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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.