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
Trang 1Solve problems in single and
three-phase low voltage circuits
Topic 4: Inductance in
AC Circuits Part A
Trang 2Inductance in AC Circuits
Inductive Component
into a coil consisting of many turns, normally wound around some form of iron core
(and store) energy in an electromagnetic field
Trang 3Inductance in AC Circuits
Key Characteristic
CHANGE IN CURRENT
either oppose an increase in current, or resist a decrease in current
INDUCTANCE, symbol L, measured in Henries (H)
L
Trang 4Inductance in AC Circuits
Effect in an AC circuit
changing (ie alternating between positive flow and negative flow), an inductive component in an AC circuit continually acts to oppose the change in
current
constant opposition to the flow of alternating
current
Trang 5Inductance in AC Circuits
This opposition to alternating current flow is called INDUCTIVE REACTANCE.
Where:
– XL is the inductive reactance in Ohms (Ω)
– 2π is a constant
– ƒ is the frequency in Hertz (Hz)
– L is the inductance in Henries (H)
XL = 2π ƒ L
Trang 6Inductance in AC Circuits
Important!
current flow like RESISTANCE, but it is NOT the same as resistance, even though both are
measured in Ohms
RESISTANCE can NOT be simply added to find the total opposition to current flow in a circuit
Trang 7Inductance in AC Circuits
Key Advantages
electromagnetic field
WITHOUT consuming a large quantity of power (not heating excessively), unlike a resistor
Trang 8Inductance in AC Circuits
Examples of Inductive Components
Trang 9Inductance in AC Circuits: Ohm’s Law
VL
IL XL Ohm’s Law – Inductive component Simple Inductive Circuit
VL
VS ƒ
IL
L
Trang 10Inductive Reactance: Exercises
VS=230V ƒ=50Hz
IL=?
L=0.25H
VS=230V ƒ=50Hz
IL=7.32A
L=?
Q1 Determine:
Inductive reactance XL, and
Current though inductor IL
Q2 Determine:
Inductive reactance XL, and Inductance of inductor L
Trang 11Inductive Reactance: Exercises
A 230V, 50Hz AC supply is to be applied to a fluorescent light fitting If the current for the lamp needs to be limited to 0.8A max,
determine the appropriate value of
inductance required by the ballast.
Trang 12Inductance in AC Circuits: Inductance
in Series and Parallel
L1
VS ƒ
VS ƒ
IS
L2
L1
L2
Inductive Reactance in Series
X L Total= X L1+X L2+…
Inductive Reactance in Parallel
1 = 1 + 1 +…
X L Total X L1 X L2…
Trang 13Series Inductive Circuit
L1
VS ƒ
L2
Kirchoff’s Voltage Law
•The ‘sum’ of the voltage drops in the circuit will equal the supply voltage
Vs = VL1 + VL2+…
[Purely Inductive circuit only]
VL1 VL2
Trang 14Parallel Inductive Circuit
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 = IL1 + IL2+…
[Purely Inductive circuit only]
VS ƒ
IS
L1
L2
IL2
IL1
Trang 15Inductance in AC Circuits: Exercises
Determine
•XL Total
•IS
•IL2
VS=230V ƒ=50Hz
IS
L2=2.4H
L3=1.2H
IL3
IL2
L1=1.6H
IL1
L1=0.25H
VS=230V ƒ=50Hz
L2=0.1H L3=0.2H
Determine:
•XL Total
•IS
•VL3
IS
Trang 16Inductance in AC Circuits: Exercises
Q1 Answers: Series
– XL Total = 172.79 Ω
– IS = 1.33 A
Trang 17Inductance in AC Circuits: Exercises
Q2 Answers: Parallel
– XL Total = 167.6 Ω
– IS = 1.37 A
Trang 18of inductance in AC circuits, including:
– Understand the concept of inductive reactance;
– Understand the application of Ohm’s Law to inductive
circuits;
– Understand and be able to apply Kirchoff’s Voltage law to a purely inductive circuit;
– Understand and be able to apply Kirchoff’s current Law to a purely inductive circuit;
– How to make calculations involving V, I, and XL in
series/parallel circuits.