Topic 6 AC circuit analysis topic a6

Bài giảng ngành Điện: Giải các bài toán trong mạch điện điện thế thấp một pha và ba pha (Phần A) gồm các chủ đề sau Solve problems in single and threephase low voltage circuits Part A Content Topic 1 Sinusoidal Alternating Voltage and Current_Topic_A1 Topic 2 Phasors_Topic_A2.ppt Topic 3 Resistance in AC Circuits_Topic_A3 Topic 4 Inductance in AC Circuits_Topic_A4 Topic 5 Capacitance in AC Circuits_Topic_A5 Topic 6 AC Circuit Analysis_Topic_A6 Topic 7 Resonance_Topic_A7 Topic 9 Harmonics_Topic_B9

Solve problems in single and

three-phase low voltage circuits

Topic 6: AC Circuit

Analysis Part A

AC Circuit Analysis: Impedance

 Practical AC circuits often consist of resistive,

inductive, and/or capacitive components in many varying combinations.

 These components will combine to produce an

overall opposition to the flow of AC current.

 This total opposition to the flow of AC current is

called IMPEDANCE.

 Symbol Z, measured in Ohms (Ω)

– Impedance may consist of any combination of resistance, inductive reactance, and / or capacitive reactance.

AC Circuit Analysis: Ohm’s Law for AC

Ohm’s Law – AC circuits

AC Circuit Analysis: Determining

Impedance

 Determining Impedance involves two

methods, depending upon the type of circuit being analysed.

– For SERIES circuits: requires the use of the

impedance triangle

AC Circuit Analysis: Determining Impedance

AC Circuit Analysis

Series Circuits

AC Circuit Analysis: Series R-L Circuit

L=0.15H

VS=230Vƒ= 50Hz

R = 25Ω

Determine the following:

•Impedance Z

•Supply current IS

•Voltage across Resistor VR

•Voltage across Inductor VL

•Phase Angle Ø between

VS and IS

AC Circuit Analysis: Series R-L Circuit Process

 Step 1: Determine Inductive reactance XL

AC Circuit Analysis: Series R-L Circuit Process

 Step 4: Calculate voltage drops (Ohm’s law)

 VR = IS x R

 VL = IS x XL

 Step 5: Draw the phasor diagram, use

phasor addition to determine position of VS, and measure phase angle Ø

AC Circuit Analysis: Series R-L Circuit

Process – Phasor Diagram

IS (reference ~ series circuit)

VR

VL VS Check that VS measured

here matches the actual value for VS for the circuit

Step 6: Measure the phase angle (Ø) between VS and

IS

C-I-V-I-L

AC Circuit Analysis: Series R-L Circuit Process

 Final Answer

 IS is … Amps and LAGS/LEADS the VS by …oE

 Note: We always describe what the CURRENT is doing with respect to the VOLTAGE, irrespective

of which is the reference.

AC Circuit Analysis: Series R-L Circuit

AC Circuit Analysis: Series R-L Circuit

L=0.25H

VS=230Vƒ= 50Hz

R = 100Ω

Determine the following:

•Impedance Z

•Supply current IS

•Voltage across Resistor VR

•Voltage across Inductor VL

•Phase Angle Ø between

VS and IS

AC Circuit Analysis: Series R-L Circuit

AC Circuit Analysis: Series R-C Circuit

C = 100μF

VS=230Vƒ= 50Hz

R = 68Ω

The process for analysing a Series R-C circuit is exactly the same

as for a series R-L, except that the capacitive reactance (X C )

formula is used instead of the inductive reactance (X L ) formula.

AC Circuit Analysis: Series R-C Circuit Process

 Step 1: Determine Capacitive Reactance XC

AC Circuit Analysis: Series R-C Circuit

Step 6: Measure the phase angle (Ø) between VS and

IS

C-I-V-I-L

AC Circuit Analysis: Series R-C Circuit

AC Circuit Analysis: Series R-C Circuit

C = 33μF

VS=230Vƒ= 50Hz

R = 22Ω Determine the following:

•Impedance Z

•Supply current IS

•Voltage across Resistor VR

•Voltage across Capacitor VC

•Phase Angle Ø between VSand IS

AC Circuit Analysis: Series R-C Circuit

AC Circuit Analysis:

Series R-L-C Circuit

L=0.25H

VS=230Vƒ= 50Hz

R = 50Ω C = 150μF

Due to the nature of the two reactive components, the inclusion of the capacitor will produce a capacitive reactance that will act to CANCEL out the inductive reactance produced by the inductor (or vice-versa) The result will be a net reactance (X)

X = X Bigger – X Smaller

AC Circuit Analysis: Series R-L-C Circuit Process

 Step 1: Determine Inductive reactance X L

AC Circuit Analysis:

Series R-L-C Circuit - Phasor Diagram

IS (reference ~ series circuit)

Step 7: Measure the phase angle (Ø) between VS and IS

C-I-V-I-L

VR+L

VL

C-I-V-I-L

AC Circuit Analysis: Series R-L-C Circuit

AC Circuit Analysis

Parallel Circuits

AC Circuit Analysis: Determining

Impedance

 Determining Impedance involves two

methods, depending upon the type of circuit being analysed.

– For SERIES circuits: requires the use of the

AC Circuit Analysis: Determining Impedance

AC Circuit Analysis:

Parallel R-L Circuit

L=0.15H

VS=230Vƒ= 50Hz

Determine the following:

AC Circuit Analysis: Parallel R-L

 Step 3: Draw a scaled phasor diagram

 Supply Voltage as REFERENCE

 Use phasor addition to determine the Supply Current (IS)

 Measure phase angle Ø

 Step 4: Determine Impedance Z

 Z = VS / IS

Measure the phase angle (Ø) between VS and IS

C-I-V-I-L

AC Circuit Analysis: Parallel R-L

AC Circuit Analysis:

Parallel R-C Circuit

VS=230Vƒ= 50Hz

Determine the following:

AC Circuit Analysis: Parallel R-C

AC Circuit Analysis: Parallel R-L-C

Circuit

L=0.15H

VS=230Vƒ= 50Hz

AC Circuit Analysis: Parallel R-L-C

 Step 3: Draw a scaled phasor diagram

 Supply Voltage as REFERENCE

 Use phasor addition (IR and IL and IC) to determine the Supply Current (IS)

 Measure phase angle Ø

 Step 4: Determine Impedance Z

 Z = VS / IS

AC Circuit Analysis:

Parallel R-L-C Circuit - Phasor Diagram

VS (reference ~ parallel circuit)

Step 6: Measure the phase angle (Ø) between IS and

AC Circuit Analysis: Parallel R-L-C Circuit

Parallel R-L-C Circuit

L=600mH

VS=230Vƒ= 50Hz

AC Circuit Analysis: Parallel R-L-C Circuit

AC Circuit Analysis

 Now complete the prac on Analysis of R-L-C circuits