Browsing by Author "Van Nierop, Johan H"

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    Electric field mill for the simultaneous measurement of electric field strength and ion current diensity
    (1995) Sellars, Malcolm; Van Nierop, Johan H
    In the last 20 years, the use of high voltage direct current (HVDC) power transmission has grown considerably. With the increase in the number of HVDC transmission lines and in the transmission voltages, concern has increased as to possible health effects. For research on these health effects to be carried out, it is necessary to measure the electrical environment ofHVDC transmission lines accurately. The electrical environment ofHVDC transmission lines is characterised by: Electric field strength E [Vim];Ion current density J [A/m²] ;Space charge density p [C/m³ ]. Typical values measured under HVDC transmission lines are: E = lOkV/m, J = 400nA/m² . This thesis describes the design, construction and testing of an electric field mill capable of measuring electric field strength from 0 to 25kV/m (resolution = lOV/m), and ion current density from 0 to 1000 nA/m² (resolution = 20nA/m² ). The electric field readings have an accuracy of ±8%. The ion current density readings have an accuracy of ±12%. The field mill was tested in the laboratory in a simulated HVDC environment, and found to give good performance. For operation under a HVDC line, the field mill design will need some alterations to make it weatherproof. The design considerations described in this thesis should be helpful in the design of electric field mills in general.
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    A frequency converter to power a soudronic VAA20 welding machine
    (1991) Jacques, R; Malengret, Michel; Van Nierop, Johan H
    This thesis covers the design, manufacture and testing of a frequency converter, that transforms three phase AC 380V, into one phase AC 50 to 120Hz, 100 to 650V. The inverter output is intended to power a Soudronic VAA2 O welding machine. The input to the converter was stepped down and rectified to generate an unregulated DC bus of 250V. A full bridge transistorised inverter was controlled by a 6809 microprocessor that generated pulse width modulated waveforms to derive a desired inverter output current and frequency. A base drive was developed to control the power transistor in the inverter. It facilitates the rapid switching of the transistors and provides them with overcurrent protection. The inverter was originally constructed in push-pull configuration. At 20KVA this type of inverter was found to be undesirable, so a full bridge configuration was used in the final design. The converter has been installed and is operating successfully. Many recommendations are made for the improvement of future converters. The changes will improve the operation of the converter and can also reduce the size, cost and weight of it.