Murari Mohan Saha

Use of local measurements to estimate voltage-stability margin

Estimating the proximity of power systems to voltage collapse in real-time still faces difficulties. Beside the data management and computational issues, any central-control method is subject to the reliability of long-distance data communications. In the paper, the authors describe a new data-processing method to estimate the proximity to voltage collapse. The method (code-named SMARTDevice, for Stability Monitoring And Reference Tuning Device) employs only local measurements-bus voltage and load current-and calculates the strength of the transmission system relative to the bus. The collapse occurs when the local load approaches this value. The method is simple enough so that it can be implemented in a numerical relay. The performance of SMARTDevice is compared against the conventional undervoltage relays. It is shown that the latter can misoperate while the new device does not. SMARTDevice is in fact a new breed of voltage relay whose setpoint is automatically tuned to the power system condition.

Fault Location on Power Networks

Electric power systems will always be exposed to the failure of their components. When a fault occurs on a line, it is crucial for the fault location to be identified as accurately as possible, allowing the damage caused by the fault to be repaired quickly before the line is put back into service. Fault Location on Power Lines enables readers to pinpoint the location of a fault on power lines following a disturbance. If a fault location cannot be identified quickly and this causes prolonged line outage during a period of peak load, severe economic losses may occur and reliability of service may be questioned. The growth in size and complexity of power systems has increased the impact of failure to locate a fault and therefore heightened the importance of fault location research studies, attracting widespread attention among researchers in recent years. Fault location cannot be truly understood, applied, set, tested and analysed without a deep and detailed knowledge of the interiors of fault locators. Consequently, the nine chapters are organised according to the design of different locators. The authors do not simply refer the reader to manufacturers documentation, but instead have compiled detailed information to allow for in-depth comparison. Fault Location on Power Lines describes basic algorithms used in fault locators, focusing on fault location on overhead transmission lines, but also covering fault location in distribution networks. An application of artificial intelligence in this field is also presented, to help the reader to understand all aspects of fault location on overhead lines, including both the design and application standpoints. Professional engineers, researchers, and postgraduate and undergraduate students will find Fault Location on Power Lines a valuable resource, which enables them to reproduce complete algorithms of digital fault locators in their basic forms.

A new accurate fault locating algorithm for series compensated lines

Summary form only given as follows. This paper presents a new, accurate and robust fault locating algorithm for series compensated lines. The algorithm is developed as a one-end fundamental frequency based technique and offsets both the series compensation effect and the reactance effect resulting from the remote end in-feed. The method uses phase coordinates (abc) instead of symmetrical components [012]. The basic algorithm is presented for a line compensated by one three-phase bank of series capacitors. The presented fault locating method has been extensively tested using the EMTP model of a 400 kV 300 km transmission line. The enclosed results demonstrate very high accuracy and robustness of the algorithm.

Algorithms for locating faults on series compensated lines using neural network and deterministic methods

This paper investigates a scheme to improve the reach measurement of distance relays and fault locators for series compensated power lines. A deterministic method and a feedforward neural network method have been implemented for online calculation of the voltage across a nonlinear capacitor installation. These techniques are compared and incorporated into a new relaying scheme which is independent of the series capacitor installation, operation of the capacitor protection, and the surrounding power system elements. The proposed scheme is simple and accurate and requires only local voltage and current at the bus. Detailed testing using EMTP has been done to show the benefits of the new adaptive scheme. The results demonstrate the suitability of the techniques for real world applications.

Accurate location of faults on power transmission lines with use of two-end unsynchronized measurements

This paper presents a new algorithm for locating faults on two-terminal power transmission lines. Unsynchronized two-end voltages and currents are processed for determining the sought distance to fault and the synchronization angle. The calculations are performed initially for the lumped model of a transmission line. Then, these results are used as the initial data for the Newton-Raphson method-based iterative calculations, in which the distributed parameter line model is utilized. The delivered fault location algorithm has been tested and evaluated with the fault data obtained from versatile ATP-EMTP simulations. The sample results of the evaluation are reported and discussed.

First zone algorithm for protection of series compensated lines

This paper presents a new first zone algorithm for distance protection of series compensated lines. The algorithm detects faults with the reach of 75-85% of the line length by measuring two distinctive impedances, using three adequate regions on the impedance plane and applying appropriate logic functions. The algorithm estimates instantaneous values of the voltage drop across the series capacitors online, and compensates for this signal when calculating the impedance valid for faults behind the series capacitors. The other impedance (without compensation) is calculated for faults in front of the series capacitors. An explicit selecting procedure for the two impedances is not required since the presented relaying method asserts directly the fault within or outside the first zone. The algorithm is presented in detail and extensively tested using the EMTP model of a 400 kV 300 km transmission line. The enclosed results demonstrate high speed, dependability and security of the new algorithm.

Accurate Noniterative Fault-Location Algorithm Utilizing Two-End Unsynchronized Measurements

This paper presents a new two-terminal impedance-based fault-location algorithm, which takes into account the distributed parameter line model. The algorithm utilizes unsynchronized measurements of voltages and currents from two ends of a line and is formulated in terms of the fundamental frequency phasors of symmetrical components of the measured signals. First, an analytical synchronization of the unsynchronized measurements is performed with use of the determined synchronization operator. Then, the distance to fault is calculated as for the synchronized measurements. Simultaneous usage of two kinds of symmetrical components for determining the synchronization operator makes that the calculations are simple, noniterative, and at the same time highly accurate. The developed fault-location algorithm has been thoroughly tested using signals of Alternate Transients Program-Electromagnetic Transients Program versatile simulations of faults on a transmission line. The presented evaluation shows the validity of the developed fault-location algorithm and its high accuracy.

A self-organizing fuzzy logic based protective relay-an application to power transformer protection

In the paper the fuzzy logic based multi-criteria protective relay for a three-phase power transformer is presented. Twelve criteria used to stabilize the relay are introduced and integrated by means of multi-objective decision-making methods. The introduced protection scheme contains several internal functions and coefficients which are subject to off-line pre-installation self-setting. Three unique procedures are delivered for self-adjusting the relay, and thus, making it self-organized. The results of testing show significant gains in both sensitivity and selectivity of the self-organized relay compared with traditional approaches.

Dynamic compensation of capacitive voltage transformers

This paper presents the digital algorithm for on-line dynamic compensation of the secondary voltage of a capacitive voltage transformer (CVT). The adopted CVT model together with the assumed simplifications is given first. Next, the compensating algorithm based on digital inversion of the CVT transfer function is derived. Frequency domain analysis and quantitative evaluation of the compensation follow. The ATP-EMTP simulations are included that show the improvement of the measurement of protective criteria quantities as a result of dynamic compensation of a CVT.

A Fault-Location Method for Application With Current Differential Relays of Three-Terminal Lines

This paper presents a new method for locating faults on three-terminal power lines. Estimation of a distance to fault and indication of a faulted section is performed using three-phase current from all three terminals and additionally three-phase voltage from the terminal at which a fault locator is installed. Such a set of synchronized measurements has been taken into consideration with the aim of developing a fault-location algorithm for applications with current differential relays of three-terminal lines. The delivered fault-location algorithm consists of three subroutines designated for locating faults within particular line sections and a procedure for indicating the faulted line section. Testing and evaluation of the algorithm has been performed with fault data obtained from versatile Alternate Transients Program-Electromagnetic Transients Program simulations. The sample results of the evaluation are reported and discussed.