Concept Design Review (CoDR) Shore Station DC Breaker Cable model Transient Analysis Components

NEPTUNE

Shore Station

Configuration of Shore Station

SHORE STATION… Power supply Selection Off-the-shelf Buck regulator. General ratings:  Output Voltage = 10 kV DC  Output Range = 9 – 15 kV  Voltage tolerance within 2%.  Output Power = 200 kW  Current Limiting Capability = twice the rated current = 20 A.  Local and remote control functions  Self diagnostics capabilities

SHORE STATION… Power supply Selection Potential vendor for shore stations Manufacturer: Diversified Tech Model: Custom made. Specifications:  Input: 3 phase 13.8 kW service.  Output: 10kV / 200kW using the HV buck regulator technology.  Over current protection: Above 40A. Solid state system will act as current limiter.  Dimensions: 40” by 36” by 42” estimated.

SHORE STATION… Surge Protection Spark gap arresters Metal oxide varistor (MOV) ceramic, polymer or silicon rubber insulator Surge arresters are selected based on several ratings Energy absorption capability (or energy withstand capability) Maximum continuous operating voltage (MCOV) Temperature rise.

SHORE STATION… Vacuum Switches (Breaker) Types: Air Air-blast Magnetic quencher Oil Sulfur hexafluoride gas (SF6) Vacuum Solid-state

SHORE STATION… Vacuum Switches Vacuum breaker is used for systems under 36 kV. Pollution-free Fast Reliable Compact Light weight Requires small energy to operate.

SHORE STATION… Vacuum Switches Potential manufacturer: Kilovac or Jennings Specifications:  Contact Arrangement: Normally Open.  Rated Operating Voltage:28kV  Max. Current: 40A.  Max. Contact Resistance: 0.02 ohm.  Release time < 20 ms  mechanical lifetime > 2 million cycles.

DC Circuit Breaker

DC CIRCUIT BREAKER R1R2 S1 S2S3 S4 C

S2S3 R1R2 S1S4 C DC CIRCUIT BREAKER … Stage 1- Normal closure

S2 R1R2 S1 S4 C S3 DC CIRCUIT BREAKER … Stage 2 - Interruption  Current is routed through C  Size of C is selected to prevent restrikes

R1R2 S1 S2S3 S4 C DC CIRCUIT BREAKER … Stage 3 – Discharging of Capacitor  Cap is discharged through R2  to set the circuit for next switching

R1R2 S1 S2 S3 C S4 DC CIRCUIT BREAKER … Stage 4 – Soft Starting  Soft starting resistance R1 reduces  the inrush current during energization

S2S3 R1R2 S1S4 C DC CIRCUIT BREAKER … Stage 5 – Normal closure

Components Selection Vacuum Switches Voltage Rating Withstanding Voltage > 25kV Continuous Current Rating 20A or higher Release time Faster release time means smaller capacitor is required. Release time < 20 ms Lifespan, measured in cycles of operation Millions of operations

Components Selection Capacitor Voltage Rating 15-20kV rating Capacitance 1-10μF, depending on node location Size up to 600 cubic inches Lifespan Measured in hours of operation

Components Selection Resistors 2 Resistors: soft close and capacitor discharge Resistance value: Both are currently specified at 1kΩ Peak Voltage Rating: 10-20kV Peak Energy Rating Power dissipation more important in this application than average power, as resistors will be used for brief (less than one second) intervals

Components Selection Diodes

V RRM (maximum repeat reverse voltage): 20-25kV Continuous forward current Based on normal operation > 50 A Maximum Transient Current > 300A di/dt ratings > 100A/s Reverse leakage current ~ A Type: Stacked Hockey Puck

Cable Model

Cable Model …inductance

flux linkages theory a) the core b) the sheath. c) the insulation.

Cable Model …inductance Cable Inductance Where: = Total flux associated with the cable. = Total cable current.

Cable Model …Resistance The resistance per unit length of a tubular conductor is given by: The total cable resistance is thus given by:

Cable Model …Capacitance The cable capacitance per unit length can be calculated by the formula: Where,  is the permittivity of the insulator. d is the outer radius of insulator c is the inner radius of insulator.

Cable Model …Seawater The current return is through the seawater. In near DC conditions the sea-water resistance and inductance are calculated as: R = m/km. L = mH/km. These values are frequency dependent.

Cable Model …Composite model For transient simulation, the steel core and copper sheath can be modeled as a composite conductor  comp = *10 -8 m.  comp =

Results …

Transient Simulation Normal Switching Fault

TRANSIENT ANALYSIS… ATP

TRANSIENT ANALYSIS… What is ATP?  ATP is a universal program system for digital simulation of transient analysis of transmission systems.  ATP has extensive modeling capabilities including power electronics, control, protection, etc.

Simulation Circuit… Normal Switching

Simulation Circuit… Switching Timing N1 N2 N3 N

Current at the input of Node 3

Voltage at the input of Node 3

Voltage across the left diode in Node 3

Simulation Circuit… Fault Condition

Voltage across load in Node 2

Current entering Node 2

Simulation Circuit… Restrike

t = (t open -  t) Switch closed t = t open Switch open: initial arcing t =( t open +  t) Capacitor charging

Simulation of Restrikes t open V max RESTRIKE Initial Arcing Time Voltage

Simulation Results

Fault Simulation with restrike

Fault Simulation without restrike