Yu Yixin

Fault location of two-parallel transmission line for non-earth fault using one-terminal data

Summary form only as given. An accurate fault-location algorithm for the two-parallel transmission line of a direct ground neutral system is presented. The algorithm employs the faulted circuit and healthy circuit of a two-parallel line as fault-location model, in which remote source impedance is not involved. It effectively eliminates the effect of load flow and fault resistance on the accuracy of fault location. It embodies an accurate location by measuring only one local end data and it is used in a procedure that provides the automatic determination of fault types and phases, rather than require an engineer to specify them. Simulation results have shown the effectiveness of the algorithm under the conditions of nonearth faults (phase-to-phase fault and three-phase fault with and without earth-connection).

Optimal planning of distribution substation locations and sizes — model and algorithm

A new method is presented in this paper to solve the optimal planning problem of distribution substations. The procedure proposed here does not require candidate substation locations and can automatically select the optimal sizes, locations and service areas of substations in power distribution systems. In addition, an effective solution algorithm is also presented.

Non-intrusive method for on-line power load decomposition

A novel non-intrusive method for on-line power load decomposition is introduced. This method is based on the following fact, that in normal operation states of electrical appliances, steady-state currents (including fundamental current and harmonic currents) of electrical appliances have normally certain statistical regularity. In such cases, a power load current can be approximately estimated by the linear superposition of the currents components of n main types of electrical appliances, when the power load consists of n main types of electrical appliances. The subject of the power load decomposition is to calculate a group of reasonable weight coefficients by an optimization method, so that the estimation current has the maximum similarity with the real current. The experimental results indicate that this method of load decomposition not only has higher precision and better stability but also is easy to be realized on-line.

Chaotic phenomena and small signal stability region of electrical power systems

In this paper, chaos phenomena and its influence on the power system small signal stability region (SSSR) are studied. We first review the studies on the SSSR, and point out that it is very important to make clear whether there exist some chaotic components on the boundary of the SSSR. Next, with some analytic skills of nonlinear dynamic system, we give a complete bifurcation diagram of a chaos existing in a sample power system, from a limit cycle (period-1) to chaotic state through cascading period-doubling bifurcation. The characteristics of the system energy varying in the continuous bifurcation are also shown. Thus a conclusion that chaos is always out of the Hopf bifurcation components (HB) on the SSSRs boundary. Based on this conclusion and some further studies, we confirm that, from the viewpoint of power system engineering, we do not need to consider the existence of chaos in the SSSR and its boundary. Therefore greatly simplifying the study of SSSR. Moreover, some aspects of the attractive regions of chaos and limit cycle are also studied, which is helpful to understanding some mistakes in some previous articles.

Relationship of chaos and small signal stability region

In this paper, chaotic phenomena and its impact on the small signal stability region (SSSR) of power systems are studied. A typical period-3 trajectory in a simple power system is presented for the first time. Theorem Sarkovskii and Theorem Li-Yorke are used to identify the existence of chaos in power systems. This method can avoid the confusion caused by pseudo-chaos and incomplete period doubling bifurcation phenomena. Moreover, the influence of chaos on the small signal stability region has been investigated and we conclude that, from the engineering point of view, it is not necessary to consider the existence of chaos in the studies of SSSR and its boundary. This excludes the unnecessary complexity in the study of SSSR.

An asynchronously coordinating load flow calculation algorithm for the distributed energy management system (DEMS)

Trends in modern power systems are promoting traditional EMSs to develop towards the form of distributed energy management system (DEMS). The communication network is a very important composing part of DEMS. Based on the two-level hierarchically coordinating mechanism model of a DEMS presented in this paper and by taking the unpredictable communication time delay into account, an asynchronously coordinating load flow algorithm for DEMS has been proposed. The test results show that the asynchronous algorithm is of much more practical value than its synchronous counterpart.<<ETX>>

Equivalent network for determination of voltage stability limit

In order to improve the efficiency of power system voltage stability analysis a new static equivalent method is presented in this paper including the selection of the correlation area using L/sub 1/ index described in detail. The correlation area selected from the external area is composed of generators, buses, transformers and loads. The proposed equivalent method is a kind of modified Ward-type equivalent. This method can increase the computation velocity and remain the precision of the voltage stability limits. Test results of a real power system have proved that this new equivalent method is promising for voltage stability study of power system.

An accurate algorithm for fault distance estimation of two-parallel transmission line based on one-terminal sampling

An accurate numerical algorithm of fault location estimation for triple line-ground fault involving different phases from each of two-parallel lines is presented in this paper. It is based on one-terminal voltage and current data. The loop and node equations comparing faulted phase to nonfaulted phase of two-parallel lines are introduced in the fault location estimation modal, in which source impedance of remote end is not involved. The effect of load flow and fault resistance are effectively eliminated on the accuracy of fault location, therefore an accurate algorithm of locating a fault is derived. The algorithm is demonstrated by digital computer simulations.

Application of robustness theory in the analysis of subsynchronous oscillation [of power systems]

In this paper, the applicability of the recently developed frequency-domain, matrix-norm robustness theory for the analysis of subsynchronous oscillations in a power system is explored. Based upon structure preserving multivariable feedback model, a set of new robustness theorems are developed. These theorems can be used to analyse the effects of parameter perturbations on the stability of subsynchronous oscillations in a power system and can provide useful measures for evaluating the tolerance of the system to modeling errors. An example is provided to demonstrate the effectiveness of these theorems.<<ETX>>