Jovitha Jerome

Assistant Professor

Key words:

Distribution automation, Electric machinery, Power quality, Power system operation, State estimation

Research description:

Prominent features of electrical distribution are radial or near radial structure; multiphase, unbalanced, grounded or ungrounded operation; dispersed generation; multiphase, multi-mode control distribution equipment; unbalanced distributed loads and extremely large number of branches/nodes. In order to perform the desired functions of distribution management system (DMS), a data acquisition system for distribution networks is needed similar to the real time supervisory control and data acquisition system (SCADA) of energy management system (EMS) used for transmission networks. Some of DA application functions are distribution power flow, distribution state estimation, distribution short circuit analysis, distribution fault location, distribution feeder reconfiguration, and distribution feeder voltage and var control. However, the on-line power flow and state estimation algorithms employed in EMS cannot be used in a DMS. This is because the basic structure of the EMS on-line power flow and state estimation is based on the assumptions which are not generally valid for distribution systems. The transmission systems are generally assumed to operate under balanced three-phase conditions, and the network is a symmetrical three-phase system that is fully described with its positive sequence network. The R/X ratio of distribution lines in general are high and the fast decoupled models and solution methods based on the assumption that R/X ratio of lines are quite small, may fail to provide solution to the distribution networks. The distribution systems may also require information of all the phasor quantities, as the system is generally unbalanced.

In view of the above, the research concentrates on the development of new and robust algorithms related to network configuration, power flow analysis, reactive power compensation, state estimation and fault analysis for application in distribution automation.

For reliable supply of power to consumers, distribution networks are fed from alternative sources/substation feed-points. In real time environment distribution network configuration changes dynamically due to switching. Real time network model depends on the correctness of the network topology determined from the telemetered data. This research presents a network topology processing (NTP) algorithm suitable for distribution networks. A simple data structure for distribution network connectivity information storage is proposed for efficient implementation of network topology processing. The developed method has been tested on a large distribution network with several feeders.

An efficient load flow solution technique is required as a part of the distribution automation system for taking various control and operation decisions. A robust three-phase power flow algorithm is presented in this research. This method exploits the radial nature of the network and uses forward and backward propagation technique to calculate branch currents and node voltages. The proposed method considers all aspects of three-phase modelling of branches and detailed load modelling. The merits of the method are, guaranteed convergence even for heavily loaded network with poor voltage profile. The method has been tested on practical distribution systems with many feeders emanating from grid substation with large number of nodes and branches. The application of the proposed method is also extended to find optimum location for reactive power compensation and network reconfiguration for planning and day-to-day operation of distribution networks.

Distribution state estimators (DSE) will also play a critical role in distribution management system to estimate those real-time system states which are unable to be obtained from the limited measurement instruments in the distribution network. The success of DAS largely depends on the availability of reliable database of the control centre and thus requires an efficient state estimation (SE) solution technique. An efficient three-phase state estimation algorithm for application to radial distribution networks is presented . The method estimates the line flows, node voltages and loads at each node based on the measured quantities. The SE cannot be executed without adequate number of measurements. The extension of the method to the network observability analysis and bad data detection is also discussed. The proposed method has been tested on a few sample and practical distribution networks with simulated data for real-time measurements.

Unlike in transmission system, distribution networks may not be provided with protective devices or circuit breakers in each branch of the feeder. Though, RTUs may be installed at various nodes/branches of the feeder for various measurements, circuit breakers may be only at the substation/switching station in the network. For any fault in the feeder, a large part of the feeder, may be isolated depending on the circuit breaker installation. For the purpose of speedy repair work and maintenance, it is important to find the exact fault location and type of fault. An algorithmic approach for finding the location and type of fault based on the three phase measurements obtained for state estimation is presented. Results of the simulated fault conditions on practical distribution systems are also presented.

Several 11 kV sample systems of 12 node, 18 node, 19node, 28 node, 38 node and a 132/33 kV practical system with 7 major feeders, nearly 1000 nodes, several switching stations/feed-points are used for testing the proposed algorithms in this research. Results of the studies indicate that the developed algorithms are suitable for application to practical systems.

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