1. Power Monitoring And Control System (PMACS) NEPTUNE Preliminary Design Review 4-5 December 2003 Chen-Ching Liu, Ting Chan, Kevin Schneider

2. Overview Compliance matrix PMACS State estimation and topology error identification Load management and emergency control Fault location

3. Compliance Matrix SEF50Voltage limit adjustable +/-10%Yes SEF51Current Limit adjustable down to 1AYes SEF52Shore stations capable of coordinating power outputsYes SEF53Power Flow direction in any segment of system is arbitraryYes SMA1Fault location to within 1km without underwater interventionYes SPE2Peak power delivered 100kW, 10 kV, 10AYes SPE15All shore station equipment can operate off single UPSYes

4. Base 46 node system 2 shore stations 46 BU’s 46 Science nodes 3000 Km of cables

5. PMACS

6. PMACS functions are performed at two shore stations, and possibly a third control station input signals are received from science nodes command sequences are sent to science nodes

7. State Estimation and Topology Error Identification

8. State Estimation By using a limited number of measurements, the state of the system can be estimated Allows for the identification of “bad” data Reduce errors in estimated states

9. Unobservability Issue backbone up to 100 km long “extension cord” single-conductor spur cable to science node, 2½ water depths branching unit science node up to 1 km short “extension cord” sensor Instrument module

10. Weighted Least Square (WLS) : Column vector of measured science node voltages and currents :Column vector of estimated BU voltages

11. Calculated Residual Helps to identify “bad data” Gives an estimate of the accuracy of the estimation n: number of measurements

12. Topology Error Identification Allows for the possibility of a single back bone breaker being out of position Method should also work for multiple breakers out of position, but this has not been verified

13. Method of Topology Error Identification Voltage at each shore station is varied independently Variation of residual is then examined

14. Correct Topology

15. Incorrect topology

16. Load Management and Emergency Control

17. Load Management Uses values from science nodes, shore stations, and state estimation to determine if the current system load violates any limits Interfaces with Observatory Control System Performs traditional security assessment in a limited manner

18. Power Flow with Zener Diodes Where: P G i =Power injected at node I, source P D i =Power removed at node I, load. Y ik =Resistance of the line between node I and k V Z =Voltage drop of zener diodes m=number of BU’s

19. Emergency Control If/when the load management module determines that a system limit has been violated, emergency control attempts to correct the problem Can adjust shore station voltages Can shed load at science nodes

20. Adjustment of Shore Station Voltage The sensitivity coefficients of the node(s) that have violated a limit are calculated The shore station voltage is then adjusted by the amount calculated

21. Load Shedding The science node loads are tentatively categorized into three load classes 1) High 2) General 3) Deferrable

22. Load Shedding Cont. The sensitivity coefficients of the node(s) that have violated a limit are calculated The load is then shed by the amount calculated

23. Fault Location

24. Determine the location of backbone cable fault to within  1 km Use voltage and current measurements at two shore stations Models include cable resistances and BU voltage drops

25. Assumptions Faulted link is known based on result of state estimation Network topology is known and fixed (all breakers closed onto the fault) Resistances of cables and BU voltage drops can be calculated using state estimation BU voltage drops are constant assuming Zener diodes are operating in saturated region

26. Fault Current Characteristics Type 1 – I f from each end known Type 2 – I f from each end not known Type 3 – I f from one end known

27. Fault Location Formulation For a Zero-  ground fault, multiple non-linear equations can be set up based on Ohm’s Law and Loop Analysis – V Node = V Previous Node + I Link * R Link + BU Voltage drop All breakers closed onto the fault Negative shore station voltage outputs

28. Distance Calculation Cable resistance = 1  /km BU voltage drop = 15.2V per link (Zener diodes in saturated region) Measurement errors = 0.01% (voltage and current)

29. Voltage and Current Requirements If faulted link is known before taking measurements – Apply predetermined voltage levels at both shore stations – Ensure backbone currents in branches are sufficient without causing over-current violation If faulted link is not known before taking measurements – Increase current outputs at both shore stations until the total current output reaches limit