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A new approach is proposed to solve the directional overcurrent relay coordination problem, which arises from installing distributed generation (DG) in looped power delivery systems (PDS). This approach involves the implementation of a fault current limiter (FCL) to locally limit the DG fault current, and thus restore the original relay coordination. The proposed restoration approach is carried out without altering the original relay settings or disconnecting DGs from PDSs during fault. Therefore, it is applicable to both the current practice of disconnecting DGs from PDSs, and the emergent trend of keeping DGs in PDSs during fault. The process of selecting FCL impedance type (inductive or resistive) and its minimum value is illustrated. Three scenarios are discussed: no DG, the implementation of DG with FCL and without FCL. Various simulations are carried out for both single- and multi-DG existence, and different DG and fault locations. The obtained results are reported and discussed. Index Terms--Directional overcurrent relay coordination, distributed generation (DG), fault current limiter (FCL), looped power delivery system (PDS), short-circuit analysis.

With the publishing of IEC 61850, the global communication standard for substation automation system (SAS), interoperability issue between intelligent electronic devices (IEDs) from different venders has been resolved. However, the overall performance and extensibility of this communication network are still left unanswered. This paper introduces the modeling technique of IED generic models and the setup of a research platform for resolving those issues using the OPNET Modeler. These configurable IED models allow the engineers to easily build SAS network model with different topologies for all kinds of substations so that the dynamic performance issues could be studied and rules could be developed to guide the SAS network planning and design. Some examples of using those models to construct SAS network as well as the network performance simulation results are also included in this paper. Index Terms--Generic models, IEC 61850, intelligent electronic device (IED), OPNET Modeler, substation automation system (SAS).

In this paper, a study conducted to analyze the factors influencing the current transformer (CT) dimensioning for numerical relays is presented. The study identifies the factors contributing to the CT dimensioning. It analyzes the influence of system parameters on the dimensioning factor and also identifies the critical applications and conditions that determine the CT dimensioning. The errors introduced in phasor estimation of saturated current signals are also described in this study. Index Terms--Current transformer (CT), CT saturation, discrete Fourier transform (DFT), knee point voltage, numerical relays, phasor estimation, remanent flux, steady-state error, transient error.

In this paper, a comprehensive analysis of the impact of series capacitor on the performance of communication-aided distance protection schemes of transmission lines is presented. It is shown that not only the series capacitor and its overvoltage protection affect the distance protection of its line, but also the adjacent lines would experience protection problems. Mitigation of this problem is proposed by using new communication-aided schemes. The proposed schemes use the information available at the substation to inhibit relay malfunctions. The performance of the techniques is studied for different series capacitor locations in the transmission line. Real Time Digital Simulator (RTDS) and four sophisticated commercial relays are used for testing. The results verify the impact of series capacitor on the conventional communication-aided schemes and also the effectiveness of the proposed methods. Index Terms--Communication-aided distance schemes, pilot relaying systems, power system protection, protective relaying, series capacitor, series compensated line.

This paper presents a comprehensive analysis of the impact of TCSC on the protection of transmission lines. The TCSC is considered as a dynamical device and its transient process is modeled in order to have the response to disturbances based on its own control strategy. It is shown that not only the TCSC affects the protection of its line, but also the protection of adjacent lines would experience problems. The analysis is done first analytically by using simple models, then the power system and the protective relays are simulated in detail by Real Time Digital Simulator (RTDS). Finally, the simulation results are validated by using a commercial relay. Index Terms--FACTS devices, power system protection, protective relaying, series compensation, thyristor controlled series capacitor (TCSC).

Data packets based high-speed digital communications have opened the door for new types of applications in power system protection and control. The main obstacle in adopting Ethernet-type networks for time-sensitive communications was the data transfer characteristic of these networks. With baud rates in the gigabit-per-second range, the industry has started adopting the Ethernet networks as a viable alternative, not only because of their lower cost. This paper presents an open-system approach in which protective hardware equipment is designed to work in a clustered environment, sharing resources, data, and diagnostic functions with similar units. The Ethernet network, being capable to accommodate transparently a wide range of protocols, is used to connect the protective hardware. A model was developed for the Ethernet network to be incorporated into the power system simulation. The characteristics required from a digital relaying algorithm to be able to work with signal samples sent across data packets based networks are described in this paper. The proposed solution is implemented using a modified adaptive least-square-error algorithm and tested on a protection system that was integrated into the power system model. Index Terms--Data communication, open systems, power system protection, power system relaying, protective relaying, sampled data systems.

This paper presents a method for calculating zone-2 setting of distance relays without causing coordination problems. The proposed method is based on the impedance seen by distance relays when faults are simulated on the reach of zone-1 of primary relays for the maximum and minimum generation outputs of the power system. It is shown that the proposed method increases the reach of zone-2 relays without causing coordination problems. The proposed method is modified for use in an adaptive protection system. It is shown that further improvements can be achieved when settings are calculated using the proposed method and the prevailing system conditions. Measures to alleviate the impact of communication failure are discussed. The proposed method and its adaptive version were applied to an existing power system and some results are reported in the paper. Index Terms--Adaptive protection, backup relaying, distance relays, power system protection.

This paper describes the design, implementation and testing of an adaptive distance relay. The relay uses a fault detector to determine the inception of a fault and then uses data windows of appropriate length for estimating phasors and seen impedances. Hardware and software of the proposed adaptive relay are also described in this paper. The relay was tested using a model power system and a real-time playback simulator. Performance of the relay was compared with a fixed data window distance relay. Some results are reported in this paper. These results indicate that the adaptive distance relay provides faster tripping in comparison to the fixed data window distance relay. Index Terms--Adaptive relaying, distance relays, line protection, microprocessor-based relays.

This paper describes the development of a microprocessor based system, based on four different physical phenomena, for reliable and accurate detection and location of arcing in dry-type transformers. The proposed technique was tested for actual arcing, generated on a 15-kVA, 230/115-V Y/[DELTA] transformer enclosed in a 30' X 30' X 21' metallic enclosure. Some results showing the performance of the detection and location system are presented in the paper. The technique can be applied to detect arcing in metal-clad low-voltage/medium voltage switchgear, drives, gas insulated switchgear (GIS), generator bus-ducts, and other metal-clad electrical apparatus against arcing. Index Terms--Dry-type transformers, low-level arcing, on-line monitoring.

This paper describes the development of a multisensor device, based on four different physical phenomena, for reliable detection of low-level arcing faults in metal-clad switchgear. The proposed device was tested for actual arcing, generated on a low-voltage motor control center panel, feeding a dry type 15 kVA, 230/115 V Y/[DELTA] transformer. Some results showing the performance of the developed device are presented in the paper. The device can also be applied for detection of arcing in power electronic drives, dry type transformers, gas insulated switchgear, generator bus-ducts, and other metal-clad electrical apparatus. Index Terms--Arcing faults, metal-clad switchgear, multisensor-based protection.

An adaptive system for protecting a distribution network should determine and implement relay settings that are most appropriate for the prevailing state of the power system. This paper presents a technique for determining coordinated relay settings. The technique uses the Simplex two-phase method; Phase I determines whether the constraints selected for illustrating the conditionality between primary and back up relays are feasible, and Phase II finds the optimal relay settings. A looped distribution system, protected by directional overcurrent relays, was used for testing the technique. The tests were conducted in a laboratory environment; some results from those tests are reported in the paper.

An adaptive loss evaluation algorithm for power transmission systems is proposed in this paper. The algorithm is based on training of artificial neural networks (ANNs) using backpropagation. Due to the capability of parallel information processing of the ANNs, the proposed method is fast and yet accurate. Active and reactive powers of generators and loads, as well as the magnitudes of voltages at voltage-controlled buses are chosen as inputs to the ANN. System losses are chosen as the outputs. Training data are obtained by load flow studies, assuming that the state variables of the power system to be studied take the values uniformly distributed in the ranges of their lower & upper limits. Load flow studies for different system topologies are carried out and the results are compiled to form the training set. Numerical results are presented in the paper to demonstrate the effectiveness of the proposed algorithm in terms of accuracy and speed. It is concluded that the trained ANN can be utilized for both off-line simulation studies and on-line calculation of demand and energy losses. High performance has been achieved through complex mappings, modeled by the ANN, between system losses and system topologies, operating conditions and load variations. Keywords: capacity loss, energy loss, artificial neural network, power transmission systems

This paper describes a digital technique for protecting busbars. The technique uses positive- and negative-sequence models of the power system in a fault-detection algorithm. While phase voltages and currents are used to detect faults, parameters of the power system are not used. An analysis of the performance of the proposed technique during ct saturation and ratio-mismatch conditions is presented. The performance of the technique was investigated for a variety of operating conditions and for several busbar configurations. Data generated by emtp simulations of model power systems were used in the investigations. The results indicate that the proposed technique is stable during ct saturation and ratio-mismatch conditions. Index Terms--Busbars, current transformer saturation, microprocessor-based relays, symmetrical components.

The continuity of power supply is maintained by reconfiguring a power system as its operating state changes. The reconfiguration is done by opening and closing circuit breakers and isolators. An improper operation of a switch can damage equipment and/or adversely affect the quality of the supply to the customers. Switching operations are performed by operators (as well as by substation controllers) using pre-defined guidelines including interlocking of switches. A major obstacle in using computerized switching schemes is that interlocking logic has to be designed specifically for each substation. This paper describes the design of a software application that can be used to automatically generate interlocking schemes for substations. The software has two components, one to generate the interlocking scheme from the substation data and the other to generate switching instructions and implement them. Three examples of interlocking schemes are included in the paper. Index Terms--Substation control, Interlocking schemes, Switching operations, Computer-aided design (CAD).

Turn to turn faults usually cause smaller changes in the phase currents of a shunt reactor when fewer turns are involved. Designing a sensitive and reliable algorithm for turn to turn fault detection in shunt reactors still remains a challenge. In this paper, a novel hybrid differential algorithm has been proposed to detect turn to turn faults in shunt reactors. The proposed algorithm calculates the difference between normalized negative sequence terminal voltage and normalized negative sequence reactor current phasors. This difference value is used for detecting turn to turn fault in shunt reactors. The proposed algorithm can also identify the faulty phase. This is a significant improvement with respect to the existing negative or zero sequence based methods. The proposed algorithm does not need neural CT. Impedance values of the shunt reactors are also not needed in the calculations. The proposed algorithm can be applied to both solidly and impedance grounded shunt reactors. The performance of the proposed algorithm is evaluated using PSCAD simulations. It is found that the proposed algorithm is sensitive enough to detect lower level turn to turn faults. The proposed algorithm performs satisfactorily during system unbalances, reactor energizations, external faults, off-nominal frequency, and switch onto fault scenarios, etc. [ABSTRACT FROM AUTHOR]

Legacy distance protection introduces an intentional delay before the trip command for zone 2 internal faults. Instantaneous fault clearance in such faults can be achieved if distance relays are equipped with reliable communication. However, communication channel is not available or enabled in some lines. Besides some channels are prone to faults occurred on the line degrading their reliability. To overcome such drawbacks in instantaneous fault clearance, a local algorithm is proposed that uses the relay local signals to accelerate the trip for zone 2 internal faults. The change seen in the relay impedance resulted by remote circuit breaker operation (RCBO) is the decision criterion in this method. The related impedance change equations are analytically derived and formulated. It is shown that the proposed method outperforms the similar approaches and improves their shortcomings in light-and no-load conditions and zero resistance faults. While most of the methods in the literature are not sensitive enough to detect single-phase RCBO, which is common during single-phase transient faults, significant improvement is attained by the proposed method in this regard. Performance of the proposed method is investigated under various fault and system conditions. Simulation results disclose high reliability of the proposed algorithm during all these conditions. [ABSTRACT FROM AUTHOR]

A new approach is proposed to solve the directional overcurrent relay coordination problem, which arises from installing distributed generation. (DG) in looped power delivery systems (PDS). This approach involves the implementation of a fault current limiter (FCL) to locally limit the DG fault current, and thus restore the original relay coordination. The proposed restoration approach is carried out without altering the original relay settings or disconnecting DGs from PDSs during fault. Therefore, it is applicable to both the current practice of disconnecting DGs from PDSs, and the emergent trend of keeping DGs in PDSs during fault. The process of selecting FCL impedance type (inductive or resistive) and its minimum value is illustrated. Three scenarios are discussed: no DG, the implementation of DG with FCL and without FCL. Various simulations are carried out for both single- and multi-DG existence, and different DG and fault locations. The obtained results are reported and discussed. [ABSTRACT FROM AUTHOR]

Phasor estimation algorithms for protective relaying are required to filter out unwanted components from the input signals and retain only the components of interest. The components to be removed include harmonics and the decaying-exponential transient (dc offset) component. They affect the accuracy and the speed of convergence of the phasor estimation algorithms to a great extent This paper presents a new technique, which effectively removes the harmonics and the decaying dc component present in the input signals, within half a cycle of the power system frequency. This is achieved by means of a simple computational procedure using three off-line look-up tables. The proposed algorithm has been tested for a wide variety of signals to assess its performance. The performance is also compared with the two most popular half-cycle phasor estimation algorithms; the half-cycle least error squares algorithms and the mimic plus half-cycle Fourier algorithm. The test results show that the proposed relaying algorithm has a faster convergence and better accuracy compared to these previously proposed algorithms. The results also indicate that the proposed algorithm converges to its final value within half a cycle of the power system frequency as compared to the other two algorithms, which take more than half a cycle to converge, when a decaying dc component is present in the input. [ABSTRACT FROM AUTHOR]

Proposes a system modeling concept and an algorithm based on abductive inference for handling diagnostic problems in electrical power transmission networks. Scope of the system modeling technique and the algorithm; Basic concepts of the proposed technique; Fault diagnosis using abductive inference; Fault diagnosis algorithm; Test results of the proposed technique; Processing speed of the diagnosis module; Conclusions.