Electricity Supply to Africa and Developing Economies: Challenges and Opportunities Assessing the need for additional surge arresters in an uprated high voltage substation Author: Peet Schutte Co-Author: Chris van der Merwe Eskom Holdings SOC Ltd Paper Number 6.04 Session 6 16 November 2017
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Electricity Supply to Africa and Developing Economies: Challenges and Opportunities
Assessing the need for additional
surge arresters in an uprated high
voltage substation
Author: Peet Schutte
Co-Author: Chris van der MerweEskom Holdings SOC Ltd
Paper Number 6.04
Session 6
16 November 2017
Electricity Supply to Africa and Developing Economies: Challenges and Opportunities
Presentation outline
• Introduction
• Back-flashover simulation
• Simulation results
• Conclusion
• Acknowledgements
Electricity Supply to Africa and Developing Economies: Challenges and Opportunities
Introduction
• When a substation system voltage is uprated, surge arresters with higher protective levels are installed.
• Protective levels of arresters will determine the maximum over-voltages at the arrester terminals.
• Internal and external insulation may possibly be stressed to a point of failure.
• Insulation coordination studies are valuable to determine over-voltage stress on both internal and external insulation.
• In 88 kV substations, phase-to-earth clearance should not be less than 1000 mm and relates to an estimated 530 kV BIL.
Electricity Supply to Africa and Developing Economies: Challenges and Opportunities
Simulation results: Surge arrester energy
0 10 20 30 40 50 60 70 80 90 100 110 1200
100
200
300
400
500
600
Line entrance arrester energy without busbar arrestersLine entrance arrester energy with arresters at bus couplerLine entrance arrester energy with busbar arresters on both end551 kJ maximum energy rating
Line entrance arrester energy without busbar arrestersLine entrance arrester energy with arresters at bus couplerLine entrance arrester energy with busbar arresters on both end551 kJ maximum energy rating
Arrester Energy
Time (us)
Ene
rgy
(kJ)
Electricity Supply to Africa and Developing Economies: Challenges and Opportunities
Conclusion
• Uprating the system voltage in a substation will require higher rated surge arresters.
• With higher protective levels, safety margins between withstand levels of external insulation are reduced.
• The evaluation of over-voltage stress caused by a back-flashover close to the substation results in the following :– Increasing the separation distance to 140 m will result in breaking through
the BIL of both internal and external insulation.
– This scenario is highly unlikely, but additional busbar arresters will improve the safety margins throughout the substation.
– The standard Eskom practice to install MOV arresters at the line entrance and power transformers reduces the probability of large separation distances.
– Optimising the over-voltage protection for non-recoverable insulation will result in decreasing the probability of recoverable insulation failing.
– Busbar arresters are to be installed to increase the safety margins where long conductor distances separate equipment from installed arresters.
Electricity Supply to Africa and Developing Economies: Challenges and Opportunities
Acknowledgements
• Mr. Chris van der Merwe
• Eskom
• CIGRE
Electricity Supply to Africa and Developing Economies: Challenges and Opportunities