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1. Current Sense Resistor R Current Sense Resistor The resistor is used to convert the current flowing the in part into a voltage for the AT3600 to measure e The voltage produced V x R should be in the range 10mV to 1V e To minimize waveform distortion the resistor should be less or equal to 1 ohm e Check the power consumed I2R and choose a suitably rated resistor 2003 Voltech Instruments All rights reserved CONSTANT CURRENT aL ECHNOTES Step down Transformer The step down transformer is used to increase the current capability of the AT3600 and to better match the voltage across the part to the characteris tics of the AT3600 source e Ratio should provide required current with good margin e VA rating must be greater than VA required to energize the part and the sense resistor e An external ac source may be used to increase the VA rating of the AT3600 s generator Worked Example A laminate core is to be tested in accordance with IEC60404 2 Under a constant ac current of up to 3A 1V at 50Hz in the primary test winding the secondary voltage is measured and limits are applied in terms of the recti fied mean voltage rms scaled Resistor To produce 100mV at 3A R 100mV 3A R 0 333 Ohm Choose 0 5 Ohm standard value V 3A x 0 5 Ohm V 1 5V W 1 52 x 0 5 W 1 125 Choose 2W standard part Resistor is 0 5 Ohm 2W Voltage produced will2. Cautions e Always observe the health and safety precautions stated in the latest issue of the Voltech AT3600 user manual e Do NOT connect the power and sense nodes of the energized voltage together for the constant current circuit With prolonged use you may damage protec tion devices inside the AT3600 e Use properly rated and sound connections Under normal conditions the AT3600 will safely ramp current up and down If connections are undone during the middle of a test dangerous voltages may be generated by the part under test The Voltech AT3600 and ATi Automatic Transformer Testers 2003 Voltech Instruments All rights reserved VOLTECHNOTES Voltech Instruments Ltd 148 Sixth Street Harwell International Business Centre Harwell Didcot Oxon OX11 ORA U K Telephone 44 0 1235 834555 Facsimile 44 0 1235 835016 E mail sales voltech co uk Voltech Instruments Inc 11637 Kelly Road Suite 306 Fort Myers FL 33908 U S A Telephone 1 239 437 0494 Facsimile 1 239 437 3841 E mail sales voltech com www voltech com Note While every care has been taken in compiling the information for this publication Voltech Instruments cannot accept legal liabil ity for any inaccuracies Voltech Instruments reserves the right to alter product specifications without notice and whenever necessary to ensure optimum performance from its product range VPN 104 151 1
3. measures the rectified mean voltage and multiplies that by 1 11 This option is offered as a means of comparing the measurements with those made by mean sensing analog meters and calculated parameters that require rectified mean 2003 Voltech Instruments All rights reserved gt A CONSTANT CU ENT Conclusions The versatile AT3600 transformer tester already provides an unrivalled range of tests for checking the construction and performance of a wide range of coils and transformers By following the above guidelines users can also seamlessly inte grate the testing of cores and transformers under constant ac current conditions into the AT3600 environment providing high speed PASS FAIL testing and accurate detailed test results for analysis Appendices Adding Other Tests To include other tests such as R simply use extra nodes to connect directly across the windings in the normal way You will have to add and extra dummy winding in the schematic and use those terminal names in the program Adding extra tests in this way does not interfere with the operation of the constant current drive explained here Extending the Constant Current Range To test very high VA transformers the drive may be extended by using an exter nal ac source 500VA is available from the AT3600 s internal generator 2003 Voltech Instruments All rights reserved CONSTANT CURRENT JOI ECHNOTES
4. VOLTECHNOTES IEC60404 Testing with Constant AC Current Voltech VPN 104 151 1 e INCOM NaS ot 4 TESTING TRANSFORMERS AND CORES WITH CONSTANT CURRENT IEC60404 It is a requirement of IEC60404 2 that measurements of core loss are made under constant ac current test conditions Ideally current transformers will also be tested with constant ac current drive Most general purpose transformer test equipment does not have the ability to provide a high level of constant ac current drive The AT Series transformer testers from Voltech contain a wide variety of programmable signal sources These are used to test multiple parameters at high speed on parts ranging from surface mounting ferrite inductors to steel laminate transformers of a few kVA By following the guidance given in these notes customers may also configure the AT3600 to test cores inductors and transformers under constant ac current conditions Features of Constant Current AC Drive on the AT3600 e Constant current is fully programmable for amplitude and frequency e Simultaneous measurement of rms or rectified mean rms scaled voltage e Current carefully ramped up and down under software control e Can use external ac source to extend the VA range e Integrates into normal test sequence with all other tests available on an AT3600 including HiPot Equipment Required e AT3600 e AC Interface e VOCX test MAGX is useful during pro
5. be 1 5V 2003 Voltech Instruments All rights reserved ECHNOTES CONSTANT CURRENT Step down Transformer Look for a stock transformer with say a 5A secondary current rating A stock transformer will usually have a 110 and or 230V primary VA rating is that of the part plus the current sense resistor VA 3A x 1 1 5 V 7 5VA Choose a 7 5VA or greater transformer with a 5A low voltage secondary Toroidal transformers are ideal since they will have low losses For example Primary 230V Secondary 2 x 6V 2 5A The secondaries are connected in parallel to provide a 6V 5A output 230V 6V 5A AC Interface AC Interface Transformer Drive Output Input from External Source The step down transformer will supply the part under test and the current sense resistor in series The step down transformer s secondary voltage Vs being Vs 1 5V 1V 2 5V The AT3600 must supply 2 5 x 230 6 to the primary of the transformer 2 5 x 230 6 95 8V The AT3600 can supply 270V so 95 8V is well within its capability 2003 Voltech Instruments All rights reserved CONSTANT CURREN NOLTEC HANIS J It is convenient to use the MAGX test at first since this will confirm that the desired current is being generated In the previous connection diagram the return or Iow end of the sense resistor has been connected to node 5 and the higher voltage
6. end of the resistor connected to node 3 For optimum accuracy it is important that the physical low connection is also designated as the low terminal in the program New Part Voltech Test Program Editor it Schematic Tester Server Setup Help Dc tl S g z 2 gt RRi 2 poo zg Ra Ce 7 f For Help press F1 aaa fat Astan Oa EO Enbor Micos US Votech E Testing Tianst P CorelDRAW 7 E New Part OLR 518PM Next you must set up the External Source in the Editor The source type is AT Output Transformer and you are required to enter the nominal turns ratio of the transformer Remember that the AT3600 will trim the output voltage by comparing the desired voltage from the program with that measured across the programmed sense terminals The ratio is used to establish a target for voltage ramp up when the tester starts the test Using 2003 Voltech Instruments All rights reserved ECHNOTES CONSTANT CU the correct ratio will optimize test speed In this case the ratio is modified because when the desired 1 5V is achieved across the resistor the step down transformer must also supply the 1V across the part under test For 1 5V programmed the step down transformer delivers 2 5V Ratio 230 6 x 2 5 1 5 63 9 1 That is for every 1V programmed the AT3600 must supply 63 9V to the primary of the step down transformer Ext
7. ernal Sources Source Type None Manual Line Supply Transfomer 2306 Behiman300vac Transformer 230 6 Behiman 30V4C far Output Transformer Voltage or Turns ratio AT output Interface AC input Curent Sense Current Sensing Current Transformer ratio fi i feo Pri Sec New Save Delete In the MAGX test simply enter the required voltage V across the resistor to program the constant current I In this case enter 1 5V 2003 Voltech Instruments All rights reserved CONSTANT CURRENT MOL ECHNOTES Magnetising Current External Source x Test Parameters Integration Voltage fis Cm Cy C Shot Medium Frequency 50 Hz kHz C Long Terminals High Terminal Low Terminal PRH 7 r Magnetising Current Limits gt lt Minimum jo Cu Cm CA C kA C lt Maximum jo Cu Cm CA CT kA weoue comen With an AT3600 connected to the PC Editor and the circuit assembled as shown previously you may now press the Measure button to run a MAGX measure ment If the current measured is as desired then all is well If not simply adjust the program voltage to suit If the tester should fail to return a result check the wiring and settings carefully Now secondary connections may be made for VOCX tests Note that VOCX has the option to measure rms voltage or mean sense rms scaled voltage For the mean sense option the tester
8. gram development 2003 Voltech Instruments All rights reserved CONSTANT CURRENT VOLTECHNOTES e Acurrent sensing resistor e A step down power transformer Basic Principle Constant current ac testing uses the normal VOCX test to control the current and make the secondary voltage measurement e The current to be controlled I is converted to a voltage V by means of a current sensing resistor R e The voltage V is connected to the sense terminals of the AT3600 which would normally be used to measure the energizing voltage e In the PC Editor the voltage V is used as the energized voltage e When VOCxX is performed the AT3600 will trim the source such that the desired current is provided V R e The transformer secondary voltage is measured in the normal way as the result of the VOCX test e The AT3600 adjusts the source voltage to maintain a constant ac current through resistor R AC Transformer Interface Under Test AT3600 Sense 2003 Voltech Instruments All rights reserved ECHNOTES CONSTANT CURRENT Connection Diagram Step down Transformer AC INTERFACE FIXTURE 0 Fie Vokes Conran a lectual property rights of whatever S embeded Ins dove re FUSE 10A FF and shall remain the property of See user manual Voltech Instruments Secondary Voltage Connections LOW Node Sense Only HIGH Node Sense Only
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