Transcript 150LECTURE12CHAPTER12TRANSFORMERS Lecture Notes Page

FOWLER CHAPTER 12
LECTURE 12 TRANSFORMERS
TRANSFORMERS CHAPTER 12
TRANSFORMERS ARE MULTIPLE WINDING INDUCTORS.
WORK ON THE PRINCIPLE OF MUTUAL INDUCTANCE.
TRANSFORMERS ARE 2 OR MORE COILS LINKED BY MAGNETIC FLUX.
PRIMARY COIL INDUCES A VOLTAGE IN A SECONDARY COIL BY MUTUAL INDUCTANCE.
THE AMOUNT OF MUTUAL OR SELF INDUCTION IS MEASURED IN HENRY’S.
Electrical Transformer Tutorial
http://www.youtube.com/watch?v=GMePE7NZcxw
How electric motors work
http://www.youtube.com/watch?v=Q2mShGuG4RY
YOU TUBE: Transformer Animation
YOU TUBE: How Transformers Work
http://www.youtube.com/watch?v=VucsoEhB0NA
http://www.youtube.com/watch?v=ZjwzpoCiF8A
SYMBOLS
TRANFORMER WINDINGS
TRANSFORMERS TRANSFER POWER FROM PRIMARY TO SECONDARY WINDINGS.
PRIMARY TAKES ELECTRICAL ENERGY AND CONVERTS IT TO MAGNETIC ENERGY
SECONDARY TAKES MAGENTIC ENERGY AND CONVERTS IT TO ELECTRICAL ENERGY.
THERE IS NO PHYSICAL COUPLING BETWEEN THE PRIMARY AND SECONDARY WINDINGS.
STEP UP/DOWN TRANSFORMERS
STEP UP
STEP DOWN
COEFFICIENT OF COUPLING (COC)
THE PORTION OF FLUX THAT LINKS ONE COIL TO ANOTHER.
COC CAN VARY FROM 0 TO 1.
AT 1, ALL THE FLUX IS COUPLED.
COC CAN ALSO BE EXPRESSED. AS A %.
100% = COUPLING OF 1.
COUPLING IN Fe CORE TRANSFORMERS IS NEARLY 100%. SINCE THERE IS
LITTLE FLUX LEAKAGE INTO THE AIR.
AIR CORE TRANSFORMERS HAVE LOW COC DUE TO THE HIGH RELUCTANCE OF AIR,
CAUSING A LARGE AMOUNT OF LEAKAGE.
THIS IS CALLED LEAKAGE FLUX.
THIS CAN BE CONTROLLED SOMEWHAT BY SPACING THE COILS CLOSER TOGETHER.
IF COILS ARE PERPENDICULAR TO EACH OTHER COC IS CLOSE TO ZERO.
CHANGING VOLTAGE VAULES
STEP UP, STEP DOWN TRANSFORMERS.
WITH 100% COULPING THE TURNS RATIO AND VOLTAGE RATIO ARE EQUAL.
ADVANTAGES OF HIGH VOLTAGE TRANSMISSION LINES
STEP UP TRANSFORMER
AT POWER PLANT
20KV
500A
10 MW
400KV
25A
10 MW
LONG DISTANCE
TRANSMISSION LINES
STEP DOWN DISTRIBUTION
TRANSFORMER AT SUBSTATION
400KV
25A
20KV
500A
10 MW
TO LOADS AND OTHER
STEP DOWN
TRANSFORMERS.
EFFICIENCY OF TRANSFORMERS
IN THE REAL WORLD CORES AND COILS OF TRANSFORMERS CONVERT SOME ELECTRICAL
ENERGY INTO HEAT.
EFFICIENCY OF TRANSFORMERS IS EXPRESSED IN TERMS OF POWER.
PSEC
% EFFICIENCY 
100
PPRI
EX.12-3 P309 WHAT IS THE EFFICIENCY OF A TRANSFORMER WITH A INPUT OF1880W INTO
THE PRIMARY COIL AND 1730W OF OUTPUT FROM THE SECONDARY COIL.
PSEC
% EFFICIENCY 
100
PPRI
1730
100  92%
1880
1880  1730  150W
% EFFICIENCY 
150W LOSS, CALLED POWER LOSS.
POWER LOSS IN TRANSFORMERS IS CAUSED BY:
1.HYSTERSIS LOSS: CAUSED BY RESIDUAL MAGNETISM LEFT IN THE CORE EACH
TIME THE FIELD REVERSES, WHICH CAUSES HEAT LOSS.
HYSTERSIS LOOP, THE NARROWER THE LOOP, THE LESS THE LOSS.
HYSTERSIS LOSSES INCREASE WITH THE FREQUENCY OF PRIMARY CURRENT.
Steel has a "fat" hysteresis loop. It is difficult to demagnetize, so steel is used
for permanent magnets. Substances, such as soft iron, with thin hysteresis
loops, are used for transformer cores.
Eddy Currents, Magnetic Braking and Lenz's Law
http://www.youtube.com/watch?v=otu-KV3iH_I
2. EDDY CURRENT LOSS
ARE INDUCTED CURRENTS IN THE CORE FROM ITS OWN MAGNETIC FLUX.
THESE EDDY CURRENTS FLOWING THRU THE CORES RESISTANCE PRODUCES HEAT.
What Is Eddy Current
http://www.youtube.com/watch?v=zJ23gmS3KHY
HOW CAN WE REDUCE EDDY CURRENT LOSES?
BY INSULATING EACH LAMINATION OF THE CORE WITH A THIN LAYER OF OXIDE.
THIS INCREASES THE RESISTANCE OF THE CORE WHICH REDUCES HEAT LOSS SINCE,
I
V
V
AS R , I 
R
R
Eddy Current Demo. http://www.youtube.com/watch?v=Yu1uRvErM80
3. COPPER LOSS
POWER LOSS IN THE WINDINGS OF THE TRANSFORMER.
CAN BE FOUND FROM P= I²R, R IS THE OMIC RESISTANCE OF THE WINDING TURNS.
LOSS AND EFFICIENCY
TRANSFORMERS ARE MOST EFFICIENT WHEN FULLY LOADED.
EFFICIENCY DECREASES AS THE LOAD DECREASES.
WHY? CURRENT FLOW IN THE TRANSFORMER PRIMARY DOES NOT DECREASE IN DIRECT
PORPORTION TO THE DECREASE IN LOAD.
PRIMARY CURRENT CAUSES CORE AND Cu LOSS WHEN LIGHTLY LOADED.
TRANSFORMER CORES.
CLASSIFIED BY CORE MATERIALS. SUCH AS Fe AND AIR CORE, I AND E LAYERS ALTERNATE
IN STACKING WHEN BUILDING THE CORE. MAKES AN AIR GAP WHICH HELPS KEEP
THE INDUCTANCE MORE CONSTANT FOR DIFFERENCE CURRENTS.
Disassembling laminated transformer core
http://www.youtube.com/watch?v=B8fTLXs50lU
TYPES OF TRANSFORMERS
CLASSIFIED BY USE: POWER TRANSFORMERS, @ 60Hz, FROM 115 TO 1000’S VOLTS.
USED FOR POWER DISTRIBUTION AND LIGHTING.
CONTROL TRANSFORMERS :USED BY SMALLER RECTIFIERS AND CONTROL CIRCUITS
USING RELAYS SOLENOIDS.
AUDIO TRANSFORMERS. WORK AT FREQUENCIES UP TO 20KHz.
RF TRANSFORMERS f (RADIO RANGES) CAN BE Fe OR AIR CORE.
CONSTANT VOLTAGE TRANSFORMERS:
PROVIDE STABLE SECONDARY VOLTAGE, DESPITE VARING PRIMARY VOLTAGE.
ISOLATION TRANSFORMER
HAVE EQUAL PRIMARY AND SECONDARY VOLTAGE, USED TO ISOLATE ELECTRICAL
EQUIPMENT FROM THE POWER DISTRIBUTION SYSTEM.
VARIOUS ISOLATION TRANSFORMERS
MORE ISOLATION TRANSFORMERS
AUTO TRANSFORMER: PRIMARY WINDING IS PART OF THE SECONDARY WINDING AND
VICE-VERSA.
1,000 MVA, 1050/525kV single-phase autotransformer
VARIABLE TRANSFORMER: WORK AT POWER FREQUENCIES. THESE ARE
AUDIOTRANSFORMERS WITH AN ADJUSTABLE SECONDARY.
IMPEDANCE MATCHING (IM) P.317
THIRD MOST COMMON USE FOR TRANSFORMERS IS IM
WHY? WHEN IM OF SOURCE IS MATCHED TO IM OF THE LOAD. MAX. POWER TRANSFER OCCURS.
A TRANSFORMER CAN MAKE A LOAD APPEAR TO THE SOURCE LARGER OR SMALLER THEN IT
ACTUAL IS.
REFLECTED IMPEDANCE (Z) FROM THE SECONDARY
APPEARS TO THE PRIMARY AS BEING EQUAL.
TRANSFORMER RATINGS
VOLTAGE RATING ARE SPECIFIED FOR PRIMARY AND SECONDARY
WINDINGS UNDER LOAD AND NO LOAD CONDITIONS.
POWER RATINGS:
GIVEN IN WATTS GOING TO A RESISTIVE LOAD
Full Load Current Ratings of Self-CooledThree-Phase Transformers208 -7200V
Line to Line Voltage
kVA
208
240
480
600
2400
4160
7,200
30
83.3
72.2
36.1
28.9
7.22
4.16
2.41
45
125
108
54.1
43.3
10.8
6.25
3.61
75
208
180
90.2
72.2
18.0
10.4
6.01
112.5
312
271
135
108
27.1
15.6
9.02
150
416
361
180
144
36.1
20.8
12.0
225
625
541
271
217
54.1
31.2
18.0
300
833
722
361
289
72.2
41.6
24.1
500
1,388
1,203
601
481
120
69.4
40.1
750
2,082
1,804
902
722
180
104
60.1
1,000
2,776
2,406
1,203
962
241
139
80.2
1,500
4,164
3,608
1,804
1,443
361
208
120
2,000
.....
4,811
2,406
1,925
481
278
160
2,500
.....
.....
3,007
2,406
601
347
200
3,000
.....
......
3,609
2,887
722
416
241
3,750
.....
.....
4,511
3,608
902
520
301
5,000
.....
......
.....
4,811
1,203
694
401
7,500
.....
.....
......
.....
1,804
1,041
601
10,000
.....
......
.....
.....
2,406
1,388
802
SERIES AND PARALLEL WINDINGS P.230
SOME TRANFORMERS CAN BE BUILT WITH MULTIPLE PRIMARY AND SECONDARY
WINDINGS WHICH CAN BE CONNECTED IN SERIES OR PARALLEL.
3 PHASE TRANSFORMERS
500 KVA 3 PHASE TRANSFORMERS
3 PHASE TRANSFORMER UNDER CONSTRUNTION
ULTIMATE USE FOR TRANSFORMERS: A SUPERCONDUCTING FUSION REACTOR
MAGNETIC CONFINMENT CONTAINTER FOR A PLASMA FUSION REACTOR
DRAWING SHOWING HOW MAGNETIC FIELDS COMPRESS 1 MILLION DEGREE PLASMA
INTERIOR OF A FUSION REACTOR