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ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 SAIT, JABALPUR DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING LABORATORY – ELECTRICAL DRIVES (B-312A) SUBJECT - ELECTRICAL DRIVES SUBJECT CODE: EX-702 BRANCH – EX SEMESTER - VII (GRADING) LIST OF EXPERIMENTS 1. To control the speed of 3-Φ Slip Ring Induction Motor using Static Kramer System. 2. To study the operation of Parallel Inverter. 3. To study the operation of Series Inverter. 4. To study and perform the operation of speed variation of PMDC motor using single phase bridge converter. 5. To study and perform the operation of full wave half controlled SCR bridge with motor load- PMDC motor 6. To study Speed Control of DC Motor using Single Phase Half Controlled Rectifier. 7. To study and perform the operation of speed control of Universal Motor in open loop and closed loop system (P&PI). 8. To study Speed Control of Universal Motor using Single Phase Half Controlled Rectifier 9. To study of Voltage Commutated Chopper. DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 1 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 INDEX S. NO. NAME OF EXPERIMENT PAGE NO. DATE DEPARTMENT OF ELCTRICAL & ELCTRONICES SIGN. REMARKS Page 2 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR __/__/20__ 2015-16 EXPERIMENT NO.-1 Aim: - To control the speed of the 3N slip ring Induction motor using the PEC16HV10B trainer module. Apparatus Required:i. PEC16HV10B module. ii. 3 phase slip ring Induction Motor iii. 3 phase transformer. .iv Patch chords. v. Inductor (150mH). vi. Tachometer. Theory:In the static Kramer drive, the step power from the rotor of Slip Ring Induction Motor is converted to DC voltage which is then converted to line frequency and pumped back to the ac source. As the slip power can flow only in one direction, this system offers a sub-synchronous speed control. As the power flow is from rotor circuits to supply, static Kramer drive offers a constant torque operation. Speed Control of 3 Phase Slip Ring Induction Motor Slip-Ring Induction motors are preferred in applications with the requirement of high starting torque, high over load capacity, nearly constant speed and low starting current. Applications include driver for Line shafts, Pumps, Lights, Generators, Winding Machines, Mills etc. This manual discusses about the static Kramer system of slip power Recovery for speed control of 3N slip Ring induction motor module. In this system, the slip power is connected to DC by means of a solid state rectifier and by using static slip power recovery scheme the excess power is again fed back to the supply. The amount of power fed back depends on the firing angle of the inverter, 3N supply voltage and DC voltage to the inverter. PRINCIPLE OF THE STATIC KRAMER SYSTEM A sub synchronous static Kramer drive scheme is shown. It consists of 3N slip ring induction motor, a rectifier bridge, a filter, an inverter bridge and a transformer. In this scheme of speed control, slip power is recovered from the rotor of 3N slip ring induction motor and is fed back to the supply line through rectifier, inverter and transformer. The slip frequency alternating current is first rectified by Diode Bridge and this unidirectional current is smoothed by a filter circuit after which it is fed to the 3-inverter. This inverter is line commutated. The slip power returned to the supply depends upon the inverter terminals and the 3-phase supply voltage. The function of the 3-phase transformer is to match the inverter output voltage with the 3-phase supply voltage. The speed control is achieved by varying the firing angle of the inverter. By varying firing angle, the voltage taken from the supply is reduced and so speed of motor is reduced. The usual range of firing DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 3 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 angle is for 90° to 160°for a wide speed range. The power flow through the rectifier is unidirectional, therefore, only sub-synchronous speeds below the normal value are obtainable. Since the slip power is returned to the supply, the scheme illustrated in Fig. results in a constant torque drive Circuit Diagram:- Procedure 1. Switch ON the 3N AC Power Supply to the module. 2. Switch ON the power ON/OFF switch of the module. 3. The pulse release switch should be in OFF condition and the pulse cable should not be Connected. 4. Now check the “Phase Sequence” of the 3N AC i/p at the 3N SCR Bridge firing circuit Test points r, y, and b. 5. Now check the test points r, y,b and the secondary output of the step down transformer r, y, b are at “In Phase” using CRO at dual mode. They should be in phase with each other. If they are not at in phase, change the connection of the transformer and make them in Phase. 6. Now connect the pulse cable. 7. Keep the pot meter at minimum position. 8. Connect the lamp load across the 3N SCR converter output. 9. Switch ON the pulse release switch. 10. Slowly vary the pot meter and verify the converter output. 11. Now switch OFF the pulse release switch and remove the lamp load connection. 12. Now connect the 3N SCR bridge output positive to the negative of the 3N diode bridge Output at the right side of the module. DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 4 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 13. Connect the iron core inductor (0mH) tapping to the positive of the 3N diode bridge Output and connect the 150mH output to the negative of the 3N SCR bridge output. 14. Connect the positive of 3N SCR bridge output to the negative of the 3N diode bridge Output. 15. Now switch ON the stator MCB and the three phase diode bridge MCB at the back side Of the module. 16. Switch ON the pulse release switch. 17. Vary the pot meter gradually from the minimum position till it reaches 1450rpm (rated Speed). Note: The motor should be in no-load condition, 18. Check the speed of the 3N slipping motor using tachometer. Table S. No Firing Angle " (deg) Speed N(rpm) Result: Thus the speed of the 3N slip ring Induction motor using the PEC16HV10B trainer module. Precaution: 1. Using isolation transformer. 2. All the cables and patch chord should be made through 15A wire. 3. Don’t load the motor above 7.5A of rotor current. 4. Don’t vary the pot meter once the motor reaches To view the converter output waveform at the CRO or the 3N AC input should be Isolated 1450 rpm DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 5 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR DEPARTMENT OF ELCTRICAL & ELCTRONICES 2015-16 Page 6 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 EXPERIMENT- 2 AIM: - To study the operation of Parallel Invertors. Apparatus Required:1. Single phase Parallel inverter kit (10 V/2 Amp) 2. D.C. Power supply (11V/2 Amp) 3. Firing circuit 4. CRO 5. Load Theory:Principle of parallel operation of inverter Balance between generated and consumed real (P) and reactive (Q) power indicates the stable operation of a power system. Therefore, implementing effective control over P and Q is very important from the operational and control points of view. The real (P1) and reactive (Q1) power transferred from the inverter to the common bus or grid can be calculated as described in [1] and from the following diagram, as shown in Fig. 1; P1 = E1Vg cos1 Zg,1 − V2 g Zg,1 cos g,1 + E1Vg Zg,1 sin1 sin g,1 (1) Q1 = E1Vg cos1 Zg,1 − V2 g Zg,1 sin g,1 − E1Vg Zg,1 sin1 cos g,1 (2) Here E1 and Vg represent the inverter output voltage and grid voltage, respectively. For only real power transfer, Vg and E should have the same amplitude with a phase angle difference. Different amplitude of voltage with the same phase will give a reactive power circulation. When both of the magnitude and phase angle differ between the two voltage sources, it causes real and reactive power flow. Control of frequency dynamically controls the power angle and hence, the real power flow. As the output impedance of the inverter CIRCUIT DIAGRAM:- DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 7 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 Procedure CRO Settings Time (X) Axis : 5ms/div Voltage (Y) Axis : 20V/div Probe: 1:10 CRO Probe is suitable one. Initial Settings Ensure the 230V Power Supply is in proper with Tester. Ensure the CRO is working properly with probe checking and proper ground line axis. Experiment Steps The connections are made as per the circuit diagram given above. When the load is Rheostat, then it must be in maximum position. Turn on the SW2 and observe the waveform across between G1&K1 and G2&K2. And ensure it is like triggering pulse given in model graph. Turn ON SW1 and observe the waveform across the R load. Measure the X-axis time interval of ON time of Load Voltage and OFF Time of Load Voltage. Adjust the value of Firing angle and note down the load voltage and frequency Repeat the step 5. Repeat the experiment for different values of α and note down Vo. DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 8 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 Table S.No Result F output (Hz) Scr off time (ms) Above experiment are done and results are verified DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 9 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR DEPARTMENT OF ELCTRICAL & ELCTRONICES 2015-16 Page 10 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 EXPERIMENT-3 AIM: - To study the operation of series Invertors. Apparatus Required:- 1. Single phase series inverter kit (10 V/2 Amp) 2. D.C. Power supply (11V/2 Amp) 3. Firing circuit 4. CRO 5. Load Theory Basic Series Inverter Circuit Fig.1 shows the circuit of a series inverter. The commutating elements L and C are such that R, L and C form an under damped circuit. The capacitor has an initial voltage E c, Thyristorised Th1 is turned on first by an external pulse. Since Th 1 is already forward biased (due to dc voltage V), Th1 starts conducting and a current I flows in the circuit through Th 1, C, L and load. Because of under damped nature of the circuit the current is not constant but has the wave shapes as shown in fig.2. It rises to maximum value and then decreases to zero. When the current is at its peak value, the voltage across capacitor is nearly equal to supply voltage V. After this the current starts decreasing but the voltage across the capacitor continues to increase as it is still getting charged. When the current becomes zero the voltage across capacitor is maintained at V+E c. The voltage across L is zero. The time interval ab must be more than time toff of the thyristor. This is necessary to ensure that the stored charges in Th1 are reduced to zero so that at point b Th1 is in completely off state. At point b when Th 2 is turned on by an external gate pulse the anode of Th2 is positive (with respect to cathode) due to charge on capacitor Th2 starts conducting. The capacitor discharges and the current I flows through the circuit in the direction opposite to that in the start. The current reaches its negative peak value and then decreases to zero at point c when Th2 is turned off. The above sequence of operation is repeated in the next cycle when Th1 is turned on. The frequency of the output voltage is – Circuit diagram DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 11 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 Procedure 1. 2. 3. 4. Connecting are made as show n in the circuit diagram. Select values of c = ,L= Set input voltage to 5 volts. Apply trigger voltage; observe corresponding output voltage (ac voltage and wave forms) at load terminal. 5. Note down the voltage & frequency of output wave form. 6) The o/p ac voltage is almost equal to the two times of the dc i/p voltage OBSERVATION: Note down the value of voltage and frequency. And draw the waveforms. S.N. VOLTAGE (VS) CURRENT(IS) DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 12 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 RESULT: The waveforms are determined. The o/p ac voltage is almost equal to the two times of the dc i/p voltage PRECAUTIONS: 1) All the connection should be tight... 2) The electrical current should not flow the circuit for long time, otherwise its temperature will increase and the result will be affected. 3) It should be care that the values of the components of the circuit is does not exceed to their ratings (maximum value). 4) Before the circuit connection it should be check out working condition of the entire Component. DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 13 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR DEPARTMENT OF ELCTRICAL & ELCTRONICES 2015-16 Page 14 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 EXPERIMENT-4 AIM: - To study and perform the operation of speed variation of PMDC motor using single phase bridge convertor. Apparatus Required:1 .Power thyristors 2. Rheostat 3. CRO 4. Transformer (1-phase) 230V/24V 5. Connection wires Theory:Speed Control of DC Series Motor Speed control of dc series motor can be done either by armature control or by field control. Armature Control of DC Series Motor Speed adjustment of dc series motor by armature control may be done by any one of the methods that follow, 1. Armature resistance control method: This is the most common method employed. Here the controlling resistance is connected directly in series with the supply to the motor as shown in the fig. diagram The power loss in the control resistance of dc series motor can be neglected because this control method is utilized for a large portion of time for reducing the speed under light load condition. This method of speed control is most economical for constant torque. This method of speed control is employed for dc series motor driving cranes, hoists, trains etc. 2. Shunted armature control: The combination of a rheostat shunting the armature and a voltage applied to the armature is varies by varying series rheostat R 1. The exciting current can be varied by varying the armature shunting resistance R2. This method of speed control is not economical due to considerable power losses in speed resistances. Here speed control is obtained over wide range but below normal speed. Rheostat in series with the armature is involved in this method of speed control. The 3. Armature terminal voltage control: The speed control of dc series motor can be accomplished by supplying the power to the motor from a separate variable voltage supply. This method involves high cost so it rarely used. DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 15 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 Field Control of DC Series Motor The speed of dc motor can be controlled by this method by any one of the following ways – 1. Field diverter method: This method uses a diverter. Here the field flux can be reduced by shunting a portion of motor current around the series field. Lesser the diverter resistance less is the field current, less flux therefore more speed. This method gives speed above normal and the method is used in electric drives in which speed should rise sharply as soon as load is decreased. 2. Tapped Field control: This is another method of increasing the speed by reducing the flux and it is done by lowering number of turns of field winding through which current flows. In this method a number of tapping from field winding are brought outside. This method is employed in electric traction. CIRCUIT DIAGRAM:- As in PMDC motor the field is produced by permanent magnet, there is no need of drawing field coils in the equivalent circuit of permanent magnet dc motor. The supply voltage to the armature will have armature resistance drop and rest of the supply voltage is countered by back emf of the motor. Hence voltage equation of the motor is given by, Where I, is armature current and R is armature resistance of the motor. Eb is the back emf and V is the supply voltage. DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 16 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 Procedure 1) Connecting are made as show n in the circuit diagram. 2) Select values of c =, L = 3) Set input voltage to 5 volts. 4) Apply trigger voltage, observe corresponding output voltage (ac voltage and wave forms) at load terminal. 5) Note down the voltage & frequency of output wave form. 6) The o/p ac voltage is almost equal to the two times of the dc i/p voltage Advantages of Permanent Magnet DC Motor or PMDC Motor PMDC motor has some advantages over other types of dc motors. They are: 1. 2. 3. 4. No need of field excitation arrangement. No input power in consumed for excitation which improves efficiency of dc motor. No field coil hence space for field coil is saved which reduces the overall size of the motor. Cheaper and economical for fractional kW rated applications. Disadvantages of Permanent Magnet DC Motor or PMDC Motor 1. In this case, the armature reaction of DC motor cannot be compensated hence the magnetic strength of the field may get weak due to demagnetizing effect armature reaction. 2. There is also a chance of getting the poles permanently demagnetized (partial) due to excessive armature current during starting, reversal and overloading condition of the motor. 3. Another major disadvantage of PMDC motor is that, the field in the air gap is fixed and limited and it cannot be controlled externally. Therefore, very efficient speed control of DC motor in this type of motor is difficult. Applications of Permanent Magnet DC Motor or PMDC Motor PMDC motor is extensively used where small dc motors are required and also very effective control is not required, such as in automobiles starter, toys, wipers, washers, hot blowers, air conditioners, computer disc drives and in many more. DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 17 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR DEPARTMENT OF ELCTRICAL & ELCTRONICES 2015-16 Page 18 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 EXPERIMENT-5 AIM: - To study and perform the operation of full wave half controlled SCR Bridge with motor load PMDC motor. Apparatus required: Trainer kit, Patch cards, Multi meter, Connection wires Theory:- The single phase fully controlled rectifier allows conversion of single phase AC into DC. Normally this is used in various applications such as battery charging, speed control of DC motors and front end of UPS (Uninterruptible Power Supply) and SMPS (Switched Mode Power Supply). All four devices used are thyristors. The turn-on instants of these devices are dependent on the firing signals that are given. Turnoff happens when the current through the device reaches zero and it is reverse biased at least for duration equal to the turn-off time of the device specified in the data sheet. When an uncontrolled (diode) converter is to be simulated, all 4 devices should be fired at a delay angle of 0⁰. When a semi-converter is to be simulated, the lower two devices can be fired at 0⁰ and 180⁰ respectively and the upper two devices are fired at α and 180⁰+α. Normally in a fully controlled converter, the current transfer takes place from T1 to T2 instantaneously without any time delay. But when a source inductance is present, the stored energy in Ls has to be expended before the current transfer or commutation takes place from T1 to T2. Because of this, T1 and to T2 will conduct simultaneously from α to α+u (where u is the overlap angle) causing short circuiting of the DC load during the overlap period u. This is known as commutation overlap. When the thyristor converter has a resistive load, both the DC current and voltage will be in phase. As soon as the positive half-cycle ends, the current through thyristors T1 and T11 will be reaching zero this causes the voltage pulses to be spreading from firing angle α to π as shown. Both the current after which they would be reverse biased due to the supply voltage embarking into negative half-cycle. in the DC link (Idc) and the current in the source (Is) will be discontinuous on completion of this unit you will under frequency pulse train can be used after validating the same with line synchronized SCR triggering. DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 19 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 Circuit diagram Procedure 1) Connect the circuit as per wiring schedule given bellow. The arrangement ensures SCR full wave fully controlled bridge receiving firing pulses from ‘Ramp firing Section’ of INV/CON Panel. DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 20 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 2) Put ON the rectifier with 100W lamp load. 3) Observe the wave forms per the diagram. 4) Keep 2p6w switch on LSPT card at 4’Th position. Conclusion High frequency getting turns on the SCR repeated, and fires it at appropriate time when Anodes Cathode is forward biased current is ready to pass overcoming the inductance effect. The arrangement also helps in spreading the current though out the SCR junction area at a faster rate and avoids hot spot formation and subsequent damage of SCR. DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 21 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 EXPERIMENT-6 AIM: - To study speed control of DC Motor using single phase half controlled Rectifier PMDC motor. Apparatus Required:Trainer kit, Patch cards, Multi meter, Connection wires Theory:The single phase half controlled rectifier allows conversion of single phase AC into DC. In this we understand how controlled half wave SCR based converter functions and also its associated waveforms.TH1 conducts only when its anode is positive w.r.t & a synchronized gate pulse is applied to it. During positive half cycle of input AC (as anode is positive w.r.t cathode) if gate pulse is given at an angle α (ref wave form fig) then SCR will conduct for π- α.During negative half cycle of input this SCR is reverse biased so it will not conduct even gate pulse is applied. We can vary the conduction period of an SCR by varying the firing angle. The angle between starting of AC waveform and firing instance is known as firing angle where as the angle between firing instance and end of the respective half cycle is known as conduction angle. if firing angle increases then conduction angle decreases & vice versa. V0 =1/2π 0∫∏ VmSinwtd (wt) = Vm/2π (1+cos α) DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 22 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 Procedure:For this configuration only one SCR is required. Choose any one SCR from con/Lnv panel. The Lamp load is available on top board .For input AC use 100W lamp as load. Make the connections as per wiring sequence given above to form half wave-controlled converter. All connection should be done using patch chords provided. The firing pulse selector switch should be kept on 4th position for getting required gate pulse. By doing so you are selecting UJT relaxation oscillator based SCR firing. Now put on AC mains. Connect CRO across load & observe change in conduction angle by varying the conduction angle control pot on LSPT panel. Take the reading as per following table. Use 300V DC meter from top board for this purpose CIRCUIT DIAGRAM:- Table Output DC Half wave control. DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 23 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR Sr Firing Angle Peak Average voltage(Vm) voltage Vdc 2015-16 On 300V DC meter Conclus ion SCR can be used as controlled half wave Rectifier. It can be fired at any point in half conduction cycle. Thus controlled DC voltage EXPERIMENT-7 AIM: - To study speed control of Universal motor in open loop & close loop( P&PI). Apparatus Required:Trainer kit, Patch cards, Multi meter, Connection wires Theory:The Universal Motor is a phase angle triac controller having all the necessary functions for universal motor speed control in washing machines. It operates in closed loop configuration and provides two ramp possibilities. The TDA 1085C triggers a triac accordingly to the speed regulation requirements. Motor speed is digitally sensed by a tachogenerator and then converted into an analog voltage. The speed set is externally fixed and is applied to the internal linear regulation input after having been submitted to programmable acceleration ramps. The overall result consists in a full motor speed range with two acceleration ramps which allow efficient washing machine control (Distribute function). Additionally, the TDA 1085C protects the whole system against AC line stop or variations, over current in the motor and tachogenerator failure. DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 24 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 Procedure:Thyrister actuator panel EMT9 is used to control DC power & same is supplied to universal motor. 1. Make the connection as per wiring sequence provided. 2. Do not connect motor terminal to respective sockets. 3. Use 230V/100W lamp load, to check proper control (smooth o/p) voltage regulation. 4. Switch off the trainer ensures some load is applied on motor. 5. Before switch ON the trainer ensure some load is applied on motor 6. Keep SP pot on EMT9 at minimum position 7. Now switch ON the trainer ensure some load EMT9 to get I/P to motor CIRCUIT DIAGRAM:- DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 25 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 Table Open loop, Close loops (P&PI) Sr I/P motor (V) 1A SPEED (OPEN) (p) (PI) Conclus ion 1) Do not run universal motor without some load as speed. 2) Speed drops in open loop considerably. 3) Speed drops somewhat in close loop (p) DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 26 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 4) Speed is well regulated under close loop(PI) EXPERIMENT-8 DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 27 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 AIM: - To study speed control of Universal Motor using single phase half controlled Rectifier PMDC motor. Apparatus Required:i) Universal kit ii) CRO iii) Batch cards motor iv) Universal motor Theory:a) Firing Circuit: This unit generates line synchronized 2 pulse transformer isolated trigger pulses. These trigger pulses can be used to trigger. (i) Single phase AC phase control using SCR’s ( Anti parallel SCR’s) (ii) Single phase AC phase control using triac. (iii) Single phase half wave rectifier (single SCR) (iv) Single phase Full wave rectifier (Two SCR’s) (v) Single phase half controlled bridge rectifier (Two SCR’s & Two diodes) power circuits. The firing circuit is based on zero crossing detector, ramp generator, op-amp comparator and amplifier / pulse transformer isolation method. Front Panel Details: 1. Power: Mains switch for firing circuit with built in indicator 2. Firing angle: Potentiometer to vary the firing angle from 180o to 0o 3. SCR / Triac: Selection switches for trigger O/P 1 for SCR/Triac 4. OFF/ON: Switch for trigger O/Ps with soft start feature. 5. Trigger O/Ps: T1 / TR: T2: Trigger O/P for SCR2 Power Circuit: The power circuit consists of 2 SCR’s, 3 diodes and a Triac. The power devices are mounted on suitable heat sink for power dissipation. The snubber circuit is connected for dv/dt protection. A fuse is also provided in series with the devices for short circuit or over current protection. In the input side a 59 MCB is provided to switch ON/OFF the supply to the power circuit. A voltmeter and an ammeter is provided to measure the Input / Output voltage and current. Front Panel Details: 1. AC input: Terminals to connect AC input 2. AC output : AC supply terminals after the MCB to be connected to power circuit. 3. MCB: A 6A / 2 pole MCB for ON/OFF the AC supply to the power circuit 4. T1 & T2 : SCR’s 16 Amps / 600 volts 5. D3 & D4 : Diodes – 16amps / 600V 6. Dm: Freewheeling diode 7. TR : Triac – 10 amps / 600 volts 8. Voltmeter: 3 ½ Digit digital AC/DC Voltmeter to measure input / output voltage 9. Ammeter : 3 ½ Digit digital AC/DC Ammeter to measure current DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 28 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 Procedure:1) Make the inter connections in the power circuit as given is the circuit diagram. 2) Switch ON the firing circuit and observe the trigger outputs. 3) Make sure that the firing pulses are proper before connecting to the power circuit. 4) Then connect the trigger output from firing circuit to corresponding SCR’s / Triac. 5) In the power circuit initially set the AC input to 30 volts. Switch ON and MCB. Switch ON the Trigger outputs switch. Select the SCR / Triac selection switch and observe the output wave forms across ‘R’ load by varying the firing angle potentiometer. 6) If the output wave form is proper then you can connect the motor & increase the input voltage to rated value 0230V gradually. Vary the firing angle and note down output voltage and speed of the motor. Note: 1) If you are not getting the output after all proper connections interchange AC output terminals, after switch OFF the MCB. This is just to synchronize the power circuit with firing circuit. CIRCUIT DIAGRAM:- DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 29 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 Table Sr Input Voltage Vin Firing Angle Output Voltage – V0 Output Current I0 Speed RPM Result: Thus the speed control of Universal motor is performed by varying armature voltage through phase controlled converter Conclusion 1) Do not run universal motor without some load as speed. 2) Speed drops in open loop considerably. 3) Speed drops somewhat in close loop (p) 4) Speed is well regulated under close loop(PI) DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 30 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 EXPERIMENT-9 AIM: - To study of voltage Commutated Chopper.. Apparatus Required:i) Trainer kit ii) CRO iii) Batch cards motor iv) Chopper Theory:The junctions of any semiconductor exhibit some unavoidable capacitance. A changing voltage impressed on this junction capacitance results in a current, I = C dv/dt. If this current is sufficiently large a regenerative action may occur causing the SCR to switch to the on state. This regenerative action is similar to that which occurs when gate current is injected. The critical rate of rise of off-state voltage is defined as the maximum value of rate of rise of forward voltage which may cause switching from the off-state to the on-state. Since dv/dt turn-on is non-destructive, this phenomenon creates no problem in applications in which DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 31 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 occasional false turn-on does not result in a harmful affect at the load. Heater application is one such case. However, at large currents where dv/dt turn-on is accompanied by partial turn-on of the device area a high di/dt occurs which then may be destructive. The majority of inverter applications, however, would result in circuit malfunction due to dv/dt turn-on. One solution to this problem is to reduce the dv/dt imposed by the circuit to a value less than the critical dv/dt of the SCR being used. This is accomplished by the use of a circuit similar to those in Figure 3.8 to suppress excessive rate of rise of anode voltage. Z represents load impedance and circuit impedance. Variations of the basic circuit are also shown where the section of the network shown replaces the SCR and the R-C basic snubber. Since circuit impedances are not usually well defined for a particular application, the values of R and C are often determined by experimental optimization. A technique can be used to simplify snubber circuit design by the use of nomographs which enable the circuit designer to select an optimized R-C snubber for a particular set of circuit operating conditions. Another solution to the dv/dt turn-on problem is to use an SCR with higher dv/dt turn-on problem is to use an SCR with higher dv/dt capability. This can be done by selecting an SCR designed specially for high dv/dt applications, as indicated by the specification sheet. Emitter shorting is a manufacturing technique used to accomplish high dv/dt capability Procedure:1) Make the inter connections in the power circuit as given is the circuit diagram. 2) Switch ON the firing circuit and observe the trigger outputs. 3) Make sure that the firing pulses are proper before connecting to the power circuit. 4) Then connect the trigger output from firing circuit to corresponding SCR’s / Triac. 5) If the output wave form is proper then you can connect the motor & increase the input voltage to rated value 0-230V gradually. Vary the firing angle and note down output voltage and speed of the motor. Note: DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 32 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 6) If you are not getting the output after all proper connections interchange AC output terminals, after switch OFF the MCB. This is just to synchronize the power circuit with firing circuit. CIRCUIT DIAGRAM:- Table Sr Input Voltage Vin Firing Angle Output Voltage – V0 Output Current I0 DEPARTMENT OF ELCTRICAL & ELCTRONICES Speed RPM Page 33 ST. ALOYSIUS INSTITUTE OF TECHNOLOGY, JABALPUR 2015-16 Result: Above experimen t are done and results are verified Conclusion 1) Do not run universal motor without some load as speed. 2) Speed drops in open loop considerably. 3) Speed drops somewhat in close loop (p) 4) Speed is well regulated under close loop (PI) DEPARTMENT OF ELCTRICAL & ELCTRONICES Page 34