Study of 1-phase AC to DC controlled converter (both fully controlled And half controlled)

Transcription

1 Study of 1-phase AC to DC controlled converter (both fully controlled And half controlled) Object: To study the performances of single phase half-controlled bridge Rectifier. A. In configuration A. B. In configuration B. Apparatus: 1. Experimental set up. 2. Dual Trace Oscilloscope. 3. M.C. Voltmeter (0-300 v),ammeter (0-3 amp.) 4. M.I. Voltmeter (0-300 v) ohm rheostat, Inductive coil ohm std. resistance. Procedure: A. Study of configuration A 1. Check the trigger- circuit. Refer to the last experiment. Fig. P.E Connect up the power circuit as in configuration A. Switch on the trigger Circuit. 3. Connect probe to one of the oscilloscope channel for observing voltage waveform across the secondary terminals of the step down(230-6v.) transformer in the triggering circuit. Synchronize the oscilloscope onto this signal(reference).adjust level control and time base control to get one complete cycle of the input A.C voltage commencing from its zero crossing, displayed. 4. With the 185 ohm rheostat connected between L1 and L2 and the variac set to 80% position. Switch on the power circuit supply.(in case of mal operation refer to B2 of experiment P.E.-4). 5. Observe the voltage waveform across the load, the std. resistance (current), each of the thyristors and the diodes. Connect the std. resistance in series with each of the semiconductors and observe the current waveform in the A.C line. Read off α from the oscilloscope display. Sketch the above waveform in time phase relationship with the reference for α = 10, 30, 90, 120, 150 and 170. Plot VDC( calculated ) vs α and VDC(measured) vs α on the same graph paper. VAC VDC measured VDC calculated

2 6. Switch off supply to power circuit. Connect the inductance between terminals L1 and L2.Set the variac to zero output position and switch on the supply again. 7. With α set at the minimum, gradually increase the variac output till the ammeter reads 3 amps. 8. Repeat A-3 and A Connect a F.W.D. across the inductance and observe the waveform again. Observe also the current through the F.W.D. Plot them in time phase relation to the reference. 10. Remove the F.W.D. with α set low, get a steady display on the oscilloscope of the output voltage of the rectifier. Switch off the trigger circuit and observe how the output voltage decays.(a strong oscilloscope might be used here to observe this fast phenomenon. But it can also be viewed on an ordinary C.R.O. if keenly observed. For repeated displays, switch on and off the trigger circuit power several times-allowing for the load current to build up to its steady state value.) B. Study of configuration B. 1. Repeat all the steps in part A of the experiment. Questions: 1. Explain the difference in the performance of the two circuits in step Can the pulse transformers be done away with in any of the above circuits? 3. Compare the performances of a single phase fully controlled and a half controlled bridge converter?

3 STUDY OF 1-PHASE FULLY CONTROLLED BRIDGE CONVERTER Object : Study of A. The triggering circuit of a single phase fully controlled converter. B. Single phase fully controlled converter. Apparatus : Procedure : 1. Experimental set up. 2. Dual trace oscilloscope. 3. M.C. voltmeter( 0-300v), ammeter. 4. M.I. voltmeter( 0-300v) ohm rheostat, Inductive coil ohm std. resistance. A. Study of triggering circuit. Fig. P.E.-4.1 Triggering circuit. 1. Study the triggering circuit. Identify all the components given in the diagram. 2. Switch on power to the trigger circuit only. 3. Connect both the GND. Probes of the oscilloscope to any two cathodes of the S.C.R.s.The line leads are to be clipped on to the respective gates. On CHOP mode synchronize the oscilloscope on any one of the inputs. Set Time base control to 5 m.sec.(select line Trigger for oscilloscope if available). 4. Observe the pulse width and the phase relation of the trigger pulses for the two thyristors. Observe the details of the pulses to the gate of any one of the thyristors. Change time - base position, if necessary. Trace all the pulses on a graph paper. Remove all the probes.

4 B. Fully controlled single phase converter. Fig. P.E Fully controlled converter. 1. Connect up the power circuit as in (Fig. P.E.-4.2.). Between L1 and L2 connect the 185 ohm rheostat. Switch on all power supplies. FWD not to be connected. 2. Observe the load voltage waveform and the current waveform by observing the drop across the STD. resistance. Read off α from the oscilloscope display. Note the meter readings. Calculate VDC from the measured value of VAC and α. Tabulate: Fig. P. E. 4.3 VAC V DC measured V DC calculated Plot VDC vs α for both measured and calculated VDC. (The circuit will malfunction if the trigger circuit power supply(a.c. line 230v)is out of phase with that fed to the power circuit. Reverse trigger circuit supply, at the plug if necessary ). 3. With the STD. resistance in series with the A.C. line observe the current waveform on the oscilloscope. Connect the second probe to the secondary of the step-down transformer in the triggering circuit to observe the time phase relation of the former to those already observed.

5 4. With the STD. resistance in series with the thyristors, observe the current waveform through them. Observe also the voltage waveform across the thyristors. Plot all the observed waveforms in time phase relationship with the A.C. supply Voltage(display in the second trace). 5. Connect a transformer coil in series with the rheostat. Set rheostat at about 100 ohms. Repeat B-2, B-3 and B-4 with and without the FWD. Questions: 1. Comment on the effect on Power Factor of the FWD. 2. Explain how the fully controlled converter can be made to operate as an inverter. Draw the necessary power circuit and sketch a typical voltage and current waveform.