Theses and Dissertations (Power Engineering)

Permanent URI for this collection

https://hdl.handle.net/10352/195

Browse

Browsing Theses and Dissertations (Power Engineering) by Author "Walker, J. J., Prof."

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    A testing and verification protocol for a modern bus bar transfer scheme based on the transfer philosophy and theory of voltage decay
    (Vaal University of Technology, 2020-04) Van Rooyen, Johannes Petrus; Le Roux, B. J.; Walker, J. J., Prof.
    This dissertation focuses on the creation of a testing protocol or procedure for verification of a modern motor bus bar transfer scheme. There are four main transfer methods addressed during this study and with it the main parameters affecting the operation of such a system. The complete construction of the simulation and training panel is described and with it the outline of the testing protocol for using this panel is given. Some simulation work was done to calculate the correct verification times based on mathematical formulation to lay out the criteria for verification of transfer methods when testing with a modern three phase test bench. On completion of result documentation, a detailed analysis is conducted to generate the testing protocol which is also discussed in detail. From the test results obtained it was possible to accurately test the 4 common transfer methods using the theory of voltage decay as a guideline, but the protocol will have to be adjusted to suit individual transfer system needs as each transfer system may be unique in design and function although the basic principles outlined during this report will stay the same. Possible steps to take when adjusting the protocol were addressed and some future work for testing motor bus bar transfer schemes was suggested.
  • Thumbnail Image
    Item
    Correlation of different methods to determine the corona inception stress on overhead conductors under HVDC application
    (Vaal University of Technology, 2022-04-06) Sibanyoni, H. M. B.; Djeumen, J. S.; Walker, J. J., Prof.
    This dissertation’s focal point is on the correlation of different methods to determine the corona inception stress on overhead conductors under high voltage direct current (HVDC) application. The corona phenomenon is one of the key elements that should be considered when designing high voltage (HV) transmission lines. This phenomenon is known to compromise the efficiency of transmission lines and may cause electromagnetic interference (EMI) in telecommunication lines. Corona measurement methodologies form an integral part in the detection, measurement and isolation of corona discharges. The international electro-technical commission IEC 60270 specification addresses the electrical method using a coupling capacitor and acquisition unit for the detection and measurement of partial discharges. However, there are also non-conventional methods available, namely the inductive method, which uses high frequency current transformers (HFCT), acoustic methods and optical methods for detection of corona discharges (corona camera). These above-mentioned corona measurement methodologies have various advantages and disadvantages with the main difference being in the location of the sensor. The coupling capacitor is connected directly to the main circuitry of the power system, the HFCT is connected in the earth connection and the acoustic sensor as well as the corona camera being placed at a safe distance away from the system. The electrical method using a coupling capacitor is the only method that can be calibrated to measure current by means of electromagnetic coupling. The HFCT transforms the leakage current containing a frequency bandwidth flowing in the earth connection that are due to corona discharges. The corona camera visualises, locates the corona discharge point and displays the partial discharge intensity by detecting the ultraviolet radiation photon count rate. For the purpose of this dissertation, the following corona measurement methods are under review: Electrical method, inductive method and optical method. The acoustic method was not reviewed because the location of the corona measurement device is the same as that of the optical method, which is at a safe distance away from the power system. The corona measurement tests were performed in a high voltage laboratory using a corona cage. The test methodology was based on gradually increasing the voltage until the corona inception voltage is reached for both positive and negative polarities. The results show a difference in the measured inception voltage for the different methods and that the location of the corona measurement devices has an impact on the measured corona inception voltage. The results indicate that connecting the corona measurement device directly to the main circuitry of the system, as is the case with the electrical measurement method using a coupling capacitor, will be the most sensitive method and result in the lowest measured corona inception voltage.
  • Thumbnail Image
    Item
    Displaced neutral on woodpole structures with 300 kv basic insulation level rating (BIL)
    (Vaal University of Technology, 2022-03-06) Becker, Taryn Robin; Britten, A. C., Prof.; Walker, J. J., Prof.
    The influence that the geometry of the woodpole structure has on the voltage developed across the 500 mm basic insulation level (BIL) coordination gap and conductive bonding accessories is discussed in this dissertation to further understand possible reasons for failures of woodpole structures as experienced in the field. A scaled woodpole structure comprising of porcelain insulators was erected under laboratory conditions to assess the relationship between the voltage developed across the 500 mm insulation coordination gap under balanced and unbalanced system conditions. Other parameters including the leakage current behaviour as well as the phase relationship between the under these conditions were also investigated. The laboratory scaled structure was energised using three single phase 132 kV voltage transformers. Furthermore, a two-dimensional model was developed to simulate the electric field condition in and around the phase insulators and the coordination gap using QuickfieldTM, a finite element (FEM) simulation software. The experimental, as well as the simulation results, showed that the configuration of the insulators has an influence on the voltage developed across the coordination gap. The two structures with different insulator configurations were considered with porcelain insulators. The difference between these configurations was the installation of the insulators, for configuration 1 all the insulators were erected in the vertical upright position whereas for configuration 2 the outer two insulators were inverted downwards in the strain position. The magnitude of the BIL voltage developed across the gap was the highest for configuration 2 under balanced conditions in comparison to configuration 1 when all the insulators are upright, this condition is true for both the laboratory model and well as the simulation model. Certain scenarios were used to compare the scaled woopole model and the 2D FEM model. The parameters such as voltage, leakage current and phase relationship under balanced and unbalanced conditions were considered. Based on the more common network faults such L-L fault, L-G fault, L-L-G and L-L-L-G faults, the approach looks at a more specific fault and the impact this fault has on the deterioration of the wooden structure. The emphasis is on what occurs in the field when a phase is disconnected from its insulator or when more than phase is disconnected from the structure. Included in the analysis, is the influence of the insulator geometry and its role. Findings from the laboratory structure and FEM model indicated that the worse-case condition was for configuration 2, when phase B is disconnected from structure. When two phases were disconnected, results from the FEM model indicated that configuration 1 was worse-case compared to that of the laboratory structure have higher values measured on configuration 2 when only phase A is connected to the structure.