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

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 (t 3 ) elapses: t 3 = 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 V ss > V bu > 0 Shore station reverses voltage - V ss < V bu < 0 t1t1 t2t2 t3t3 Spur cable fault isolation Backbone cable fault isolation Wait for fault measurements on shore 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

S1 S2 S3S4 O1 O3 O2 O4 Controller2Controller1 backbone Science Node spur cable C R

Closing process Control To Science 0V

Operation modes Control To Science 0V+500V

Operation modes Control To Science 0V+500V

Operation modes Control To Science V

Operation modes Control To Science +500

Operation modes Control To Science 0V

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 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 Fault locationS1S2S3S4 Left side of BUOpen Closed Right side of BUOpen ClosedOpen

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: 12 3 Choices: –Fixed connection point –3 way BU A: B: 12 3

3 way BU_A controller 12 3 Backbone connections To Science Spur cable connections

3 way BU_B To Science controller 12 3 Backbone connectionsSpur cable connections

Fault isolation for fixed connection BU Fault is isolated by surrounding BU’s

Fault isolation for 3 way BU_B controller Controller functions the same way as 2 way BU’s 12 3

Fault isolation for 3 way BU_B To Science 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.