A South African review of harmonic emission level assessment as per IEC61000-3-6

Large-scale renewable power producing plants are being integrated into South African networks. Network operators need to ensure that Renewable Power Plants (RPP) do not negatively affect the power quality levels of their networks, as harmonics amongst others could become a concern. IEC 61000-3-6 details a method for allocating voltage harmonic emission limits for distorting loads. This method works well for the allocation of emission limits; however it does not address the management of harmonic emissions once a plant is connected to the network. The management of harmonic emissions requires that network operators measure or quantify the emissions from loads and generators to determine compliance. Post-connection quantification of harmonic levels and compliance is a challenge for network operators. The question asked is “How should a network operator measure/quantify the harmonic emissions of a load/generator to establish compliance with the calculated limits as per IEC 61000-3-6”. This paper reviews within a South African context methods of assessing harmonic emission levels and then evaluates these methods by means of field data. Opportunities for improvement are identified and operational requirements discussed

Extending the functionalities of shear-driven chromatography nano-channels using high aspect ratio etching

An new injection system is presented for shear-driven chromatography. The device has been fabricated by high aspect ratio etching of silicon. The performance of the injection slit is studied through the aid of computational fluid dynamics, and the first experimental results are presented

Design and implementation of injector/distributor structures for microfabricated non-porous pillar columns for capillary electrochromatography

A previously proposed foil definition is applied in the design of injector/distributor structures for solid microfabricated column structures for capillary electrochromatography. In addition to a typical bifurcated distributor, an optimized design alternative with two different configurations is experimentally evaluated. Optimized designs yielded a flat profile for the injected sample with a maximum of 3% variation from the mean width, while it went up to 18% for the typical bifurcated distributor. The implemented electrokinetic injection approach enabled controlling the volume of the injected sample accurately without sacrificing the compactness of the device design. The width of the injected sample was directly proportional to the injection time, namely 165 and 218 μm base widths were obtained for 0.6 and 0.8 s of feeding, respectively. Reducing the external porosity of the distributor by 85% compared to the typical design, optimized distributors caused a decrease in the mean flow velocity of up to 70%. However, having a flat initial plug shape enabled the separation of a mixture of Coumarin 440, 460, 480 and 540 at 1 mm downstream of the injection point in 80 s, while it was even not possible to detect the C440 signal for a typical bifurcated design

Exploring the speed limits of liqui chromatography using shear-driven flows through 45 and 85 nm deep nano-channels

We explored the possibility to perform high speed and high efficiency liquid chromatographic separations in channels with a sub-100 nm depth. The mobile phase flow through these nano-channels was generated using the shear-driven flow principle to generate high speed flows which were the equivalent of a 12000 bar pressure-driven flow. It was found that the ultra-fast mass transfer kinetics prevailing in this range of small channel depths allow to drastically reduce the C-term contribution to band broadening, at least up to the upper speed limit of our current set-up (7 mm s−1 mobile phase velocity), leaving the inescapable molecular diffusion (i.e., B-term band broadening) as the sole detectable source of band broadening. Due to the greatly reduced mass transfer limitations, 50000 to 100000 theoretical plates could be generated in the span of 1 to 1.5 seconds. This is nearly two orders of magnitude faster than the best performing commercial pressure-driven UHPLC-systems. With the employed channel depths, we appear to have struck a practical lower limit for the channel miniaturization of shear-driven flows. Despite the use of channel substrates with the highest grades of optical flatness, the overall substrate waviness (on the order of some 5 to 10 nm) can no longer be neglected compared to the etched channel depth, which in turn significantly influenced the local retention factor and band broadening