Circ rlc paralel
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Circ rlc paralel

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bazele electrotehnicii

bazele electrotehnicii

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  • 25-1
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Circ rlc paralel Circ rlc paralel Presentation Transcript

  • Unit 25 R-L-C Parallel Circuits
  • Unit 25 R-L-C Parallel Circuits
    • Objectives:
    • Discuss parallel circuits that contain resistance (R), inductance (L), and capacitance (C).
    • Compute the values of an R-L-C parallel circuit.
    • Compute all circuit values.
  • Unit 25 R-L-C Parallel Circuits
    • Objectives:
    • Discuss the operation of a parallel resonant circuit.
    • Compute the power factor correction for an AC motor.
  • Unit 25 R-L-C Parallel Circuits
    • In the R-L-C parallel circuit, the voltage is the same across all the component branches. However, the currents through the branches will have a phase shift based on the various component properties.
    • Inductive current lags the voltage.
    • Capacitive current leads the voltage.
    • Resistive current is in phase with the voltage.
  • Unit 25 R-L-C Parallel Circuits Phase relationships of current and voltage.
  • Unit 25 R-L-C Parallel Circuits R-L-C parallel circuit schematic.
  • Unit 25 R-L-C Parallel Circuits
    • Circuit Values
    • Z = total impedance of the circuit
    • I T = total circuit current
    • I R = resistor current flow
    • P = true power (watts)
    • L = inductance of the inductor
    • I L = inductor current flow
    • VARs L = reactive power of the inductor
  • Unit 25 R-L-C Parallel Circuits
    • Circuit Values
    • C = capacitance of the capacitor (farads)
    • I C = capacitor current flow
    • VARs C = reactive power of the capacitor
    • VA = volt-amperes (apparent power)
    • PF = power factor
    • angle θ = degrees of phase shift (theta)
  • Unit 25 R-L-C Parallel Circuits
    • Impedance
    • Z = 1 / √ (1/R) 2 + (1/X L – 1/X C ) 2
    • Z = R x X / √( R 2 + X 2 )
    • Inductance and Inductive Reactance
    • L = X L / 2 π F and X L = 2 π FL
    • Capacitance and Capacitive Reactance
    • C = 1 / 2 π F X C and X C = 1 / 2 π FC
  • Unit 25 R-L-C Parallel Circuits
    • Resistive Current
    • I R = E / R
    • Inductive Current
    • I L = E / X L
    • Capacitive Current
    • I C = E / X C
  • Unit 25 R-L-C Parallel Circuits Vector diagram of currents.
  • Unit 25 R-L-C Parallel Circuits Reducing vector currents.
  • Unit 25 R-L-C Parallel Circuits
    • True Power
    • P = E x I R
    • Reactive Power
    • VARs Total = √(VARs L – VARs C ) 2
    • Apparent Power
    • VA = E x I T
    • VA = √P 2 + (VARs L – VARs C ) 2
  • Unit 25 R-L-C Parallel Circuits
    • Power Factor
    • PF = Watts / VA
    • Angle Theta
    • Cosine θ = PF
  • Unit 25 R-L-C Parallel Circuits Example circuit #1 values.
  • Unit 25 R-L-C Parallel Circuits Example circuit #2 given values.
  • Unit 25 R-L-C Parallel Circuits
    • Parallel Resonance
    • Parallel resonant circuits are often called tank circuits. The special properties of this circuit can be used to heat treat sections of metal pipe and welds.
  • Unit 25 R-L-C Parallel Circuits Example resonant circuit at 1200 Hz.
  • Unit 25 R-L-C Parallel Circuits Tank circuit with circulating current.
  • Unit 25 R-L-C Parallel Circuits Induction heating system.
  • Unit 25 R-L-C Parallel Circuits Frequency controls heat penetration depth.
  • Unit 25 R-L-C Parallel Circuits
    • Power Factor Correction
    • Power factor correction can be done at either the load or the service. In each situation a capacitor or capacitor bank is connected in parallel.
  • Unit 25 R-L-C Parallel Circuits Determining motor power factor.
  • Unit 25 R-L-C Parallel Circuits Equivalent motor circuit.
  • Unit 25 R-L-C Parallel Circuits Capacitor used to correct motor PF.
  • Unit 25 R-L-C Parallel Circuits
    • Review:
    • The voltage applied to all legs of an R-L-C parallel circuit is the same.
    • The current flow in the resistive leg will be in phase with the voltage.
    • The current flow in the inductive leg will lag the voltage by 90 °.
    • The current flow in the capacitive leg will lead the voltage by 90°.
  • Unit 25 R-L-C Parallel Circuits
    • Review:
    • Angle theta for the circuit is determined by the amounts of inductance and capacitance.
    • An L-C resonant circuit is often referred to as a tank circuit.
    • When an L-C parallel circuit reaches resonance, the line current drops and the total impedance increases.
  • Unit 25 R-L-C Parallel Circuits
    • Review:
    • When an L-C parallel circuit becomes resonant, the total circuit current is determined by the amount of pure resistance in the circuit.
    • Total circuit current and total impedance in a resonant tank circuit are proportional to the Q of the circuit.
  • Unit 25 R-L-C Parallel Circuits
    • Review:
    • Motor power factor can be corrected by connecting capacitance in parallel with the motor. The same amount of capacitive VARs must be connected as inductive VARs.