Sharif Digital Repository

The size and complexity of modern power systems necessitate the use of Frequency Dependent Network Equivalents (FDNE) for part of the system. In order to give realistic simulation the frequency response of the equivalent must mach that of the system it represents. In this paper a method for developing FDNE is presented and demonstrated by approximation its admittance matrix Y by rational function in the frequency domain based on vector fitting method. The developed FDNE is accurate and efficient. An example showing the accuracy and efficiency of the developed FDNE when used to reduce a radial network is presented. ©2006 IEEE  

Recent system wide disturbances have demonstrated the need for automatic system protection schemes to prevent such cascading disturbances. In this paper, an adaptive under-voltage load shedding scheme using model predictive control is proposed to protect power system against voltage instability. The proposed scheme calculates the criticality of the system based on the measurements of voltage magnitudes and reactive power generations and then in case of voltage instability a model predictive based step-sized load shedding scheme will be triggered. The speed and amount of load shedding steps are adapted to the severity of contingency in the affected region. By devising the grid into the... 

Secondary voltage control is used to re-adjust the reference values of automatic voltage regulators of generators. The performance of the secondary voltage control strongly depends on pilot node selection. In this paper the two proposed control laws for secondary voltage control are discussed and then an immune based algorithm is proposed to solve the optimal pilot node selection problem. The proposed algorithm is based on the clonal selection theory. The merit of immune algorithm lies in pattern recognition and memorization capabilities. Also, to provide independency of electrical zones a decoupling factor based on electrical distance concept is proposed. To verify the network observability... 

The paper presents a new approach that assists power system restoration planning with regards to control of temporary overvoltages (TOVs) due to transformer energization. The frequency-domain analysis in combination with analytical calculations is applied to find an optimum resonance condition. The analytical equations are based on sensitivity analysis for single frequencies and are extended to total sensitivity calculation. After an introduction of the phenomenon of overvoltages during power system restoration and harmonic resonance overvoltages, basic principles of their control are explained. Also, an algorithm is introduced for the results evaluation of harmonic resonance studies where... 

During power system restoration, it is necessary to check the phase angle between two buses before closing circuit breakers to connect a line between them. These angles may occur across a tie line between two systems or between two connected subsystems within a system. In case of large Standing Phase Angle (SPA) difference the synchrocheck relay does not allow closing of the breaker for this line. Therefore, this excessive SPA has to be reduced before attempting to connect the line. In this paper a new and fast method for reducing SPA is presented. For this purpose, the standing phase angle difference between two specific buses is represented in terms of sensitivity factors associated with... 

The paper presents a new approach that assists power system restoration planning with regard to control of temporary over-voltages (TOV) due to transformer energization. The frequency domain analysis in combination with analytical calculations is applied to find an optimum resonance condition. The analytical equations are based on sensitivity analysis for single frequencies and are extended to total sensitivity calculation. After an introduction to the phenomenon of overvoltages during power system restoration and harmonic resonance overvoltages, basic principles of their control are explained. An algorithm is introduced for the results evaluation of harmonic resonance studies where it is... 

An important subject in load pick up during power system restoration is the selection of suitable load steps, especially in the initial phase of restoration. Operators are often concerned with the size of the load that can be safely picked up and the effectiveness of the generation reserve. Load pick up in small increments tends to prolong the restoration period. With large increment, there is always the risk of falling into a frequency decline and to a recurrence of the system outage. In this paper, a novel method for dynamic calculation of load steps is presented. The proposed method considers the dynamics of system components, as well as their limitations and uses a suitable form for... 

In the United States electricity market standard, when several transmission service requests (TSRs) are made for a specific pair of power injection/extraction points, the independent system operator (ISO) must allocate the available transmission capability (ATC) associated with the pair to the requests. An ATC allocation must determine the amount of accepted requests as well as the priority of the accepted requests during emergencies. The requests could have different types (recallable/non-recallable), tariffs, and time frames and these factors must be properly considered in ATC allocation. This paper proposes a method for optimal ATC allocation in the planning horizon which incorporates the... 

When there are transmission service requests for a specific sink/source pair in a transmission system, the ISO must allocate the ATC of that pair to the requests. Since the requests could have different types, tariffs and time frame, the allocation must be accomplished in a sound and fair manner that considers various aspects of the requests. This paper proposes an approach to allocate the ATC to transmission service requests in both operating and planning horizons. The proposed method considers types and tariffs of requests in a nonlinear optimization which maximizes the expected net revenue of ATC allocation. The solution to the optimization problem gives the amount of accepted requests.... 

This paper evaluates the reliability impact of UPFC application in power system. The paper proposes a new reliability model for the UPFC which is capable of considering different operating states of UPFC. The model is then applied to a test system to study the reliability impacts of UPFC. The impacts of operating points of different states of the model on the system reliability are analyzed. The role of model parameters in reliability impacts of UPFC is analyzed through the sensitivity analysis. A comparative study is finally conducted to illustrate the applicability of the proposed model compare to that of existing UPFC reliability models. The abilities and deficiencies of the proposed... 

This paper investigates various approaches to relieve the transient stability constraint in restructured power systems. The approaches adopted fall into two broad categories: those based on eliminating the constraint in the least-cost way and those based on eliminating with the least possible rescheduling. The latter group can, on the other hand, emerge in the form of a pool-protected policy in which the bilateral contracts are rescheduled to maintain the stability or in the form of a contract-protected policy in which the realizable bilateral contracts are maximized while minimizing the rescheduling in pool market. Transient energy function (TEF) method is used as a tool to calculate the... 

A system protection scheme is proposed to mitigate cascaded voltage collapses. Based on the post-contingency conditions of either existence or non-existence of an equilibrium solution, and with regard to the stability and security criteria, the proposed scheme finds the optimal set of remedies. The proposed stabilising scheme brings the non-equilibrium post-contingency operating point back inside a stable region, and then passes this point to the securing scheme. Also, to enhance the performance of the stabilising scheme, a sensitivity analysis method is presented to detect the most effective remedies. The proposed securing scheme converts the stable, but insecure operating point, to a... 

This paper presents a practical reactive power valuation method, for the purpose of the reactive power pricing, in which the VAr value is decomposed into two components. These components are basically different from those already employed in the literature. Using a security constrained optimization model, the proposed scheme allocates two specific amounts of MW transactions to each generator as a dynamic reactive power source. One of these allocated amounts represents the contribution of the VAr resource to the shipment of active power, while the other one represents the contribution to the protection of the system against voltage instability. The final VAr value is derived using the... 

This paper presents a reactive power valuation method with regard to its effect on realization of MW transactions. The security constraint optimization model in which the objective function is maximization of transactions is solved by the genetic algorithm approach. The proposed scheme allocates a specific amount of MW transactions to each dynamic reactive power source. An index is introduced to derive VAr value from the calculated optimal parameters of power network. This index represents the system-wide effect of MVAr sources on MW transactions implementations. Application of proposed method has been illustrated using IEEE 30 and 14 bus test systems. Results are discussed and compared in... 

This paper describes an approach for unit start-up sequence determination during power system restoration. This approach is based on the backtracking search method, which determines the generating starting times to maximize the MWh load served over a restoration period and guarantee optimality of the start up sequence. The dynamic characteristics of different types of units and system constraints have to be considered. The shortest path, i.e., the path that requires the minimal number of switching actions, between the supplying unit and load is selected unless it is not feasible. Simulation tests, carried out on 39-bus New England test system, verify the effectiveness of the proposed method.... 

In this paper, an accurate fault location algorithm for series compensated power transmission lines is presented. Distributed time domain model is used for modeling of the transmission lines. The algorithm makes use of two subroutines for estimation of the fault distance - one for faults behind the series capacitors and another one for faults in front of the series capacitors. Then a special procedure to select the correct solution is utilized. Samples of voltages and currents at both ends of the line are taken synchronously and used to calculate the location of the fault. The proposed algorithm is independent of fault resistance and does not require any knowledge of source impedance. The... 

In this paper, an accurate fault location algorithm for series compensated power transmission lines is presented. A distributed time domain model is used for modeling of the transmission lines. The algorithm makes use of two subroutines for estimation of the fault distance-one for faults behind the series capacitors and another one for faults in front of the series capacitors. Then a special procedure to select the correct solution is utilized. Samples of voltages and currents at both ends of the line are taken synchronously and used to calculate the location of the fault. The proposed algorithm is independent of fault resistance and does not require any knowledge of source impedance. The... 

In this paper we propose a new fault location algorithm for power transmission lines based on one terminal voltage and current data. A distributed time domain model of the line is used as a basis for algorithm development. The suggested technique only takes advantage of post-fault voltage and current samples taken at one end of the line and does not require filtering of DC offset and high-frequency components of the recorded signals, which are present during transient conditions. Another advantage of the proposed method is the application of a very narrow window of data i. e. less than 1/4 of a cycle. The paper also proposes two different algorithms for lossless and lossy line models.... 

Available transfer capability (ATC) is a measure of the transfer capability remaining in a transmission system. Application of unified power flow controllers (UPFCs) could have positive impacts on the ATC of some paths while it might have a negative impact on the ATC of other paths. This paper presents an approach to evaluate the impacts of UPFCs on the ATC from a cost/worth point of view. The UPFC application worth is considered as the maximum cost saving in enhancing the ATC of the paths due to the UPFC implementation. The cost saving is considered as the cost of optimal application of other system reinforcement alternatives (except for UPFC) to reach the same ATC level obtained by UPFC...