Modabber Ahmed Khan

Generation and harmonics in interior permanent magnet wind generator

This paper investigates the harmonics of voltages and currents of interior permanent magnet wind generators for wind energy conversion system (WECS). The generated voltages of an interior permanent magnet wind generator (IPMWG) are fed to a three-phase diode bridge rectifier in order to produce dc power. However, the use of diode bridge rectifier introduces high intensity of harmonics in the generated currents of the IPMWG. The harmonic contents of laboratory 1 kW, 5 kW, and 45 kW interior permanent magnet wind generators for wind energy system are analyzed for different rotor speed of the wind turbine. The fast Fourier transform (FFT) is used to determine the voltage and current harmonics of an IPM wind generator. The analyses have revealed that 5th, 7th, and 11th harmonics are significant in the generated currents of the IPMWG using the straight type magnet in the rotor. It is also to be noted from these analyses that both fundamental and 5th harmonics of output currents of the IPMWG vary linearly with the rotor speed of the wind turbine.

High-throughput nucleotide sequence analysis of diverse bacterial communities in leachates of decomposing pig carcasses

The leachate generated by the decomposition of animal carcass has been implicated as an environmental contaminant surrounding the burial site. High-throughput nucleotide sequencing was conducted to investigate the bacterial communities in leachates from the decomposition of pig carcasses. We acquired 51,230 reads from six different samples (1, 2, 3, 4, 6 and 14 week-old carcasses) and found that sequences representing the phylum Firmicutes predominated. The diversity of bacterial 16S rRNA gene sequences in the leachate was the highest at 6 weeks, in contrast to those at 2 and 14 weeks. The relative abundance of Firmicutes was reduced, while the proportion of Bacteroidetes and Proteobacteria increased from 3–6 weeks. The representation of phyla was restored after 14 weeks. However, the community structures between the samples taken at 1–2 and 14 weeks differed at the bacterial classification level. The trend in pH was similar to the changes seen in bacterial communities, indicating that the pH of the leachate could be related to the shift in the microbial community. The results indicate that the composition of bacterial communities in leachates of decomposing pig carcasses shifted continuously during the study period and might be influenced by the burial site.

Design and performance of a double-layered interior permanent magnet generator

This paper introduces the design and performance analysis of an interior permanent magnet generator (IPMG) for applications in low speed wind turbine systems. The developed design is based on optimizing the geometry of double-layered permanent magnets (PMs), which are buried in the rotor body of an IPMG. The geometry of the double-layered permanent magnets is optimized and simulated using the 2-D finite element analysis method (FEA). The optimization of the PMs is established based on the induced electromotive force (EMF), harmonic contents of the stator current and torque ripples at low speeds. The optimization shows that the π-shape double-layered permanent magnets geometry is capable of inducing an EMF with the high magnitude and low harmonic contents, along with producing stator currents with the low harmonic contents and minimum torque ripples.

A Study on Filtration Effect of Anaerobic Digestion Wastewater by Composition of Filtration Layer Materials

This study was carried out to compare the filtration effect of anaerobic digestion waste water by compost filtration bed. Three types of filtration systems were set for filtration test following to composition of bedding materials. Two filtration systems were filled with sawdust, rice-hull and wood-chip. And the other was filled with sawdust and rice-hull. Anaerobic digestion waste water was applied evenly on the surface of the filtration bed with spraying nozzle. The concentration of nitrogen, biochemical oxygen demand (BOD), suspended solids (SS) of anaerobic digestion waste water was decreased by filtration treatment. The total nitrogen content was decreased from 1,313 mg/L to 1,090~1,293 mg/L and BOD concentration was decreased from 529.7 mg/L to 125~162.3 mg/L, respectively. The SS content was decreased from 69~79% by filtration process. In addition, the electrical conductivity (EC) was decreased from 10.22 ds/m to 7.91~8.31 ds/m.

Diagnosis and Protection of Stator Faults in Synchronous Generators Using Wavelet Transform

This paper presents a novel application of wavelet transform for the diagnosis and protection of stator faults in synchronous generators. The instantaneous powers of the wavelet packet transformed coefficients (dd2) of line voltages and currents decomposed up to the second level of resolution of the wavelet packet tree using a mother wavelet are used to detect and differentiate different faulted conditions from normal (unfaulted) conditions. The performance of this newly devised protection technique is evaluated by simulation results as well as by experimental results. The complete protection scheme incorporating the wavelet power based detection algorithm successfully implemented in real-time using the ds1102 digital signal processor board for a laboratory 1.6 kW three-phase synchronous generator. The stator phase unbalance, single line to ground (L-G) fault, line-to-line (L-L) fault and turn-to-turn fault are investigated in order to evaluate the performance of the protection technique. In order to prove the superiority of the proposed protection technique over the conventional techniques, a comparison between the proposed and the conventional discrete Fourier transform (DFT) based diagnosis scheme is made at different dynamic operating conditions.

Effect of Aeration on Fertilization and Sludge Accumulation of Pig Slurry

Two types of reactors were set to investigate the change of characteristics of pig slurry by aeration during fertilization period. One system was equipped with air diffuser to supply oxygen to pig slurry for liquid fertilization, but there was no air diffuser in the other system. Air supply to the experimental systems was regulated by air flow meter. The reactors were set up in the laboratory to protect the pig slurry from external condition such as temperature and humidity changes. Maintaining optimal pH range in the experimental reactors is an important factor for liquid fertilization of pig slurry. In this study, pH ranges of aerobic reactor and anoxic reactor was 7.04~7.19 and 7.34~7.81, respectively. The temperature of aerobic reactors was 2~3°C higher then indoor temperature. The amount of sludge accumulated at the bottom layer of non-aerated reactors was 4~5 times more than that of aerated reactors. (