A novel frequency computation technique suitable for single or three phase voltage signals is proposed. The method is based on a generalization of the zero crossing detection to a level crossing detection. This yields several estimates of the frequency within one cycle. A composite "best estimatet" is obtained by an appropriate weighted average of these estimates. The method is insensitive to amplitude variations, unbalance and is capable of tracking small frequency deviations in as short a duration as a fraction of a cycle. The measurement scheme is particularily suitable for integration with the digital schemes for real-time monitoring control and protection of power systems.

A New Technique for Rapid Tracking of Frequency Deviations Based on Level Crossings

This paper describes the design and test results of a Kalman filtering based digital distance protection scheme. A brief review of voltage and current Kalman filters is followed by sensitivity analysis due to incorrect model parameters. The complete scheme for fault detection, classification, zone computation, and fault location calculation is tested for all types of faults at different locations using simulated data. The major parts of the scheme were tested using the available recorded data. The test results indicated that the proposed scheme has a mean operating time of a quarter of a cycle, insensitive to incorrect model parameters, and represents a low computer burden.

A New Kalman Filtering Based Digital Distance Relay

This paper presents a novel method of classifying transmission line shunt faults. Most algorithms that are employed for analyzing fault data require that the fault type be classified. The older fault type classification algorithms are inefficient because they are not effective under certain operating conditions of the power system and may not be able to accurately select the faulted transmission line if the same fault recorder monitors multiple lines. The technique described in this paper has been proven to accurately identify all ten types of shunt faults that may occur in an electric power transmission system. The other advantage of this technique is that it can be used where multiple transmission lines are present. It is able to identify the faulted line even if secondary effects are recorded in the unfaulted lines.

An accurate fault classification technique for power system monitoring devices

The paper describes a method of determining transient apparent impedances of faulted transmission lines, as would be seen by a digital distance relay. Typical relay operating results are presented. The method described in this paper may be applied to any existing digital distance relay and digital filter algorithms, and therefore enables one to seek out what may be considered the best of optimal relay and filter algorithms.

Determination of Transient Apparent Impedances of Faulted Transmission Lines

In this paper we present a simple and practical algorithm for the estimation of uncertain parameters of linear systems. The uncertainty is twofold, involving random observation noise, and possible jumps in the parameter values. The jumps may occur at unknown points in time, and are of unknown magnitudes and directions. The algorithm is based on the Kalman filter, with a single-sample hypothesis test, which is used to employ a three-state decision rule (yes, no, maybe). The "maybe" choice invokes a fading memory Kalman filter. The overall algorithm contains the constant parameter filter, fading memory filter, and the set of tests and rules that enable it to switch back and forth between the two filters. Application examples are presented.

Kalman filter with hypothesis testing: A tool for estimating uncertain parameters

The design of a computer based impedance relay is discussed and a multi-function approach is proposed which incorporates metering, fault arcniving and frequency monitoring. Results from a prototype installation are presented.

P. W. Davall

Papers

A Software Design for a Computer Based Impedance Relay for Transmission Line Protection