SINGLE PHASE CYCLO CONVERTER WITH R & RL LOADS

SINGLE PHASE CYCLO CONVERTER WITH R & RL LOADS
SINGLE PHASE CYCLO CONVERTER.docx (Size: 15.79 KB / Downloads: 55)
AIM:
To verify the operation of single phase Cyclo Converter with R and RL Loads and to
observe the output and input waveforms
APPARATUS:
S.No EQUIPMENT Qty
1. Iφ Center tapped
Transformer
2. Iφ Cyclo Converter power
circuit with firing unit
3. Rheostat 1
4. Inductive load 1
5. Voltmeter(MI) 1
7. CRO with (1:10) Probe 1
8. Patch cards 1 set
THEORY
The circuit diagram of 1φ cyclo converter with R and RL load are shown in fig.
Construction ally there are four SCR’s T1, T2, T3 &T4.Out of them T1, T2 are responsible for
generating positive halves forming the positive group. The other two T3, T4 are responsible for
negative haves forming negative group. This configuration and waveforms are shown for ½ and
1/3 of the supply frequency. Natural commutation process is used to turn off the SCR’s.
A) For RLoad: During the half cycle when point A is positive with respect to O, SCR T1 is
in conducting mode and is triggered at wt =α then current flows through positive point
AT1loadnegative O. In the negative half cycle when B point is positive with respect to
the point O,SCR T1 is automatically turned off due to natural commutation and SCR T2 is
triggered at wt = π+α. In this condition the current flows through BT2loadO.
) For RLLoad:
When A is positive with respect to O forward biased SCR T1 is triggered at wt=α and the
current start to flow through AT1RLO. Load voltage becomes zero at wt=π but load
current will not become zero at this angle due to inductance. It becomes zero at wt =β
which is called extinction angle. So it is naturally commutated at wt=β. After half cycle
point B positive with respect to point O. Now at angle wt=π+α. T2 is triggered and the load
current takes path from BT2RL_o and its direction is positive as in the previous case.
The load current decays zero at wt =π+β and SCR T2 is naturally commutated.
In the half cycle when O is positive with respect to B point, T4 is triggered instead of T1
at an angle of wt= (2π+α). Now the load current flows through OLRT4B but the
direction of load current reversed. When the load current becomes zero at an angle wt=
(2π+α) , T4 naturally commutated because the voltage is already reversed at wt = 3π.When
wt = (3π+α) and point O, is positive with respect to point A,T3 is triggered then the current
flows through OLRT3A , and the direction of load current is same in previous case. In
the next half cycle again T1 will triggered like this we get one cycle of output frequency for
two cycles of input frequency, when the frequency division switch is at 2.
PROCEDURE:
A) For RLoad:
1. Connect the circuit as shown in figure.
2. Verify the connections from the lab instructor before switch on the supply.
3. Keep the rheostat position value given by the lab instructor
4. Switch ON the supply and note down the frequency of input voltage from the
CRO.
5. Set the frequency division switch at 2 and note the readings of time period of
output voltage waveform for different set of firing angles
6. Calculate the practical value of output frequency by reciprocating the value of
time period and theoretical value of frequency will be found from frequency
division setting 

