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
Network Vault
Designed to Self Clear

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

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