Download self induction - Montgomery College

SELF INDUCTION
DURING AC FLOW, MAGNETIC
FIELD IS NOT CONSTANT. AN
OPPOSING ACTION WITHIN THE
COIL IS PRODUCED
SELF INDUCTION
• INDUCED VOLTAGE IN AC CIRCUIT WILL
OPPOSE THE SOURCE VOLTAGE
• IF THE SOURCE OF EMF INCREASES, THE
INDUCED COIL VOLTAGE WILL OPPOSE IT
AND ATTEMPT TO REDUCE IT.
• IF THE SOURCE OF EMF DECREASES, THE
INDUCED COIL VOLTAGE WILL ATTEMPT TO
INCREASE IT.
• LINE VOLTAGE COMPENSATOR WHICH
TAPS OFF OF THE AUTOTRANSFORMER IN
THE X-RAY CIRCUIT
MUTUAL INDUCTION
• IT IS NOT NECESSARY TO
PHYSICALLY MOVE A MAGNET TO
PRODUCE A CURRENT FLOW
• THE INTENSITY OF THE MAGNETIC
FIELD, IF IT CHANGES, WILL PRODUCE
A CURRENT FLOW
• HOW DOES THIS WORK?
• Placing an electromagnetic near the coil
and alternating the current through the
electromagnet.
• Therefore, mutual induction can only be
generated with AC.
TRANSFORMERS
• Transform potential and current energies
to higher or lower intensities using
electromagnetism.
• Operate only on AC current
• Transformers change the magnitude of
current and the voltage in AC circuit
• Step-up transformer
• Step down transformer
TYPES OF TRANSFORMERS
• CLOSED CORE
• “SQUARE
DOUGHNUT OF
MAGNETIC
MATERIAL
Autotransformer
•
•
•
•
Single iron core with only one winding
Acts as both primary and secondary
Works on self induction
Used for line voltage compensator by
stepping up voltage or stepping down
voltage as needed
• Not suitable as a high voltage transformer
SHELL TYPE TRANSFORMER
• “TRAPS” MORE MAGNETIC FIELD
LINES IN PRIMARY WINDOW
• MORE EFFICIENT
• USED IN X-RAY EQUIPMENT
ELECTROMAGNETISM AS IT
APPLYS TO X-RAY UNITS
• AUTOTRANSFORMER=SELF
INDUCTION (BASED ON LENZ’S LAW)
• LINE VOLTAGE COMPENSATOR IS
TAPPED OFF OF THE
AUTOTRANSFORMER
• KVP MAJOR AND MINOR ARE TAPPED
OFF OF AUTOTRANSFORMER
• Step up transformer: converts Voltage to
Kilovoltage
• Step down transformer: reduces voltage
but increases current to supply to the
filament (x-ray filaments need between 3-6
amps to heat up and “burn off” number of
electrons for the mA station selected)
RECTIFICATION
SOUNDS NASTY!
Rectifiers
• Changes AC to DC
• X-ray units require AC current for
transformers
• X-ray Tubes need DC current
RECTIFIERS
• Electronic device (diodes)
• Located between secondary side of stepup transformer and x-ray tube
• Vacuum-tube Type
• Solid State Diodes
X-ray unit
• Line Voltage Compensator
• Autotransformer (increases voltage 100400)
• Adjusts and reads voltage
• Has a # of connections located along its
length
High voltage generator
• High voltage transformer
• converts low voltage into kVp needed for
production of x-rays
• Filament transformer
• Rectifiers
TRANSFORMER LOSSES OR
INEFFICIENCY
• Resistance : current and copper wire
• hysteresis: alternating reversal of
magnetic field
• eddy current: (Lenz’s law) currents that
oppose the changing magnetic field
causes loss in efficiency (page 102-103)