Topic 3 resistance in AC circuits topic a3

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 3: Resistance in

AC Circuits Part A

Resistance in AC Circuits

 Resistive Component

– Any device that consists of a ‘conductor’ with an atomic

structure that does not allow electrons to move as easily as

a normal conductor

– A resistive component’s function is to convert electrical

energy into heat energy

 Key Characteristic

CURRENT

– It achieves this by slowing the flow of electrons by not

allowing them to cascade through as quickly

Resistance in AC Circuits

 Symbol ~ R

 Unit of measurement ~ OHMS (Ω)

Resistance in AC Circuits

 In a purely resistive AC circuit, the circuit can

be analysed using the same principles as DC circuits.

– Ohm’s Law

– Resistors in Series

– Resistors in Parallel

– Kirchoff’s Voltage Law

– Kirchoff’s Current Law

Resistance in AC Circuits: Ohm’s Law

VR

Ohm’s Law – Resistive component Simple Resistive Circuit

VR

VS ƒ

IR

R

Resistance in AC Circuits: Resistance

in Series and Parallel

R1

VS ƒ

VS ƒ

IS

R2

Resistance in Series

RTotal= R1+R2+…

Resistance in Parallel

1 = 1 + 1 +…

RTotal R1 R2…

Kirchoff’s Voltage Law: Series

Resistive Circuit

R1

VS ƒ

R2 Kirchoff’s Voltage Law

•The ‘sum’ of the voltage drops in the circuit will equal the supply voltage

Vs = VR1 + VR2+…

[Purely resistive circuit only]

Parallel Resistive Circuit

VS ƒ

IS

R1

R2

Kirchoff’s Current Law

•The ‘sum’ of the currents entering

a junction will be equal to the sum

of the currents exiting the junction.

Is = IR1 + IR2+…

[Purely resistive circuit only]

IR2

IR1

Power in a Resistive Circuit

 Since a resistor converts electrical energy into heat, then POWER is dissipated.

 This can be calculated by:

P = VI

Or

P = I2R

Or

P = V2/R

Resistance In AC Circuits: Exercises

VS=230V ƒ=50Hz

IS

R2

R3

R1

IR3

100Ω

Determine:

•RTotal

•I S

•VR2

•IR3

•PR2 Question 1:

Resistance In AC Circuits: Exercises

 Answers

 RTotal = 94.4Ω

 IS = 2.44A

 VR2 = 108V

 IR3 = 1.08A

 PR2 = 146W

Resistance In AC Circuits: Exercises

VS=50V ƒ=50Hz

IS=4A

R2

R3

R1

IR3

20Ω

Determine:

•IR2

•R 2

•PR1

IR2 Question 2:

Resistance In AC Circuits: Exercises

 Answers

 IR2 = 2.5A

 R2 = 12Ω

 PR1 = 80W

Resistance In AC Circuits: Exercises

VS=? V ƒ=50Hz

IS

Determine:

•VS

•I S

•R2

R2

R3

R4

IR3=1.5A

5Ω

? Ω

10Ω

IR2

R1 25Ω

IR4=2A Question 3:

Resistance In AC Circuits: Exercises

 Answers

 VS = 25V

 IS = 3A

 R2 = 30Ω

 At this stage, you should have a clear understanding

of resistance in AC circuits, including:

– Understand the concept of resistance in AC circuits;

– Understand the application of Ohm’s Law;

– Understand and be able to apply Kirchoff’s Voltage law to a purely resistive circuit;

– Understand and be able to apply Kirchoff’s current Law to a purely resistive circuit;

– How to make calculations involving V, I, R, and P in

combined series/parallel circuits