Network studies and mitigation of high 132 kV fault currents in eThekwini electricity.

This thesis does not contain text, graphics or tables copied and pasted from the Internet unless expressly acknowledged and the source is indicated in the thesis and in the reference sections. The growth of the world population has led to an increase in the demand for electricity. Passive targets were chosen for the network studies, as active targets are in the development stage at the 132 kV voltage level.

High-impedance transformers and current-limiting reactors increase network losses, but can be used to limit fault currents to predetermined values.

Introduction

Background
Problem Statement
Key Objectives of the Research
Thesis Structure

This was investigated and tested in the network studies carried out. The technical, financial and practical aspects, together with short, medium and long term increase in FCLs were considered in the research. The past and future growth are discussed together with the standards and operation of the network.

The investigated options are capable of mitigating high FCLs, with a few having greater effect than others.

Literature review

Faults
Fault Current Levels (FCL)
Fault Analysis
Causes of the High Network Fault Currents
Safety
High Fault Current Mitigation Measures
Network Performance and Power Quality
Impacts of Fault Current Limitation on Existing Protection Schemes
Fault Current Limiter Location
Analysis of Fault Levels in HV networks
Chapter Summary

High FCLs indicate the network's ability to supply power and are a measure of its robustness. Essentially, a decrease in source impedance will cause an increase in FCLs in the network. ES is one of the largest in the world and a leader in Africa, responsible for almost all generation capacity.

This includes ensuring that network fault currents are maintained below equipment values. Passive measures act on the network at a given moment and become part of the network. Topological measures involve configuring the network to reduce the level of errors and can be achieved by introducing a higher voltage level, dividing the network into subnets and splitting buses.

Spacing of busbars and networks is one of the most cost-effective ways to reduce fault levels. This option will be more expensive, but will benefit the network in the long term by improving the flexibility and robustness of the network. The losses of the overall network will improve due to more power being transmitted at a higher voltage.

One of the first criteria that is checked in every network is the voltage at the various junctions and clients. The response characteristics of the FCLD should be studied under voltage using actual test results. If abnormal conditions occur in the network due to disturbances or circuit parameters moving outside specified areas, the affected area or areas will need to be isolated.

When simulation packages are used, the results obtained give an approximation of the network behavior in the event of a fault level.

The eThekwini Electricity Network

Existing Network Design

26 The research investigation focuses on the fault current levels at the 275/132 kV and the 132/11 kV SSs and the analysis of the FCLs experienced at the 132 kV rails.

Table 6: eThekwini Electricity HV Network [33]

Demand Forecast

The EC is a very popular tourist, sports and events destination and hosted group and knockout matches, including the quarter- and semi-finals of the World Cup. The Durban International Convention Center hosts international conventions such as the World Aids Conference and the Conference of the Parties (COP17). The peak of the year is generally seen in the summer months due to the hot summers experienced and an increase in cooling required.

To reduce peak consumption, geysers were installed in households in 2012-13 at no cost to the customer. As part of the GLF, an Economic Development Study forecast was conducted to give an indication of future size, spatial distribution and characteristics of the population for the period [18]. The main triggers for development in EM have been identified as the King Shaka Airport and Dube Tradeport, the Port of Durban Harbor Expansion, the Cato Ridge Cargo Hub and the Durban Dig-Out Port to be built on the old airport site, south of the city centre. .

There are cases where customers prefer unfixed offer due to the higher cost of a fixed offer. The switched fixed supply is when the network needs to be reconfigured to restore supply to the customer. Reconfiguration of the network is performed by turning on or off components of the network.

There will be a temporary loss of supply to the customer while this takes place and supply is fully restored. Should there be a fault on the 275kV network and that 275/132kV network is SS unable to supply its entire 132kV load, the network will have to close points on the 132kV network to prevent loss of supply.

Chapter Summary

Each region would have its own source of 132 kV power, which would be supplied by several 275/132 kV substations.

Network Studies

Study Methodology
Power System Study Simulations
Study Procedure
Problems with the study
Chapter Summary

The detailed model was used for network studies performed with the Power System Simulation (PSS®E) package, version 33.5. The calculated fault levels were the expected root mean square values of the AC component of the fault level in the bolted fault at the substation. In order to get a long-term view of error levels and to plan accordingly, the network models used to conduct the study were the most forward-looking at the time of the study.

The study was conducted at EE's most strategic inlet from ES, 275/132 UÇK SS, which supplies approximately 40% of EM, more cargo than any other inlet within EM. To carry out the upgrade, a 5th transformer has been installed to maintain the supply and simulations. SS is supplied by Hector SS by 2 single circuit overhead lines (OHTL) and a single OHTL by Georgedale SS, both owned and operated by ES and located west of EM.

The study is based on the information in the models which is a snapshot of the network in time. Network performance due to outages may not be a reflection of how the network operates. As a result, the assumptions would have to take care of the worst case scenario, so the maximum loads for SS, ohtl and cables were in the simulations.

Network parameters such as generator outputs and transformer tap change positions are not possible to predict or precisely determine, especially for the ES network. The base case results show the FCLs, if no mitigation measures are put in place, and were used to determine the effectiveness of the solution.

Figure 14: EE Network model single line drawing in PSS®E Fault Level Assumptions:

Results and discussions

Base Model
Splitting the 132 kV Network
Interconnection at 275kV between Klaarwater, Umgeni and Durban North
The Effect of Generation
Reduced 275/132 kV Transformation
Splitting of the 132k busbar at KLA SS and a reactor testing
High impedance transformers of fault current limiting reactors
Chapter Summary

Reducing the 132 kV interconnection increases the system impedance and reduces the FCL in the network. 39 The system should still maintain its level of security and remain healthy if parts of the network lose power due to network failures. The introduction of higher system voltages can be very cost-effective as a long- to medium-term strategy together with grid splitting to allow interconnection to 275 kV.

This method is effective in making the network more secure and improving the reliability of the network after the 132 kV network has been reduced by creating open points. Expansion of the 275 kV network to connect the Umgeni SS to Durban North will result in alternative power being provided to Durban North and Ottawa SS and is shown in Figure 18. Expanding the 275 kV network will create a 275 kV ring and support is provided to the SS in the north of the EM.

A reduction in transformation at KLA SS, by turning off the fifth transformer, reduced the FCL by 2-3 kV at most SSs. The reactor would not be feasible in this case as the FCLs on one of the bars are above 40 kV. In the case of the KLA SS, an FCL of 31.5 kA should be used, as opposed to the expected 40 kA.

A network contingency plan must be drawn up for supply losses to all mini-grids. The 275 kV interconnection of the mini-grids will mitigate the increasing FCLs and provide a strong backbone for the 132 kV mini-grids.

Figure 16: Splitting of the 132 kV Network

Conclusion

6] Cigre Working Group A3.23, Application and Feasibility of Fault Current Limiters in Power Systems, Electra, June 2012. Guideline on the Impact of Fault Current Limiting Devices on Protection Systems, Cigre Working Group A3.16, February 2008. 11] T.Bengani, “Eskom Transmission Development Plan”, Eskom Transmission Planning F Jones, “2015 was a Record Year for Renewable Investments”, Modern Power Systems, April.

Temple, "White paper on fault current limiters - impedance study of FCLs in relation to increase in power generation of the system", May 2009. 23] J.K Raghubir, "Reliability based network planning and design at Eskom KwaZulu-Natal", Eskom Technology Conference, KwaZulu-Natal, November 2012. Stephan, "A technical and economic comparison between traditionally used and emerging fault level management options at distribution voltages", Eskom Power Plant Engineering Institute, 2015.

Booth, G.M Burt, "Operational control and protection impplications of fault current limitation in distribution networks", Electra No211, December 2003. 37] Ethekwini Economic Department, "Planning Inanda, Ntuzuma, KwaMashu (INK) Nodal Economic Development Profile", Ethekwini Municipality , januar 2016. 41] Ethekwini Transport Authority, "Integrated Transport Plan", Ethekwini Kommune, juli 2015 [42] Ethekwini Kommunes Boligafdeling, "Ethekwini Kommuneplanlægning.

Karady, "Comparison of four different types of ferromagnetic materials for fault current limiter applications, IEEE Transaction on Power Delivery, Volume 28, July 2013. Breuer, "Applications of superconducting fault current limiters in electric power transmission systems" , IEEE Transactions on Superconductivity, Volume 15, June 2005.

Network open points

Network simulation Results