A selective single-phase-to-ground fault protection for neutral un-effectively grounded systems

A novel scheme for error current compensation of current transformers (CTs) is presented. The method is to apply Hall current transducers (HCTs) based on magnetic force balance to detect and compensate the error current so as to eliminate the error of CT caused by its exciting current. Theoretical analysis and experimental tests clearly illustrate the performance of the proposed scheme. After compensation, the accuracy of the common CT is increased 500 times from 0.5% (5000 ppm) to 0.001% (10 ppm) at the condition of burden Z/sub b/=1 /spl Omega/, cos /spl phi/=1. A self-calibrating method is adopted for a current transformer with the wind ratio of 1:1.

Novel method of error current compensation for Hall-effect-based high-accuracy current transformer

This paper aims to solve the optimal power problem (OPF) incorporating flexible AC transmission systems (FACTS) devices using Gravitational Search Algorithm (GSA) that minimizes the fuel cost function in the problem. In the optimization problem, Thyristor controlled series compensation (TCSC) and thyristor controlled phase shifter (TCPS) FACTS devices are considered to find their optimum location in transmission lines. In order to evaluate the effectiveness of proposed algorithm, it has been tested on modified IEEE 30 bus system and compared with particle swarm optimization (PSO) and hybrid tabu search and simulated annealing (TS/SA) approach which are used in solving the same problem and reported before in the literature. Results show that GSA produces better results than others and has fast computing time for solving OPF problem with FACTS.

Optimal power flow incorporating FACTS devices using Gravitational Search Algorithm

Single-phase-to-ground fault is the most frequently occurred short-circuit fault in distribution network, and it is urgent to develop new methods to detect fault feeder correctly. The paper compares the fault-feeder selection theories using transient signals with those of using steady signals, and the application of transient signal is emphasized. By analyzing the characteristics of the Peterson-coil-grounded system, the paper proposes a novel algorithm to select fault feeder based on the transient signals and wavelet packet. It records the post-fault transient zero-sequence current of each feeder, and wavelet packet is used to extract the supply fundamental frequency and high frequency components. Finally the current and its components are used to detect fault feeder. This method is accurate and adaptive for the Peterson-coil-grounded system. Case study validates the effectiveness of the new algorithm for various fault modes in neural ineffectively grounded systems.

Single-phase-to-ground fault feeder detection based on transient current and wavelet packet

Today, the Hall sensor based current measurement is being widely used as they have both AC and DC current measurement capability. The factors such as ratiometric error of Hall sensor, earth or other magnetic effects in sensor location, sensitivity errors originating from temperature or magnetic core, deteriorates measurement linearity. This requires that measurement results are evaluated with mathematical analysis methods. In this study, a closed loop Hall Effect current transformer was designed and its linearity in measurement results is examined by real time parameter estimation based on the least squares method so measurement accuracy was improved and real time observation of linearity error was provided.

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The Design of a Hall Effect Current Transformer and Examination of The Linearity with Real Time Parameter Estimation

This paper devotes research to the single phase to ground fault line detection problem in neutral nondirect earthed power systems. A concept of fault measures is introduced to quantitatively describe the degree of the fault indication in each line for flexible and reasonable fusion of multi criteria. A wavelet based transient method is proposed to extend the use of fault information. Fault measure algorithms for transient, steady state magnitude and steady state phase angle are formulated respectively. D-S evidence theory is introduced to deal with the fusion of multi criteria. An example obtained from a practical fault is provided to verify the effect of the fault measures, the transient detection method and the D-S combination. The example shows that the novel resorts proposed in this paper can really improve the performance of fault line detection.

Multi-criteria relaying strategy for single phase to ground fault in MV power systems

In this paper the basic principle, modeling and simulation of a Hall current transformer are presented. The Hall current transformer is a kind of electronically compensated current transformer based on zero flux. By analyzing the magnetic circuit, electric circuit and electronic circuit of a Hall current transformer, its model was built using a first-order differential equation. On this basis, to find the solution, the authors obtain the transient response. By analyzing its characteristic equation they find the feedback amplifier gain's stability limit. By analyzing the secondary current steady-state component, they find the factors which affect its error and, by simulation, they calculate the Hall current transformer's errors under various conditions.

The Hall current transformer modeling and simulation

This paper presents a new method to incorporate flexible AC transmission system (FACTS) devices in optimal power flow (OPF) problem. Through power injection model of FACTS devices, their control to power system is expressed as the additional power equations at the nodes and the branches where FACTS devices are located. These additional power equations are convenient in combination with OPF algorithm based on nonlinear interior point (IP) programming. A two-part calculation structure is introduced in order to make full use of the existing OPF algorithm and related software in EMS. Digital simulations of the modified IEEE 30-node system located with multiple FACTS devices are present to test the effectiveness and efficiency of this work. The study also shows that FACTS devices are capable of providing an economically and technically attractive solution to power systems congestion problems.

Song Jiahua

Papers

Multi-criteria relaying strategy for single phase to ground fault in MV power systems

The Hall current transformer modeling and simulation

A nonlinear interior point based optimal power flow algorithm incorporating series FACTS devices