Federico Coffele University of Strathclyde (UK) federico.coffele@eee.strath.ac.uk

1. Detailed Analysis of the Impact of Distributed Generation and Active Network Management on Network Protection Systems Federico Coffele University of Strathclyde (UK) federico.coffele@eee.strath.ac.uk RIF Session 3 – Paper 0428

2. Overview • Test Case Network • Protection System • Simulated Scenarios • Analysis Methodology • Findings • Conclusions • Future Work Federico Coffele – UK– RIF Session 3 – Paper 0428

3. Test Case Network United Kingdom Generic Distribution Network (UKGDS) HV Overhead Type A Network. The high-level characteristics of this model are as follows: • rural area • long circuit length • low customer density • overhead construction • radial topology • large overall size Federico Coffele – UK– RIF Session 3 – Paper 0428

4. Protection System Federico Coffele – UK– RIF Session 3 – Paper 0428

5. Simulated Scenarios Types of DG: • Inverter interfaced generators (e.g. photovoltaic generation, electric vehicle to grid, etc.) • Synchronous and induction (e.g. combined heat and power (CHP), biomass, landfill, wind generators, etc.) The overall level of DG penetration has been simulated from zero up to a combined total capacity equal to 100% of the network load capacity in steps of 5%. Network automation: Further scenarios have been added to reflect changes in the topology of the network, i.e. closing and shifting the positions of normally open points (NOP). Federico Coffele – UK– RIF Session 3 – Paper 0428

6. Methodology Federico Coffele – UK– RIF Session 3 – Paper 0428

7. Findings The following protection problems have been investigated by the protection performance analysis: • Sympathetic tripping • Overload tripping • Blinding • Grading degradation Beside to the investigation of the problems, possible solutions have been analysed and there advantages/disadvantages have been evaluated. Federico Coffele – UK– RIF Session 3 – Paper 0428

8. Sympathetic tripping • Sympathetic tripping may occur when the contribution of DG lead to a situation where non-directional overcurrent relays mal-operate at the same time as, or before, protection on the faulted zone. • Considering the test case network with DLT protection, the incidence of sympathetic tripping due to synchronous DG is: Federico Coffele – UK– RIF Session 3 – Paper 0428

9. Solution • Directional overcurrent protection? It works but it is an expensive solution! • IDMT protection instead of DTL protection: It works and it is a cheap solution. Federico Coffele – UK– RIF Session 3 – Paper 0428

10. Overload tripping Overload tripping may occur if DG interface protection operates (either correctly or incorrectly) and results in the addition of previously “hidden” load. This was observed in the scenarios where DG penetration exceeded 55% and network automation was available to reconfigure the network after a permanent fault. Permanent fault Fault Federico Coffele – UK– RIF Session 3 – Paper 0428

11. Protection grading degradation When the network topology is changed, the protection grading between OCRs might not be valid anymore. Considering this specific case, PMAR-B tripping is unnecessary and could cause disconnection of several customers and 2 DG units. Permanent fault Fault Federico Coffele – UK– RIF Session 3 – Paper 0428

12. Solution • One very attractive solution is to implement an adaptive overcurrent protection system. • The protection system is composed of: • New overcurrent relays • Adaptive protection controller • The adaptive protection controller monitors the distribution network and amend the protection settings to optimize the performance of the protection system. Federico Coffele – UK– RIF Session 3 – Paper 0428

13. Conclusions • Considering a typical UK distribution network the simulation outcomes show that the protection systems can mal-operate. • Solutions to the discussed problems are: • Sympathetic tripping can be avoided with correct protection settings. • Overload tripping due to false tripping of generator interface protections can be avoided improving the generator interface protection • Protection grading degradation can be solved implementing an adaptive overcurrent protection system. Federico Coffele – UK– RIF Session 3 – Paper 0428

14. Future work • Simulation of the UKGDS model and network automation within RTDS. • Implementation of the protection system with commercial IED. • Demonstration of the protection problems and further analysis. • Development and testing of the proposed solutions. Federico Coffele – UK– RIF Session 3 – Paper 0428