Download Transformers

Rad Physics Review 2
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Transformers
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A transformer changes the intensity of
alternating voltage and current.
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Mutual Induction
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Transformers
A device in which two coils are placed near one another without electrical
connection. The number of turns in the coils differs, causing a change in currnet
in the secondary coil; this serves to either increase or decrease the voltage.
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http://harphys.com/wp-content/uploads/2010/10/transformermovie-clip.swf
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Types of transformers
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Air core
Open core
Closed core
Shell type
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Air core transformer
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Open core transformer
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Closed core transformer
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Shell type transformer
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Step up vs Step-down
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If you increase the number of turns on the right, the voltage coming off the
transformer will increase in proportion.
Using the numbers in the example above, you can see that the right side has
four times more turns. As a result, the voltage on the right has increased
four times (from 100 V to 400 V). The voltage has been stepped up by a factor
of four.
Because current is inversely proportional to voltage, you can see that stepping
up the voltage pays a price ... the current on the right is only a quarter of what it
was on the left. Step-up transformers increase the voltage, but decrease the
current. In our example above, the current went from 10 A to 2.5 A, a reduction
of by a factor of four
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If you decrease the number of turns on the right, the voltage coming off the
transformer will decrease in proportion.
Using the numbers in the example above, you can see that the right side has
one fifth the number of turns. As a result, the voltage on the right is only
one-fifth as large. The voltage has been stepped down by a factor of five (1000
V down to 200 V).
Because current is inversely proportional to voltage, you can see that stepping
down the voltage gives a bonus ... the current on the right is five times what it
was on the left. Step-down transformers decrease the voltage, but increase the
current. In our example above, the current went from 2 A to 10 A, an increase by
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a factor of five.
Transformer law
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Ns
Np
If the turns ratio is greater than 1 the transformer is a step-up transformer.
If the turns ratio is less than 1 the transformer is a step-down transformer
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Autotransformer (kVp selector)
self-induction
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RECTIFICATION
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X-RAY CIRCUIT
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RECTIFICATION
PROCESS BY WHICH
ALTERNATING CURRENT IS
CHANGED TO PULSATING
DIRECT CURRENT
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ALTERNATING CURRENT
1 PHASE
A/C ( UNRECTIFIED)FREQUENCY 60 Hz
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60 POSITIVE PULSES/SEC
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60 NEGATIVERadPULSES/SEC
60 POSITIVE
PULSES
60 NEGATIVE
PULSES
120 PULSES
60 FULL CYCLES
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BATTERY – CURRENT
OUTPUT
STEADY D/C
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D/C HALF WAVE RECTIFIED
D/C HALF-WAVE – 60 POSITIVE PULSES/SEC
NEGATIVE PULSES ARE SUPPRESSED
1 Physics
PULSE/CYCLE
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D/C FULL WAVE RECTIFIED
D/C HALF-WAVE – 120 POSITIVE PULSES/SEC
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2 PULSES/CYCLE
D/C -3 PHASE 6 PULSE
CURRENT
D/C 3 PHASE 6 PULSE – 6 PULSES/CYCLE
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D/C - 3 PHASE 12 PULSE
D/C 3 PHASE 12 PULSE – 12 PULSES/CYCLE
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DIODES OR VALVE TUBES HELP
RECTIFY A/C CURRENT
ELECTRONS
DIODE
VALVE TUBE
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X-RAY TUBE FORWARD BIAS
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REVERSE BIAS
-
+
NO
X-RAY
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FORWARD vs REVERSE
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RECTIFICATION TYPES
►HALF-WAVE
►FULL WAVE
►THREE PHASE SIX PULSE
►THREE PHASE TWELVE PULSE
►HIGH FREQUENCY SINGLE PHASE
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RECTIFICATION
NO RECTIFICATION
HALF-WAVE
FULL-WAVE
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3 PHASE RECTIFICATION
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3 PHASE RECTIFICATION
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HIGH FREQUENCY
RECTIFICATION
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HALF-WAVE RECTIFICATION
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HALF-WAVE RECTIFICATION
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FULL-WAVE RECTIFICATION
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FULL-WAVE RECTIFICATION
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FULL-WAVE RECTIFICATION
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3 PHASE 6 PULSE
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3 PHASE 12 PULSE
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HIGH FREQUENCY
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VOLTAGE RIPPLE
►HALF WAVE------------------- 100%
►FULL WAVE ------------------ 100%
►3 PHASE 6 PULSE ----------- 13%
►3 PHASE 12 PULSE ---------- 4%
►HIGH FREQUENCY ---------- <1%
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RIPPLE
100%
100%
100%
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RIPPLE-3 PHASE
13%
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RIPPLE-HIGH FREQUENCY
<1%
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Home-made x-ray apparatus
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CHECKING FAILURE OF
RECTIFICATION SYSTEM
►SPINNING TOP TEST – 1 PHASE
EQUIPMENT
►SYNCHRONOUS SPINNING TOP
TEST3 PHASE WITH LONGER EXPOSURE
TIMES
►OSCILLOSCOPE- 3 PHASE
EQUIPMENT WITH SHORT
EXPOSURE TIMES
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SPINNING TOP TEST
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RESULT OF SPINNING TOP
TEST- 1 PHASE - DASHES
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HALF- WAVE RECTIFICATION
# OF DASHES = TIME (SEC) x 60 PULSES
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FULL- WAVE RECTIFICATION
# OF DASHES = TIME (SEC) x 120 PULSES
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RESULT OF SYNCHRONOUS
SPINNING TOP TEST-3PHASE
ARC
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3 PHASE RECTIFICATIONLONGER EXPOSURE TIME
DEG. OF ARC = 360°/ sec x TIME (sec)
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UTILIZING OSCILLOSCOPE
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UTILIZING OSCILLOSCOPE
RECTIFIED SYSTEM
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1. Main breaker - this is where the alternating current comes from to power the
circuit.
2. Exposure switch - when you push the button to start an exposure this switch closes
to start the exposure.
3. Autotransformer - this is where you adjust the kVp for the exposure.
4. Timer circuit - this part of the circuit stops the exposure.
5. High-voltage step-up transformer - this transformer bumps the voltage up so that
the x-ray tube has very high voltage to make the electrons have enough energy to
form x-rays.
6. Four-diode rectification circuit - this makes the current only go in one direction
through the x-ray tube.
7. Filament circuit variable resistor - this variable resistor adjusts the current going to
the filament.
8. Filament step-down transformer - this transformer steps the voltage down and
therefore the current up.
9. X-ray tube - this is where the x-rays are created.
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10. Rotor stator - this rotates the anode.
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Control
Factor
Electrical Device and Location in
Circuit
kVp Selection
kVp Level
Autotransformer (between incoming
line and exposure switch)
mA Selection
Filament Current
Variable resistor (in filament circuit
between incoming line and step-down
transformer)
Time Selection
Length of exposure
Timer circuit (between exposure switch
and step-up transformer)
Rotor Switch
Speed of rotating anode
Stator (separate circuit from stator of
anode motor)
Exposure Switch
Moment of exposure
Switch (between autotransformer and
timer circuit)
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