MOROKA MAIN – 11 kV Bus Bar Normalisation Network Alternatives Case Study

1. MOROKA MAIN – 11 kV Bus Bar Normalisation Network Alternatives Case Study Presenter name: Brendon Pietersen Email Address:pieterbf@eskom.co.za Contact Number: 011 711 2606

2. Geographical location N N1 Soweto Supply Area Moroka Main Supply Area N12 15 km 0

3. Existing Moroka Supply AreaSatellite Substations Jabavu Satellite Substation Moroka Satellite Substation Pimville Satellite Substation Dhlamini Satellite Substation

4. Load Forecast

5. Problem Description The fault levels at the Moroka Main substation and the Moroka Main’s satellite substations have been exceeded. The Moroka Main 132/11 kV substation supplies four 11 kV satellite (switching) substations. The Moroka Main 132/11 kV 11 kV network is configured such that the Transformer 4 is in parallel with Transformer 3, and Transformer 3 is in parallel with Transformer 1. The transformers are paralleled via the Pimville, Jabavu, Moroka and Dhlamini satellite substations. Due to high loads during the peak season, the bus-section breakers of the satellite substations are kept N/C. With the bus-sections N/O, the primary feeders of the satellite substations would not be able to sustain the load.

6. Moroka Main 11 kV Satellite Substations’ Bus Bar Layout Indicating Satellite Substation Location and Fault Levels 28.5 kA 31.3 kA 35.6 kA 33.6 kA 24.8 kA 32.1 kA 23 kA 30.4 kA

7. Project Background • The maximum fault level (under normal conditions) was determined to be 35.6 kA. • The fault level at the 11 kV bus bars of the satellite substations ranges from 23 kA to 32 kA. • DIgSILENT was used to determine the fault levels. • The rated short circuit currents for the 11 kV feeder breakers at Moroka Main 132/11 kV is 31.5 kA at 3 s. • The rated short circuit currents for the 11 kV feeder breakers at the satellite substations is 25 kA at 2 s. • The feeders coming out of the 11 kV Bus Bar at Moroka Main 132/11 kV consist of 185 mm2 and 150 mm2 XLPE Cu cables. • The 1 s fault current rating for the 185 mm2 cable is 26.5 kA and 22 kA for the 150 mm2 cable. • The minimum trip times for the MV feeder breakers are 0.8 seconds to 1.2 seconds.

8. Schematic Diagram: Existing

9. Possible Alternatives • The possible alternatives, based on the Planning Standard for solving the problem of Fault Levels being exceeded are: • Network Reconfiguration • Re-conductor Lines • Upgrade Equipment • Additional Lines and/or Substations • Increases Voltage Level • Fault Limit Reactor • High Impedance Transformer • The Moroka Main substation supplies a cable network, i.e. lines cannot be re-conductored. • Additional Lines and/or Substations will increase the fault level. • High impedance transformers were not considered due to costs considerations. • To increase the voltage level, the whole 11 kV network will have to be upgraded to a 22 kV network. In total there is approximately 174 km cable installed in the Moroka Main network. The costs of 1 km of 185 mm2 XLPE Cu 3-core cable could be approximately R1 million. Therefore, the costs for just replacing the cable would be about R174 million. • Therefore, the available options are to Reconfigure the network or Upgrade the existing equipment to meet the high fault levels or Installing Fault Limit Reactors to reduce the fault levels.

10. Options Considered • To reduce the fault levels under normal conditions, the 132/11 kV transformers should not be paralleled. • Option 1: Open satellite substations bus-section breakers. (Reconfigure Network) • Option 2: Reconfigure 11 kV bus bar • Since the location of some of the primary feeders of the satellite substations cause the paralleling problems, some of the primary feeders must be relocated such that the substation’s transformers are not paralleled. • Some of the normally open points in the Pimville reticulation network must be changed to balance the loads at the Moroka Main’s 11 kV bus bars. • Option 3: Replace all the 11 kV breakers at the satellites substations with breakers rated above 36 kA fault current. (Upgrade Equipment) • Option 4: Install Fault Limit Reactors to reduce the fault levels.

11. Hi Level Scope of WorksOption 1: Open Satellite Substation bus-section breakers • Keep the bus-section breakers for all the satellite substations N/O. • No Costs. • The problem with this option is that the load will not be distributed evenly across the primary feeders of the satellite substations. • As can be seen from the Moroka satellite substation, Moroka 3 feeder will experience more load than Moroka 1 and Moroka 2. • This can be overcome by reconfiguring the network on the secondary feeders such that Moroka 3 only takes a third of the satellite substation’s load. • The risk is that when one of the primary feeders experiences a fault and the satellite substation’s bus-section may need to be closed. • Or if one of the secondary feeders experiences a fault and load has to be added to Moroka 3.

12. Schematic DiagramOption 2: Proposed Layout Reconfigure the 11 kV feeders’ cables at the 11 kV feeder breakers at Moroka Main as follows: • Swap MORM2/2279 with DHLAMINI 3 • Swap JABAVU 1 with PIMVILLE 3 • Swap JABAVU 2 with PIMVILLE 5 • Swap PIM4/11484 with MOROKA 3

13. Moroka Main 11 kV Satellite Substations’Option 2: New Bus Bar Layout Indicating Satellite Substation Location and Fault Levels 18.4 kA 18.4 kA 18.4 kA 18.4 kA 15.6 kA 16.3 kA 14.5 kA 16 kA

14. Hi Level Scope of WorksOption 2: Change N/O points N/O N/C N/C N/O N/O • On PIM Ring 1 • Make N/C • PIMVILLE6/PIM1/3B • PIMVILLE7/PIM1/3C • Make N/O • Between PIM1/8 and PIM1/3B • PIM1/459 feeder breaker. • Between PIM1/1291 and PIM1/69

15. Hi Level Scope of WorksOption 2: Change N/O points N/O N/C N/C N/O N/O • On PIM Ring 4 • Make N/C • Between PIM4/4/2650 and PIM4/2549 • Make N/O • Between PIM4/3222 and PIM4/3166 • Between PIM4/1233 and PIM4/1264 • Between PIM4/2621 and PIM4/2618

16. Hi Level Scope of WorksOption 2: Change N/O points N/O N/O N/O N/C N/O N/C N/C N/C • On PIM Ring 5 • Make N/C • Between PIM5/3938 and PIM5/3938 feeder breaker • PIM5/5883A and PIM5/5883A feeder breaker • Between PIM5/5278 and PIM5/8524 • Make N/O • PIM5/3895 feeder breaker • PIM5/11533 feeder breaker • Between PIM5/3896 and PIM5/3897 • PIM5/11665 feeder breaker

17. Project Costing DetailOption 2 • Costs include: • 160 m 185 mm2 XLPE Cu cable for each swap (Recommendation from Cable Department, i.e. 80 m cable for each feeder) • 8 cable joints. • ED costs for changing of settings and recommissioning.

18. Hi Level Scope of WorksOption 3: Replace 11 kV Feeder Breakers at Satellite Substations • Replace all the oil insulated 11 kV feeder breakers and bus-section breakers at the Moroka Main satellite substations with new SF6 11 kV feeder and bus-section breakers: • At the Pimville substation replace 18 feeder breakers and replace the two bus-section breakers with 2500 A bus-section breakers. • At the Dhlamini substation replace 9 feeder breakers and 1 bus-section breaker. • At the Jabavu substation replace 15 feeder breakers and 1 bus-section breaker. • At the Moroka 11 kV substation replace 7 feeder breakers and 1 bus-section breaker. • Ensure the breakers are rated for a fault level of higher than 36 kA. • Upgrade the stats metering and protection where necessary. • This option will also require the upgrading of cables. The primary feeders’ cables will need to be replaced with 300 mm2 XLPE Cu 3-core cables. The standard cable smaller than 300 mm2 XLPE Cu 3-core cable is 185 mm2 XLPE Cu 3-core cable which has a fault current rating of 26.5 kA. • Feeders’ cables that have miniature substations would also need to be upgraded to at least 185 mm2 XLPE Cu 3-core cable. For the satellite substations where the fault level is 29 kA this will not be sufficient.

19. Project Costing DetailOption 3: Replace 11 kV Feeder Breakers at Satellite Substations

20. Hi Level Scope of WorksOption 4: Installing Fault Limit Reactors • Four Fault Limit Reactors from High Voltage Technology (HTS) will used. • Each fault limit reactors has a rating of 2100 A, 17 % impedance and losses of 21.6 kW. • The fault limit reactors cause a volt drop of 4 % at the 11 kV bus bar.

21. Option 4: Substation with Fault Limit Reactors FLR FLR 17.64 kA 19.3 kA FLR FLR 21.0 kA 20.2 kA 16.7 kA 20 kA Voltage Drops from 102 % to 98 % at 11 kV Bus Bar 16.2 kA Costs per FLR = R1 000 000 Total Costs = R4 000 000 19.6 kA

22. Option Summary

23. Conclusion and Recommendation • Implementation of Option 1, Option 2 and Option 4 will reduce the fault levels at the Moroka Main’s substation 11 kV bus bar. • Option 1 is not viable as it may result in overloading of some the satellite substations’ primary feeders. • Option 4 will reduce fault levels, but will also reduce the source voltage. • Option 3 will not result in a drop in the fault levels, but will cater for the high fault levels. Option 3 will also yield the highest costs. • It is recommended Option 2 be implemented as this option will result in reduced fault levels, the satellite substations’ primary feeders will not be overloaded and the option will cost significantly less than Option 3 and Option 4.