Power Transfer Limit Research Articles

Experimental verification of fuzzy excitation control system for multi-machine power system

A fuzzy excitation control system (FECS), based on the fuzzy theorem and having the function of both AVR and PSS, was established to improve power system stability. This paper includes the results of experiments of the FECS on the AC/DC power system simulator of the CRIEPI. The FECS is compared with the conventional quick-response excitation system with optimized PSSs on a 4-machine long distance fish-bone type power system and various system configurations. The results show that the FECS increases the power transfer limit more than 20 (%) without any parameter tuning.

Hybrid Extended Equal-Area Criterion for Fast Transient Stability Assessment with Detailed Power System Models

The use of fast direct methods to evaluate the stability of power systems can benefit planning studies and operation planning. The existing Extended Equal-Area Criterion (EEAC), developed in 1988, enabled calculation much faster than timedomain simulations, but failed to deal with large and detailed dynamic systems. Based on it, we propose a new method, which is a Hybrid Extended Equal-Area Criterion (HEEAC), where time-domain simulations are used with a stability assessment provided by EEAC. HEEAC discriminates critical from non-critical machines, and yields a set of stability indicators such as critical clearing times, power transfer limits or power generation limits. The method has been applied to the French EHV system, with detailed generator and load models. The perfonnances are good both in tenns of computing speed and accuracy.

A discrete-time model of thyristor controlled series compensators

The current trend in power systems is to use power electronic devices to enhance both system stability and power transfer limits. A recent point of interest is the use of thyristor control devices in series compensation of AC transmission lines. In this paper a linearized, discrete-time model of a thyristor controlled series compensated line is presented. The samples for these discrete models are obtained at the peaks of the capacitor voltage of the series compensator. Since these peaks are broad rather than sharp spikes they are quite good indicators of variations in the fundamental component. During transients this will result in variation from uniform sampling. However, the system degenerates to a uniform sampled system in the steady state and thus all the standard tools for the analysis of the standard discrete-time model can be applied. The model developed is validated through digital computer simulation studies.

Maximum power transfer capability within the voltage stability limit of series and shunt compensation schemes for AC transmission systems

A new method of determining the maximum power transfer capability of a high voltage AC transmission line with different series and shunt compensation schemes is presented. The method determines the maximum power transfer limit by finding the critical value of the receiving-end current beyond which the power cannot be increased by increasing the value of the current because of voltage instability. Simple analytical expressions for the critical or limiting values of the receiving-end quantities (power, voltage and current) and the corresponding phase shift between the sending- and receiving-end voltages are derived. The proposed method was applied to a transmission line with several series and shunt compensation schemes to determine the various critical quantities. The critical quantities obtained for those schemes were also compared. The influence of various factors such as the line length, load power factor and the degree of series and shunt compensation on the maximum power transfer capability was also investigated.

Static VAR system auxiliary controllers for damping torsional oscillations

A new concept is presented according to which a midpoint-located static VAR system (SVS) with appropriate auxiliary control can be simultaneously employed for damping torsional oscillations and enhancing the steady state power transfer limit. Two new SVS auxiliary control signals designated as computed internal frequency (CIF) and computed rotor frequency (CRF), which can be locally synthesized, are proposed. Various locally available signals for SVS control are examined in respect of their ability to stabilize all the torsional modes. It is shown from eigenvalue analysis that with a suitable choice of signal and SVS auxiliary controller parameters, the desired objective can be achieved even when the transmission line is compensated at a level where one of the torsional modes is critically destabilized.

Oscillatory Stability Considerations in Transmission Expansion Planning

Due to fast economic growth on the island of Taiwan, load demand in Taiwan Power Company (TPC) has been rapidly increasing in the past ten years and is expected to continue throughout the next decade. By 1995, the peak load demand in Taiwan is forecasted to reach 16,000 MW, an increase of 60% from the present level of 10,000 MW. Several new generating units have been under construction to meet the future demand. As a result, additional transmission lines are needed to avoid overloads on present lines. The objective of this paper is to report the results from a recent study which was aimed at reaching an optimal transmission expansion plan by comparing the relative merits of three feasible alternatives: EHV lines (345 KV), UHV lines (765 KV), and HVDC lines (± 250 KV). At present, the main factors considered in transmission expansion planning in TPC are the maximum power transfer limits, fault currents, transient stability, system losses, and cost [1]. In addition to these factors used in current practice, oscillatory stability of the power system under each expansion plan will be extensively studied. In particular, the low frequency electromechanical oscillations which tend to appear in a longitudinal power system such as the one in Taiwan will be investigated. The dampings of these oscillation modes are essential in system operation and planning, especially in the case when the transmission line is heavily loaded.

Oscillatory stability considerations in transmission expansion planning

Experience with the transmission expansion planning of a longitudinal power system is reported. To reach an optimal choice among several feasible expansion plans, indices such as maximum power transfer limits, fault currents, transient stability, system losses, and cost, which have been widely used by utilities, are computed to compare the relative merits of these alternatives. In view of past experience with low-frequency oscillations taking place in the study system, oscillatory stability of the power system under each expansion plan is examined in detail by means of eigenvalue-eigenvector analyses. Recommendations are made with regard to future expansion plans on the basis of the present study.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

UHV Stability Study Tokyo Electric Power Company

Tokyo Electric Power Company is studying a 15 GW future system expansion. The added generation will be concentrated in a nuclear energy park, connected by a limited number of transmission corridors to the load center in the Tokyo urban area. One study reported in this paper to support this expansion is the determination of the UHV power transfer limits imposed by system stability for alternative transmission plans.

Optimal Control of Electrical Power Systems Containing Controlled Reactors Part 1: Effect of Controlled Reactors on the Transient Stability Limit

This paper considers the effect of controlled reactors connected to an EHV long transmission line on the transient stability power transfer limit of the system. It is shown that this effect may be substantial and depends on the parameters of the controlled reactors themselves (time constant and control range) as well as on the degree of series capacitive compensation and the prefault operating conditions of the line. The optimum values of the controlled reactor parameters under transient conditions have been determined. The results obtained provide a good basis to continue the study to show the damping effect of the controlled reactors in case of large disturbances in the system.

Optimal Control of Transients in Electrical Power Systems Containing Controlled Reactors Part 2: Optimal Control Problem Solution

This paper studies the optimal control of transient processes in electrical power systems for the purpose of damping the system oscillations arising due to faults. Using a second order nonlinear model of the system, an optimal transient response has been obtained with controlled shunt reactors, which have proved to be effective in improving the transient stability power transfer limit of the system1. A combined control of reactors, excitation and turbine has been applied to a third order nonlinear model of the system and the possibility of coordination between different controls to get optimal transients have been shown. The Pontryagin's maximum principle has been utilized to formulate the optimization problem and the produced nonlinear two-point boundary value problem was solved using a modified quasilinearization algorithm.

A Practical Approach to Unit Commitment, Economic Dispatch and Savings Allocation for Multiple-Area Pool Operation with Import/Export Constraints

A straight forward and computationally efficient method is presented for including the area import/export constraints (power transfer limits) in the unit commitment and economic dispatch procedure. The savings resulting from a unified unit commitment and economy interchange of power, including the added constraints of area import/export limits, can be analyzed on a daily, monthly and annual basis. A procedure for allocating savings among the participating companies forming a pool on an equitable basis is presented. A comprehensive computer program has been developed utilizing the concepts presented in this paper, and is presently being tested on the Texas Utilities and Texas Municipal Power Pool systems.