,A ROTATING FLUX COMPRESSOR FOR ENERGY CONVERSION *

Transcription

1 ,A ROTATING FLUX COMPRESSOR FOR ENERGY CONVERSION * P Chowdhri, T W Linton and J A Phillips Los Alamos National Laboratory Los Alamos, New Mexico Smmary The rotating flx compressor (RFC) converts rotational kinetic energy into an electrical otpt plse which wold have higher energy than the electrical energy initially stored in the compressor An RFC has been designed in which wedge-shaped rotor blades pass throgh the air gaps between sccessive trns of a solenoid, the stator Magnetic flx is generated by plsing the stator solenoids when the indctance is a maximm, ie, when the flx fills the stator-solenoid volme Connecting the solenoid across a load conserves the flx which is compressed within the small volme srronding the stator periphery when the rotor blades ct into the free space between the stator plates, creating a minimm-indctance condition The niqe featres of this design are: (1) no electrical connections (brshes) to the rotor; (2) no conventional windings; and (3) no maintenance The device has been tested p to 5,000 rpm of rotor speed Introdction The rotating flx compressor (RFC) converts rotational kinetic energy into an electrical otpt plse which wold have higher energy than the electrical energy initially stored in the compressor The principle of the flx compressor can be explained by Fig 1 The flx compressor is a variable indctor, where the indctance is varied by external means It is charged from a crrent sorce when it has its maximm indctance Lmax The crrent sorce is disconnected at the end of the charging period, and the indctance of the flx compressor ~s forced towards its minimm vale Lmin" The load 1~ LS also connected to the flx compressor at the same time Becase of the conservation of flx linkage, the load crrent increases, if Lmax >> 1~ Ths, Both the final crrent and the final energy be many times their initial vales if ~ax (~in+ L~? In a rotating flx compressor, increase Ln the final energy is accomplished at expense of the kinetic energy of the rotors, ie, slowing the rotor speed can» the the by The mechanism by which the indctance of a flx compressor is varied can be explained by Figs 2 and 3 In Fig 2a, a solenoid is charged from a crrent sorce while a cylinder of high electrical condctivity is moving towards the air core inside the solenoid In Fig 2b, the crrent sorce is disconnected and the load 1~ is connected, when the condcting cylinder is abot to enter the solenoid core Figre 2c shows the condition at the end of the cycle As the condcting cylinder moves into the solenoid core it displaces the core magnetic flx and sqeezes it arond the solenoid trns This effectively redces the solenoid indctance Hence, the solenoid indctance is Lmax in Fig 2a, while it is Lmin in Fig 2c In the rotating flx compressor, the condcting cylinder of Fig 2 becomes the rotor and the solenoid the stator (Fig 3a) When the stator solenoid (Fig 3b) is energized, the magnetic field lines fill the central region Under this condition, the solenoid has the maximm indctance Lmax The rotors, consisting of a nmber of parallel plates, pass between the windings, Fig 3c Magnetic field lines are ct, reform abot the windings, and the magnetic energy which filled the solenoid is now compressed between the plates and the sides of the windings (Fig 3d) A large decrease in volme (indctance) takes place Figre 4 shows the cross-section of a two-solenoid rotating flx compressor when the wedge-shaped rotor passes over the central air core of each solenoid The hatched parts represent the compressed magnetic flx (1) or, (2) Similarly, i (1/2) Ii2~ax (3) f (1/2) "If2(~in + L~) (4) Fig 1 Schematic for flx-compression test and, ~ax (5) B - s I - I s, s, s s, (a) (b) (c) *work performed nder the aspices of the US Dept Energy of 661 Fig 2 Flx compression by a moving metallic cylinder

2 Report Docmentation Page Form Approved OMB No Pblic reporting brden for the collection of information is estimated to average 1 hor per response, inclding the time for reviewing instrctions, searching existing data sorces, gathering and maintaining the data needed, and completing and reviewing the collection of information Send comments regarding this brden estimate or any other aspect of this collection of information, inclding sggestions for redcing this brden, to Washington Headqarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Site 1204, Arlington VA Respondents shold be aware that notwithstanding any other provision of law, no person shall be sbject to a penalty for failing to comply with a collection of information if it does not display a crrently valid OMB control nmber 1 REPORT DATE JUN REPORT TYPE N/A 3 DATES COVERED - 4 TITLE AND SUBTITLE A Rotating Flx Compressor For Energy Conversion 5a CONTRACT NUMBER 5b GRANT NUMBER 5c PROGRAM ELEMENT NUMBER 6 AUTHOR(S) 5d PROJECT NUMBER 5e TASK NUMBER 5f WORK UNIT NUMBER 7 PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Los Alamos National Laboratory Los Alamos, New Mexico PERFORMING ORGANIZATION REPORT NUMBER 9 SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10 SPONSOR/MONITOR S ACRONYM(S) 12 DISTRIBUTION/AVAILABILITY STATEMENT Approved for pblic release, distribtion nlimited 11 SPONSOR/MONITOR S REPORT NUMBER(S) 13 SUPPLEMENTARY NOTES See also ADM IEEE Plsed Power Conference, Digest of Technical Papers , and Abstracts of the 2013 IEEE International Conference on Plasma Science Held in San Francisco, CA on Jne 2013 US Government or Federal Prpose Rights License 14 ABSTRACT 15 SUBJECT TERMS 16 SECURITY CLASSIFICATION OF: 17 LIMITATION OF ABSTRACT SAR a REPORT b ABSTRACT c THIS PAGE 18 NUMBER OF PAGES 4 19a NAME OF RESPONSIBLE PERSON Standard Form 298 (Rev 8-98) Prescribed by ANSI Std Z39-18

3 0E38!E ~- {a) [J~E3~0~E3 (c) (b) ~ y ~ ~ 0 je je 3 the device is maintenance-free Fig 6 A photograph of the complete assembly is shown in Tests on the RFC The circit for testing the RFC is similar to Fig 1 The crrent sorce is for banks of 70-mF electrolytic capacitors charged to variable voltages Initially s 2 is closed and s 1 is open The RFC is broght to the reqired speed, and the capacitor,banks are charged to the reqired voltage The capacitor banks are then discharged by an ignitron (not shown) in series with s 2 The switch s 1 is closed and s 2 opened at the peak of the discharge crrent The seqence of ignitron firing, opera tion of s 1 and s 2, and oscilloscope triggering is done by a time-delay generator which in trn is triggered by an electrical plse generated by an opto-electronic sensor copled to the RFC rotor The delay time for the switch operation is varied with the rotor speed so that the peak of the capacitor-bank discharge crrent occrs when the rotor blades start to obstrct the stator Fig 3 Mechanism of flx compression by rotating condcting disks Fig 4 Cross-section of a two-solenoid rotating flx compressor and its wedge-shaped rotor Fig 5 Rotor blades and stator plates of the Los Alamos rotating flx compressor Los Alamos Design of Rotating Flx Compressor The present RFC model consists of 16 alminm stator plates and 15 alminm rotor blades, each 095 em thick, as shown in Fig 5 The stator plates are connected sch that they form two pairs of 16-trn solenoids The rotor blades rotate in the 115 em wide air gaps between the sccessive stator plates The otside diameter of a stator plate is 5525 em The stator cores are tear-drop shaped to prodce relatively high rate of rise of the otpt crrent near the minimm indctance The rotor blades are rotated by an air trbine The niqe featres of this design inclde: 1 no electrical connections (brshes) to the rotor ie, switches that initiate the otpt electrical plse are located otside the generator; 2 the device is strdy becase there are no conventional windings either on the rotor or on the stator; and 662 Fig 6 Los Alamos rotating flx compressor

4 cores Tests were performed at varios rotor speeds to measre crrent amplification Figre 7 shows typical oscillograms of the load and inpt crrents with one pair of 16-trn stator-solenoids in circit Discssion When the rotor blades sweep inside the free space between the stator plates, the magnetic flx is displaced and compressed arond the periphery of the stator plates, decreasing the indctance of the RFC system A smaller confinement volme of the magnetic flx reslts in smaller indctance, The flx compression that depends pon the Lma~/(Lmin + L~) ratio will ths be larger the smaller the Lmin for specified Lmax and L~ The magnetic flx, however, is not entirely confined within the free space between the stator plates and the rotor blades The flx diffses into the rotor and the stator materials As the magnetic flx diffses into these materials, the effective volme of flx confinement increases, ths increasing Lmin and degrading flx compression If a condcting plate is exposed to a plsed magnetic field, the time-domain analysis of flx diffsion throgh the plate can be performed starting with the one-dimensional diffsion eqation Ths, Fig 7 Otpt and inpt crrent profiles of the rotating flx compressor Rotor speed = 5000 rpm Load indctance L~ = 002 ]lh Upper trace: Otpt crrent, 2kA/div; 1 ms/div Lower trace: Inpt crrent, 108 ka/div; 1 ms/div One pair of 16-trn stator-solenoids in circit 10,---~ ,----,---, RFC MODEL I 9 8 (o]l)(dh/dt) (6) where H magnetic field, o electrical condctivity of the condcting plate, Jl permeability of the condcting plate, x depth within the plate from its srface, and t time Assming a step-fnction magnetic field, ie, o~-~~-~2~~3~~4~~5~~6 ROTOR SPEED- RPM x I0-3 and, ( 7a) Fig 8 Crrent amplification vs rotor speed L~ = 002 ]lh One pair of 16-trn stator-solenoids in circit Lim H (x,t) = 0 x+oo the soltion becomes ~(x,t) = H 0 erfc[(x/2)1(o]l/t)] (7b) This is the soltion for the magnetic field diffsing inside a condcting plate by an applied step-fnction magnetic field The soltion for any other type of time-varying magnetic field is obtained by applying the convoltion integral Eqation (8) shows that the depth of flx penetration will be less for highly condctive materials It also shows how the flx penetrates the condcting plate as a fnction of time Translating this to the rotating flx compressor, the flx penetration will be smaller the faster the rotor blades sweep pass the stator cores In other words, the higher the rotor speed the higher will be the L ax/~in ratio, and conseqently the higher will be t~e crrent amplification Figre 8 shows the measred variation of the crrent amplification as a fnction of the rotor speed (8) 663 The Lm x condition occrs when the magnetic flx flows throg~ the stator cores nobstrcted by the rotor blades The Lmax can be significantly improved, and so will the crrent amplification, if the stator cores are filled with a ferromagnetic material and the rotor blades are also partially bilt with the ferromagnetic material We have initiated work on a ferromagnetic RFC The indctance and resistance of the RFC were measred with an impedance bridge at three freqencies for varios rotor positions (Fig 9) One pair of 16-trn stator-solenoids was in circit The Lm x is the highest (29 ]lh) at 120 Hz and the lowest (23J ]lh) at 10 khz At high freqencies, the excitation crrent tends to flow along the innermost periphery of the stator coils srronding the central air core, As the magnetic flx is confined within a smaller volme nder this condition, the Lma~ is also smaller The L!llin likewise, is the highest ~5 ]lll) at 120 Hz and the lowest (19 ]lh) at 10 khz Dring flx compression, the magnetic flx diffses into the srronding metals, penetrating frther into the metals for lower freqencies Ths, for lower freqencies, the volme of the confined magnetic flx will be larger, and hence the Lndn higher

5 ,/"" ',, ~ / ', z 120HZ UJ 20 / ~\ ' <( ' \ } khz t; 15 \ / 10kHZ ::J Cl z :\,; 10 \ / 5 \ ', \ ' ' ' \ \,' e \ I e ' ; ';;--;;; ROTOR POSITION-DEGREES ~ 50 I w z 40 <( "' iii w 30 a: LL a: kHZ 1kHZ ~ ~-----/ HZ I ROTOR POSITION-DEGREES (a) (b) Fig 9 RFC impedance as a fnction of rotor position, measred with an impedance bridge One pair of 16-trn stator-solenoids in circit (a) indctance; (b) resistance The calclated vale of Lmax for the 32-trn stator, assming niform crrent distribtion, is 332 ~H, and that of a single trn 025 ~H The variation of the RFC resistance with rotor position is small at 120 Hz, bt prononced at 10 khz (Fig 9b) The RFC resistance has three components: 1 blk resistance of the stator coils, 2 contact resistance between stator coils, and 3 effective resistance of the eddy-crrent losses dring flx diffsion As mentioned earlier, the excitation crrent tends to flow along the innermost periphery of the stator coils srronding the central air core dring the period of Lmax' ie, when the rotor blades are not obstrcting the central air cores of the stators Higher the excitation-crrent freqency the smaller the cross-section of crrent flow, and hence higher the blk resistance Magnetic flx is deflected as the rotor blades start to obstrct the stator core This redistribtes the stator crrent, forcing it to flow over a larger cross-section, ths redcing the blk resistance to crrent flow However, flx diffsion generates eddy-crrent losses, introdcing more resistance The total resistance rises dring flx compression at 120 Hz, indicating that the effective resistance of the eddy-crrent losses is predominant However, at 1 khz and 10 khz, the total resistance drops dring flx compression, indicating that the decrease of the blk resistance is more prononced than the increase cased by the eddy-crrent losses The calclated de resistance of the RFC is 24 mq, compared to the measred de resistance of 34 mq, The difference is cased by the contact resistance between the 32 trns of the stator The switches s 1 and s 2 of Fig 1 are stationary fast-acting mltiple-contact switches installed external to the RFC The opening switch s 2 is immersed in pressrized hydrogen to minimize arcing and hence erosion In recent experiments, we have replaced the closing switch s 1 with a silicon rectifier This prevents reverse crrent to flow throgh the load, enables faster transfer of crrent to the load and shortens arc interrption time of s 2 even frther We plan to replace s eventally by 2 solid-state switches Conclsions We have performed magnetic flx compression with a rotating flx compressor of simple design which does not need brshes or sliding contacts, and which does not have conventional windings either on the rotor or on the stator Flx compression was achieved with crrent amplification increasing with rotor speed to 64 at 5,000 rpm Ack~owledgements The athors acknowledge the contribtions of many of their colleages, particlarly to G A Barnes, J G Garcia and K H Milder for help with the tests; and to A R Wilson, Jr for the original RFC constrction 664