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

Aditya Upadhye

Outlineo NEPTUNEo Power system requirementso Two design alternatives

Version 1 Version 2

o Cable analysiso Modelso Simulation resultso Conclusions and future work

NEPTUNE

Explorer Plate

Pacific Plate

Gorda Plate

Juan de Fuca Ridge

North American Plate

Nedonna Beach

Junction Box

Cable

study area

Plate

Juan de Fuca

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

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

Power System Design Protection

Sectionalizing circuit breaker Breaker control

Monitoring and control Current – voltage measurements State estimation

Shore station control hardware / software

Power System Design: Version 1

Version 1 Circuit

Node dc-dc converterand controlelectronics

Backbone cable

Spurcable

CircuitBreaker

Back-biaseddiodes

Science Loads

NODE

10kV

400V

DC Circuit Breaker

Need During initial energization For fault isolation

Required featuresTo force a current zero and minimize arcingTo prevent breaker restrikes

DC Circuit Breaker

R1 R2

S1

S2 S3

S4

C

Open Circuit

DC Circuit Breaker

R1 R2S1

S2 S3

C

S4

Soft Closing

DC Circuit BreakerClosed circuit

S2 S3

R1 R2

S1 S4

C

DC Circuit BreakerCapacitor charging

S2

R1 R2S1

S4

C

S3

DC Circuit Breaker

R1 R2S1

S2 S3

S4

C

Capacitor discharging

DC Circuit BreakerHardware 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

DC Circuit Breaker

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

Hardware prototype test results

Power System Design: Version 2

Version 2 Circuit

Node dc-dc converterand controlelectronics

CircuitBreaker

Back-biaseddiodes

Science Loads

NODE

BRANCHINGUNIT

10kV

400V

Branching Unit

BUController

1

BUController

2

Science Load Dummy Load

I 1 I 2

I 3

I1 I2 I3

S1

S2

S3

S5 S6

12V 12V

Z1 Z3 Z2

Solenoid of S1 Solenoid of S2Solenoid of S3

I 4

L2L1

I4 I1 I2 I3 I4

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

12V

2-5A

Solenoid # 1

Solenoid # 2

2-4A

12V 0V

0.5A

0.5A

Modes of Operation Normal Fault Fault-locating Restoration

Special case System startup

Normal mode

Fault?

Systemshutdown

Yes

No

Fault locatingmode

StateEstimation

Is faultlocated?

Systemshutdown

Restorationmode

Raisevoltage to

10kV

No

Yes

System startup

1. Current measurement atshore2. Communication from nodesexperiencing voltage collapse3. PMACS determining nodesthat drop-out.

PMACS determiningpresence of fault and its

location

Comparison of Version 1 and Version 2

Conventional approach to power system design

Based on the philosophy that cable faults are rare but possible

Version 1 Version 2

Response to a fault is at the local level by the nearest circuit breaker

Response to a fault is at the system level by the shore station controls

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 increasedReliability is low

Electromagnetic Transients Program (EMTP)

Alternate Transients Program

ATP Theory

o ATP is a universal program system for digital simulation of transient phenomena of electromagnetic as well as electromechanical nature

o With this digital program, complex networks and control systems of arbitrary structure can be simulated

o Trapezoidal rule of integration

Cable Parameters

ALCATEL OALC4 Cable

SteeltubeØ: 2.3 mm

Optical

fibers

Compositeconductor

Steel wiresstrand

Thixotropic

J elly

Insulating sheath Ø 17mm

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

Inductance Calculations

T i e

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

T

cableL

i

Where icable is the total current in the cable

Results

Theoretical values

ATP values ALCATEL values

R (/km) 1.03 1.03 1.00

L (mH/km) 0.3947 0.3948 0.4

C (F/km) 0.179 0.179 0.2

Simulation Models

Version 1: Opening of Circuit Breaker

t = (topen-t)

Switch closed

t = topen

Switch open: initial arcing

t =( topen +t)

Capacitor charging

Simulation of Restrikes

RESTRIKE!!!

Initial Arcing Periodtopen

Vmax

Restrikes: Simulation Circuit

10kVDC

250 kmCable

250 kmCable

S1

S3S2

S4Rd

C

Rs

Load Z1

NODE A

Sf

NODE B

Load Z2

Capacitor Current

1

2

3

Restrike

No Restrike

1

2

Capacitor Voltage

1

2

1

2

3

Restrike

No Restrike

Simulation Results

Maximum voltage across switch

Travel time of switch

Minimum value of capacitor to prevent

restrikes (F) 15 kV 5 ms 2

15 kV 10ms 5

15 kV 18 ms 10

25 kV 15 ms 1

25 kV 18 ms 1

25 kV 20 ms 1

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

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.

Fault Analysis

Version1: Simulation Circuit

100km

DC

Shorecurrentlimiting

NODE A

LOAD Z1

100km NODE B

LOAD Z2

50km

50km

LOAD Z3Sf

Results of Current Limiting: Shore Output voltage and Current

1

2

3

1

3

2

Current

Voltage

Voltage and Current at Node 2: No Current Limiting

1

2

3

1

2

3

Current

Voltage

Capacitor Current of Node 2

1 2

3

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:

A. Value of pre-insertion resistanceB. Response time of control circuitryC. Distance of fault from the shore station

Simulation Circuit

DC

'X'km

BU A

LOAD Z

100km

BU B

LOAD ZDC

V1V2

900km

Sf

Pre-insersion

resistance

X=100km/1200km

Results: Vary Response Time

0

100

200

300

400

500

600

0 10 20 30 40 50 60

Response time of shore (ms)

I^2

t v

alu

es

Faultdistance=100km

Faultdistance=1200km

Results: Vary Fault Distance

0

50

100

150

200

250

0 200 400 600 800 1000 1200 1400

Distance of fault from shore (km)

Peak C

urr

en

t Tra

nsie

nt

(A)

0

100

200

300

400

500

600

0 200 400 600 800 1000 1200 1400

Fault distance from shore.

I^2t

valu

es.

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

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