- Figure A shows circuit for the RL phase shift control.
- It consists of one step down transformer which consists of center taped secondary winding.
- The RL circuit is connected in series with transformer secondary winding.
- The voltage drop across R is bd = IR and voltage drop across inductor is ad = IXL.
- The voltage drop across cd is given to the gate – cathode terminal of the SCR.
- There should be phase difference Ф between anode voltage and gate voltage.
- As the variable resistance changes, the voltage drop across bd changes. Figure B shows vector diagram for RL phase shift circuit.
ab = Voltage drop
across transformer secondary winding
bd = Voltage drop
across resistance
ad = Voltage drop
across inductor
As the centre tapping
transformer ac = cb
tan α = ad / bd
= IXL / IR
α =
tan-1 ( ωL / R )
As ac = cb, the angle
Ф = 2α
Ф =
2 tan-1 ( ωL / R )
- As the value of resistance increases, the voltage drop across R increases resulting Ф decreases.
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