1. Review of Distribution Network Protection Lonnie Malek Oncor Electric Delivery Distribution Planning

2. Review of Distribution Network Protection • Oncor’s Downtown Networks • Contingency Considerations in Distribution Networks • Protection Considerations for Distribution Networks • Oncor’s Network Protection Review • Lessons Learned

3. Review of Distribution Network Protection • Oncor’s Downtown Networks • Seven Total Networks • Network Substation Design • Three Transformers per Substation • Double Synchronized Ring-bus • 12 Distribution Feeders per Network • Network Delivery Voltages • 4 kV and 15 kV Single-customer Spot Network • 277/480 volt Single-customer Spot Network • 120/208 volt Grid-connected Vaults

4. Review of Distribution Network Protection • Contingency Considerations for Downtown Networks • Oncor’s Design is 2nd Contingency • No outages under any 1st or 2nd contingency event • Load modeling must account for every combination of 2nd contingency • Loss of any 2 combinations of equipment • Substation transformers • Primary feeders • Vault transformers • Sister feeder consideration

5. Review of Distribution Network Protection • Contingency Considerations for Downtown Networks (Cont.) • X • X

6. Review of Distribution Network Protection • Protection Considerations for Distribution Networks • Transmission Lines • Substation Transformers • Substation Ring Bus • Distribution Primary Cable • Vault Transformers • Vault Secondary Bus • Distribution Street Grid • Network Substation • Designed to Self Clear • Network Vault

7. Review of Distribution Network Protection • Protection Considerations for Distribution Networks (Cont.) • B • B Substation • 480 v Spot Network • B • B • Customer • Service • V • P • B • B • B • B • V • P • Network Protector • V • P • V • P

8. Review of Distribution Network Protection • Protection Considerations for Distribution Networks (Cont.) • B • B Substation • B • B • 480 v Spot Network • Customer • Service • V • P • B • B • B • B • V • P • V • P X • X F • V • P

9. Review of Distribution Network Protection • Oncor’s Network Protection Review • Catalog existing settings and drawings • Model fault scenarios • Verify coordination • Document findings / make revisions

10. Review of Distribution Network Protection • Lessons Learned • Street grid voltage can dip below 0.9 PU during certain fault conditions • Relay power redundancy is important • Verify coordination and reach with back-up device(s) during 1st contingency situations • Systems with Y-Y vault transformer connections require additional considerations when modeling faults • Do not let high reliability in your network mask the importance of network maintenance

11. Review of Distribution Network Protection Thank You!