Sukumar M. Brahma

Effect of distributed generation on protective device coordination in distribution system

Protection of a power system is an extremely important aspect as the duality and scheme of protection decides system reliability, controllability and stability. This paper concentrates on the protection of a distribution system in the light of developments in distributed generation (DG). The conventional distribution system is radial in nature, characterized by a single source feeding a network of down-stream feeders. The protection system has traditionally been designed assuming the system to be radial. After connecting DG, part of the system may no longer be radial, which means the coordination might not hold. The effect of DG on coordination will depend on size, type and placement of DG. This paper explores the effect of DG on protective device coordination such as fuse-fuse, fuse-recloser and relay-relay. In each case, depending on size and placement of DG, there are some margins in which the coordination may hold and certain cases, where no margin is available. These conditions are identified for each case through coordination graphs.

Microprocessor-based reclosing to coordinate fuse and recloser in a system with high penetration of distributed generation

Coordination between reclosing devices (recloser) and fuse has been traditionally done in radial power distribution systems. With increasing penetration of distributed generation, the system loses its radial nature and this coordination may not hold. This paper identifies this problem using illustrative coordination graphs. An actual system is then analyzed to find out new performance requirements from the recloser to be able to coordinate with the fuse in the new system configuration. It is shown that traditional reclosers are unable to meet these requirements. It is further shown that microprocessor-based reclosers are fully competent to meet all requirements. As an example, one such actual recloser is used to successfully coordinate with a fuse under worst possible fault conditions. A method to choose recloser curves to achieve coordination is also stated. Finally, the system is simulated on PSCAD/EMTDC/sup (R)/ software and it is proved that the recloser curves chosen in the analysis holds perfectly well in operation.

Fault location on a transmission line using synchronized Voltage measurements

Many methods for fault location using synchronized phasor measurement have been reported in literature. Most of these methods use voltage and current measurements at one or both ends of a transmission line. Accuracy of current measurement is limited by the accuracy of the current transformers (CT) used. This paper describes a fault-location method for transmission lines using only synchronized voltage measurements at both ends of the line, eliminating the inherent error due to CT. The method can be applied to transposed and untransposed lines. The method is tested using results from a steady state fault-analysis program and EMTP.

Distance Relay With Out-of-Step Blocking Function Using Wavelet Transform

Out-of-step blocking function in distance relays is required to distinguish between a power swing and a fault. Speedy and reliable detection of symmetrical faults during power swings presents a challenge. This paper introduces wavelet transform to reliably and quickly detect power swings as well as detect any fault during a power swing. The total number of dyadic wavelet levels of voltage/current waveforms and the choice of particular levels for such detection are carefully studied. A logic block based on the wavelet transform is developed. The output of this block is combined with the output of the conventional digital distance relay to achieve desired performance during power swings. This integrated relay is extensively tested on a simulated system using PSCAD/ EMTDCreg software.

Fault location scheme for a multi-terminal transmission line using synchronized Voltage measurements

This paper describes a new scheme to locate a fault on a multi-terminal transmission line. It describes a simple new algorithm to identify the faulted section first. Then, to exactly locate the fault on this section, a method is described that uses the synchronized voltage measurements at all terminals. The main advantage of this method is that the current-transformer errors in the current measurements can be avoided. Since these errors can be as high as 10%, the fault location is extremely accurate with this method. The scheme can work for transposed as well as untransposed lines and is free of prefault conditions. The paper, after describing the scheme, describes very promising results from an Electromagnetic Transients Program simulation of a multi-terminal transmission line.

Fault Location in Power Distribution System With Penetration of Distributed Generation

It has been shown that coordination between protective devices in distribution systems in the presence of significant distributed generation (DG) will be disrupted. With the recent trend of adopting and integrating renewable resources and microgrids with distribution systems, it is probable that distribution systems will have significant and arbitrary penetration of DG in the near future. This will change the distribution systems to multisource unbalanced systems where protective devices may not coordinate. The fault location in this type of system will be a challenge. This paper describes a general method to locate faults in this type of system. The method uses synchronized voltage and current measurements at the interconnection of DG units and is able to adapt to changes in the topology of the system. The method has been extensively tested on a 60-bus distribution system for all types of faults with various fault resistances on all sections of the system, with very encouraging results.

Distribution System Analysis to support the Smart Grid

The “Smart Grid” refers to various efforts to modernize the power grid through the application of intelligent devices. This paper describes current thinking by members of the Distribution System Analysis Subcommittee (DSA SC) on how distribution system analysis might evolve to support the Smart Grid. Various issues related to Smart Grid and distribution system analysis are identified. The essential characteristics of distribution system analysis tools to support these issues are discussed. Relevant activities of the DSA SC are described.

Detection of High Impedance Fault in Power Distribution Systems Using Mathematical Morphology

A high impedance fault (HIF) is characterized by a small, nonlinear, random, unstable, and widely varying fault current in a power distribution system. HIFs draw very low fault currents, and hence are not always effectively cleared by conventional overcurrent relays. Various schemes are proposed to detect such faults. This paper presents a method to detect HIFs using a tool based on mathematical morphology (MM). The method is implemented alongside the conventional overcurrent relay at the substation to improve the performance of this relay in detecting HIFs. It is rigorously tested on standard test systems using PSCAD/EMTDC® to generate test waveforms, and Matlab® to implement the method. Simulation results show that the proposed method is fast, secure, and dependable.

Overview of mathematical morphology in power systems — A tutorial approach

Use of mathematical morphology (MM) in power system has been reported recently in open literature. However, MM has not been adequately discussed as a filtering tool for power system signals. This paper takes a tutorial-approach and explains the concept of MM, its derivative processes, basic MM based filters and their applications through simple reproducible examples. Characteristics of MM based filters and their associated delays are explained. The paper also shows the effect of varying different filter and signal parameters on the performance of MM based filters. The process of event detection using MM based filters is described as a typical application. Finally, a comprehensive list of the published applications of MM is provided.

Investigating the Option of Removing the Antialiasing Filter From Digital Relays

Digital relays traditionally employ sampling rates of less than 100 samples/cycle. In order to avoid aliasing due to fault transients, these relays employ an analog antialiasing filter before critical-sampling (Nyquist rate) the input waveforms coming from instrument transformers. In many applications of electrical engineering, oversampling (greater than the Nyquist rate) has long been used to simplify the requirements of an antialiasing filter with a sharp cutoff; in some cases, the filter can even be eliminated. This paper investigates this option for a digital relay. The performance of a traditional digital relay is compared with a method that uses oversampling without using an antialiasing filter. By processing a comprehensive array of fault waveforms from Electromagnetic Transients Program simulations, a suitable oversampling rate is suggested. A comparison of phasor estimates using the traditional relay and the proposed method is made for different operating and fault conditions. The results suggest that oversampling can eliminate the antialiasing filter traditionally employed in digital relays.