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Abstract
Voltage and current harmonics seriously affect electricity power supply quality. Such hannonics produced by electronic devices and non-linear loads in the. network create major problems to the quality of the power network. The harmful effects of harmonics on equipments can be long term effects and/or instantaneous effects. The long term effects are mainly thermal producing additional losses and overheating of the equipments causing excessive aging or even damage to transformers and associated rotating machines.
The instantaneous effects of harmonics are associated with failures, malfunctions or downgraded performance of devices through displacement of zero crossing of voltage wave \j’ and current wave causing errors in measurements of measuring instruments and performance
.’ of protective relays which lead to increase in the energy consumption measurements and malfunctions of the power system protective relays.
The purpose of this study is to present the current state of knowledge of the effects of waveform distortion on fault impedance measured by digital distance relays.
Protective relays are designed for 50 hertz sine-wave operation, and all perform reliably in the ’; absence of significant wave distortion. Even with the growing base, the nonlinear loads of pulse rectifiers, variable speed drives, and uninterruptible power supplies, the wave distortion
; must be severe before a distinction can be made. This study investigates the severe case of six ;pulse rectifier current waveforms. Collectively, this example provides the background to ,discuss the philosophy of ideal response and draw conclusions as to the degree of wave distortion effect.
Microprocessor relays execute algorithms that are mathematical procedures. They produce ranalytic characteristics that can be described accurately by an equation. ’We therefore have the . pportunity to calculate the response to specified waveforms. This study presents the response f microprocessor relays to such waveforms as odd harmonics produced by six pulse onverter.
e key to the behavior of microprocessor relays is the output of the digital filter. This is tained by sampling sine-wave currents and/or voltages at discrete time intervals. A fixed
umber of instantaneous samples per cycle are converted to digital quantities by an AJD nverter and stored for processing.
igital filtering is the simple process of multiplying the successive samples by predetermined efficients and then combining them to obtain digital quantities representing the phasor . mponents of the input.
ennore, in this study digital filter is introduced to filter out harmonics and de component m relay input distorted waveform, then filter is tested to show how that filter is able to tract fundamental from distorted waveform.
uency spectrum is calculated for filter input and output waveforms to indicate harmonic tent and filter efficiency.
the other hand, this study illustrates that, for the particular system to be studied, the-first¬e protection of the digital distance relays will overreach due to harmonics.