1. New proposed BU circuit and control logic design University of Washington

2. Outline Current BU circuit design Proposed BU circuit design Current sequence of operation Proposed sequence of operation Implementation issues BU controller design Lab test High voltage circuits (component requirements and availability) Transient process simulation in network scenario

3. Current BU circuit design Control To Science

4. Problems with current BU circuit Shunt branch current: –The current in shunt branch must be high enough to drive one controller and two solenoids. When the system is energized with fault, the low voltage in the system may not close the switches. In some simulation cases, even without fault, if the solenoid current is 100mA, the backbone current could exceed 10 A. Shunt resistance: –It is always connected to the system, a constant source of unwanted heat dissipation. –It is hard to compute the fault location with the resistances in the circuit

5. Problems with current BU circuit Memory –The sequence of operation needs to be stored in the controller. Controller command is needed to close the switches. –Controllers must be powered before taking any switching actions.

6. New proposed BU circuit design Controller Science Node

7. Advantages of proposed circuit No storage of –switch status –Previous modes of operation. Less zeners are used. Controller intervention is not needed to close the switches. It is only used to isolate a fault. Diode in shunt branch blocks the current when shore station voltage is negative. –Power consumption in the shunt resistance is only temporary during the closing process. –Fault is easier to be located without shunt resistances in the network.

8. Proposed Sequence of Operation

9. Startup mode Assume a fault exists Fault identification Delay T1 Normal mode Normal mode with some switches open Fault isolation Delay T2 -5kV +5kV -10kV -5kV -10kV No faultFault exists

10. Sequence of Operation Startup without fault Startup Fault Identification Delay T1Normal +5 kV-5kV-10kV Startup with fault Startup Fault Identification Delay T1 Fault Isolation Delay T2 Normal with open switches +5KV-5kV-10kV Actions of PMACS Fault location measurements Measurement to identify faulty cables

11. Description of operations Startup: Energize the network at a positive voltage to close all switches without controller intervention (a lower voltage might be needed to limit the backbone current to 10A if there is a fault in the network). Fault identification: –System is energized at low negative voltage –If |V| >1kV inhibit any switching action (opening) because fault is not within one cable section. –If |V| <1kV, BU computes V/I in all directions and compare with thresholds. The threshold is related to the cable length. Fault isolation: –System is energized at low negative voltage –Open switches after a delay based on the V/I ratio Normal: Energize the system at –10kV.

12. Proposed BU Control Actions The closing of the science load and backbone switches is done simultaneously without controller intervention. Controller is only active during fault identification and isolation modes. Controller can differentiate between faults in spur cable and in the backbone

13. BU controller Main function: –Opening switches in the fault isolation mode when low voltage (under 1kV) is detected Task modules: –System mode detection –Fault identification –Fault isolation

14. BU controller Microprocessor + peripherals logic circuit + relays

15. BU controller function and design The controller can be implemented using microprocessor or logic circuit and relays. Advantage of using microprocessor: –Only software programming is needed. –Qualified microprocessor maybe available. Advantage of using logic circuit and relay: –Simpler –Cheaper

16. Laboratory Test (Ann Tran)

17. Voltage and current sensing Controller Science Node

18. Measurement requirements Voltage measurement: –Ranges from –10kV to +10kV. Accuracy is not a big concern. –Input/output isolation is required. Isolation level > 10kV. Current measurement: –Ranges from –10A to +10A. Accuracy is not a big concern. –Input/output isolation is required (considering the current measurement from the other end of the switch to the controller). Isolation level > 10kV.

19. Measurement availability Hall effect voltage transducer with voltage divider –LEM LV 100-4000: Measuring range: -6000V ~ +6000V Isolation: RMS voltage for AC, 50Hz 12kV Without voltage divider: ? Current Transducer LEM APR50B10: –Measuring range: 10,25,50A –Isolation: RMS voltage for AC, 50Hz 5kV

20. Transient simulation Simulation network 1 23 4 5

21. Transient simulation BU simulation circuit

22. Transient process simulation in network scenario 1 2 3 Capacitor voltage Solenoid current

23. Transient process simulation in network scenario 1 4 5 Capacitor voltage Solenoid current

24. End

25. Current control logic design Concept of operations in Boston report: Voltage Mode m(Meaning) Operation to be performed +500*Fault locationClose all BB breakers. Disconnect all science nodes - 500*Fault clearingOpen breaker closest to fault -1000Connect Science Node Measure resistance of spur cable to science node: close switch if good -5000 (or more) NormalInternal monitoring only: No switch operations at full voltage * These mean current-limit operation at the shore station Appropriate sequencing gives unambiguous operation

26. Concept of operations Un-powered +500V Fault Locating Mode, + 500 V Initial switch state is unknown Shore station is in current limit operation Regardless of whether a fault is present –Positive voltage is sensed –Backbone breaker is closed –Science node connection is opened If there is a fault, its location is measured from shore Return to unpowered state after fault location determined

27. Concept of operations Un-powered -500V Fault Clearing Mode, -500V Initial BB switch state is closed Shore station is in current- limit operation If a fault is present –Time-coordinated protection begins when current becomes non-zero –Unit closest to fault trips first If no fault is present –Backbone breakers remain closed In either case, status is stored

28. Concept of operations - 500V -1000V Science Connecting Mode, -1000 V Initial science node switch state is open Shore station is constant voltage operation Spur cable resistance is measured at low current –If no fault detected, spur switch closes –If fault detected, spur switch stays open In either case, status is stored

29. Concept of operations -1000V-10kV Normal Mode, -6000 V to – 10,000 V The control knows what the switch status is The control knows that is is in the Normal Mode If a fault occurs during Normal Mode operation –No switch action results –Shore station enters current limit mode

30. Concept of operations Un-powered -10kV Controlled shutdown from normal mode Shore station shuts the system down There is no change in the state of any switch The location of faults, if any, is not known to the shore station If the shutdown is not because of a fault, the fault location step can be omitted

31. Proposed control logic design Concept of operations: Voltage Mode m(Meaning) Operation to be performed +5000*Reset processClose all BB breakers. Disconnect all science nodes - 5000*Fault clearingOpen breaker closest to fault -6000 (or more) NormalInternal monitoring only: No switch operations at full voltage * These mean current-limit operation at the shore station No sequencing info is stored in the controllers

32. Concept of operations Un-powered +5000V Startup (Fault Locating Mode), + 5000 V Initial switch state is unknown Shore station is in current limit operation Regardless of whether a fault is present –Positive voltage is sensed –Backbone breaker is closed –Science node connection is closed (opened) (If there is a fault, its location is measured from shore) Return to unpowered state (after fault location determined)

33. Concept of operations Un-powered -5000V Fault identification and isolation (Clearing) Mode, -5000V Initial BB switch state is closed Shore station is in current- limit operation If a fault is present –Time-coordinated protection begins when current becomes non-zero and voltage lower than 1kV. –Unit closest to fault trips first If no fault is present –All (Backbone) breakers remain closed (In either case, status is stored)

34. Concept of operations - 500V -1000V (Science Connecting Mode, -1000 V) Initial science node switch state is open Shore station is constant voltage operation Spur cable resistance is measured at low current –If no fault detected, spur switch closes –If fault detected, spur switch stays open In either case, status is stored

35. Concept of operations -1000V-10kV Normal Mode, -6000 V to – 10,000 V The control knows what the switch status is The control knows that it is in the Normal Mode If a fault occurs during Normal Mode operation –No switch action results –Shore station enters current limit mode

36. Concept of operations Un-powered -10kV Controlled shutdown from normal mode Shore station shuts the system down There is no change in the state of any switch The location of faults, if any, is not known to the shore station If the shutdown is not because of a fault, the fault location step can be omitted

37. What will happen if fault exists during startup mode?

38. Fault in radial branch during reset process 7kV 0V Node 5

39. Fault in radial branch during reset process 7kV 0V Node 5

40. Fault in radial branch during reset process 1kV 0V Rest of radial cable is isolated. The section behind the fault has no impact on fault location algorithm.

41. Fault in the loop during reset process 8kV7kV

42. Fault in the loop during reset process 8kV7kV

43. Fault in the loop during reset process 1kV2kV A Voltage at A could be low but should still be above the SIDAC break over voltage. The switch behind the fault still can be closed.

44. Fault between shore station and the network 10kV

45. Fault between shore station and the network 10kV

46. Fault between shore station and the network The network will lose one energy source. However, the switches should be able to close with the voltage from the other source. 10kV 0V

47. Conclusion The network will be closed as expected in any case.

48. Component requirements: Capacitance Voltage: voltage over capacitor will not exceed SIDAC break over voltage, which should be within 100V. It is a low voltage capacitor. Capacitance: solenoid of latching switch needs to be energized over a certain time (5-10ms) with a current over a certain value. Capacitance needs to meet both of these requirements, typically around 1e-4 F.

49. Component requirements: SIDAC Break over voltage V BO : –This is the maximum voltage that will be added across the two solenoids in series. It needs to meet the requirement of the solenoid to close the switch. –The voltage is also the lowest voltage under which BU could close its switches in startup mode. It needs to be as low as possible. –Proper value is around 40~100V. Current: –Maximum current is V BO / (R solenoid *2). It should be below 1A.

50. Component requirements: Diode Voltage: diode needs to withstand 10kV in the normal situation. Current: –There will be current in the diode only when the network is positively energized. –The current is equal to BU voltage divided by shunt resistance. –Its value will influence the capacitance charging time, thus the time to close the switches. –If we can bear a longer time to close all the switches in the network, this current could be set to a very low value by using a big shunt resistance or low shore station voltage. A reasonable value is around 0.2 A.

51. Component requirements: Shunt resistance Resistance: –Value of resistance decides the charging current of capacitance –And the voltage variation range in the network, which is shown below.

52. Component requirements: Shunt resistance The bigger the resistance, the smaller the voltage variation in the network. But the cap charging time will be increased. Around 50,000 ohms is recommended. (Equivalent shunt branch resistance is 25,000 ohms.) Power: When using 50,000 ohms resistance, the biggest shunt resistance current will be 0.2 A, assuming the shore station voltage is 10kV. So the maximum power dissipated by it is 2 kW. And it will only last tens of seconds.

53. Component availability This will be presented by Ann.