K.K. Li

Overcurrent relay coordination by evolutionary programming

Abstract This paper presents a novel optimization technique based on evolutionary programming for overcurrent (OC) relay coordination in ring fed distribution networks. Since the problem has multi-optimum points, ordinary mathematical based optimization techniques will fail. Evolutionary programming is a stochastic multi-point searching optimization algorithm and is capable of escape from local optimum problems. When used in OC relay coordination, the chance of obtaining global optimum relay settings is thus drastically increased. The developed technique will make sure that the relay grading pairs will operate in correct grading order. It can also handle the resultant relay operation due to the changes of fault current distribution as a result of circuit breaker operation while the fault still exists. The relay grading requirements such as changes of fault level and system configuration, are reflected in the optimization process as constraint checking. The difficulties in the application of evolutionary programming in a highly constrained system will also be discussed.

Agent-based self-healing protection system

This paper proposes an agent-based paradigm for self-healing protection systems. Numerical relays implemented with intelligent electronic devices are designed as a relay agent to perform a protective relaying function in cooperation with other relay agents. A graph-theory-based expert system, which can be integrated with supervisory control and a data acquisition system, has been developed to divide the power grid into primary and backup protection zones online and all relay agents are assigned to specific zones according to system topological configuration. In order to facilitate a more robust, less vulnerable protection system, predictive and corrective self-healing strategies are implemented as guideline regulations of the relay agent, and the relay agents within the same protection zone communicate and cooperate to detect, locate, and trip fault precisely with primary and backup protection. Performance of the proposed protection system has been simulated with cascading fault, failures in communication and protection units, and compared with a coordinated directional overcurrent protection system.

Multi-objective transmission network planning by a hybrid GA approach with fuzzy decision analysis

In this paper, power system transmission network planning is formulated as a multi-objective mathematical optimization problem. In this context, three objectives: investment cost, reliability and environmental impact are considered in the optimization. To overcome the drawback of conventional mathematical optimization method in arriving at local optimum solution, a genetic algorithm approach is developed, from which several possible planning schemes are generated. This is followed by a fuzzy decision analysis method to select the optimum solution scheme. Case study results on a large 220 kV transmission network planning problem are presented to show the methodologys feasibility and efficiency.

Context Information-Based Cyber Security Defense of Protection System

With the development of a substation automation system, it is now feasible for the intelligent electronic devices-based protection system to collect its measurements from electronic instrument transformers through a communication network such as an Ethernet-based local-area network. The application of a wide-area broadband network in power utilities introduces underlying danger for protection systems to maloperate when receiving fake data packages from an intruder. This paper proposes identifying a vicious fault by using context information, such as voltage and current, of the same substation. When the protection system detects a fault based on measurements transmitted through a network, it collects all measurements of the substation and feeds these data to a probabilistic neural network. Thereafter, the fault caused by fake data that differs from the known fault pattern can be identified and blocked.

Application of an innovative combined forecasting method in power system load forecasting

Abstract To fully integrate the advantages of several forecasting models and improve the accuracy of load forecast results, the application of the combined forecasting method to power system load forecasting is introduced in this paper. The evolutionary programming and fuzzy comprehensive evaluation methods are employed to deduce the weight coefficients of each model. Practical cases are studied using the two methods and tested to be feasible and effective.

Multi-agents based protection for distributed generation systems

As a result of deregulation, distributed generation (DG) systems with distributed generators installed in the middle or low voltage networks become popular in distribution systems. Traditional protections developed in radial systems are difficult in coordination and in protecting against high impedance fault (HIF), sometimes it may cause nuisance tripping in the DG systems. A decentralized multi-agent based protection with capability of HIF detection, fault location and load shedding for the DG systems is proposed in the paper. Digital relay is designed as a relay agent which is capable of searching for information from other relay agents, interacting with other relay agents and performing tasks of protection with autonomy and cooperating. The agent based protection scheme is also presented. EMTP simulation results show that the proposed agent based protection scheme can remove the influence of load switching operations, protect against HIF, electric shock. The prototype of relay agent is developed, the research is now in progress on testing the prototype in dynamic power system.

On-site safety evaluation for earth fault in mining power systems

Many mining power systems utilize ineffectively grounded sources to restrict the residual current of single-phase earth fault in order to reduce outage and shock hazard. In practice, with the system expansion, topology changing and insulation aging, the potential residual current and zero sequence voltage for earth fault vary dynamically and some arcing earth faults can easily cause overvoltage and induce multiple faults. In order to improve the system safety, on-site condition monitoring, safety evaluation and preventive maintenance for an earth fault are proposed in this paper. Some techniques for on-line parameters-measurement based on the resonance-measurement principle are presented. Power system operation states are classified into normal secure state, alert state, incipient fault state and fault state. Some security enhancement methods (preventive action and remedial action) for each state are implemented. The prototype for safety evaluation has been developed and installed in industry power systems for several years.

A Tabu Search Approach to Distribution Network Reconfiguration for Loss Reduction

Distribution network reconfiguration for loss minimization is a complex, large-scale combinatorial optimization problem. A new efficient and robust algorithm for he reconfiguration of distribution networks in order to reduce the power energy losses under normal operating conditions is presented in this article. The developed algorithm is based on a tabu search (TS) approach, which is a recent member in the family of modern heuristic methods. Tabu search is used for efficiently obtaining the near-optimal solutions of combinatorial optimization problems, which makes it suitable to solve the problem of distribution network reconfiguration. The components of proposed TS-based method and effective schemes, which aim at speeding up the solution methodology, are also presented. To demonstrate the validity and effectiveness of the proposed method, three test systems with different sizes are studied. The numerical results reveal that the proposed method is promising.

Ideal operating region of digital distance relay under high resistance earth fault

Abstract Remote end infeed has caused a lot of problems to distance relay measurement especially under high resistance earth fault conditions. The measured impedance may be larger or smaller than the actual value. This paper describes the main factors which affect the ideal distance relay operating region and how it is related to the active and reactive power flow in the line. This would help to solve the problems in the development of an intelligent adaptive digital distance relay which does not need communication links from the remote end of the line or the system control centre.

Grounding faulted feeder detection with fault resistance measurement in mining power systems

Many mining power systems have been operated with floating neutral or high resistance grounded. The earth fault current is no more than a few tens of amperes. Traditional earth fault detection methods based on zero sequence current have poor sensitivity in this case. For improvement, a fault detection scheme with fault current and fault resistance measurement is presented in the paper. It can detect high impedance grounding faults (HIGF). The scheme has been verified by EMTP simulation, and fault detection prototype has been developed and tested. Results show that the scheme has with high sensitivity and robustness.