Effrina Yanti Hamid

Wavelet-based data compression of power system disturbances using the minimum description length criterion

This paper introduces a compression technique for power disturbance data via discrete wavelet transform (DWT) and wavelet packet transform (WPT). The data compression leads to a potential application for remote power protection and power quality monitoring. The compression technique is performed through signal decomposition up to a certain level, thresholding of wavelet coefficients, and signal reconstruction. The choice of which wavelet to use for the compression is of critical importance, because the wavelet affects reconstructed signal quality and the design of the system as a whole. The minimum description length (MDL) criterion is proposed for the selection of an appropriate wavelet filter. This criterion permits selection not only of the suitable wavelet filter but also the best number of wavelet retained coefficients for signal reconstruction. The experimental study has been carried out for a single-phase to ground fault event, and the data compression results of using the suitable wavelet filter show that the compression ratios are less than 11 % and are reduced to more than a half of that percentage value by implementing an additional lossless coding.

Impact of the 1997–98 El Niño Event on lightning activity over Indonesia

The 1997-98 El Niflo was one of the strongest El Nino Southern Oscillation (ENSO) events of this century. The major impact of the sea surface temperature (SST) change during this El Niflo event was the shift in convection activity from the western to the central and eastern Pacific ocean affecting the response of rain-producing cumulonimbus. As a result, convective rainfalls were suppressed near the Western Pacific regions and the Maritime Continent including Indonesia. On the other hand, the lightning activity during the El Nino period increased in contrast (on the average by 57%). As observed by the Tropical Rainfall Measuring Mission (TRMM) Lightning Imaging Sensor and Precipitation Radar, the convective storms during the El Nino were more intense. This was supported by the evidence that the El Nino storms had greater vertical developments and thicker zones containing ice phase precipitation.

Wavelet packet transform for RMS and power measurements

This paper proposes an approach based on wavelet packet transform (WPT) for root mean square (RMS) and power measurements. The algorithm can simultaneously measure the distribution of the RMS and power with respect to individual frequency bands from the wavelet coefficients associated with each voltage current pair. The advantage of the WPT is that it can decompose a waveform into uniform frequency bands, which are important for identification of harmonic components and measurement of harmonic parameters. The algorithm is validated using simulated waveforms.

Wavelet and Wavelet Packet Compression of Power System Disturbances

This article introduces a compression technique for power disturbance data via discrete wavelet transform (DWT) and wavelet packet transform (WPT). The data compression leads to a potential application for remote power protection and power quality monitoring. The compression technique is performed through signal decomposition up to a certain level, thresholding of wavelet coefficients, and signal reconstruction. The choice of which wavelet to use for the compression is of critical importance, because the wavelet affects reconstructed signal quality and the design of the system as a whole. The minimum description length (MDL) criterion is proposed for the selection of an appropriate wavelet filter. This criterion permits to select not only the suitable wavelet filter but also the best number of wavelet retained coefficients for signal reconstruction. The experimental study has been carried out for a single-phase to ground fault event, and the data compression results of using the suitable wavelet filter show that the compression ratios are less than 11% and are reduced to more than a half of that percentage value by implementing an additional lossless coding.

TRMM/LIS observations of lightning activity over Indonesia

A general statistical description of lightning activity on and around Indonesia is reported. Analysis on the collected data from a space-based lightning sensor, TRMM/LTS, during 18 months observation reveals that this region has high number of lightning flashes. Based on space-based measurement, the authors have made a lightning frequency map over Indonesia and temporal variation of lightning activity over the five biggest islands in Indonesia, which are useful for the lightning protection design of power transmission systems. The majority of the flashes are on the land and the western part experiences higher lightning occurrence than the eastern part. General patterns of the diurnal lightning activity are mainly characterized by the lightning activity in the afternoon.