USER`S MANUAL
Contents
1. 37 HII BRIDGE RECTIFIER DIODE to ELE EE E 39 1 5 5 40 PANEL B EXP 2 INDUCTIVE LOAD SMOOTHING INDUCTANCE 42 44 PANEL B EXP N 4 48 PANEL B EXP N 5 DC pp 50 PRACTICAL WORKS CONTROLLED 52 I HALF WAVE AND FULL WAVE CENTER TAPPED RECTIFICATION 53 PANEL G RESISTIVE LOAD eue cetus teen E pt EE vu 55 SCRs BRIDGE REC TIBIER enean tere Ee 58 PANEL D EXP N 1 ACTIVE LOAD grex eye debo axes 59 PANEL D EXP N 2 DC MOTOR iei ente etm E ER nee etia de 65 IN SCRs DIODES BRIDGE RECTIEIER 22225 66 PANEL D EXP 3 67 PANEL D EXP N 4 DC MOTOR ath ber Er RR ipa cans 72 PREAMBLE With the development of switching components and digital processing electrotechnics is taking a major place in industrial activities as in electrical engineering power distribution transports improvement Nowadays power and control electronics appear to have many applications2. Commute 4 into wave generator mode 1 Warning connect properly the terminals of the battery gt Continuous conduction 2 Verify that continuous conduction is reached The red indicator is on 3 Sketch V t Uc t ic t and is t when 120 4 Fill the following table 100 105 110 115 120 125 pata 1 C theoretical P practical P theoretical Ic practical 5 Plot Uc Ic P 63 6 Verify after the table Uc Ui Un E 7 Why does Uc t sign and not ic t makes P to be negative Which value for makes the power from load to source to be maximal When 120 how we tune Tune the circuit in order to reach P SW 8 What about power sign according to rectifier or wave generator mode What about the source voltage frequency and the voltage frequency across the load gt Disrupted conduction 1 Chose 30 and remove the inductance Visualize Uc t and ic t 64 PANEL D EXP N 2 DC MOTOR LOAD 0 1 H to 1 4 variable inductance ref PSYJR or a 20 mH inductance ref CO 105 series with a dc motor ref SH 90 24 1 Supply first the inductor of the motor then its armature 2 Visualize Uc t across the motor terminals How does the motor behave when a is increasing from zero 3 Visualize ic t and tell why the conduction is disru
3. U practical theoretical Ic practical Ic theoretical P practical P theoretical 5 Plot Uc Ic P 6 Verify after the table Uc Ui Un E 7 Visualize Ur t in ac and dc mode What the meaning of U Determine the inductance internal resistor 8 Measure and calculate Ry Rp r where Rh is the 10 Q load resistor 47 Tc r the battery internal resistor r 9 Connect a free wheeling diode D in parallel with the load What about Uc t and 2 10 Power 61 The transformer supplies Ps A A 2 Py Pang Ic where Uc cosa The apparent power is given by V m 55 1 4 2 When 30 and 60 measure P S and calculate the power factor Compare with 0 9 cos o How we consider a in time scale gt Disrupted conduction 1 Chose 30 and remove the inductance Visualize Uc t and ic t What is the interest of this circuit if the load is a battery 2 Replace the previous inductance by a 20 mH one or dismantle transformer coils What about Uc b and ic t Deal with the flats on Uc t waveform 3 Tune Ry while the disrupted conduction is reached limit 62 C Wave generator mode LOAD 100 5 7 A 320 W or 15 4 5 A 320 W rheostat Rh 24 V battery or 12 V variable inductance Lmax 1 2 H
4. P theoretical 69 Plot Uc 00 Ic 0 P Verify after the table Uc Ur Ug E Visualize U t in ac and dc mode What about U Determine the inductance internal resistor rp Measure and calculate Ry Ry f where Rh is the 10 Q load resistor E E Ic r the battery internal resistor r Express cas a function of V E Ry andr So find oj What about Uc and a if we want 0 7A Connect a free wheeling diode D in parallel with the load What about Uc t and is t What about the conduction time interval of each rectifier component What is the action of the free wheeling diode Power we assume the bridge is lossless The transformer supplies Ps PM INe Poa Ic where Uc Ta Cosa n The apparent power is given by Chose 30 continuous conduction 70 SCRs bridge rectifier Measure V Uc and Ic Measure or calculate PS Measure or calculate S Is Calculate k compare it with 0 9 cos 30 e SCRs diodes bridge rectifier Tune a for Uc Uscrs Show that Pscrs diodes Pscrs Work out Is from an area analysis is t on scope So find S e Compare both power factors 71 PANEL D EXP N 4 DC MOTOR Same questions as Panel D exp n 2 and make a comparison with Panel D exp n 3 72 004 0 49 000
5. 48 gt Continuous conduction 1State the changes about ipl b 1520 ip3 t 14 0 and the voltage across the load 2 Sketch Uc t and ic t 3 Hill the following table L H 0 13 0 4 0 6 0 8 1 1 2 Verify Uc UL Ug E Why U z0 Measure Rr Ry r ry where Rh is the load resistance r the battery internal resistor r rp inductance internal resistor r gt Disrupted conduction Replace the previous inductance by a 20 mH inductance or dismantle transformer coil What about Uc t and ic t 49 PANEL B EXP N 5 DC MOTOR t ircui AC BRIDGE RECTIFIER 22 Mains 230V 50Hz RECTIFIER WAVE 200 VA Current probe SCOPE Current probe DC Motor CO 105 PSYJR SH90 24 FR 90 DYN 90 ip 0 30V DC Supply 50 LOAD In a first time a 20 mH inductance is used ref CO 105 and in a second time a variable inductance is used Both are placed in series with a dc motor ref SH 90 24 4 Supply the inductor of the motor then its armature Visualize and deal with U t waveform What about the different steps Notice the motor speed 5 Visualize lc t through the motor and explain why t
6. 2 What about Uc and U 2 Hill the following table DIODE U Drev I HALF WAVE RECTIFICATION FULL WAVE RECTIFICATION 36 PANEL A EXP 2 INDUCTANCE LOAD A Circuit LOAD 10 Q 5 7 A 320 W or 15 Q 4 5 A 320 W rheostat Rh and coil with its iron core gt Half wave rectification and are placed We use a0 1 1 4 H variable inductance with an internal resistor 10 Q 1 Picture the circuit 2 From the previous survey resistive load what changes are encountered towards 1100 122 0 and 0 2 Justify the expression continuous conduction What about the inductance towards the shape of Uc t 3IfL L 0 1H L l 05H L L3 1 2 H sketch Uc t and ic t Verify Uc t Urh t Uj t when L 1 2 H Why 0 502 Give the theoretical expression of Uc 4 Note that remains unchanged whatever L value DC mode Measure this value and compare it with its theoretical expression c Where 5 wheeling diode D is placed in parallel with the load Show that D has action 37 6 The current wave ratio is given by T a e gt Where is the rms part of ic t How does behave compare to L 7 Give a conclusion about the function of the inductance Make a comparison between ant T 2 for L ranging from 0 1 H to 1 4 H Plot t f L 4 V 3r 2Lo fi
7. TAPPED RECTIFICATION Both applications remind the operative mode of diode in power electronics and underline the fact that it behaves in ac to dc conversion as a commutating switch Half wave survey is available by means of center tapped circuit The load is placed between the middle point of the transformer winding M and both cathodes S of D and Dp Each transformer winding is connected by connection straps to the anode of each diode We can use only one connection strap in order to realized a half wave rectifier see figl a and fig1 b 29 gt Half wave rectification Figl b Full wave rectification is obtained when two connection straps are used simultaneously see figl c Full waverectification 30 It would be better to use an analog scope with the following characteristics memory function vertical sensibility 10V div 20V div INV mode for both channels Source triggering and chopped mode are suitable A digital scope makes the visualization of 50 kHz signals much easier than an analog scope Moreover it allows mathematics operations as average sum Fourier transform and cursors may be suitable to check conduction interval times 3l PANEL A EXP N 1 RESISTIVE LOAD A Circuit diagram LOAD 10 Q 5 7 320 W or 15 Q 4 5 A 320 Rheostat Rn gt Half wave and full wave rectification Two arrangements are used Uc t 32 No connection strap
8. U t 67 NON SYMMETRICAL BRIDGE 6 Ue t 00140 Commute 4 in rectifier mode Place meters for Uc IC Uc Ic and P A Preliminary survey induced load 1 For 0 lt lt 180 change from symmetrical arrangement to non symmetrical In both cases Visualize and compare Uc t and ic t Visualize and explain the currents waveforms through each rectifier component Explain briefly the action of each arrangement 2 Chose 60 in symmetrical arrangement 68 Using a differential probe visualize and sketch V t Uc t imni t 1 2 0 1 0 1 0 1 2 0 is t and ic t Explain briefly the action of this circuit State the name of the conducting components below the gate signals chronograms 3 Commute 11 12 13 and 14 in order to obtain a SCRs bridge Compare these waveforms with the previous ones Tuning o compare Ucand while passing from SCRs bridge to SCRs diodes bridge B Active inductance load We add a 6V or 12 V accumulators cell Same questions as before Make a comparison with the previous results and show that disrupted conduction is reached for a remarkable value of o called a 2 Place the load in order to show the reversing function of a SCRs bridge 3 Hill the following table SCRs diodes bridge Lo U practical theoretical Ic practical Ic theoretical P practical
9. fields and provide for electrotechnics many ambitious prospects Teachers from technical and professional departments where practical work must be a priority are naturally ready to motivate pupils and students to follow electrotechnics studies The present bench deals with ac to dc conversion INTRODUCTION An ac to dc converter supplies dc voltage or dc current to a load from an ac source An ac to dc converter is symbolically pictured as pr Electromechanic converters have been replaced by power electronics where switching systems based on semiconductor components are more and more efficient Those systems present many advantages as low dimensions low cost maintenance free silent high efficiency high flexibility at use SETTINGS This bench presents several originalities so much convenient than educational It contains all devices required for single phase ac to dc conversion such as rectifiers diodes and SCRs and can be used for high school practical works The bench is used with four removable panels on which clearly appears the following conversion chain ac source 230 V Transformer Rectifier dc load 50 Hz This bench constitutes a convenient help for the teacher during demonstration lectures and its utilization is strongly recommended for pupils who chose to follow a practical teaching Rectifier circuits can be chosen by means of four removable panels suited to specific applicat
10. harmonic ELECTRICAL CHARACTERISTICS This device complies with secured voltages Less than 50 V rms ac Less than 120 V dc A Power supply Transformer apparent power S 200 VA 1 Full wave center tapped rectifier power supply Power supply 2 x 15 V rms 154 2 sin at V 154 2 sin at 2 Bridge circuit power supply According to dc load one winding only V t 1542 sin full winding vOs 30 2 sin ox B Power rectifier components The bench is a closed box In order to avoid overheating it is recommended to oversize rectifiers diodes and SCRs 1 Rectifier diode We must consider Maximal average forward current IFAv or I Maximum peak repetitive forward current or IFRM Repetitive peak inverse voltage VRRM We will impose gt gt VRRM gt gt 50V and the rectifier package must fit with location 194 plastic type A fast rectifier can be used and speed characteristics must be taken in account Reverse recovery time ty Maximum reverse current Ip or Example POWER RECTIFIER 194 Plastic Package Trav 6A 200 752 VRRM 400 MR 754 600 MR 756 2 SCR SCR owns the same characteristics as a rectifier but we must be add Holding current Latching current I Gate trigger current Gate trigger voltage Current slew rate conducting state di dt Voltage slew rate blocking state dv
11. rectification Connection straps separately used Half wave rectification can be studied with either C connection strap fig l a or C2 connection strap fig 1 b 0 Fig 1 b 53 gt Full wave rectification fig 1 c Both connection straps Ith t 5 2 0 Fig l c Remarks 1 The angle of lag ou is calculated after the diodes conduction times natural switching 2 Previous results will be seen again and applied to SCRs This allows to make an easy comparison between controlled and uncontrolled components First result When cathodes of 2 SCRs are biased eachother the conducting SCR is the one whose anode s potential is superior to the anode s potential of the other SCR The conducting SCR forces its anode s potential to the cathode of the other SCR Second result When anodes of 2 SCRs are biased eachother the conducting SCR is the one whose cathodes s potential is inferior to the cathode s potential of the other SCR The conducting SCR forces its cathode s potential to the anode of the other SCR Third result The on state of a SCR involves the other SCR to be in the off state 54 PANEL C RESISTIVE LOAD A SCRs control 1 When a 30 and a 120 visualize the gate signal of Ty on channel 1 and the gate signal of on channel 2 respectively named G and G2 BNC socket Compare the scope display with the bench LCD display 2 Give the conducting date
12. t and Ic t Deal with every waveforms and notice how conduction times are changed 43 PANEL B EXP N 3 ACTIVE LOAD Battery behaves as dc load and can be considered as an ideal dc voltage generator in series with a resistor Such load does not need any smoothing inductance A circuit LOAD 10 2 5 7 320 W or 15 Q 4 5 A 320 Rheostat Rh ref ECO 2 and a 6V or 12 V battery ref CO 106 44 B Action of the circuit gt Tensions waveforms 1 Sketch V t and Uc t separately or use a differential probe in order to visualize both signals Sketch 0 and E 2 Visualize Vpi t and 3 Visualize Vp2 t and 0 gt Currents waveforms 1 After Urn t graph sketch ic t 2 With the current probe visualize ipi t 15200 ip3 t and 4 4 3 Visualize the transformer secondary output current is t C Action analysis gt First half of cycle Specify the considered interval and the sign of V t 2 Give any instantaneous relation between Uc t ic t Ry and E 3 When V t E show that no current passes through the load and verify that Uc t E Verify that all diodes are in off state 4 When V t gt E state the conducting diodes Give their repetitive peak inverse voltage Measure the on state interval of the conducting diodes Derive the following expression V42 ic b V2 n ot R h 45 From this equation specify Verify tha
13. 3 FEATURES I LOCATION OF CONTROLS AC DC CONVERSION BRIDGE RECTIFIER 54 1 POWER COMPONENTS CURRENT 230 50 ANGLE OF DELAY ANGLE CONTROL 9 OFF POWER STAGE 14 1 Title of the circuit 2 Power switch 3 Power supply indicator 4 Rectifier or Wave generator selector for controlled rectifiers only 5 Current probe terminals Imax 6 A 6 Coaxial output for the current probe to scope 0 5 V A 7 Angle of lag display while control 8 is turned on 8 Angle of lag control 9 First half winding of the source transformer indicator orange 10 Second half winding of the source transformer indicator orange 11 Rectifier or SCR selector Left position D off right position Thi off D on 12 Rectifier or SCR selector Left position Th2 D2 off Right position off D2 on 13 Rectifier or SCR selector Left position off Right position off on 14 Rectifier or SCR selector Left position D4 off Right position Ty4 off D4 on 15 indicator red when 11 is on left position 16 chain 17 indicator green when 11 is on right position Rectifier mode 0 lt lt 180 Wave generator mode 100 lt lt 170 BNC socket output for G gate signal same as G3 of 20 kHz 1 range pulses 15 18 19 T indic
14. NGLE OF DELAY ANGLE CONTROL OFF PANNEL D 24 PRACTICAL WORKS UNCONTROLLED RECTIFICATION I PRELIMINARY SURVEY ON DIODES ASSOCIATION The aim of this survey is to introduce uncontrolled components as diodes rectifiers The following applications need power supply A Cathode biasing DL green LED DL red LED DC power supply 0 30 V R 1kQ W resistance Circuit 25 Let s fill the following table vw Ve eT VairVa2 15 V 10 V VaisVa2 10 V 15 V First result When cathodes of these 2 diodes are biased eachother the conducting diode is the one whose anode s potential is superior to the anode s potential of the other diode This result will be generalized specially with three phase rectifier circuits by comparison of anode s potential If lt lt and lt lt Vaz then a diode can be considered as a switch ideal component and its threshold voltage will be neglected Therefore we can picture a diode as an one way switch Conduction state closed switch Vp 0 V Blocking state open switch ip 0 A This hypothesis will be justified when we use the bench Second result For a common cathodes association we notice that the conducting diode forces its anode s potential to the cathode of the other diode This result could be generalize
15. R 4 PROBE OR 51 THe 84 4 gt 4 DIFFERENTIAL PROBE ISOL600 1 10 TRMS PROBE TO SCOPE 0 5 VIA OF CURRENT TO SCOPE 18 III REMOVABLE FRONT PANELS UNCONTROLLED RECTIFICATION PANEL A FULL WAVE CENTER TAPPED RECTIFIER TWO DIODES PANEL B BRIDGE RECTIFIER DIODE 19 SINGLE PHASE AC DC CONVERSION UNCONTROLLED RECTIFICATION Current probe Imax 6A FULL WAVE CENTER TAPPED RECTIFIER TWO DIODES OFF PANNEL A 20 SINGLE PHASE AC DC CONVESRSION BRIDGE RECTIFIER DIODE CURRENT PROBE Q Cen Uc LOAD Imax 6A D4 D3 PANNEL B OFF 21 REMOVABLE FRONT PANELS CONTROLLED RECTIFICATION PANEL SCRs CENTER TAPPED RECTIFIER TWO SCRs PANEL BRIDGE RECTIFIER FULL SCRs OR SCRs AND DIODES 22 SINGLE PHASE AC DC CONVERSION 2 CURRENT PROBE RECTIFIER WAVE GENERATOR OFF S 200 VA ANGLE OD DELAY ANGLE OFF TH2 lt gt D2 SCRs CENTER TAPPED RECTIFIER TWO SCRs PANNEL C 23 SINGLE PHASE AC DC CONVERSION BRIDGE RECTIFIER An RECTIFIER WAVE GENERATOR S 200 VA LOAD Imax 6A A
16. USER S MANUAL SINGLE PHASE DIRECT CURRENT CONVERSION TEST BENCH REF CO 1000 SINGLEPHASE AC to DC CONVERSION BENCH CO 1000 TABLE OF CONTENTS PREAMBLE orem 3 INTRODUCTION E AME S AUR ERE MEE RU 4 SETTINGS 5 TECHNICAL SPECIEICATIONS eu deese reo ee ecu po veo oan 6 I SECURITY ENVIRONMENT AND 12 6 I ELECTRICAL CHARACTERLDSTICS o PE Svo ap cot ne fena 7 III INSTRUCTIONS OF USE AND 11 IV FUSES AND POWER COMPONENTS 12 FEATURES 5s EAE E 14 LLOCATION OF CONTROLS erue Ex I ead 14 II MEASURE AND VIZUALIZATION 6 17 III REMOVABLE FRONT PANELS UNCONTROLLED RECTIFICATION 19 IV REMOVABLE FRONT PANELS CONTROLLED RECTIFICATION 22 PRACTICAL WORKS UNCONTROLLED 25 I PRELIMINARY SURVEY ON DIODES 25 HALF WAVE AND FULL WAVE CENTER TAPPED RECTIFICATION 29 21 8 32 22
17. ator red when 12 is on left position BNC socket output for G2 gate signal same as G3 of 20 kHz 27 range pulses chain 20 Dz indicator green when 12 is on right position 21 indicator red when 13 is on left position 22 Ds indicator green when 13 is on right position 23 indicator red when 14 is on left position 24 Daz indicator green when 14 is on right position 25 Connection strap V t to circuit 26 Connection strap V t to circuit 27 Connection strap link between rectifier devices 1 and 4 First half of the bridge circuit 28 Connection strap link between rectifier devices 2 and 3 Second half of the bridge circuit 29 Connection strap 15 V power supply 30 Load connections full wave center tapped rectifier mode 31 Load connections bridge rectifier mode 32 Rectifier indicator green bridge rectifier mode 33 Wave generator indicator red bridge rectifier mode 34 Power components Rectifiers SCRs First row Tro Second row Di D2 D4 16 MEASURE AND VISUALIZATION OF CURRENTS Every currents can be visualized or measured by means of the different connection straps positions OUTPUT TRANSFORMER CURRENT PROBE OR 51 TH1 lt gt gt 01 84 gt 4 CURRENT THROUGH RECTIFIER 1 PROBE on A 54 gt 04 17 CURRENT TROUGH RECTFIE
18. be is based on Hall effect It is made of a primary stage high current plugged within the circuit CURRENT PROBE and the secondary stage is plugged to a scope BNC socket Galvanic insulation is made between both stages This probe can measure ac dc and TRMS currents The maximum current must be 6A and the probe sensitivity is 0 5V A E Angle of lag control and display 1 Trigger Triggering is synchronized with mains and a pulse transformer provides a galvanic insulation 2 Angle of lag This tuning is realized by means of a potentiometer Two different modes are available Rectifier mode 0 lt a lt 180 Wave generator mode 100 lt lt 170 The beginning of conduction is obtained with rectifier diode for 0 10 3 Angle of lag external control The angle of lag can be controlled by an external dc voltage 0 lt Ver lt 12V for O lt a lt 180 4 Angle of lag display Its measure can be obtained either from the LCD display of the bench or from a scope screen 5 Pulse chains Two channels First channel 20 kHz pulse chains applied to and G2 range a 180 Second channel 20 kHz pulse chains applied to G3 and G4 range 180 360 III INSTRUCTIONS OF USE AND SECURITY The user should scrupulously respect for his own security and the one of the bench the main following recommendations 1 Look after the different devices such as seers emergency stops meter
19. d to These results will be seen again with center tapped circuit 26 B Anodes biasing DL3 green LED DL red LED Vx3 DC power supply 0 30 V R 1 W resistor Circuit Let s fill the following table Vka Uk DL DL Mese ed 15 V 10 V Vii Va 10 15 First result When anodes of these 2 diodes are biased eachother the conducting diode is the one whose cathode s potential is inferior to the cathode s potential of the other diode 27 Second result For a common anodes association we notice that the conducting diode forces its cathode s potential to the anode of the other diode As the previous survey these results can be generalized C Bridge rectifier diode DL green LED DL green LED DL red LED DL red LED U variable power supply 0 30 V R 1kQ W resistance Circuit 28 gt U 0andU 0 note the state of diodes measure the potential in A then in B with respect to P or N explain the behavior of the circuit after the two previously filled tables justify the fact that The conduction of a diode involves the other to be in blocking state Remarks These results suppose that a load is connected Diodes transformer are supposed idealized and encroachment is ignored This confirms the representation of diodes by ideal switches II HALF WAVE AND FULL WAVE CENTER
20. dt Turn off time tq SCRs are protected against overvoltage by means of RC circuit We must also consider Rims on state current ITRMS Average forward current Iray Repetitive peak off state voltage Vprm VRRM Peak on state voltage As for rectifiers fast SCRs can be used looking at package type TO 220 Example POWER SCR PLASTIC PACKAGE TO 220 AB 8 12 200 72 4 2N 6396 TIC 126 B 400 MCR 72 6 2N 6397 TIC 126 D C Load Whatever the load the maximum current Imax must equal 6A either with half bridge or full bridge arrangements We can use the following loads Load resistor Rheostat ref TUBE 320 W 100 5 7 150 4 5 A 22 0 3 8 A 33 3 1 A for best use low resistance load must be adopted Inductance loads Variable inductance 0 1 H to 1 4 H 10Q 2A ref PSYJR Smoothing inductance 20 mH 3A ref CO 105 Dismantle transformer coils with or without iron core Winding 125 250 500 1000 Active load Accumulator cell lead ref CO 106 6V 12V 24V DC motor ref SH 90 24 Armature supply 24V 6 4 A Inductor supply 24V 0 62 A Speed detector 200Hz 5V AC 1000 rpm Magnetic brake ref FR 90 Braking voltage 0 10 V DC Current 0 60 mA The previous devices are just given as examples and other kind of loads could be used provided that electrical characteristics of the bench are respected D Current probe LEM LEM pro
21. fter voltages waveforms explain the action of the circuit 1 Show that the diode behaves as a switch and verify the following expressions V t Uc t t C only V2 t Uc t Vp2 t only 2 Give a conclusion about diodes threshold voltage and the secondary winding of the transformer supposed ideal Remark State under each waveform the name of the conducting diode 3 After the waveforms of currents justify the behavior of each diode 4 Compare the current passing through the load and the one passing through the diode gt Full Wave rectification After voltages waveforms explain the action of the circuit 1 Describe briefly half wave rectification compared to full wave rectification and deal with Uc t 2 Compare diodes maximum inverse voltage value and shape 3 Explain why superposition method is not available in these conditions 4 After currents waveforms justify the state of each diode and verify the following expression ic t ipi t ipa t 5 Show that ic t is a one way current from S to M 6 After waveforms give a conclusion about this converter 35 E Remarkable values 1 Compare your results with the following table LOAD Uc T Ic Uc Uc Ic Ic AC DC DC HALF WAVE I I V V V V Ic Ic RECTIFICATION 2 Rh 2 FULL WAVE I I V V 2V V I 21 RECTIFICATION CTIFICATIO Rh 42 T How to measure the part Uca of Uc t
22. h diode Sketch ip t gt ips t and ip4 t current in each diode Sketch the transformer output current is t and the load current ic t 4 Explain the action of the circuit the diode is idealised Verify instantaneous relations of voltage and current State the name of conducting diodes 5 Measure U and and verify Ohm s law across the load 6 We notice wave phenomenon with 7 and let s introduce T wave ratio F shape factor Fill the following table Uca Uc fs U F 1 DC AC AC DC U 1 Practical results Theoretical 0 48 1 11 results EN U 0 Bd n 42 17 18 average value of Uc t Uca is the rms value of the ac part of Uc t U is the rms value of Uc t 40 Deal with these results What about and F 2 We would measure the rms value V of V t with a magnetoelectric meter dc mode only Show that across the load U V 7 Which passive component could enhance this wave phenomenon 41 PANEL B EXP N 2 INDUCTANCE LOAD SMOOTHING INDUCTANCE In power electronics currents are often waving and that may trouble loads Losses may appear with dc motors for example Therefore we place a high value inductance called smoothing inductance in series with the load That make the current to become rather constant This experiment deals with the function of a smoothing inductance in series with a resistive load Rh LOAD Resistor Rh a
23. he conduction is disrupted What about the different peaks 6 Connect a 20 mH smoothing inductance What about uc t and ic t waveforms What about the conduction mode Visualize and deal with Uc t and ic t 7 Replace the previous inductance by a variable inductance ref PSYJR Specify the conduction mode and deal with Uc t and IC t Why does motor speed decrease gt We chose L 0 1 H Visualize and deal with Uc t and IC t Measure and deal with U ds Measure and deal with Calculate the internal resistor of the variable inductance Measure Uy and verify Uc Uy UL Compare Uc with its theoretical expression Can the speed motor be modified After the previous results give a method to determine the armature resistor and the speed factor k 51 PRACTICAL WORKS CONTROLLED RECTIFICATION The aim of these practical works is to introduce the SCR This component is a controlled switch When its gate is correctly biased a SCR is in conducting state It remains in this state as long as the current through it becomes nil or a reverse voltage is applied to it With a SCR we can obtain a constant tuneable voltage across the load This is very useful in servings applications when motor speed must be adjusted An other application is the wave generator which action is to get back power from the load during braking intervals subway 52 I HALF WAVE AND FULL WAVE CENTER TAPPED RECTIFICATION gt Half wave
24. ion PanelA Full wave center tapped rectifier gt Panel Bridge rectifier diode gt Panel SCRs full wave center tapped rectifier gt Panel D Bridge rectifier SCRs SCRs diodes A single bench with its four panels allows to study all kind of ac to dc conversions singlephase and with the same case the teacher will choose the corresponding panel to each practical work An immediate comparison between controlled and uncontrolled components is available by means of switch which commutes a SCR into a diode This may introduce motor speed variation For active inductance load rectifier or wave generator mode is displayed by two indicators Rectifier mode the load is supplied by mains Wave generator mode the load added to a generator supplies mains TECHNICAL SPECIFICATIONS I SECURITY ENVIRONMENT AND EMC A Security This bench uses secured connections however it is recommended to use a high differential circuit breaker 30 mA The socket power unit must be grounded CLASS 1 case Primary and secondary windings power supply transformer are respectively protected by two fast fuses 4 A and 6 3 A Electronic stage is protected by a 500 mA fuse Warning Refer servicing to qualified personnel only B Environment Use 10 C to 40 C Storage 0 to 50 C C EMC This bench complies with European EMC rules Mains interference output terminals interferences radiated interferences mains
25. mute 11 and 12 and notice uncontrolled rectification 3 Explain the action of this circuit 4 What about 0 and 180 7 5 Show that ic t is unidirectional current from S to M 56 C Remarkable values 1 Fill the following table Uc practical Uc theoretical Tc practical theoretical 2 Plot Uc f a Point out the uncontrolled rectification 3 Find these practical results for half wave rectification Compare these results with full wave rectification results 57 FULL SCRs BRIDGE RECTIFIER The four previous diodes are replaced by controlled components Commute 11 12 13 and 14 into SCRs position 58 PANEL D EXP N 1 ACTIVE LOAD A Circuit V Tha t 0 Rectifier Wave generator 59 B Rectifier mode LOAD 10 Q 5 7 320 W or 15 Q 4 5 320 W rheostat Rh 6 V battery or 12 V variable inductance Lmax 1 2 H Commute 4 into rectifier mode SCRs control 1 When a 30 visualize on channel 1 and on channel 2 2 Guess and sketch G3 and G4 Continuous conduction 1 Place meters for Uc Ic Uc Ic and P 2 Verify that the conduction is continuous The green indicator is on Tune up to continuous conduction limit Call this value 3 Sketch V t Uc t ic t and is t when 30 60 4 Fill the following table wg Jd p
26. nd a variable inductance L ref PSYJR 1 Draw the circuit We chose L 1 2 H 2 Visualize and sketch V t and Uc t Sketch Vpi t Vp2 t and Vp4 t voltage across each diode Sketch ip t ip t 1 0 and ip4 t current in each diode Sketch the transformer output current is t and the load current ic t Explain the function of the inductance and specify the condition of conduction Compare these signal shapes with the previous experiment resistive load What about the inductance and the shape of Uc t Verify the following expression Uc t Um t UL t 3 Compare U with V 2 Measure U and compare with its theoretical value X T Measure and verify this value from the relationship between U and Rr r Ry 4 Power As diodes are idealized no losses appear between the secondary of the transformer and the load We assume that Ps Pioa Uc Ic 42 Measure Ps and with wattmeter upstream and downstream arrangements We assume that S V Is even if Is is not a sine wave Show that Is and write S as a function of and Calculate the power factor k Compare k with 0 9 theoretical value Deal with its high value Find this result with a phaseshift method 6 Disrupting conduction Replace the previous inductance by a dismantle transformer coil with and without iron core L 125 windings 12 250 L5 500 L4 1000 Deal with Uc
27. pted 4 We place a variable inductance Tell about the conduction mode and deal with the action of this smoothing inductance Why does the speed decrease L 20 1 H continuous conduction Visualize Uc t and ic t Compare these waveforms with the ones obtained in Panel D exp n 1 Verify Uc Ur What do you notice while the inductance is removed 5 Place the inductance again and brake gently the motor up to disrupted mode is reached Replace the previous inductance by lower ones Visualize Uc t and ic t What about the conduction mode Act on L or the brake and see how conduction is modified 6 Hill the following table continuous conduction L 0 1 H Uc practical N speed 7 After the table verify that Uc Uy Ui 8 Plot Uc f a and 65 SCRs DIODES BRIDGE RECTIFIER This type of circuit can not be used for wave generator applications It offers the best power factor and its control is more flexible than a full SCRs bridge Each arm of the bridge contains one SCR and one diode in series Two arrangements are used e Symmetrical bridge fig 1 e Non symmetrical bridge fig 2 66 PANEL D EXP N 3 ACTIVE INDUCTANCE LOAD COMPARISON BETWEEN SCRs BRIDGE AND SCRs DIODES BRIDGE LOAD 100 5 7 320 15 Q 4 5 320 W rheostat Rh 6V battery or 12 V 1 2 H max variable inductance SYMMETRICAL BRIDGE Urn t Ue t
28. rst harmonic approximation Confirm these results if we consider I Work out T without L 1 R Compare values respectively to L values and show that qt when Rr lt lt 2Lo 342 Lo gt Half wave rectification Remove Wechose L 0 13 H 1 Visualize and deal about conduction conditions Sketch Uc t and ic t Explain why t is not a half wave tension Explain ic t waveform 2 Place in parallel with the load a free wheeling diode D Explain why Uc t is a half wave tension Explain ic t wave form what happens while L is increasing Deal with the free wheeling diode 38 III BRIDGE RECTIFIER DIODE Full wave rectification is reached with center tapped transformer Very used for symmetric dc power supply it is not very suitable for high voltage applications In this second case a bridge rectifier diode is used The transformer is not a center tapped on and it is smaller than the previous one On the inverse cycle each diode has only transformer voltage across its terminals Bridge rectifier circuit 11 12 13 and 14 are in right position diode mode MAINS 230V 50 2 39 PANEL EXP 1 RESISTIVE LOAD LOAD 100 5 7 320 W or 15 4 5 320 Rheostat Rh 1 Picture the circuit 2 Sketch V t and Uc t How to visualize simultaneously both signals 3 Sketch Vpj t Vp2 t Vp3 t and Vp4 t voltage across eac
29. s B Tensions waveforms gt Half wave rectification 1 Visualize V t on channel 1 ground potential is M point Explain why the tops of the sine wave are flat Give the maximum value of V t Place the load between S and M points Use C connection strap only 2 Keep V t on channel 1 and visualize Uc t on channel 2 Give the maximum value of Uc t 3 Keep these settings and use INV and ADD functions in order to visualize Vp t Give the maximum value of Vpi t Remove place 4 Visualize V gt t on channel 1 and Uc t on channel 2 Give the maximum value V of V t Compare V t to V2 t and V with 5 Keep these settings and repeat 3 in order to visualize Vp2 t Give the maximum value Va of Vp t 33 gt Full wave rectification Both connection straps 1 Sketch Uc t and measure its frequency 2 Visualize Uc t after removing and placing again successively and 3 Both straps are placed sketch Vp t Vp2 t below Uc t and give their maximum values C Currents wave forms gt Single wave rectification only 1 Visualize and picture t and ic t below V t graph only 2 Visualize and picture ip t and ic t below V2 t graph gt Full wave rectification Both straps are placed 1 What about 1 1 0 and 1 0 2 2 Sketch ic t below 0 V2 t and Uc t 34 D Operating analysis gt Half wave rectification A
30. s scope at the beginning and at the end of each practical work session 2 Work out an operative method before every manipulation 3 The yellow and green coloured earth terminal of the module must be connected by means of earth wire same colour to the power supply desk and to the loads that are endowed with 4 Use secured 4 mm wires only 5 To avoid electrical shock any intervention must be done after disconnecting the ac power cord 6 Once the circuit is checked by the teacher this latter will switch on the desk power supply 7 Do not overpass the maximum ratings of power components and loads 8 In order to measure and visualise current do not plug nor disconnect cords of the buckle if current has not been cut off 11 WARNING The bench is a class device the metallic part of the current probe is grounded The utilisation of a differential probe is necessary if the measure of the current is not referenced to the mass of the installation One use 0 1922 5 W or 1 Q 40 W shunts while being careful to connect the mass correctly to one of their terminals 9 In order to measure and to visualise any tension connect scope and voltmeter at last Think about the utilisation of a differential probe if any mass problem is encountered 10 Use carefully accumulators cell beware of short circuit IV FUSES AND POWER COMPONENTS REPLACEMENT No particular maintenance is required for this bench However install i
31. s of Ty and Ty when o changes from 0 to 180 What about the pulses chain What is the main advantage of such control Measure the frequency of these pulses B Circuits LOAD 10 Q 5 7 A 320 W or 15 Q 4 5 A 320 W rheostat Rh Half wave controlled rectification connection strap only 1 Visualize Vi t on channel 1 and Uc t on channel 2 What about Uc t towards variations When 60 sketch V t Uc t and 2 Keep these settings and use INV and ADD functions in order to visualize 1 0 Verify the following expression Vit 0 0 3 Commute 11 while 0415 tuned 55 Compare Uc with Uc in non controlled rectification Explain why a SCR is often called controlled diode 4 Explain briefly the action of the circuit and notice when Ty is in the on state Remove C and place C 5 Visualize V t on channel 1 and Uc t on channel 2 What about Uc t towards variations When a 60 sketch V2 t Uc t and Go 6 Keep these settings and use INV and ADD functions in order to visualize 2 0 Verify the following expression Vo t 0 2 9 7 Compare this circuit with the previous one 8 Explain briefly the action of the circuit and notice when Ty is in the on state Full waverectification and C used 60 1 Visualize Uc t after removing and placing again successively and 2 Com
32. t At is centred on T 4 Second half of cycle Specify the coincided interval and the sign of V t 2 Same survey as before Derive the following expression VIA E sin ot h h i gt Full cycle 1 Verify that ic t is a unidirectional current and the conduction is not continuous 2 Deal with is t waveform What is the action of the bridge towards the battery 3 Note the characteristics of the battery Calculate the time needed to load the battery under current condition How can we regulate the load current D remarkable values gt Average currents Assuming 2 2 1 At cos CTI jt h 46 Where T 20 ms Measure and compare it with the previous equation Show that RE 1 Measure and find the alternative part I I and find the wave ratio Q Ic gt Average voltage across the load Measure Ucand compare with Uc Ic Power Measure the incoming power at the load Calculate E Deduce losses P u P Determine the efficiency n B T Measure the apparent power at the output of the transformer and compare with S V I V Ic P T Calculate the power factor k 47 PANEL B EXP N 4 ACTIVE INDUCTANCE LOAD A Circuit LOAD From the previous experiment let add in series with the load a variable inductance
33. t in a dry place and avoid any inclined position WARNING Unplug the module from the power source before replacing any fuse or damaged component beware of active loads A Fuses replacement WARNING Any fuse replacement must be done with a fuse which presents the same characteristics type size 1 Power stage Fuses are placed on the rear panel in fuse holders Primary winding mains One 4 A 250 Vpp 5 x 20 mm fast fuse Secondary winding Two 6 3 A 250 Vpp 5 x 20 mm fast fuses 2 Electronic stage Electronic stage is protected by fuse holder soldered on printed circuit 12 Primary winding mains One 500 mA 250 Vpp 5 20 mm temporized fuse B Power components replacement WARNING If one or some components are damaged it is recommended to check the others devices even if they seem undamaged Power components can be unscrewed from the protective panel transparent cover 1 SCR replacement After finding the SCR location unscrew the damaged SCR place the new one place a tested SCR Verify the SCR terminals are well screwed before a new experiment 2 Rectifier replacement Adjust its terminals Unscrew the damaged rectifier place the new one the central screw is not used use a tested diode Before using verify that the tension is 15 V rms across both windings transformer while connection straps are removed and no load is connected Warning Check the load is not shorted 1
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