1. North East Pacific Time-series Underwater Networked Experiment (NEPTUNE): Power System Design, Modeling and Analysis
Aditya Upadhye

2. Outline NEPTUNE Power system requirements Two design alternatives
Version 1
Version 2
Cable analysis
Models
Simulation results
Conclusions and future work

3. NEPTUNE

4. Science requirements Communication bandwidth - Gb/s Power – 200kW
Reliability
Robustness of design
Thirty year lifetime
Maintenance and support

5. Power System Design Basic tradeoffs
Frequency: ac versus dc
Network: radial versus interconnected
Loads: series versus parallel
Shore station supply at 10kV, 200kW
Max. current-carrying capacity = 10A
User voltage = 400V / 48V
Max. power at each node = 10kW

6. Power System Design Protection Monitoring and control
Sectionalizing circuit breaker
Breaker control
Monitoring and control
Current – voltage measurements
State estimation
Shore station control hardware / software

7. Power System Design: Version 1

8. Version 1 Circuit

9. DC Circuit Breaker Need Required features During initial energization
For fault isolation
Required features
To force a current zero and minimize arcing
To prevent breaker restrikes

10. DC Circuit Breaker
Open Circuit R1 R2 S1 S2 S3 S4 C

11. DC Circuit Breaker
Soft Closing R1 R2 S1 S2 S3 C S4

12. DC Circuit Breaker
Closed circuit S2 S3 R1 R2 S1 S4 C

13. DC Circuit Breaker
Capacitor charging S2 R1 R2 S1 S4 C S3

14. DC Circuit Breaker
Capacitor discharging R1 R2 S1 S2 S3 S4 C

15. DC Circuit Breaker Hardware prototype
125V, 5A breaker circuit
Breaker control
MOSFETs drive the switch solenoids
Opto-isolator between logic circuit and driver circuit
Control logic has a counter, which continuously cycles through the breaker operations

16. DC Circuit Breaker Hardware prototype test results
Continuous Voltage: 125V
Continuous Current: 4.5A
Total Breaker Cycles: 125,000
Normal cycle switching frequency: 20Hz
Maximum cycle switching frequency: 100Hz
Maximum tested voltage: 200V
Maximum tested current: 5A

17. Power System Design: Version 2

18. Version 2 Circuit

19. Branching Unit

20. Series Power Supply Indigenous power supply for each BU
Less reliance on node converter
Use of zener diodes in reverse region
Back-to-back zener diodes

21. Modes of Operation Normal Fault Fault-locating Restoration
Special case
System startup

22. Normal Mode Objective: System voltage at 10kV
Science loads at all nodes are provided power
System voltage at 10kV
BU backbone switches are closed
BU dummy load switches are open
No fault within the network
PMACS (Protection, Monitoring and Control System) performs various measurements and estimates the system state

23. Fault Mode
Objective:
To cause system shutdown in the event of a fault and protect system components
Due to the reactive nature of the cable, any fault will cause large transients with large values of di/dt and dv/dt
BU controller does not respond to faults
The response to fault is at system level by shore station controls, which is a complete system shutdown

24. Fault-locating Mode Objective: Initial state:
To locate the fault without communications between the BUs or the BUs and the shore
Initial state:
All BU backbone switches are open
All BU dummy load switches are closed
System is energized at 3kV level
BUs are energized sequentially
When a BU backbone switch closes on a fault, it remains closed

25. Fault-locating Mode
BU dummy load switch opens after a certain delay following BU energization
Final State:
All BU backbone switches are closed
All BU dummy load switches are open
Current in network is fault current
PMACS performs calculations for locating the fault
System is shut down

26. Restoration Mode Objective: Initial state:
To energize the system and isolate the faulted cable section autonomously
Initial state:
All BU backbone switches are open
All BU dummy load switches are closed
System is energized at 5kV level
BUs are energized sequentially

27. Restoration Mode
When a BU backbone switch closes on a fault, BU opens the backbone switch to isolate the fault
Final State:
All BU backbone switches are closed
All BU dummy load switches are open
The faulted cable section is isolated
The system voltage is raised to 10kV and the system re-enters normal mode

29. Comparison of
Version 1 and Version 2

30. Version 1 Version 2 Conventional approach to power system design
Based on the philosophy that cable faults are rare but possible
Response to a fault is at the system level by the shore station controls
Response to a fault is at the local level by the nearest circuit breaker
Circuit breaker is complicated with many components
Complexity of circuit breaker is greatly reduced
Fault current is interrupted; arcing and restrikes are possible
Fault current is not interrupted; arcing and restrikes are not possible
Single node failure can cause failure in a large section of the network
Single node failure is not catastrophic for the system as that node only will be out of service
Reliability is low
Reliability is increased

31. Electromagnetic Transients Program (EMTP)

32. Alternate Transients Program

33. ATP Theory
ATP is a universal program system for digital simulation of transient phenomena of electromagnetic as well as electromechanical nature
With this digital program, complex networks and control systems of arbitrary structure can be simulated
Trapezoidal rule of integration

34. Cable Parameters

35. ALCATEL OALC4 Cable

36. Inductance Calculations
The generalized formulae were applied to the OALC4 cable
The core (steel) current caused flux linkages within
a) the core
b) the sheath
c) the insulation
The sheath (copper) current caused magnetic flux linkages within:
a) the sheath
b) the insulation

37. Inductance Calculations
Where T is the total flux linkage associated with the conductor, i is the flux linkage internal to the conductor, and e is the flux linkage external to the conductor
Where icable is the total current in the cable

38. Resistance Calculations
The resistance per unit length of a tubular conductor is given by:
The total cable resistance is given by:

39. Capacitance Calculations
The cable capacitance per unit length can be calculated by the formula:
F/m
Where,
 is the permittivity of the insulator.
d is the outer radius of insulator
c is the inner radius of insulator.

40. ATP Cable Modeling
In ATP the cable was modeled using the concept of composite conductor.
The steel core and copper sheath were treated as one composite conductor with the following properties:
comp = *10-8 m.
comp =

41. Results

42. Simulation Models

43. Version 1: Opening of Circuit Breaker
t = topen
Switch open: initial arcing
t =( topen +t)
Capacitor charging
t = (topen-t)
Switch closed

44. Simulation of Restrikes
topen
Vmax
RESTRIKE!!!
Initial Arcing Period

45. Restrikes: Simulation Circuit

46. Capacitor Current
Restrike
No Restrike

47. Capacitor Voltage
Restrike
No Restrike

48. Simulation Results

49. Current Limiting Operation
The shore station power supplies are rated at 200kW, 10kV
The steady-state system current = 10A
Under certain conditions, the system current may increase due to
Cable faults
Topology changes
Load fluctuations

50. Current Limiting Operation
The system current is limited to a value below 10A using the control circuitry in the shore station
This is done by dropping the shore voltage which in turn reduces the current
The control action is initiated only for steady-state overcurrents and not transient overcurrents.

51. Fault Analysis

52. Version1: Simulation Circuit

53. Results of Current Limiting: Shore Output voltage and Current

54. Voltage and Current at Node 2: No Current Limiting

55. Capacitor Current of Node 2

56. Version 2: Fault Studies
A pre-insertion resistance may be placed at the shore station to limit the fault current
This resistance will limit the fault current before the shore controls take the appropriate mode-dependant control action
Three controllable parameters in simulations:
Value of pre-insertion resistance
Response time of control circuitry
Distance of fault from the shore station

57. Simulation Circuit
X=100km/1200km

58. Results: Vary Response Time

59. Results: Vary Fault Distance

60. Conclusions
A sub sea observatory NEPTUNE is the first of its kind and will open up new and exciting areas of scientific research
The NEPTUNE power system implements a ‘dc network’
Version 1 dc breaker is designed and a hardware prototype was built in lab
Version 2, the preferred design choice is philosophically different from conventional terrestrial power systems
Transient studies of the system is performed using EMTP for worst-case scenarios from the point of view of component design and fault analysis
Theoretical analysis of the cable was performed and EMTP models were developed for the above

61. Future Work DC breaker prototype for Version 2
Control and monitoring systems for the above using microcontroller and/or array logic
A comprehensive transient model for the entire NEPTUNE network which is generic enough to simulate any fault type and any operating scenario