Vacuum circuit breaker for 66kA DC interruption
In both poloidal and toroidal circuits of ITER, Fast Discharge Units (FDU) will be used to dissipate quickly the energy stored in the superconducting windings of the machine in case of their quench. The current interrupting element in the FDU will be a vacuum circuit breaker (VCB), which must be able, in the worst case, to interrupt a current of 60 kA, withstanding a peak recovery voltage of 20 kV; the number of operations before the need to change the VCB should be around 2,000. Being these requirements above the operational experience of the VCBs used in existing fusion experiments, a R&D Task was launched by ITER EU Home Team for the design, construction and tests of a VCB able of fulfilling the ITER requirements. The R&D Task was assigned to Siemens AG, and the selected site for the tests was Consorzio RFX, considering that the power supply system of the RFX Ohmic Heating (OH) circuit could be easily modified to reproduce conditions very close to the ones expected in ITER.
In the R&D Task Technical Specifications the VCB to be developed is asked to interrupt 66 kA and to withstand a peak recovery voltage of 24 kV, to have some margin in the operating parameters. In addition, the VCB was required to withstand a specific energy of 8.7.GA2s at closed contacts. The tests had to include life tests performed under the operating conditions, to verify if the goal of 2,000 interruptions could be achieved.
The facility arranged at RFX site, to test the Siemens vacuum circuit breaker, includes the circuit shown in figure.
The main ratings of the circuit components are: AC/DC converters: voltage max. 1350 V current tot. max 75 kA duty cycle 5s ON/600s OFF Counterpulse banks (each): capacitance 306 microF charging voltage max. 35 kV current max. 65 kA Dummy load: inductance 6 mH resistance 2.8 mOhm current max. 70 kA voltage max. 35 kV Protection crowbar (PP): peak current 100 kA Short-circuit make switch (PMSS): current 50 kA (5 s ON/600 s OFF) 320 kA peak closing time 110 ms
|The main ratings of the circuit components are:|
|voltage||max. 1350 V|
|current||tot. max 75 kA|
|duty cycle||5s ON/600s OFF|
|Counterpulse banks (each):|
|charging voltage||max. 35 kV|
|current||max. 65 kA|
|current||max. 70 kA|
|voltage||max. 35 kV|
|Protection crowbar (PP):|
|peak current||100 kA|
|Short-circuit make switch (PMSS):|
50 kA (5 s ON/600 s OFF)
|320 kA peak|
|closing time||110 ms|