A case study of induced current unbalance as a result of capacitor failure
- Zondi, S., Bokoro, P., Paul, B.
- Authors: Zondi, S. , Bokoro, P. , Paul, B.
- Date: 2015-01-28
- Subjects: Point on wave switching , Transient voltage , Capacitor banks , Current unbalance
- Type: Article
- Identifier: uj:5143 , ISBN 978-0-86970-786-9 , http://hdl.handle.net/10210/14124
- Description: Capacitor banks rated 132 kV/ 72 MVAr are installed at the Durban North Substation of Ethekwini municipality to compensate for inductive power losses. The POW or synchronous switching technique is used for on-line switching of these banks, in a bid to minimise high magnitude induced transient voltage and current. in this study, the voltage waveform records and the percentage current unbalance, measured on and six months post commissioning of the capacitor banks are analysed in order to test the effectiveness of POW switching method, when implemented with mechanically linked 3-phase, 3-pole SF6 circuit breakers. The results obtained indicate that within 6 months of commissioning, capacitive impedance of the banks failed, as result of high magnitude induced transient current and voltage, and the percentage unbalance level observed in the neutral current grew from 2.3% to 5.7%.
- Full Text:
- Authors: Zondi, S. , Bokoro, P. , Paul, B.
- Date: 2015-01-28
- Subjects: Point on wave switching , Transient voltage , Capacitor banks , Current unbalance
- Type: Article
- Identifier: uj:5143 , ISBN 978-0-86970-786-9 , http://hdl.handle.net/10210/14124
- Description: Capacitor banks rated 132 kV/ 72 MVAr are installed at the Durban North Substation of Ethekwini municipality to compensate for inductive power losses. The POW or synchronous switching technique is used for on-line switching of these banks, in a bid to minimise high magnitude induced transient voltage and current. in this study, the voltage waveform records and the percentage current unbalance, measured on and six months post commissioning of the capacitor banks are analysed in order to test the effectiveness of POW switching method, when implemented with mechanically linked 3-phase, 3-pole SF6 circuit breakers. The results obtained indicate that within 6 months of commissioning, capacitive impedance of the banks failed, as result of high magnitude induced transient current and voltage, and the percentage unbalance level observed in the neutral current grew from 2.3% to 5.7%.
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Design of a DC overcurrent fault detection and protection scheme for DC collectors of a photovoltaic plant
- Holland, I., Bokoro, P., Paul, B., Ndlovu, E.
- Authors: Holland, I. , Bokoro, P. , Paul, B. , Ndlovu, E.
- Date: 2017
- Subjects: Photovoltaic power plants - Protection
- Language: English
- Type: Conference proceedings
- Identifier: http://ujcontent.uj.ac.za8080/10210/370432 , http://hdl.handle.net/10210/221791 , uj:22242 , Citation: Holland, I. et al. 2017. Design of a DC overcurrent fault detection and protection scheme for DC collectors of a photovoltaic plant.
- Description: Abstract: Faults in the DC collector circuits of a photovoltaic plant are a cause for major concern due to the damage they may cause to equipment. Fault protection is required for ground faults, line-to-line faults and arc faults. Typically, the magnitude of short-circuit currents of PV modules are similar to that of load currents which makes fault detection and protection difficult to carry out on the DC system. The DC collectors of a PV plant consist of combiner boxes where PV arrays are connected and inverter DC buses where combiner boxes are connected. This paper investigates the fault contribution from the PV modules on the combiner boxes and inverter DC buses in relation to typical PV module data on an isolated section of the DC network of a plant using the ETAP simulation tool. A fault detection and protection scheme for the main faults in a DC PV system is proposed based on previous research, for complete protection of the DC collector circuits.
- Full Text:
- Authors: Holland, I. , Bokoro, P. , Paul, B. , Ndlovu, E.
- Date: 2017
- Subjects: Photovoltaic power plants - Protection
- Language: English
- Type: Conference proceedings
- Identifier: http://ujcontent.uj.ac.za8080/10210/370432 , http://hdl.handle.net/10210/221791 , uj:22242 , Citation: Holland, I. et al. 2017. Design of a DC overcurrent fault detection and protection scheme for DC collectors of a photovoltaic plant.
- Description: Abstract: Faults in the DC collector circuits of a photovoltaic plant are a cause for major concern due to the damage they may cause to equipment. Fault protection is required for ground faults, line-to-line faults and arc faults. Typically, the magnitude of short-circuit currents of PV modules are similar to that of load currents which makes fault detection and protection difficult to carry out on the DC system. The DC collectors of a PV plant consist of combiner boxes where PV arrays are connected and inverter DC buses where combiner boxes are connected. This paper investigates the fault contribution from the PV modules on the combiner boxes and inverter DC buses in relation to typical PV module data on an isolated section of the DC network of a plant using the ETAP simulation tool. A fault detection and protection scheme for the main faults in a DC PV system is proposed based on previous research, for complete protection of the DC collector circuits.
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EMTP-based analysis of pre-insertion resistor and point on wave switching methodology
- Zondi, S., Bokoro, P., Paul, B.
- Authors: Zondi, S. , Bokoro, P. , Paul, B.
- Date: 2015
- Subjects: Capacitor banks , Transient overvoltage and inrush current , Single and back to back switching
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/20405 , uj:16092 , Citation: Zondi, S., Bokoro, P. & Paul, B. 2015. EMTP-based analysis of pre-insertion resistor and point on wave switching methodology. Proceedings of the IEEE AFRICON, September 2015, Addis Ababa, Ethiopia. p. 962-966. ISBN: 978-1-4799-7497-9
- Description: Abstract: The switching of high-voltage capacitor banks for reactive power and voltage control usually produces significant transients. These high amplitude disturbances have a tendency to damage or reduce the lifespan of capacitor units, thus leading to complete failure of capacitor banks. Pre-insertion resistors or inductors as well as synchronous switching (Point on Wave) methods can be used to mitigate transient phenomenon. In this work, EMTP simulations of transient voltage for single and back to back capacitor banks indicate that pre-insertion resistors methodology can significantly reduce transients, and could therefore be combined with synchronous switching to effect transient mitigation.
- Full Text:
- Authors: Zondi, S. , Bokoro, P. , Paul, B.
- Date: 2015
- Subjects: Capacitor banks , Transient overvoltage and inrush current , Single and back to back switching
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/20405 , uj:16092 , Citation: Zondi, S., Bokoro, P. & Paul, B. 2015. EMTP-based analysis of pre-insertion resistor and point on wave switching methodology. Proceedings of the IEEE AFRICON, September 2015, Addis Ababa, Ethiopia. p. 962-966. ISBN: 978-1-4799-7497-9
- Description: Abstract: The switching of high-voltage capacitor banks for reactive power and voltage control usually produces significant transients. These high amplitude disturbances have a tendency to damage or reduce the lifespan of capacitor units, thus leading to complete failure of capacitor banks. Pre-insertion resistors or inductors as well as synchronous switching (Point on Wave) methods can be used to mitigate transient phenomenon. In this work, EMTP simulations of transient voltage for single and back to back capacitor banks indicate that pre-insertion resistors methodology can significantly reduce transients, and could therefore be combined with synchronous switching to effect transient mitigation.
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Selection and coordination of surge arresters for switching transient mitigation in photovoltaic power plants
- Oliveira, R., Bokoro, P., Paul, B., Ndlovu, E.
- Authors: Oliveira, R. , Bokoro, P. , Paul, B. , Ndlovu, E.
- Date: 2017
- Subjects: Renewable energy sources , Photovoltaic power plants , Surge arresters
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/221807 , uj:22243 , Citation: Oliveira, R. et al. 2017. Selection and coordination of surge arresters for switching transient mitigation in photovoltaic power plants.
- Description: Abstract: Photovoltaic energy generation has become a popular renewable alternative to conventional energy generation that utilise fossil fuels. However, given the diversity and complexity of these PV plants, it is imperative that such plant equipment be protected against the greatest contributor to equipment failure; surges. Software simulation using EMTP-RV version 3.3, this paper implements a proposed methodology for the insulation coordination study of a PV plant. The overvoltages associated with the opening of vacuum circuit breakers, at various test points along the network are considered in order to recommend possible selection criteria of surge arresters as well as location thereof. The study finds that for a reduction of surge magnitudes from 8 p.u to within 1.2 p.u would require surge arrester energy capabilities to be greater than 2.8 kJ/kV for the medium voltage (MV) arresters , and capabilities exceeding 259kJ/kV for the low voltage (LV) arrester. For the high voltage (HV) section of the plant, no surge propagation was identified thus exempting it from the insulation coordination. The above mentioned, along with surge current and overvoltage levels comprise the findings of the study providing parameter guidelines for arrester selection.
- Full Text:
- Authors: Oliveira, R. , Bokoro, P. , Paul, B. , Ndlovu, E.
- Date: 2017
- Subjects: Renewable energy sources , Photovoltaic power plants , Surge arresters
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/221807 , uj:22243 , Citation: Oliveira, R. et al. 2017. Selection and coordination of surge arresters for switching transient mitigation in photovoltaic power plants.
- Description: Abstract: Photovoltaic energy generation has become a popular renewable alternative to conventional energy generation that utilise fossil fuels. However, given the diversity and complexity of these PV plants, it is imperative that such plant equipment be protected against the greatest contributor to equipment failure; surges. Software simulation using EMTP-RV version 3.3, this paper implements a proposed methodology for the insulation coordination study of a PV plant. The overvoltages associated with the opening of vacuum circuit breakers, at various test points along the network are considered in order to recommend possible selection criteria of surge arresters as well as location thereof. The study finds that for a reduction of surge magnitudes from 8 p.u to within 1.2 p.u would require surge arrester energy capabilities to be greater than 2.8 kJ/kV for the medium voltage (MV) arresters , and capabilities exceeding 259kJ/kV for the low voltage (LV) arrester. For the high voltage (HV) section of the plant, no surge propagation was identified thus exempting it from the insulation coordination. The above mentioned, along with surge current and overvoltage levels comprise the findings of the study providing parameter guidelines for arrester selection.
- Full Text:
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