Practical Measures to increase Distributed Generation in existing Distribution Networks

1. Practical Measures to increase Distributed Generation in existing Distribution Networks

2. Environmental Driver vs Economic Impact • Distributed Generation is driven in UK by Government Targets: • To produce 10% of the UK’s energy needs from renewable sources • To reach a total of 10GW of CHP generating capacity (an approximate doubling of current capacity) • UK Regulator prime responsibility: • To minimise the economic impact on customers • Consequently the DGCG is: • Encouraging innovation in the distribution networks • “Active Network Management” replacing “Fit & Forget”

3. Not starting with a “Green Field” • Transition is to be evolutionary not revolutionary • First step is application of “Basic Active Network Management” • Increasing the degree of network and / or generation management to increase: • the amount of generation plant connected to distribution networks • the amount of energy generated from new and existing plant

4. Short-Term Solutions • Project in Workstream 3 of the Technical Programme of UK DTI / OFGEM sponsored Distributed Generation Coordination Group • Full report will be available at: www.distributed-generation.gov.uk • Two potential rollout strategies for the solutions: • Issues readily addressed: establish “good practice” that can be adopted by all the DNOs. • Issues not fully understood: recommendations for further study to better quantify the risks & reduce the uncertainty.

5. Project Methodology • Identify possible Short-Term Solutions • Assess against 50 defined criteria: • Implications for customers • Implications for distributed generators • Implications for distribution network operators • Establish the appropriate rollout strategy • Aim to establish how far “good” engineering practice had evolved to “Best Practice” • Establish indicative costs to benchmark against network enhancement and reinforcement.

6. Short-term solutions forFault Level Management

7. Short-term solutions forVoltage Control

8. Short-term solutions forPower Flow Management

9. Two Examples • Progressive control of Power Flow • Fault Level: • Device is Available • Safety Concerns are delaying wide scale use

10. Conventional network design methodology • Generator output restricted to “firm capacity” • 12MVA

11. Post fault direct intertripping • Generator output 24MVA under normal conditions • “Post Fault” constrained to 12MVA • Generator trips if any upstream breaker trips

12. Power Flow Measurements • Generator output 24MVA under normal conditions • “Post Fault” constrained to 12MVA • Measure net export of power • Only trip if network capacity is exceeded

13. Generator Power Output Control • Take into account short term ratings and loads • Directly control generator output to within network capacity • Only trip if network capacity is exceeded

14. TripT?rip? Current-sensing Fuse IS Limiter Trigger circuit • senses rapid rise in fault current • fires a pyrotechnic charge to open the main current path • current is limited and then cleared by a parallel fuse within 10mS • There are Safety Concerns: • the IS Limiter is not intrinsically safe (i.e. fail-safe) • the integrity of the triggering supply • the inability to functionally test the equipment • the lack of an associated ‘back up’ system Is this an opportunity for a Solid State Device? Pyrotechnic charge

15. Concluding Remarks • Solutions have been identified which existing networks can accommodate now eg. • increasing impedances of components (transformers, generators and inserting reactors) • converter technologies for wind turbine generators • generator real/reactive power control • line voltage regulation • cancellation Current Transformers • post fault constraints (intertripping and generator power reduction)

16. Concluding Remarks • Some solutions require further work in order to address quality of supply or safety issues: • area-based voltage control • the use of the IS limiter • the application of sequential switching • the introduction of “split network” configurations • post fault constraints for multiple generators • Full details are given in the Workstream 3 report

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