Poster - EFDA

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					                                             Proposed High Voltage Power Supply for the ITER relevant
                                                      Lower Hybrid Current Drive system
    P.K. Sharmaa, F. Kazarianb, P. Garibaldi, T. Gassmanb, J. F. Artaud, Y.S. Baec, J. Belod, G. Berger-By, J.M. Bernard, Ph. Cara, A. Cardinalie, C. Castaldoe, S.
    Ceccuzzie, R. Cesarioe, J. Decker, L. Delpech, A. Ekedahl, J.Garcia, M. Goniche, D. Guilhem, C.Hamlyn-Harrisb, J. Hillairet, G.T. Hoang, H. Jiaf, Q.Y. Huangf, F.
     Imbeaux, S.H. Kim, Y. Lausenaz, R. Maggiorag, R. Magne, L. Marfisi, S. Meschinoh, D. Milanesiog, F. Mirizzie, W. Namkungi, L. Pajewskih, L. Panaccionee, Y.
                           Peysson, A. Saille, G. Schettinih, M. Schneider, O. Tudiscoe, G. Vecchig, S. R. Villarie, K. Vulliez, Y. Wuf, Q. Zengf
                                                                              CEA, IRFM, F-13108 Saint-Paul-lez-Durance, France.
                                                              aPermanent address: Institute for Plasma Research, Bhat, Gandhinagar, Gujarat, India.
                                                                    bITER Organization,, CS 90 046, 13067 Saint-Paul-Les-Durance,France.
                                                                               cNational Fusion Research Institute, Daejeon, Korea.
                                                                      dAssociaçao Euratom-IST, Centro de Fusao Nuclear, Lisboa, Portugal.
                                                                      eAssociazione Euratom-ENEA sulla Fusione, CR Frascati, Roma, Italy.
                                                                             fInstitute of Plasma Physics, CAS, Hefei, Anhui, China.
                                                                          gPolitecnico di Torino, Dipartimento di Elettronica, Torino, Italy.
                                                                                         hRoma Tre University, Rome, Italy.
                                                            iPohang Accelerator Laboratory, Pohang Univ. of Science and Technology, Pohang, Korea.
 Poster ID SOFT 2010 P1-16, Mon. 27th Sept., 2010.


Introduction. In the framework of the EFDA task HCD-08-03-01, the ITER Lower Hybrid Current Drive (LHCD) system design has been reviewed [1,2]. The system
aims to generate 24 MW of RF power at 5GHz., of which 20 MW would be coupled to the plasmas [1,2]. The present state of the art does not allow envisaging a
unitary output of the klystrons exceeding 500 kW, so the project is based on 48 klystron units, leaving some margin when the transmission lines losses are taken into
account. A High Voltage Power Supply (HVPS), required to operate the klystrons, is proposed. A single HVPS would be used to feed and operate four klystrons in
parallel configuration. Based on the above considerations, it is proposed to design and develop twelve HVPS, based on pulse step modulator (PSM) technology, each
rated for 90kV/90A. In this concept several independent power supplies (modular type) are stacked together and are connected in series through fast electronic
switches, like insulated gate bipolar transistors (IGBT’s) [3,4]. This poster displays the typical electrical requirements and the conceptual design of the proposed HVPS
for the ITER LHCD system.


                             Main application
                                                                                      Electrical requirements of HVPS                           Typical specification of the LHCD HVPS unit
          (a) for operating klystrons at rated power and
                                                                             * The 5 GHz. source (for LH H&CD system in                                 Parameter                                Values
          (b) to condition the klystrons.
                                                                             ITER) yet to be fully developed.                                         Voltage range                      Upto -90 kV
                                                                             * The HVPS rating estimated on existing klystrons                        Accuracy                            1% of maxi. value.
                 Functional requirements of HVPS                             efficiency (~38% min. for the highest reflection                         Ripple                              1% of maxi. value.
                                                                                                                                                      Max. current                       90 A
                                                                             coefficient).                                                            Max. CW power                      8.1 MW
* fast recovery time, switch-off time, high efficiency                       * A 600 kW RF power (with some margins for the                           Fault energy                       < 10 J
* minimal indoor/outdoor space requirements                                  operation of the klystron) at 38% efficiency leads                       Response time of load
* unconventional crow bar unit at the load end to avoid                      to 1.6 MW of beam energy that can be managed                             protection system                  < 10 sec
   complexities and minimize failure risk.                                   with 80kV/20A HVPS.                                                      Re-switching time                  < 200 msec.
* High availability target                                                   * To accommodate more margin, the rating for an                          Total no. of units                 12
* Modular approach (1 HVPS for 4 klystrons)                                                                                                           Capacity of one unit               8.1 MW
                                                                             HVPS is proposed at 90kV/90A to feed and                                 Total capacity                     97.2 MW
* flexibility to operate                                                     operate four klystrons by using a single high
   (a) over wide range of voltages (25kV – 90kV),
   (b) over wide range of pulse length (~few msecs. to 3000 secs.) &
                                                                             voltage power supply system.                                              Table-1: Typical specification of HVPS for ITER-
   (c) with train of pulses (modulation) with varying voltages/frequency                                                                                                  LH system.



 Following ITER’s power distribution layout, the high voltage electrical network includes 400 kV AC transformers, each one having two secondaries: one secondary delivers 66 kV while the other
 delivers 22 kV. All RF H&CD systems, including LHCD will be connected to the 22 kV lines. The typical grid capacity is ~97.2 MVA (90kV/90A for four klystrons x 12 units).


 First Block: The feeder lines are                                                                                                                                 Third Block: It refers to the stack of
                                                 Conceptual design of HVPS                                                                                         ninety power modules connected in series,
 connected to the 22kV busbar. The
 feeders are protected by the vacuum                                                                                                                               to convert the ac supply voltage from
 circuit breaker (VCB) with over                                                                                                                                   transformer system to regulated DC
 current relays, an earth fault relay,                                                                                                                             voltages. All the modular power supplies,
 an under voltage relay and an over                                                                                                                                each rated at 1.2kV/90A, are stacked
 voltage relay. Each VCB is rated for                                                                                                                              together and are connected in series
 24kV/300A,       with   a    breaking                                                                                                                             through fast electronic switches, like
 capability of ~3.8 kA (12.5 times the                                                                                                                             insulated gate bipolar transistors (IGBT).
 average current).                                                                                                                                                 Each of these power modules has its own
                                                                                                                                                                   dc rectification unit, protection unit,
                                                                                                                                                                   crowbar unit, control and protection unit.


 Second Block: It refers to the multi-
 secondary transformer. A cast resin                                                                                                                               Fourth Block: It accounts for control
 transformer is proposed with very low                                                                                                                             electronics, which provides regulation,
 harmonic content in the input current                                                                                                                             protection, control and interface among
 and in star-delta configuration. The                                                                                                                              all the power modules. The modulation and
 22 kV input is fed to the primary of                                                                                                                              various settings of the HVPS are
 this    transformer       and      ninety                                                                                                                         controlled through this stage. It connects
 secondary, each of 1 kV, provides ac                                                                                                                              all the modular power supplies through
                                                                                                                                Klystrons operation in
 power to downstream parts with                                                                                                                                    fibre optic cables ensuring fast control
                                              First Block   Second Block         Third Block             Fourth Block           Parallel configuration
 appropriate electrical insulation.                                                                                                                                and noise immunity.

 * Each modular power supply when activated by closing of the series IGBT switch, adds a voltage step to the total output voltage and the total output voltage, thus available, is governed by
 the number of power modules activated by closing of the series switches.
 * This scheme also guarantees the flexibility of using the HVPS even when a few power modules become faulty. The faulty power modules can be easily replaced later by stand-by modules
 kept in reserve because of its modular plug-in capability and the faulty power module may be repaired and kept ready, as stand by, for future replacement.
 * It is proposed to accommodate all the twelve HVPS in the Assembly Hall. High voltage cables would be used to connect the klystrons, placed in the LHCD source area in the same building.
 * The solid state devices available for both higher voltages and higher switching frequencies have several advantages to replace traditional system like extended life, higher efficiency, easy
 and reliable operation, etc.
 * Further series connection of ninety elementary power modules does not require direct series connection of semiconductor devices. Thus each module is designed for ~1.2 kVDC (~90A) and
 has its own DC PS.
 * Module components are low voltage devices, low cost and each step of the voltage is lower than the allowable peak-to-peak ripple and provides an additional degree of freedom in the
 dimensioning of output filter.
 * It also provides complete flexibility since the number of switched-on modules in quantized steps of voltage controls the output voltage.
 * The design also aims to enhance reliability, decrease costs, plug-in modularity, provide redundancy, components de-rating, components standardization and easy availability. However the
 above advantages come at the cost of relatively high complexity of multi-secondary transformer and cabling of multiple power modules.

                                                                                                                 References:
Conclusions:
                                                                                                                 [1] G. T. Hoang, et. al., A Lower Hybrid Current Drive System for ITER, Nuclear Fusion, 49
* In the framework of an EFDA task, the design of HVPS for 24 MW ITER LHCD system is proposed.                   (075001), 2009.

* Each HVPS would cater to four klystrons, operated in parallel configuration.                                   [2] A. Bécoulet, et. al., Steady State Long Pulse Tokamak Operation Using LHCD, SOFT-
* The HVPS employs PSM technology to operate several modular IGBT’s based power supplies.                        2010, 27th Sept. – 1st Oct, 2010, Porto, Portugal, 2010.

* In particular, the technology foreseen for the HVPS is similar to other H&CD systems in IO (in                 [3] G. Taddia, M. Pretelli, L. Rinaldi, V. Rossi, et. al., Main high voltage solid state gyrotron
particular DNB HVPS, rated 100kV/75A) and most of the components are industrially available,                     power supply 60kV/80A, Proceedings of FEL, 2006, Pg-633-636, Bessy, Berlin, Germany.
therefore detailed R&D may not be required.
                                                                                                                 [4] I. S. Roth, J. A. Casey, M. P. J. Gaudreau, M. A. Kempkes, et. al., A solid state
* As a consequence, the proto-type development time phase is ignored and delivery time estimated is              opening switch and mod anode supply for the advanced light source klystrons, Proceedings of
~7yrs.                                                                                                           EPAC, 2002, Pg-2484-2486, Paris, France.


 Acknowledements:    This work, supported by the European Communities under the contract of Association between EURATOM and CEA, was carried out within the framework of the EFDA task
 HCD-08-03-01. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

				
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