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Geomagnetically induced currents (GIC) in large power systems including transformer time response
Includes bibliographical references
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
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Department of Electrical Engineering
2016
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| _version_ | 1867613305760120832 |
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| access_status_str | Open Access |
| author | Oyedokun, David Temitope |
| author2 | Gaunt, C Trevor |
| author_browse | Gaunt, C Trevor Oyedokun, David Temitope |
| author_facet | Gaunt, C Trevor Oyedokun, David Temitope |
| author_sort | Oyedokun, David Temitope |
| collection | Thesis |
| description | Includes bibliographical references |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/16708 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:34:00.978Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2016 |
| publishDateRange | 2016 |
| publishDateSort | 2016 |
| publisher | Department of Electrical Engineering |
| publisherStr | Department of Electrical Engineering |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/16708 Geomagnetically induced currents (GIC) in large power systems including transformer time response Oyedokun, David Temitope Gaunt, C Trevor Folly, Komla A Electrical Engineering Includes bibliographical references Geomagnetically induced currents (GIC) are the result of changing geomagnetic fields which are a consequence of a geomagnetic disturbance (GMD). The flow of GIC through transmission lines and transformers across the power network could have severe consequences, if the magnitudes of the GIC are high enough. Problems that could arise from the flow of GIC in transmission networks include an increase in the amount of reactive power demand by GIC-laden transformers, half-wave saturation, excessive heating in transformers, incorrect operation of transmission line protection schemes and voltage collapse in affected sections of the network. In the past, GIC were calculated without taking the transformer's response time into account. The limitation of this approach is that the size and core type of the transformer is neglected. This may affect the assessment of GIC in the power network as the flux pattern and winding inductance distribution are not uniform across all transformer core structures. This thesis postulates that these characteristics could have far-reaching effects on the GIC that flows through a transformer as a function of time. Based on this assumption, a novel way of calculating GIC is introduced in this thesis. This method combines the uniform plane wave model and the network Nodal Admittance Matrix (NAM) method and incorporated for the first time, the transformer time response, which does not appear to have been considered in previous calculation methods. A general formula, which describes the transformer's time response to GIC was derived, followed by the derivation of the electric field induced in each transmission line. A key input to the prospective GIC with transformer time response calculation, is a set of piecewise linear equations derived from a laboratory test and PSCAD simulations. These suitably characterise the response of three transformer core structures, namely: bank of single phase (3(1P-3L)), three-phase three-limb (3P-3L) and three-phase five-limb transformers (3P-5L). Each of these core types were considered as a Generator Step-up Unit (GSU) and a Transmission Transformer (TT). The results of the laboratory experiment and simulations in PSCAD led to the conclusion that the transformer time response to GIC is irregular across the transformer cores that were tested. The 300 VA transformer core structure with the shortest response time is the 3P-3L, followed by the 3P-5L and the 3(1P-3L). For the 500 MVA transformers, the order was: 3P-3L; 3(1P-3L); and 3P-5L. The 3P-3L transformers permit the flow of GIC through the windings of the transformer over a shorter length of time. Therefore based on the order in response time, during GMDs leading to higher GIC, the prospective GIC with or without transformer time response flowing through 3P-3L transformers will be similar. Furthermore, the response time to GIC in 3P-3L, 3P-5L and 3(1P-3L) transformer core types are load-dependant. The 3(1P-3L) and 3P-5L transformers operating as TT's (modelled as transformers at 40 % load) have the longest response time to GIC, while 3P-3L transformers operating as a GSU (modelled as transformers at full load) have the longest response time to DC. The shortest response time to DC was with a GSU at light load (modelled as transformers at 80 % load), which was consistent across the three transformer core types. This correlates well with the notion that power networks could stand a better chance of surviving a high GMD when all generating units and loads are online. Three different core structures were modelled with a variation of DC current levels and load conditions, both in PSCAD and in the laboratory. These results are unique to the transformer models used, but are representative of major types of core configurations used on power networks. These results provide an indication that it is incorrect to lump the responses of all transformers and transformer time response should be taken into consideration, especially when sampling at intervals as low as 2 seconds. 2016-02-03T14:09:58Z 2016-02-03T14:09:58Z 2015 Doctoral Thesis Doctoral PhD http://hdl.handle.net/11427/16708 eng application/pdf Department of Electrical Engineering Faculty of Engineering and the Built Environment University of Cape Town |
| spellingShingle | Electrical Engineering Oyedokun, David Temitope Geomagnetically induced currents (GIC) in large power systems including transformer time response |
| thesis_degree_str | Doctoral |
| title | Geomagnetically induced currents (GIC) in large power systems including transformer time response |
| title_full | Geomagnetically induced currents (GIC) in large power systems including transformer time response |
| title_fullStr | Geomagnetically induced currents (GIC) in large power systems including transformer time response |
| title_full_unstemmed | Geomagnetically induced currents (GIC) in large power systems including transformer time response |
| title_short | Geomagnetically induced currents (GIC) in large power systems including transformer time response |
| title_sort | geomagnetically induced currents gic in large power systems including transformer time response |
| topic | Electrical Engineering |
| url | http://hdl.handle.net/11427/16708 |
| work_keys_str_mv | AT oyedokundavidtemitope geomagneticallyinducedcurrentsgicinlargepowersystemsincludingtransformertimeresponse |