Steady State Voltage Stability Limit Research Articles

Coordinated tuning of PSS and TCSC to improve Hopf Bifurcation margin in multimachine power system by a modified Bacteria Foraging Algorithm

Abstract Recent research works have reported the effects of rotor angle dynamics of generators on bifurcation related system instability. This study intends to verify the possible influence of the Power System Stabilizers (PSS) and the Thyristor Controlled Series Capacitors (TCSC), on instabilities related to the Hopf Bifurcation (HB). Recently proposed optimization algorithm known as Bacteria Foraging Algorithm (BFA) in its modified version is applied in this study to tune the controller parameters of nine numbers of PSS and two numbers of TCSC present in the 10 machine New England power system. The main objective of this work is to maximize the margin of loading in the same system before the occurrence of the HB. Moreover, the formulation of a properly designed objective function is also an important issue that affects the final result. The objective function, that is formulated only to improve the overall damping in power system, may not be sufficient to avoid the HB under stressed operating condition. Therefore, this study proposes to reformulate an eigenvalue based objective function to improve the extent of loading before the HB could occur in the system. A coordinated control of the TCSC with those of the PSS may enable the controllers to delay the point of HB, compared to the case when the PSS alone were operating in the system. At the outset, the control parameter settings of several transformer taps and PV-bus voltages of nine generators were optimized to improve the steady state Voltage Stability Limit (VSL) of the system. At these settings, the damping controller parameters are tuned to improve the loadability before the point of HB. Similar approach is adopted when the TCSCs were operating coordinately with the PSS. At the end, small perturbation cases were simulated in the system to verify the performance of designed controllers in time domain analysis. The results further establish the efficacy of the controllers

A Study on Determination of Interface Flow Limits in the KEPCO System Using Modified Continuation Power Flow (MCPF)

This paper reports a study on determining the steady-state voltage stability limit of interface flow on a set of interface lines between the metropolitan region and the neighboring regions in the Korea Electric Power Corporation (KEPCO). The interface flow limit considering severe contingencies is determined with a concept of interface flow margin, which is the active power flow margin of the key transmission lines between one region and others under a fixed load demand condition. The paper proposes a procedure to determine secure limit of active power flow on a set of specified interface lines. The procedure uses the modified continuation power flow (MCPF) tracing a path of power flow solutions with respect to generation shift to vary interface flow. In simulation, voltage stability limits of the metropolitan interface flow of the 1998 KEPCO system are determined.

A study on determination of interface flow limits in the KEPCO system using modified continuation power flow (MCPF)

This paper reports a study on determining the steady-state voltage stability limit of interface flow on a set of interface lines between the metropolitan region and the neighboring regions in the Korea Electric Power Corporation (KEPCO). The interface flow limit considering severe contingencies is determined with a concept of interface flow margin, which is the active power flow margin of the key transmission lines between one region and others under a fixed load demand condition. The paper proposes a procedure to determine secure limit of active power flow on a set of specified interface lines. The procedure uses the modified continuation power flow (MCPF) tracing a path of power flow solutions with respect to generation shift to vary interface flow. In simulation, voltage stability limits of the metropolitan interface flow of the 1998 KEPCO system are determined.

Determination of Steady-State Voltage Stability Limit Using P-Q Curve

P -V and Q - V curves are commonly used to determine the steady state voltage stability limit of a power system. In this letter, a new method of determining the voltage stability limit using the P -Q curve is presented. The boundary of the voltage stability region is first determined and then presented in the P -Q plane. For a given operating point, the voltage stability margin can easily be determined from the stability boundary in the P -Q plane. The proposed method of determining the voltage stability limit was tested on a simple system and very interesting results were found.

Steady state voltage instability assessment in a power system

With the increase of loading and exploitation of power transmission system and also due to the improved optimized operation, the problem of voltage stability and voltage collapse attracts more and more attention. The phenomenon of possible steady state voltage instability is creating serious concern among operators of large interconnected power systems. Maintaining adequate system voltage has become a major problem, as utilities are being forced to operate the system close to the thermal capability or steady state voltage stability limit. A voltage collapse can take place in power systems or subsystems quite abruptly, which requires improved continuous monitoring of the system state. There are different methods used to study the voltage collapse phenomenon, such as the Jacobian method, the simplified Jacobian method, the multiple load flow method and the voltage collapse proximity indicator method. It is proposed to modify the method of multiple load flow to obtain the weakest buses and the maximum injected powers for each bus. The method of voltage collapse proximity indicators is also simplified. These different methods are applied on a simple power system to study the problem of voltage collapse, and a comparison is made between them with indicating the merits and demerits of each.

Fast calculation of a voltage stability index

The minimum singular value of the power flow Jacobian matrix has been used as a static voltage stability index, indicating the distance between the studied operating point and the steady-state voltage stability limit. A fast method to calculate the minimum singular value and the corresponding (left and right) singular vectors is presented. The main advantages of the algorithm are the small amount of computation time needed, and that it only requires information available from an ordinary program for power flow calculations. The proposed method fully utilizes the sparsity of the power flow Jacobian matrix and the memory requirements for the computation are low. These advantages are preserved when applied to various submatrices of the Jacobian matrix. The algorithm was applied to small test systems and to a large system with over 1000 nodes, with satisfactory results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The continuation power flow: a tool for steady state voltage stability analysis

The authors present a method of finding a continuum of power flow solutions starting at some base load and leading to the steady-state voltage stability limit (critical point) of the system. A salient feature of the so-called continuation power flow is that it remains well-conditioned at and around the critical point. As a consequence, divergence due to ill-conditioning is not encountered at the critical point, even when single-precision computation is used. Intermediate results of the process are used to develop a voltage stability index and identify areas of the system most prone to voltage collapse. Examples are given where the voltage stability of a system is analyzed using several different scenarios of load increase.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>