, the optimal placement of FCL is required

FCL as a new power system device may affect other aspects of the power system performance. The important prerequisite is to evaluate different aspects before the permanent installation. In critical cases, it is needed to consider some remedial actions. Many researches have been carried out to evaluate the interaction between FCL and power system since the emerging of FCL technology. The results are available in published papers and technical reports. Regarding the importance of the subject, the following issues should be taken into consideration when FCL is applied in the system.