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 applicatio...

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Bibliographic Details
Published in:IEEE transactions on power delivery 2009-10, Vol.24 (4), p.1864-1868
Main Authors: Brahma, S.M., De Leon, P.L., Kavasseri, R.G.
Format: Article
Language:English
Subjects:
Aliasing
Analog-digital conversion
analog-to-digital converter (ADC)
Applied sciences
Arrays
Capacitors. Resistors. Filters
Connection and protection apparatus
Digital
Digital filters
digital relay
Digital relays
discrete Fourier transform (DFT)
Discrete Fourier transforms
Disturbances. Regulation. Protection
Electrical engineering
Electrical engineering. Electrical power engineering
Electrical power engineering
Exact sciences and technology
Faults
Frequency estimation
Oversampling
Phasors
Power networks and lines
power system protection
Power system relaying
Power system transients
Protective relaying
Sampling
Sampling methods
Various equipment and components
Voltage
Waveforms
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Summary: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.
ISSN:0885-8977
1937-4208
DOI:10.1109/TPWRD.2009.2028802