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.
Pages to are hidden for
"NEPTUNE Branch Unit Operations and Circuit Design"Please download to view full document