FOWLER CHAPTER 11 LECTURE 11 INDUCTANCE
Dec 23, 2015
FOWLER CHAPTER 11LECTURE 11 INDUCTANCE
INDUCTANCE, CHAPTER 11OPPOSES CHANGE OF CURRENT IN A CIRCUIT.DEVICES THAT USE INDUCTANCE (L) ARE CALLED INDUCTORS.A.K.A. AS CHOKES, REACTORS, COILS.INDUCTANCE IS THE RESULT OF A VOLTAGE INDUCTED IN A CONDUCTOR FROM A MAGNETIC FIELD.
CES 2009 - Kitchen of the Future From Powermat
http://www.youtube.com/watch?v=Z9a_Ihhtnx4
WHEN CURRENT FLOWS A MAGNETIC FIELD IS CREATED AROUND THIS WIRE. THIS EXPANDINGFIELD INDUCES ITS OWN SMALL VOTAGE IN THE WIRE.IF THE FLUX IS EXPANDING, POLARITY IS IN THE SAME DIRECTION AS THE CURRENT FLOW IN THE WIRE.IF THE FLUX IS COLLASPING, THE FLUX INDUCED IN THE WIRE IS OF THE OPPOSITE POLARITY.
IF THE FLUX IS COLASPING, THE FLUX INDUCES A CURRENT IN THE WIRE OF THE OPPOSITE POLARITY.THIS IS CALLED SELF INDUCTANCE.
INDUCTANCE OF A WIRE CAN BE INCREASED BY FORMING THE WIRE IN A COIL.
http://www.youtube.com/watch?v=NgwXkUt3XxQInductor basics
http://www.youtube.com/watch?v=X2e9x104AnEDC Theory 13 Segment 3A - Inductance & the Inductor
MUTUAL INDUCTANCE P278
OCCURS WHEN THE MAGNETIC FIELD FROM ONE WIRE INDUCTS A CURRENT IN A SEPARATEWIRE. TRANSFORMERS WORK USING MUTUAL INDUCTANCE.
YOU TUBE:DC THEORY 13 SEGMENT 3B http://www.youtube.com/watch?v=aphgli-RHm0
CONTERELECTROMOTIVE FORCE (CEMF) P.278IS THE VOLTAGE INDUCED IN A CONDUCTOR BY ITS OWN MAGNETIC FIELD IS CALLEDCOUNTER EMF OF BACK EMF.
LENZ’S LAWA CEMF POLARITY ALWAYS OPPOSES THE CURRENT THAT CREATED IT.
Eddy Currents and Lenz's Law http://www.youtube.com/watch?v=kU6NSh7hr7Q
ENERGY STORAGE AND CONVERSION. P.279
CURRENT FLOW THRU A CONDUCTOR CREATES A MAGNETIC FIELD.
INDUCTORS CONVERT ELECTRICAL ENERGY INTO MAGNETIC ENERGY.
AS CURRENT DECREASES MAGNETIC ENERGY IS CONVERTED BACK TO ELECTRICALENERGY.
INDUCTANCE DOES NOT CONVERT ELECTRCIAL ENERGY INTO HEAT, ONLY RESISTANCE CAN.
http://www.youtube.com/watch?v=STDlCdZnIswMAKE presents: The Inductor
FOR THESE 2 QUARTER CYCLES,ENERGY IS TAKEN FROM THE CURRENT. (ELECTRICAL TO MAGNETIC)
FOR THESE 2 QUARTER CYCLES, ENERGY IS RETURNED TO THE CURRENT. (MAGNETIC TO ELECTRICAL)
INDUCTORS CAUSE NO NET ENERGY LOSS.
I
INDUCTANCE OF A INDUCTOR DEPENDS ON 4 FACTORS.
1. TYPE OF CORE MATERIAL; AIR OR IRON CORE. Fe IS BETTER THEN AIR, SINCE ITS PERMEABILITY IS HIGHER ( ABILITY TO CONDUCT FLUX). CARRIES MORE FLUX. MORE FLUX CHANGE, MORE CEMF.
HENRY P. 2801 HENRY (H) PRODUCES 1 V OF CEMF THE WHEN CURRENT CHANGES AT A RATE OF 1A/S.
2.THE # OF TURNS OF WIRE; MORE TURNS, GREATER THE MAGNETIC FIELD.
3.THE DIAMETER OF THE COIL (CORE): WITH LARGER COIL DIAMETERS ALL THE FLUX LINES GO THRU THE COIL, WHICH INCREASES THE FLUX DENSITY.
4.SPACING BETWEEN TURNS OF WIRE: WHEN DISTANCE DECREASES, FIELD STRENGTH INCREASES,SINCE FLUX LINES LINK TOGETHER.
TYPES OF INDUCTORS P.282CLASSIFIED BY THE TYPE OF MATERIAL USED FOR THE CORE. CAN BE FIXED OR VARIABLE.CORES CAN MAGNETIC OR NONMAGNETIC.
INDUCTOR SYMBOLS
IN VARIABLE INDUCTORS, INDUCTION IS CHANGED BY MOVING THE POSITION OF THE CORE.
AIR CORE
OFTEN WAPPED AROUND NONMAGENTIC FORM WITH HIGH RELUCTANCE (ABOUT THESAME AS AIR.) OTHER AIR CORE MATERIALS USED:CERAMIC, PHENOLIC (HARD RESIN, MADEOF PHENOL) , USUALLY LESS THAN 5mH.
FERRITE (Fe ALLOY ), POWERED CORE, L LESS THAN 200mH
FERRITE CORE IN AM RADIO ANTENNAS
TOROID CORE: FLUX LOOPS ALL EXIST INSIDE THE CORE.
SMD INDUCTORS: L RANGES FROM nH TO mH
Fig. 11-11 Surface mount inductor positioned in the end of a small paper clip.
MOLDED INDUCTORSARE INCASED IN INSULATION MATERIAL TO PROTECT WINDINGS,CORES CAN BE AIR, FERRITE, POWERED Fe.
Band 1 2 3 4
Meaning
1st Digit
2nd Digit
Multiplier (No. of zeros)
Tolerance %
Gold x 0.1 (divide by 10) +/-5%
Silver x 0.01 (divide by 100) +/-10%
Black 0 0 x1 (No Zeros) +/-20%
Brown 1 1 x10 (0)
Red 2 2 x100 (00)
Orange 3 3 x1000 (000)
Yellow 4 4 x10000 (0,000)
Green 5 5
Blue 6 6
Violet 7 7
Grey 8 8
White 9 9
SHIELDED INDUCTORS
SHIELDED FROM EXTERNAL MAGNETIC FILEDS TO PREVENT INTERFERENCE.SHEILD ITSELF IS MADE FROM MAGNETIC MATERIAL.
LAMINATED Fe CORE.L RANGES FROM 0.1 H TO 100H.MADE FROM E AND I LAMINATIONS, STACKED TOGETHER FOR DESIRED THICKNESS.
WINDINGS ARE PLACED ON THE CENTER OF THE “E”. THIS SECTION IS TWICE AS THICK,SINCE IT CARRIES TWICE AS MUCH FLUX.
INDUCTION DEPENDS ON THE AMOUNT OF CURRENT FLOWING THRU IT.PERMABILITY DECREASES AS FLUX INCREASES.WHEN SATURATED ALMOST NO CHANGE IN FLUX OCCURS.
l
3 PHASE TRANSFORMER
3 PHASE TRANSFORMER CORES.
FILTER CHOKES P. 285
AKA LAMINATED Fe CORE INDUCTORSUSED IN POWER SUPPLIES TO SMOOTH OUT PULSATING D.C.
RF CHOKES USED IN HIGH FREQUENCY RADIO’S ETC.
RATING OF INDUCTORS.RATED BY:1. DC RESISTANCE: THE RESISTANCEOF WIRE IN THE COIL, CALLED OHMIC RESISTANCE.
2. CURRENT: AMOUNT OF CURRENT INDUCTOR CAN CARRY WITHOUT HEATING.
3. VOLTAGE: HOW MUCH VOLTAGE THE WINDING INSULATION CAN HANDLE BEFORE BREAKING DOWN.
4. QUALITY: RATIO OF REACTANCE TO RESISTANCE. HIGHER THE QUALITY THE BETTER.
5.TOLERANCE: +/- 1% COSTLY +/- 10% TYPICAL
INDUCTORS IN DC CIRCUITS.
INDUCTORS IN DC CIRCUITS FORCE CURRENT TO RISE SLOWLY.THIS IS DUE TO THE INDUCTORS CEMF.THE TIME FOR THIS TO OCCUR DEPENDS ON THE AMOUNT OF INDUCTANCE AND RESISTANCE.
IDEAL INDUCTORS IN AC CIRCUITS
IDEAL INDUCTORS HAVE NO RESISTANCE.NO ENERGY CONVERSION TAKES PLACE.NO ELCTRICAL ENERGY IS CONVERTED TO HEAT.INDUCTORS CONTROL CIRCUIT CURRENT WITHOUT POWER LOSS.
INDUCTIVE REACTANCE ( XL)
OPPOSITION OF AN INDUCTOR TO AC. XL COMES FROM THE CEMF OF THE INDUCTOR.VOLTAGE LEADS CURRENT BY 90° IN A IDEAL INDUCTOR.
XL
INDUCTIVE REACTANCE EQUATION
XL =2πfL = 6.28fLXL IS DIRECTLY PROPORINAL TO FREQUENCY f AND INDUCTANCE LWHY?1. AS f INCREASES I CHANGES MORE RAPIDLY, MORE CEMF AND REACTANCE ARE PRODUCED.2. AS L INCREASES THE MORE FLUX CHANGES AS THE CURRENT CHANGES. DO E. 11-1 P.289
OHM’S LAW FOR XL
VL = ILXLDO E.11-3 P.290
POWER IN INDUCTORS
IDEAL INDUCTOR USES NO POWER SINCE I AND V ARE 90° OUT OF PHASE.
P = IVcosØ , SINCE I AND V ARE 90° OUT OF PHASE COS90° = 0THEREFORE P = IV(0) = 0W
NO NET CONVERSION OF ENERGY TAKES PLACE.
ENERGY IS TRANSFERED BACK AND FORTH BETWEEN THE SOURCE AND THE INDUCTOR.F.11-23 P.291
REAL INDUCTORS IN AC CIRCUITS.REAL INDUCTORS USE POWER, SINCE THEY HAVE RESISTANCE AS WELL AS REACTANCE.
QUALITY: Q = XL/RTHE HIGHER THE Q OF A COIL ,THE LESS POWER IT USES.
IMPEDANCE (Z)COMBINATION OF RESISTANCE AND REACTANCE.SINCE INDUCTORS HAVE BOTH RESISTANCE AND REACTANCE, THERE IS IMPEDANCE IN AC CIRCUITS. SINCE REACTANCE IS HIGH AND RESISTANCE IS LOW. WE CAN SPECIFIC ANY INDUCTOR INTERMS OF ITS REACTANCE ONLY.
POWER LOSS IN INDUCTORSSKIN EFFECT :ELECTRONS MOVE TO OUTER SURFACE OF A CONDUCTOR AT HIGHER f, CAUSES INCREASED RESISTANCE WHICH CAN BE MEASURED WITH A VOM.
EFFECTIVE RESISTANCE AT INCREASED f IS GREATER THEN THAT MEASURED WITH A VOM.
LITZ WIREMULTICONDUCTOR CABLE OF APPROX. 44 GAUGE, INSULATED WIRE TWISTED TOGETHER, WHICH PROVIDES MORE SURFACE AREA THEN A SINGLE STRANDED CONDUCTOR, WHICH RESULTS IN LOWER RESISTANCE AT HIGHER f.
POWER LOSS IN Fe CORE INDUCTORS1. LOSS FROM CORE MATERIAL, CAUSED BY CURRENT HEATING FROM INDUCTED
VOLTAGES. 2.LOSS IN WINDINGS, HEATING CAUSED BY THE REVERSALS OF MAGNETIC FIELD.
INDUCTORS IN PARALLEL ( FINDING TOTAL INDUCTANCE)SAME AS RESISTORS IN PARALLEL
nT LLLLL
1....
1111
321
21
21
LL
LLLT
GENERAL METHOD
TWO INDUCTORS IN PARALLEL
N EQUAL INDUCTORS IN PARALLEL
n
LLT
INDUCTIVE REACTANCE IN PARALLEL
LnLLL
L
XXXX
XT 1
...111
1
321
21
21
LL
LLL XX
XXX
T
n
XX LLT
GENERAL METHOD
TWO INDUCTORS IN PARALLEL
N EQUAL INDUCTORS IN PARALLEL
YOU CAN FIND XLT BY THE ABOVE METHOD OR
TL LfXT
28.6IN PARALLEL INDUCTOR CIRCUITS THE LOWEST VALVE INDUCTOR CARRIES THE MOST CURRENT.
INDUCTORS IN SERIES P.295SERIES INDUCTANCES AND REACTANCES USE THE SAME FORMUALS AS SERIES RESISTORS.
nT LLLLL ...321
nLLLLTL LXXXX ...321
YOU CAN FIND XLT BY THE ABOVE METHOD OR
TL LfXT
28.6
OHM’S LAW
TTT LLL XIV
DC Electronics Theory 13 Segment 5 - Connecting Inductors http://www.youtube.com/watch?v=GXcxswDcUbI
TIME CONSTANTS FOR RL CIRCUITS
SIMILAR TO RC TIME CONSTANT, EXCEPT SUBSITUDE CURRENT FOR VOLTAGE
TIME CONSTANT(T) T = L/R
http://www.youtube.com/watch?v=-vznuNkEBtoRL TIME CONSTANT
1 2 3 4 5
100%
of
fin
al c
urr
ent
Time constants0
0
RL Time Constant -- Rising I
After 1 T, the inductor’s current is 63.2 % of final value. After 2 T, the inductor’s current is 86.5 % of final value.
After 3 T, the inductor’s current is 95.0 % of final value.After 4 T, the inductor’s current is 98.2 % of final value.
After 5 T, the inductor’s current is 99.3 % of final value.
The current has essentially reached its final value after 5 T.
After 1 T, the current is reduced by 63.2 % .After 2 T, the current is reduced by 86.5 % .
After 3 T, the current is reduced by 95.0 % .After 4 T, the current is reduced by 98.2 % .
After 5 T, the current is reduced by 99.3 % .
The current is essentially zero after 5 T.
Time constants0 1 2 3 4 5
100
0
% o
f st
arti
ng
curr
ent
RL Time Constant -- Falling I
36.8%
13.5%5.0% 1.8% 0.7%
PREVENTING MUTUAL INDUCTANCE
1. BY ORIENTATION OF THE AXIS.2. PHYSICAL SEPARATION3. SHEILDING
INDUCTORS IN SERIES P.295SERIES INDUCTANCES AND REACTANCES USE THE SAME FORMUALS AS SERIES RESISTORS.
nT LLLLL ...321
nLLLLTL LXXXX ...321
YOU CAN FIND XLT BY THE ABOVE METHOD OR TL LfXT
28.6OHM’S LAW FOR INDUCTORS
TTT LLL XIV
TOTAL INDUCTANCE
INDUCTIVE REACTANCE
INDUCTORS IN PARALLEL ( FINDING TOTAL INDUCTANCE)SAME AS RESISTORS IN PARALLEL
nT LLLLL
1....
1111
321
21
21
LL
LLLT
GENERAL METHOD
TWO INDUCTORS IN PARALLEL
N EQUAL INDUCTORS IN PARALLELn
LLT
LnLLL
L
XXXX
XT 1
...111
1
321
21
21
LL
LLL XX
XXX
T
n
XX LLT
GENERAL METHOD
TWO INDUCTORS IN PARALLEL
N EQUAL INDUCTORS IN PARALLEL
YOU CAN FIND XLT BY THE ABOVE METHOD OR
TL LfXT
28.6
321 LLLL IIIIT
TOTAL CURRENTNT LLLLL IIIII
321
TOTAL CURRENT