CIRCUIT DIAGRAM FOR 1-PHASE STEPDOWN CYCLO CONVERTER:
TRIGGERING CIRCUIT FOR 1-PHASE STEPDOWN CYCLO
Expt.No: Date :
SINGLE PHASE STEP DOWN CYCLOCONVERTER
WITH R AND R-L LOADS
To observe the working operation of 1- Step down cycloconverter with R and
RL loads and to plot the voltage waveforms across the load and SCRs for different
S.No. Apparatus Range Type Quantity
1. SCRs 10A/ 1200V 16TTS12 4
2. 1- Center taped step-down 230/9-0-9v,1A,18VA ----
3. Load Rheostat 145 / 2.8A Wire Wound 1
4. Inductive load (0-150mH), 2A ….. 1
5. Cathode Ray Oscilloscope, …. ….
6. 1 Step down cyclo converter …. …..
Triggering Circuit Kit
7. Voltmeter (0-30V) MI 1
8. Ammeter (0-200mA) MI 1
9. Main Circuit Breaker 230V/6A … 1
10. Connecting Wires ….. …. Required
In a 1 step down cycloconveter, the output frequency is less than the supply
frequency. These converters require natural commutation which is provided by a.c.
supply. During positive half cycle of supply, thyristors P1 and N 2 are forward biased.
First triggering pulse is applied to P1 and hence it starts conducting.
As the supply goes negative, P1 gets off and in negative half cycle of supply, P2
and N1 are forward biased. P2 is triggered and hence it conducts. In the next cycle of
supply, N 2 in positive half cycle and N1 in negative half cycle are triggered. Thus,
we can observe that here the output frequency is 1/2 times the supply frequency.
1. As the output is zero even after all the connections made properly, MCB is
switched off and A.C. input connections to the power circuit are interchanged.
This is done to synchronize firing circuit and power circuit.
2. The frequency division is changed only when the trigger pulse switch is at OFF
3. Load Rheostat is connected in the circuit with its fixed terminals only.
4. CRO is not used in dual trace mode.
1. Switch on the main supply to the firing circuit.
2. Observe the test points and trigger outputs by changing frequency division and by
varying firing angle, using CRO.
3. Switch OFF the supply to the firing circuit.
4. Make the power circuit connections as per the circuit diagram.
5. Connect the firing pulses from the firing circuit to the respective SCRs in the power
6. Switch ON the circuit breaker.
7. Switch ON the supply to firing circuit and the main supply.
8. Set the frequency division to ‘3’.
9. Vary the firing angle potentiometer and observe the waveforms across the load
and note down the readings of voltmeter and ammeter.
10. Repeat the experiment for different firing angles.
11. Switch OFF the supply to the firing circuit and main supply.
Vm Sin 2 2
Sin 2 2
Output voltage , V0 V
For 630 ; Vm 9 2 V .
9 2 Sin 0.7 2 9 1
V0 rms gp 0.35 = 2.04 0.019 2 = 7.28643V.
Vm Sin 2
2 V Sin 2 Sin 2 2
Output Voltage , V0 d m
rms 2 2 2
For 180 0.1 C ; Vm 9 2 V ; 2160
9 2 6 Sin 5 Sin 0.2
rms 2 5 2 2
1.1 0.065 0.00548 2
1.1 0.05952 = 9.35 V.
Hence, studied and observed the working operation of a 1 step-down cyclo
converter with R and R-L loads and also observed the voltage waveforms across the
load for different firing angles.
Voltage across the load
V0 (volt )
(firing angle 600 )
(firing angle 600 )
From the experiment conducted, it is concluded that, due to the presence of
non-linearities in the center-tap transformer, the voltage across the load differ
practically and theoretically. Also, it is observed that the output frequency is less than
the input frequency (f 0< fi) and hence it acts as step down cycloconverter.