NEPTUNE Branch Unit Operations and Circuit Design by she20208

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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


                   Juan de Fuca Ridge


               Pacific Plate
                                       Juan de Fuca
                                                      Nedonna Beach
                                           Plate
                      Junction Box
                                                         North
                               Cable                     American
                                                         Plate

  study area                       Gorda Plate
              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)
          BU operation timing chart
        All switches             Wait for fault   Spur cable        Backbone
         are closed              measurements        fault          cable fault
                                   on shore        isolation         isolation




                                                               t3
                                          t2
                t1
Shore station            Shore station
    closes             reverses voltage
Vss > Vbu> 0            - Vss < Vbu < 0
  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 closing
                              S1


backbone                      S2                          backbone

           Controller1   S3         S4           Controller2

              O1                                    O2
                                             C
              O3                                    O4



                                         R


                         spur cable
                              Science
                               Node
               Closing process


0V                                         0V

     Control                     Control




                    To Science
             Operation modes


+500V                                    0V

        Control                Control




                  To Science
             Operation modes


+500V                                    0V

        Control                Control




                  To Science
             Operation modes


+500V                                    +500

        Control                Control




                  To Science
            Operation modes


+500                                    +500

       Control                Control




                 To Science
          Operation modes


0V                                    0V

     Control                Control




               To Science
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
   Fault location     S1     S2        S3          S4

   Left side of BU    Open   Open      Open        Closed

   Right side of BU   Open   Open      Closed      Open




  Current direction tells fault is on which side
  Zener voltage (0 or 6.8V) tells current direction
  Capacitor voltage tells zener voltage
  Different capacitor is related to different switches to be
    opened
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:
                1            2

                    3
     • B:

            1                    2

                        3
                 3 way BU_A
    controller
1                          2
                                       2

                            1                           3




                   3                   To Science

    Backbone connections       Spur cable connections
                 3 way BU_B
    controller
1                          2
                                   2

                           1                        3




                   3               To Science

    Backbone connections   Spur cable connections
Fault isolation for fixed connection


   BU




   Fault is isolated by surrounding BU’s
Fault isolation for 3 way BU_B
           controller
 1                                       2




                             3
  Controller functions the same way as 2 way BU’s
    Fault isolation for 3 way BU_B

                           2

                 1                      3



Controlled by both of the two
controllers on branch 1

                          To Science


         Controller functions the same way as 2 way BU’s
               Conclusion
• BU operation and circuit design for 2 way
  BU’s are also applicable for 3 way BU’s.

								
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