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Submitted on 1 Jan 1984
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THE LIQUID NITROGEN COOLED MAGNET FOR THE EINDHOVEN MHD BLOW DOWN FACILITY
W. Merck, Th. Roman, J. Rauch, E. Violi, R. Maix
To cite this version:
W. Merck, Th. Roman, J. Rauch, E. Violi, R. Maix. THE LIQUID NITROGEN COOLED MAGNET
FOR THE EINDHOVEN MHD BLOW DOWN FACILITY. Journal de Physique Colloques, 1984, 45
(C1), pp.C1-595-C1-598. �10.1051/jphyscol:19841120�. �jpa-00223590�
JOURNAL DE PHYSIQUE
Colloque C1, suppl6ment au no 1, Tome 45, janvier 1984 page Cl-595
THE LIQUID NITROGEN COOLED M A G N E T FOR THE EINDHOVEN MHD BLOW DOWN FACILITY
X.F.H. Merck, Th. oma an', J. ~ a u c h ~ , E. v i o l i r and R.K. Maixr Eindhoven University of TeehnoZogy, D p t . o f EZectricaZ Engineering, Eindhoven, The NetherZands
*BBC Brown Bovery & Co. Ltd., Dpt. for Magnets and Superconductors, 8050 Ziirich, SwitzerZand
RBsum6
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L'installation MHD Blow Down de 11Universit6 Technique dlEindhoven est le premier g6ndrateur MHD B cycleferm6de puis-sance 6lev6een Europeoccidentale. Son6lectro-aimant sans fer prgsentedesbobines Z t d t e s r e l e v 6 e s r e f r o i d i e s Bl'azoteliquide.
Unaperqu succinctestdonn6 surlaconceptionet 11ex6cution de cet aimant. I1 est suivi de quelques informations sur les per- formances de l'aimant qui ont donn6 entiere satisfaction. La puissance 6lectrique maximum atteinte par le g6n6rateur MHD a 6t6 de 360 kW pour une induction magngtique de 5.13 T.
Abstract
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The Eindhoven MHD Blow Down Facility is the first high-power closed cycle MHD plant in Western Europe. The core- less saddle-shaped magnet has liquid nitrogen cooled excitation coils. An outline of the concept and the realization of the magnet is presented. This is followed by information on its performance, which has given full satisfaction. The maximum electric power generated in the MHD channel is 360 kW at an induction level of 5.13 T.I
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INTRODUCTIONThe magnet is part of the Magneto-Hydro-Dynamic Blow Down Experiment of the Eindhoven University of Technology. Fig. 1 gives an impression of the experimental set up. The test rig was built to study the eherav conversion in a ., ..
closed cycle MHD genera- tor with an argon-cesium mixture as the working fluid /1/. The MHD gen- erator is located with all its electrode connec- tion cables and water hoses inside the 35x35 crn2 warm bore of the magnet
(fig. 3).
Fig. 1
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Blow Down Test Rig at the laboratory of the Direct Energy Conver- sion Division, Eindhoven University of Technology.Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19841120
(21-596 JOURNAL DE PHYSIQUE
I1
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DESIGN AND MANUFACTURE MHD Magnet Technical DataMaximum Magnetic Field 5.3 T
Electric Power Supply (pulse mode) 5000 A, 1200 V
Pulse length 40 s
Cooling System LN2
Temperature rise/pulse 70 K
Weight of coils 6.4 t
Total weight 14.4 t
Coils
Each of the two coils consists of 32 pancakes forming a monolithic block, to increase the stiffness and strength of the coils. The saddle-shaped coils (see figure 2 ) were continually wound on a two-axes winding table. The semi-hard quality of the hollow copper conductor, with an elastic limit of 220 MPa, was chosen to with- stand the high mechanical stresses of 160 MPa during pulsed opera- tion. The coil is insulated with dry glass fabric and impregnated under vacuum and pressure with Orlitherm resin. The BROWN BOVERI ORLITHERM
@
insulation system /2/ was chosen to withstand the widetemperature ranges occurr.ing during operation and has proved its worth in several cryogenic applications. The coils are cooled by liquid nitrogen flow- ing in the copper conductor.
The temperature rises from 80 K to 150 K during a single pulse.
Fig. 2
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One of the monolithic saddle-shaped magnet coils.Assembly
The mechanical resistance of the straight section of the coils is mainly ensured by a stainless steel structure cooled with liquid nitrogen (fig. 4). In order to achieve good transmission of the mag- netic forces from the coils to the support structure, stainless steel cushions filled with epoxy resin are placed in the gaps bet- ween the coils and the structure. This procedure permitted preten- sioning of the system, which was necessary to compensate for the different thermal expansion of the coil and the structure in opera- tion. To reduce thermal losses the coils and structure are placed in a stainless steel vacuum vessel. The magnet system is suspended and aligned in the vessel by means of eight vertical and four hori- zontal stainless steel cables carefully tensioned during assembly
(fig. 3 ) .
The instrumentation includes 20 thermocouples for monitoring coils and the structure temperature, as well as 16 strain gauges applied to the most critical points of the coils and structure. The voltage distribution over the four windinq sections is monitored.
Fig. 3
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Cross section through the MHD magnet.1
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magnet coil, 2-
support structure, 3-
vacuum vessel, 4-
suspension cable, 5-
warm boreElectrical and vacuum tests, carried out at BBC Brown Boveri
& Company, Ltd., and after erection on site, have confirmed that
the severe, specified re- quirements have been met in full. The assembled magnet was transported by road using a special truck with pneumatic suspension.
Fig. 4
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The magnet (coils and support structure) during assembly.I11
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PERFORMANCE AND OPEIiATION Magnetic FieldThe specified magnetic induction of 5 T with a homogeneity of
fi
5%in a volume of 1x0.2x0.2 m3 has been achieved.
Cool Down
The magnet is cooled to liquid nitrogen temperature. Cooling takes place in two main stages:
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the gas phase between ambient temperature and 150 K coil temperature-
the liquid phase below 150 K coil temperature.C 1-598 JOURNAL DE PHYSIQUE
The gas phase is necessary to prevent overstress in the magnet coils due to the unequal shrinkage which occurs with rapid cooling.
Some 17 hours are necessary to cool the magnet from room tempera- ture to 150 K. After 21 hours it reaches its low temperature at 80 K. Almost 20 tons of nitrogen are required for one cool down.
Operation
The argon flow in the Blow Down Experiment is scheduled to last 60 to 120 seconds, with full operation of the MHD generator lasting 11 seconds. During this interval the magnetic induction rises above 4.75 T. The magnet is switched on at full power after the argon flow and the cesium injection have been started (see fig. 5).
The magnetic induction rises with an initial time constant of 9.8 s and reaches its peak value after 13 s. The increasing coil resist- ance makes the induction drop again. During all runs the magnet performed excellently. A maximum induction of 5.3 T has been achie- ved. During one of the experiments (RUN 303) the generator produced 360 kW electric power for an induction level of 5.13 T.
Fig. 5
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Time sequence for switching on argon flow, cesium injection and magnet field, respectively.IV
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CONCLUSIONThe liquid nitrogen cooled magnet has satisfied all requirements.
It is an important and reliable component of the MHD Blow Down Facility at the Eindhoven University of Technology.
The facility has demonstrated the superiority of the closed cycle principle and represents a milestone in the development of MHD technology.
V
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REFERENCES/1/ Blom J.H. et al., Design of the Eindhoven 5 MW thermal MHD Blow Down Experiment, Proc. 17th Symp. on Eng. Asp. of MHD, Stanford, California, March 1978, H.4.
/2/ Koch A. et al., Insulation Systems for Magnets, Brown Boveri Publication No. CH-IM 312110.
