NEPTUNE Branch Unit Operations and Circuit Design

Shuai Lu, Prof. El-Sharkawi

EE, University of Washington

March 31, 2005

Outline

• Branch Unit (BU) functions and operations

• BU circuit for closing (startup)

• BU circuit for opening (fault isolation)– Backbone fault isolation circuit– Spur cable fault isolation circuit

Cable network connected through BU

Explorer Plate

Pacific Plate

Gorda Plate

Juan de Fuca Ridge

North American Plate

Nedonna Beach

Junction Box

Cable

study area

Plate

Juan de Fuca

BU functions

• To close backbone and spur cable switches

(connection)

• To isolate faulted backbone or spur cables

(isolation)

BU operations

• Startup (making connection): – Close and latch all switches (backbone and spur cable).

• Fault isolation:– Spur cable: If a current is detected in the spur cable, the

BU opens switches S3 and S4. The spur cable is isolated

– Backbone cable: Switches are opened after a trip time

(t3) elapses: t3 = cV, where c is a constant; V is BU

voltage.

BU operation constraints

• No communication links between BU’s and shore stations

• No communication links between BU’s

(solution: using voltage and current to communicate)• Power needed for switching and control functions

can only be taken from backbone

(solution: using zener diodes and SIDAC controlled RC circuit as power supply)

Shore station closes

Vss > Vbu> 0

Shore station reverses voltage- Vss < Vbu < 0

t1

t2

t3

Spur cable fault

isolation

Spur cable fault

isolation

Backbone cable fault isolation

Backbone cable fault isolation

Wait for fault measurements

on shore

Wait for fault measurements

on shore

All switches are closed

All switches are closed

BU operation timing chart

Fault during normal operation

• BU takes no action. – Reason: the vacuum switches cannot break the

fault current without being damaged.

• The shore stations recognize the existence of fault.

• Shore stations shut down the system

• The system restarts at low positive voltage.

BU circuit for closing

BU circuit for closingS1

S2

S3 S4

O1

O3

O2

O4

Controller2Controller1

backbone backbone

ScienceNode

spur cable

C

R

Closing process

ControlControl

To Science

0V0V

Operation modes

ControlControl

To Science

0V+500V

Operation modes

ControlControl

To Science

0V+500V

Operation modes

ControlControl

To Science

+500

+500V

Operation modes

ControlControl

To Science

+500

+500

Operation modes

ControlControl

To Science

0V0V

BU circuit for opening(Controller)

BU circuit for opening

Backbone fault isolation circuit

Backbone fault isolation description

• The charging process of capacitor is used as a timing signal. This timing doesn’t vary with BU voltage.

• Voltage divider output depends on BU voltage.• The comparison between capacitor voltage and

voltage divider output determines the trip time. • Once fault current is subsided, backbone voltage

increases and the voltage divider voltage is higher than the zener voltage. Hence, no other BU will trip.

Backbone fault isolation

• Key points:– Use constant current to charge capacitor, thus capacitor

voltage contains time information

Vc = k*t

– Compare Vc and portion of Vbu to trip switches, thus trip time is portion of Vbu

Vc = p*Vbu

k*t = p*Vbu

t = p*Vbu/k = c*Vbu

• Key points:– When fault happens at different side of BU, different

switches should be opened

Current direction tells fault is on which sideZener voltage (0 or 6.8V) tells current directionCapacitor voltage tells zener voltageDifferent capacitor is related to different switches to be

opened

Fault location S1 S2 S3 S4

Left side of BU Open Open Open Closed

Right side of BU Open Open Closed Open

BU circuit for opening

Spur cable fault isolation circuit

Spur cable fault isolation

• Key point: two conditions should be satisfied simultaneously to open spur cable switch:– Voltage divider output is smaller than zener

voltage (in fault isolation mode) – Spur cable has current flowing (fault exists)

Two paralleled diodes are fault current indicator

BU operation and circuit features

• Reasonably redundant switch connections

• Simple control circuit

• Autonomous operation (not depending on communication and power from outside BU)

Goal: High reliability

3 way connections

• Choices:– Fixed connection point– 3 way BU

• A:

• B:

1 2

3

• Choices:– Fixed connection point– 3 way BU

• A:

• B:

1 2

3

3 way BU_A

controller

1 2

3

Backbone connections

To Science

1

2

3

Spur cable connections

3 way BU_B

To Science

1

2

3

controller

1 2

3

Backbone connections Spur cable connections

Fault isolation for fixed connection

BU

Fault is isolated by surrounding BU’s

Fault isolation for 3 way BU_Bcontroller

Controller functions the same way as 2 way BU’s

1 2

3

Fault isolation for 3 way BU_B

To Science

1

2

3

Controller functions the same way as 2 way BU’s

Controlled by both of the two controllers on branch 1

Conclusion

• BU operation and circuit design for 2 way BU’s are also applicable for 3 way BU’s.