- Used to change low voltages into higher voltages or vice
versa in an AC circuit - Operate on the principle of mutual induction
TRANSFORMER
- Consists of 2 wire coils wound around an iron ring. When current flows through the primary coil, a magnetic field is created within the iron core.
- The magnetic field will then create a momentary current in the secondary coil.
- Current flows the secondary coil only when the magnetic field is changing.
- For this reason, direct current (DC) cannot be used in the primary coil to create a steady current in the secondary coil.
- It will only operate with changing electric current (AC)
Transformer
- Used to change the magnitude of current and voltage in an AC circuit.
- This change is directly proportional to the ratio of the number of turns of the secondary coil (Ns) to the number of turns in the primary coil (Np).
TRANSFORMER LAW
TRANSFORMER LAW FOR VOLTAGE:
VS/VP = NS/NP
TRANSFORMER LAW FOR CURRENT:
πΌπ/πΌπ = Nπ/πS
TRANSFORMER LAW FOR VOLTAGE AND CURRENT:
πΌπ/πΌπ = Vπ/πS
If a transformer is supplied with 500 V to the primary coil,
has 200 turns of wire in the primary coil and 40,000 turns of
wire on the secondary coil, what will be the voltage in the
secondary coil?
- (Vs / Vp)= (Ns/Np)
- 500 V (40,000 / 200)
- 500 V (200)
- 100,000 V or 100kV
- Ns/Np
- Is the ratio of the number of turns in the secondary coil to the number of turns in the primary coil.
- If the turn ratio is >1, then it is a Step-Up transformer
TURNS RATIO
There are 140 turns on the primary side of a transformer and 20,000
turns on the secondary side of a transformer. What is the turns ratio
for this transformer?
- Ns/Np
- 20,000 / 140
- 142.8 or a turns ratio of 143
TYPES OF TRANSFORMER
- Air Core Transformer
- Open Core Transformer
- Closed Core Transformer
- Shell-type Transformer
- Autotransformer
A simple transformer made
with two coils of wire in close
proximity to facilitate mutual
induction
AIR CORE TRANSFORMER
When the primary and
secondary coils have an iron
core placed within them, the
strength of the magnetic field
is greatly increased
OPEN CORE TRANSFORMER
- Built about a square donut of
magnetic material - The core is not a single piece
but rather is built up of
laminated layers of iron
CLOSED CORE TRANSFORMER
It is more efficient than the
closed-core transformer
because this type traps even
more of the magnetic field
lines of the primary windings
SHELL-TYPE TRANSFORMER
- Provides different voltages for input to the step-up and step-down transformers.
- The output of the BLANK is connected to the primary coil of the step-up or step-down transformer
- Has an iron core with only one coil, which serves as both primary and secondary transformer windings.
- The primary side has output connections which are made at different points on the coil of an BLANK; these connections are called output taps.
- In an X-ray circuit, the output of an BLANK is used to change the voltage in the primary coils of the step-up and step-down transformers
AUTOTRANSFORMER
- Converts a lower AC voltage into a
higher AC voltage and is also called
the BLANK. - Have more turns in the secondary
coil than in the primary coil - The output voltage of a BLANK is higher than the input voltage, and the output
current is always less than the input
current. - BLANK are used to
supply high voltages to the x-ray
tube.
high-voltage step-up transformer
- Produces an output voltage that is
lower than the input voltage - The number of turns on the secondary
the coil of a BLANK is less
than the number of turns on the
primary coil. - The output current in the secondary
coil of a BLANK is
greater than the input current. - Used to supply high currents to the
tube filament. - is used to decrease the incoming line voltage to 5 to 15 V and 3 to 5 A range to heat the
x-ray tube filament
filament step-down transformer
is the component which varies current resistance and acts as a variable milliampere (mA) selector for the filament circuit. This allows the technologist to select mA for various radiographic examinations.
RHEOSTAT
THREE PRINCIPAL CAUSES OF TRANSFORMER ENERGY LOSS
- I^2R LOSS (Power Loss)
- HYSTERESIS LOSS
- EDDY CURRENTS LOSS
Electric current in copper wire experiences resistance that results in heat generation. This is also called copper loss.
I2R LOSS (Power Loss)
Results from energy expended as the continually changing AC current magnetizes, demagnetizes, and re-magnetizes the core material
HYSTERESIS LOSS
These currents oppose the magnetic field that induced them, thereby creating a loss of transformer efficiency
EDDY CURRENTS LOSS
