Xu Yuqin

Research on optimization of recloser placement of DG-enhanced distribution networks

An optimization method is proposed to identify the optimum recloser placement to improve system reliability for distribution networks with distributed generators (DG). DG may reduce the number of interruptions and/or durations for customers residing within their protection zones, thus increasing the reliability of service. A composite reliability index is defined as the objective function in the optimization procedure. Then, the zone-network method is introduced for reliability evaluation. An improved genetic algorithm that named multiple-population genetic algorithm (MPGA) is used to search for the optimum solutions. Using the MPGA, the optimization can be solved with mutli-population, and the influence of improper genetic parameters can be greatly decreased and premature convergence can be overcome effectively. Simulation work is carried out based on a 69-segment 8-lateral distribution feeder with distributed generation to validate the effectiveness of the proposed method.

The method for automatic compensation and detection of earth faults in distribution network

The idea for a grounding neutral scheme for MV distribution networks is that when an instantaneous single-phase-to-earth fault occurs, the fault arc disappears automatically because of the rapid compensation of arc suppression coil current. The power supply is continuous. When a permanent single-phase-to-earth fault occurs it can detect and trip the faulty feeder in a short time. This scheme can be achieved by a TSC (thyristor switched capacitor) automatic tuning arc suppression coil with a parallel resistor. This paper presents the compensation principle of earth capacitance current and the detection methods of a faulty feeder. It also discusses the selection of the parallel resistor value. The simulation results based on EMTP-ATP show that this scheme is both correct and effective.

A Transmission Line Unit Protection Technique Based Combination Modulus by Using Mathematical Morphology

This paper presents a concept of combination modulus (CM) to solve the problem that the transient-based protection techniques may fail to detect faults under certain conditions. The CM features are analyzed and discussed in detail. A novel transmission line unit protection scheme is proposed by comparing transient current CM polarity. The mathematical morphology (MM) technique is used to extract the polarity features from fault-generated current wave signals propagating along transmission lines during a post-fault period. The simulation results of the ATP/EMTP software show that the reliability of the protection scheme proposed has been considerably improved.

Research on service restoration for large area blackout of distribution system with distributed generators

In terms of the distribution system with distributed generators (DGs) especially considering the operation of micro-grids (MGs) composed of DGs and loads, an AER (Agent-Environment-Rules) Constraint Satisfaction Problem (CSP) based model to solve the serve restoration problem in the event of a large-scale blackout in a power distribution network with DGs is proposed. All agents live in a lattice-like environment using multi-agent system, and they can not only sense their local environment but also move in it. The operation method of DGs in the process of service restoration for large area blackout of distribution system with DGs is researched for making use of the capacity of DGs sufficiently and reducing the blackout area. The asynchronous backtracking algorithm is used to solve the AER model based on CSP, the values of the agents can be exchanged, and they also can be updated by the influence between the agents and the environment. Finally, the example results indicate the feasibility of the proposed method.

Research on a New Extinction Coil Operation Mode for Resonant Earthed Neutral System

A great deal of simulation results show that sometimes there is an excessive remnant current even under fully compensated condition when a bolted single-phase-to-ground fault or a single-phase-to-ground fault with low transition resistance occurs in medium-voltage resonant earthed neutral system. In the distribution networks with low damp, the excessive remnant current will occasionally fade down slowly in several hundred microseconds. If this situation happens, the electric arc will hardly be extinguished and the malfunction may be so serious that it will bring more hazard to the distribution network. Based on the above phenomenon, the transient currents of a bolted single-phase-to-ground fault or a single-phase-to-ground fault with low transition resistance under fully compensated condition has been theoretically analyzed in the view of fundamental component. And the fault transient state equations for calculating the coherent electric parameters of a single-phase-to-ground fault have also been deduced. Their curves have been drawn by the MATLAB software and been compared with the fault transient state curves of ATP simulation. The comparison results show that the curves drawn by MATLAB software based on the equations are similar to those drawn by ATP software based on the digital model in a single-phase-to-ground fault. In order to restrain the excessive remnant fault current, a new extinction coil operation mode has been presented in this paper by in-depth analyses and a great deal of simulations.

The Automatic Following Control of Arc Suppression Coil with Thyristor Switched Capacitors

Various neutral grounding techniques are applied in medium voltage distribution networks in the world. With the applications of microcomputer technique and power electric technique in this area have led to significant modifications in arc suppression coil grounding technology. The principle and automatic following control method of arc suppression coil with TSC (thyristor switched capacitors) are described in this paper. A new grounding system with TSC arc suppression coil is developed. The results of field tests are analyzed. They show that the design of TSC arc suppression coil is correct and the automatic following system is reliability

Predicting available transfer capability for power system with large wind farms based on multivariable linear regression models

Available Transfer Capability (ATC) of power system with large farms is influenced by many factors. These factors include wind farms output, load and generators output that they are uncertain and have statistical characteristics. This paper studies the feasibility and effectiveness of prediction ATC through Multivariable Linear Regression Models (MLRM). And the system which considering transmission line thermal stability will be checked continuous flow N-l security constraints through the method of sequential Monte Carlo simulation, the Reactive Power Reserves (RPR) of power supply nodes influences on ATC will become explanatory variables as well as ATC of power system will being explained variables, then build MLRM equations to predict power systems ATC by system reactive power reserves. The improved IEEE 30-bus system and IEEE 118-bus system are the simulating examples, the results show that MLRM method can effectively predict the systems ATC and the speed of calculation is fast, also analysis and evaluates the influence of large scale wind farms to power systems ATC.

Effects of distribution generator on feeder automation and its solution

In a distribution network with a distributed generator (DG), when a short-circuit fault occurs, the magnitude and direction of fault current may be different from the fault current of distribution network without DG. Under this circumstance, the cooperation of recloser and sectionalizer or fuses might be lost. This paper analyzes these misoperations and proposes new setting principles and calculating methods of the DGs penetration level to ensure the correct isolation and clearing of fault.

The economic benefit evaluation of distribution network planning based on the LCC theory

Firstly, according to the characteristics of the distribution network, construct economic benefit evaluation index system of distribution network planning from three aspects of the technical economic benefits, the enterprise financial benefits and the national economic benefits. And considering the long-term economic benefits and the cost of the different stages of the distribution network, the Life Cycle Cost (LCC) theory is introduced into the analysis and calculation of the enterprise financial benefit evaluation index. Secondly, the weight of the economic benefit index of distribution network planning is calculated by Interval Analytic Hierarchy Process (IAHP) method in view of the complexity of the evaluation process and the uncertainty of the influencing factors. Then the fuzzy comprehensive evaluation method is used to evaluate the economic benefit of the distribution network planning scheme which can solve the problem of fuzzy and difficult to quantify. Finally, the correctness and effectiveness of the evaluation model are verified by an example analysis.