A New Method for Fault Current Limiting and Voltage Compensating in Power Systems Using Active Superconducting Current Controller

In this paper, a new method for both fault current limiting and voltage compensating using Active Superconducting Current Controller (ASCC) is proposed. The main objective of this paper is to present an appropriate control strategy for ASCC to achieve both the fault current limiting and voltage compensation purposes. Three different operating modes are defined for ASCC including normal mode, fault current limiting mode, and voltage compensation mode and a proper control strategy is designed for each mode. For the fault current limiting, the model of a typical three-phase system with ASCC is simulated and different states for current limiting in different levels are defined. Also, for the voltage compensating mode, the PI model for the line is considered and the line transmission matrix is obtained when the ASCC is connected at the sending end and middle of the line. Finally, proper settings for ASCC are determined such that the magnitude of the receiving end and the sending end voltages become equal. Simulation results using MATLAB software confirm the proper performance of the proposed method

Entropy generation of pseudo-plastic non-Newtonian nanofluids in circular duct under constant wall temperature

In this paper the second law analysis of thermodynamic irreversibilities in pseudo-plastic non-Newtonian nanofluids through a circular duct under uniform wall temperature thermal boundary have been carried out for laminar flow condition. This nanofluid consists of sodium carboxymethyl cellulose (CMC)–water and two different types of nanoparticles; namely, CuO and Al2O3. Entropy generation is obtained for various Power law number, various volume concentration of nanoparticles, various dimensionless temperature and various Reynolds number. It is found that with the decreasing Power law number and duct length values, total entropy generation at fixed Reynolds number decreases and with increasing wall temperature values, total entropy generation increases, also entropy generation decreases with increasing volume concentration of nanoparticles

A New Algorithm for Protection of Small Scale Synchronous Generators Against Transient Instability

Today, installation of small generators has been increased because of their considerable benefits in distribution systems in distributed generation. One of the most important problems for transient stability is the effects of the faults of system. Small scale generators have low constant inertia and protection relays have slow performance in distribution systems. Therefore transient instability is a probable phenomenon for the systems with these generators. In this paper, dynamic response of generator has been studied in different fault conditions and then by introducing the concept of " critical fault clearing time ", the sensitivity of this time to the fault type and also fault location parameters have been studied. Then a new protection scheme has been proposed to prevent of transient instability for small scale generator. This protection scheme uses a new evolutionary algorithm based on the active power of generator and critical fault clearing time. The proposed relay can prevent of wrong and unwanted performance. Furthermore it can disconnect the generator from the system in three phase fault near of the bus-bar before its instability. Simulation results show reliable performance of the proposed relay against system transients

Feasible Islanding Operation of Electric Networks with Large Penetration of Renewable Energy Sources considering Security Constraints

The high penetration of Renewable Energy Sources into electric networks shows new perspectives for the network’s management: among others, exploiting them as resources for network’s security in emergency situations. The paper focuses on the frequency stability of a portion of the grid when it remains islanded following a major fault. It proposes an optimization algorithm that considers the frequency reaction of the relevant components and minimizes the total costs of their shedding. The algorithm predicts the final frequency of the island and the active power profiles of the remaining generators and demands. It is formulated as a Mixed-Integer Non-Linear Programming problem and the high computation time due to a large-size problem is mitigated through a simplified linear version of the model that filters the integer variables. The algorithm is designed to operate on-line and preventively compute the optimal shedding actions to be engaged when islanding occurs. The algorithm is validated for a typical distribution grid: the minimum amount of shedding actions is obtained while the most frequency reactive resources are maintained in operation to assure a feasible frequency. Finally, time-domain simulations show that the optimal solution corresponds to the one at the end of the network’s transients following the islanding