24-01-2013, 10:48 AM
SINGLE PHASE HALF CONTROLLED BRIDGE CONVERTER WITH R & RL LOAD
CONTROLLED BRIDGE.docx (Size: 14.68 KB / Downloads: 51)
AIM:
To obtain the output waveform of single phase half controlled bridge converter with R
and RL Loads.
APPARATUS:
S.No Name of the Equipment Type Ramge Quantity
1. Single phase half
controlled converter power
circuit
2. Firing Unit 1
3. Voltmeter MI (0-60V) 1
MC (0-50V) 1
4. 1:1 Isolation Transformer 1KVA 1
5. Rheostat Wire wound 100ohm/5A 1
6. Inductive load 0-150mH 1
7. CRO
8 Patch Chords
THEORY:
Single Phase half wave controlled bridge converter with R&RL loads are shown in the
diagram.
R-Load:
During the positive half cycle of AC supply SCR T1 and diode D1 are forward biased.
The SCR T1 is triggered at a firing angle ωt=α, the output current flows through hthe
path A-T1-R-D1-B. The load current will flow until T1 is commutated by reversal of supply at
ωt=Π. During The nagative half cycle of AC supply SCR T2 and diode D2 are forward biased.
When the SCR T2 is triggered at angle ωt=(Π+α), the output current would flow through the path
B-T2-R-D2-A.
RL-Load:
The main difference between the operation of the circuit with a complex load, and with a
purely resistive load is that at end of each half-cycle of the supply voltage, the current flow is
maintained in the load circuit by the inductance of the load. The thyristor that has been
conducting, say SCR1, continues to conduct, but current transfers from diode D2 to D1 so that
the inductive back emf of the load drives current through the bridge without including the
reverse supply voltage. During this part of the cycle, the load current decays exponentially and is
unaffected by the supply voltage. When SCR2 is triggered, SCR1 is reverse biased by the supply
voltage and turns off. Current now flows from the supply through SCR2 and diode D1 into the
load. SCR1 is triggered in the next half-cycle and the sequence is repeated.
PROCEDURE:
R-load:
1. Make connections as per the circuit diagram.
2. Verify the connections from the lab instructor before switching ON the supply.
3. Keep the rheostat position and variac position as the value given by the lab instructor.
4. Switch ON the CRO and calibrate it with the input voltage.
5. Switch ON the power circuit and firing circuit.
6. Observe the output voltage wave form in the CRO.
7. Note down the readings of α from the CRO Vo from the voltmeter.
8. Also calculate the theoretical value of the output voltage from the formula and
compare it with the practical value of the output voltage, which is observed from the
voltmeter.
9. Repeat the above process for various firing angle.