This study deals with a Z-HPU (Z-source harmonic power filter unit) to suppress propagation of voltage harmonics to each bus due to resonance between line impedances in a 6.6 kV/60 Hz single-phase long distance distri...
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This study deals with a Z-HPU (Z-source harmonic power filter unit) to suppress propagation of voltage harmonics to each bus due to resonance between line impedances in a 6.6 kV/60 Hz single-phase long distance distribution lines. The 60 Hz fundamental voltage is filtered from the bus voltage by butterworth BPF (Bandpass filter), and the harmonic voltage to be suppressed is detected therefrom, and the harmonic compensation voltage and current are generated by the Z-HPU. The DC power source of Z-HPU is a bank that connects several Ballard NEXA PEMFC (Polymer electrolyte membrane fuel cells) stacks. In order to verify the harmonic propagation suppression performance of the proposed system, a case study by PSIM (Power electronics simulation tool) simulation is conducted. As a result of simulation by installing Z-HPU in parallel on bus, it can be seen that harmonics of the total bus voltage are suppressed. In particular, THD (Total harmonic distortion) in bus is the most improved from 13.3 to 5.3%. In addition, it verifies the harmonic propagation suppression characteristics in the transient state, examines the relationship between characteristic impedance and harmonic conductance for long-distance distribution lines with different line impedances, and examines the effect of these changes on the voltage THD of the terminal bus.
In the spring and summer of 1985 two surveys were conducted on the use of microcomputers by members of the Special Libraries Association. The first involved members of the Business & Finance Division, while the se...
In the spring and summer of 1985 two surveys were conducted on the use of microcomputers by members of the Special Libraries Association. The first involved members of the Business & Finance Division, while the second was taken from a sample of all members of the Association. The questions and answers dealt with several factors:1) Type of equipment and when purchased. A variety of microcomputers were acquired prior to 1983; since that time the majority responding had acquired IBMs.2) Reasons for selection of hardware and software. Availability of software packages and company policy were the chief reasons, followed by investigation and recommendation of the librarian.3) Evaluation of hardware and software. There is a tendency to purchase the most popular and well known; reviews were often found not sufficiently detailed or specific to make a decision.4) Applications. In public service the most frequent were accessing online data bases, downloading and reconfiguring data, circulation and development of individual data bases. In processing the applications depended largely upon access or availability of data from a bibliographic utility such as OCLC. Many kept internal statistical records and many also developed indexes for in-house needs. Use of micros for in-house statistics and funding were important administrative uses, as was word-processing. Staff acceptance ranged from eager anticipation and experimentation to ‘won't touch’. Many staff members would be glad to use the micro, if they knew how - but they didn't want to learn.5) Back-up of data and maintenance of equipment: an important area where awareness is growing, but still too infrequently considered.6) Training and assistance in the use of equipment and software. Most of the training was received from within the institution, such as from data-processing departments. Many individuals were self-taught. Vendors were of great help with hardware, but much less knowledgeable with the needs of the librarian for so
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