English title

Conventional fault location methods using voltages and currents of one terminal are not applicable to multiterminal transmission lines. So far some techniques have been presented to solve fault location problem for multi-terminal transmission lines. In these methods, lumped or distributed frequency domain models of transmission lines have been used. In multi terminal lines, faulty section should be detected before fault location estimation. In this paper, a method based on time domain model of transmission line is presented to identify the faulty section and to determine the location of faults for three-terminal transmission lines. In the suggested method, samples of voltages and currents at all three terminals are used for calculating the location of the fault. The proposed algorithm is independent of fault resistance, insensitive to load current and fault inception angle. Furthermore, in the method neither any knowledge about source impedance nor the fault type classification is required. Filtering of dc and high frequency components of voltages and currents signals are not necessary. The simulation results, using EMTP/ATP and MATLAB software, confirm the accuracy and precision of the proposed method.

Transmission system is one of the most important parts of the restructured power system. Insufficient or inappropriate expansion of transmission system is considered to be a major barrier to competition in electricity market. Therefore many researches have been focused on developing suitable approaches for transmission expansion planning in deregulated power systems.
This paper presents a new approach for transmission expansion planning in long term based on dynamic modeling while the method is based on the maximization of the social welfare; it also considers the view point of system policy maker through weighting generating units. The suggested method can be efficiently used for systems which are in the way of experiencing restructuring. The suggested method is tested on IEEE 14-bus system and the results are discussed.

In a realistic and large power system, the overcurrent relay coordination problem considering different network topologies and different location of faults is stated as an optimization problem with a large number of constraints. In this paper, a new index is proposed to detect and remove the inactive inequality constraints in relay coordination problem. This index is defined for each relay pairs, as the ratio of the variation of fault current passing through the primary relay to the variation of fault current passing through the backup relay. The proposed index is independent of the overcurrent relay characteristics and current and time multiplier settings of the relay, which is the most significant feature of this index. For IEC relay characteristic, it is shown that without the solving the coordination problem, the proposed index can distinguish the active and inactive inequality constraints. The 14-bus and 30-bus IEEE test systems are used to verify the performance of the proposed index. The presented results show that greater than 90 percent of the inactive constraints can be detected and removed from the set of constrains by using the proposed index. 

Encourage people to investment in small-scale electricity generation and expansion of dispersed generation (DG) may have several advantages such as, reducing the needs for investment in power plants and transmission network developments, improving the competitiveness of electricity market and moderating the costs of electrical energy procurement. In this paper, an encouraging market rule in a pay-as-bid system is proposed to accelerate the appropriate investments in DG units. The proposed rule is viewed and analyzed from the perspective of DG investor and Independent System Operator (ISO) using a novel DG placement and sizing algorithm based on Monte Carlo and Genetic Algorithm (GA). The proposed algorithm is implemented on IEEE 30-bus test system under the encouraging rule and the simulation results are presented and discussed.

Accurate locating of fault in power distribution system (PDS) can significantly improve the reliability indices. In this paper, a new simple and practical method is proposed for estimating the section and distance of fault in PDS. In the proposed method, at first the protective devises are allocated and then specially set in such a way that they are coordinated and the unique current pattern is generated at the beginning of feeder for fault in each section. For approving and analyzing the accuracy of the proposed method, the method is tested on two test feeders and one real feeder of Bushehr Distribution Company under different fault conditions. Also, in the real test system two actual faults are applied and the section of fault is correctly determined by the proposed method.

In this paper, at first, the non-detection zones (NDZ) of under/over voltage relay have been determined for constant current inverter based DG and then, an islanding detection method is presented using this relay. In the presented method, the DG direct current reference has a fixed value in normal condition, if the point of common coupling (PCC) voltage changes, I_dref is determined as a linear function of PCC voltage. In this method, I_dref is determined in terms of I_dref0 and local load direct current axes adaptively. The proposed method is evaluated in islanding and non-islanding conditions, using PSCAD/EMTDC and MATLAB software. Simulation results show that the proposed method has a proper operation in the islanding and non-islanding conditions.