This paper presents an integrated relay and its associated protection scheme for power transmission lines. The concept of integrated protection is firstly introduced, in which a centralized protection system or relay provides the protection for multiple power plants or a substation. A novel integrated protection relay based on the combination of a number of protection principles is described. In the proposed scheme, the specially designed protection relays are installed at each substation of a network and are responsible for the protection of every line section connected to the substation busbar. The combined algorithms with multiple settings are implemented into the relay to cover all the protected line sections. Simulation studies show that the proposed protection scheme is able to produce desirable performance and may offer many advantages over the existing one and great potential for future applications.

The unintentional islanding of micro-grid may cause negative impacts on distribution loads and distributed generations, so it must be detected within the acceptable duration. In this paper a new islanding detection algorithm is proposed. This algorithm introduces the frequency feedback method by the reactive power compensation to derive the frequency continuous shift. Accordingly, the islanding can be detected by monitoring the frequency within 0.1 s. The simulation results prove that this algorithm has extremely small non-detection zone, and meanwhile it presents an excellent islanding detection speed as well.

A diagnostic signal current trace detecting based single phase-to-ground fault line identification and section location method for non-effectively grounded distribution systems is presented in this paper. A special diagnostic signal current is injected into the fault distribution system, and then it is detected at the outlet terminals to identify the fault line and at the sectionalizing or branching point along the fault line to locate the fault section. The method has been put into application in actual distribution network and field experience shows that it can identify the fault line and locate the fault section correctly and effectively.

Defense systems are needed to prevent catastrophic failures of a power grid due to cascaded events. Cascaded events can be attributed to improper operations of protective relays. The most challenging problem for the design and implementation of a defense system is the performance in accuracy and speed in a real time environment. Protective devices are normally designed to operate fast in order to isolate the fault(s). This paper proposes a new methodology to distinguish line overloads from actual faults for distance relays. In order to distinguish between line flow transfers from a line outage and an actual fault, the line outage distribution factor (LODF) and generation shift factor (GSF) based power flow estimation method, and a secure peer to peer (P2P) communication structure are adopted. Computer simulations of cascaded events for a 6-bus system and the Korean power grid have been performed to establish the feasibility of the proposed scheme.

A protection system using a multi-agent concept for power distribution networks is proposed. Every digital over current relay(OCR) is developed as an agent by adding its own intelligence, self-tuning and communication ability. The main advantage of the multi-agent concept is that a group of agents work together to achieve a global goal which is beyond the ability of each individual agent. In order to cope with frequent changes in the network operation condition and faults, an OCR agent, proposed in this paper, is able to detect a fault or a change in the network and find its optimal parameters for protection in an autonomous manner considering information of the whole network obtained by communication between other agents. Through this kind of coordination and information exchanges, not only a local but also a global protective scheme is completed. Simulations in a simple distribution network show the effectiveness of the proposed protection system.

To observe the inner operating process of distance protection, a Matlab/Simulink based dynamic simulation system for microprocessor-based distance protection is designed in this paper. As a modularized design, the simulation system is composed of several modules such as fault transient calculation, startup, Fourier algorithm, phase selection, impedance computing and impedance comparison etc. Some typical simulation cases, which focus on the main factors affecting distance relay’s operation, have been simulated with the system. Simulation results show that the system is able to demonstrate the dynamic behaviors of distance protection under different operating conditions.

Although the new technology of protection and automation system of substation based on IEC61850 standard has developed rapidly in China, reliability measures depending on this technology need to be further researched. By taking advantage of convenient information sharing, two kinds of new schemes, shared backup protection unit (SBPU) and signal backup (SB), have been proposed to solve the failure problem of protective devices and current/voltage transducers respectively, and the working principle of these two schemes are also described. Furthermore, the key technologies of on-line diagnosis of protective devices’ failure and on-line status diagnosis of optical or electronic current/voltage transducers to realize the two schemes are proposed.

Vector shift (VS) is one of the typical methods used for islanding detection in distributed generations. This paper investigates the impact of both the active power imbalance and load variation on VS method. The investigation was conducted via simulation test in the power system dynamic simulation laboratory of Shandong University. The results show that it will take longer time for the VS relay to detect islanding state with the decrease of active power imbalance. In some cases, the vector shift angle is smaller than the setting and VS method would not be able to detect islanding state. In addition, the performance of VS method is impacted by the load variation in normal operation in which the distributed generator is operated in parallel with the main grid. The simulation results show that VS method would cause nuisance tripping if the load changes sharply. It can be summarized that VS method would be unable to reliably discriminate islanding state and normal system disturbances in some cases.

This paper proposes an advanced substation integrated protection communication system based on the latest development in power system. The integrated protection communication system within a substation comprises a number of major components such as the merging unit, communication network and integrated protection unit. The design and capability evaluation of the communication network based on IEC61850 are focused on. Results show that huge information from 4 merging units can be transmitted real-time via adopting 100 Mbit/s optical fiber in a substation, and the proposed communication network is able to achieve required performance.

The definition of reactive power for non-sinusoidal conditions is a controversial issue. The mathematical treatment of nonlinear loads in power systems is also unsettled. This paper starts with the decomposing of apparent power in the cases of linear and nonlinear loads. When harmonics are present, apparent power is composed of active power, reactive power, and disturbed reactive power. Linear element can be defined as the element without disturbed reactive power. This definition is based on a practical engineering concept which can separate the contribution from the apparent power into utility-duty part and custom-duty part. The field investigation of home-used facilities was conducted. Also the data acquisition in the 0.4 kV distribution systems was completed. Moreover, the loss increase due to the nonlinear loads was estimated. Nonlinear loads can be a dominant effect with respect to reactive power and power factor. Field data from a number of nonlinear load types indicate that the disturbed reactive power can cause significant losses in utility supply systems.

The modern travelling wave based fault location principles for transmission lines are analyzed. In order to apply the travelling wave principles to HVDC transmission lines, the special technical problems are studied. Based on this, a fault locating system for HVDC transmission lines is developed. The system can support modern double ended and single ended travelling wave principles simultaneously, and it is composed of three different parts: travelling wave data acquisition and processing system, communication network and PC based master station. In the system, the fault generated transients are induced from the ground leads of the over-voltage suppression capacitors of an HVDC line through specially developed travelling wave couplers. The system was applied to 500 kV Gezhouba-Nanqiao (Shanghai) HVDC transmission line in China. Some field operation experiences are summarized, showing that the system has very high reliability and accuracy, and the maximum location error is about 3 km (not more than 0.3% of the total line length). Obviously, the application of the system is successful, and the fault location problem has finally been solved completely since the line operation.

Induction motor faults including mechanical and electrical faults are reviewed. The fault diagnosis methods are summarized. To analyze the influence of stator current, torque, speed and rotor current on faulted bars, a time-stepping transient finite element (FE) model of induction motor with bars faulted is created in this paper. With wavelet package analysis method and FFT method, the simulation result of finite element is analyzed. Based on the simulation analysis, the on-line fault diagnosis system of induction motor with bars faulted is developed. With the speed of broken bars motor changed from 1 478 r/min to 1 445 r/min, the FFT power spectra and the wavelet package decoupling factors are given. The comparison result shows that the on-line diagnosis system can detect broken-bar fault efficiently.

A new fault isolation and restoration technique employing local Ethernet network for the looped MV circuit is presented. It can isolate all short circuit faults in the loop within 300 ms and restore the supply of healthy sections in less than 1.2 s. A reliable fault location method of isolating the single phase-to-ground fault (SPGF) in the non-effectively earthed network, which makes use of the fault generated trnasient signals, is also proposed. And the method locates the SPGF by examining transient zero-mode current correlation, which is not influenced by the neutral grounding mode and need no additional device. Laboratory test and simulation results show the proposed techniques are feasible, and significantly improve the supply reliability.

Embedded Ethernet technology has been utilized increasingly widely as the communication mode in the substation automation system (SAS). This paper introduces the current applying situation about embedded Ethernet in SAS First. After analyzing the protocol levels used in SAS based on embedded Ethernet and the differences between the TCP and UDP, UDP/IP is selected as the communication protocol between the station-level and bay-level devices for its real-time characteristic. Then a new kind of implementation of the embedded Ethernet is presented based on hardware protocol stack. The designed scheme can be implemented easily, reduce cost significantly and shorten developing cycle.