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Nowadays, the identification and mitigation of power quality (PQ) disturbances are very important issues for electric companies and industries. In this paper, a new method is presented for the classification of PQ disturbances. At first, the proposed characteristics are extracted from the waveforms of the disturbances using S-transform (ST). Then, based on the values of these characteristics, the types of the disturbances are determined. This method is evaluated under noisy and noiseless conditions on a database of 7000 simulated waveforms describing fourteen types of PQ disturbances, which include impulse, interruption, swell, sag, notch, oscillatory transient, harmonic, and flicker as single disturbances with their six possible combinations. The results of this study demonstrate the acceptable accuracy of the proposed method in identifying the disturbances in addition to its very low sensitivity under various noisy conditions. [ABSTRACT FROM AUTHOR]

A novel simple method is suggested in this paper to evaluate the contributions of the sources (including the generators and branches’ charging capacitances) or the loads to the branches’ reactive flows and losses separately as well as to calculate the sources’ shares in providing the loads’ reactive powers. In the method, the study system is first converted to the system, each branch of which only has reactive loss, using a new technique for modeling the generating branches based on the AC load flow results. The properties of two new matrices (i.e. injection-bus and absorption-bus matrices), which are constituted for the obtained system, are then used to derive three other matrices. These matrices, which express reactive power productions of the sources in terms of reactive power consumptions of the demands (viz. the loads and branches’ losses) and vice versa, contain the intended contributory factors. Three-bus system is applied to demonstrate the computing process of the method whereas several IEEE systems are used to show its capability to implement on the transmission systems with arbitrary topologies and sizes. Some advantages of the method compared to the earlier methods are also illustrated. [ABSTRACT FROM AUTHOR]

In a deregulated electric power system, it is important to distribute transmission losses between market participants fairly. This paper presents an effective method for active loss allocation by tracing power flow. In this method, after obtaining the alternating current (AC) load flow results of the system, it is first converted to a system in which the power flow is constant along each branch. A new matrix (i.e., power adjacency matrix) is then constructed for the system. The matrix is decoupled, and matrix operations are carried out using the submatrices to derive three other matrices. The contributions of the generators and loads of the main system to active losses of its branches and the shares of the generators in active power consumption of the loads are specified using these matrices. The proposed method is implemented on a four-bus system and several standard test systems. The results show that the method can be applied to any transmission system, and the loss allocation results are preferable to that of previous methods. [ABSTRACT FROM AUTHOR]

Power flow tracing is the most effective method for the fair apportioning the transmission losses to the users of the restructured power systems. In this study, a simple method is proposed to trace the active power flows. In the proposed method, for a given operating point obtained by the AC load flow, the so‐called injection‐bus and extraction‐bus matrices are formed for the system. By using the properties of these matrices, three other matrices are derived, which allow the active power production of the generators to be expressed in terms of the active power consumption of the loads, and vice versa. These matrices provide the opportunity to determine the contribution of each generator to active loss of each branch and active power consumed by each load as well as to allocate the active loss of each branch to each load. Implementation of this method on several systems with different topologies and sizes show that it can provide acceptable and reasonable results for loss allocation problem in a short time. [ABSTRACT FROM AUTHOR]

• New two-stage approach is proposed to prevent blackout by determining the time and scheme of intentional islanding. • The online algorithm distinguishes the coherent groups of generators without needing to the pre-selected number of groups. • New index is introduced to recognize the appropriate time of islanding through comparing its value with zero. An effective strategy for intentional islanding of a transmission system is proposed in this paper to boost its resilience under low-probability high-impact events such as man-made attacks and natural disasters, which can cause catastrophic blackouts. This strategy considers two main aspects of islanding, i.e. time and scheme. To realize the appropriate time that the system need to be intentionally islanded, a new algorithm based on analysis of the rotor angles of its generators is first presented to distinguish coherent groups of the generators. The main advantage of this algorithm is its independence to the predefined degree of coherency and number of the groups. The information obtained by grouping the generators is then used to compute a new defined indicator, whose sign change specifies the islanding time. To decide about the lines that must be disconnected for fulfillment of the islanding scheme, the initial islands are first formed by tracing the active power produced by the generators. Then, the intended scheme is devised by solving a binary linear programming (BLP) problem that minimizes the disruption of the power transferred between these islands. Comparing the proposed scheme with some existing ones shows that the proposed strategy splits two IEEE test systems into stable islands with a better voltage profile and lower imbalance between the active power generation and demand by disconnecting fewer lines, which have smaller amounts of the power flows. [ABSTRACT FROM AUTHOR]