Lecture 2 Flashcards
What are electrical transformers used to do to voltage?
They are used to transform voltage from one level to another
Differentiate between a step up & step down transformer.
A step up transformer increases the output to input ratio. A step down transformer decreases the output to input ratio.
When a varying magnetic field or flux cuts a conductor ____ is induced in the conductor
Emf
What is magnetic flux?
Magnetic flux is as a result of AC current, as it keeps changing polarity and direction so will the magnitude and direction of the magnetic field keep changing.
In a transformer:
1. The primary coil is connected to what?
2. The secondary coil is connected to what?
- AC input from the socket connected to the substation
- The circuit of the electrical equipment.
When AC current from the socket flows through the primary coil, it will cause _____ _____ to be produced.
magnetic flux
To increase the emf induced in the secondary coil, which principles make this possible? (according to Faraday’s 2nd Law)
- Increase the no. of turns in the secondary coil.
- Increase magnetic field strength
- Increase the speed of relative motion between the coil & magnet
What are the 3 main constructional parts of a transformer?
- Primary Winding
- Magnetic Core
- Secondary Winding
Is a high tension transformer a step up or step down transformer?
Step up transformer
What is the function of the high tension transformer:
Hint: think voltage, x-ray
To provide high voltages (up to 150kV in some units) needed for the production of x-rays in the x-ray tube.
The magnetic field associated with the current flowing in the primary winding is concentrated in the ______ ______.
metal core
The core of the high tension transformer is made of a ____ ____. Such as ?
metal alloy; stalloy (steel & silicon)
Definite “hysteresis”
How easily a conductor can magnetize & demagnetize
Stalloy has ____ magnetic permeability with ____ hysteresis.
Stalloy also has ______ inherent electrical resistance, coupled with the core being laminated ______ eddy current loss.
If the core of the stalloy was of _____ resistance, then it would ______ current & _____ eddy current loss as well as become _______.
high; low
high; reduces
low; conduct; increase; overheated.
What is the purpose of the oil when the entire transformer is placed in a metal tank that is filled with it?
It provides electrical insulation as well as convect heat away from the transformer.
In the high tension transformer, the primary winding is made up of _______ turns of _______ ______ wire. This wire is coated with a tough insulation medium such as ______ or ______.
a few hundred; thick copper; shellac or enamel.
In the high tension transformer, the secondary winding is made of _______ of turns of ____ ____ wire.
thousands; thin copper
Potential difference between adjacent turns is __ ____ ____ however, potential difference between different layers of the windings may be up to _______.
What is the kV difference between inner & outer layer secondary windings?
What is located between the primary & secondary windings? hint: shielding
a few volts; thousands of volts
75kV
stress shield
What does the stress shield in the high tension transformer prevent?
hint: tension, electrical insulation
The stress shield prevents the high tension current from discharging to the primary circuit in the event of breakdown of the electrical insulation between the windings.
Copper losses in the high tension transformer vary in _______ proportion to what?
What occurs as a result of copper loss?
When does no copper loss or voltage drop occur?
Direct; to the resistance of the windings & the square of the current flowing through them.
As a result of copper loss, there is heat build up & increased resistance.
When the secondary winding is not connected in circuit.
When maximum safe current is flowing in the secondary, it is said the circuit is operating under..?
a. “No Load” condition
b. “Full Load” condition
B. Full load condition
Why is transformer regulation of importance in radiography?
hint: current, voltage
Because as current flow across the circuit increases, the voltage drops.
The rating of a transformer is the statement of the ________ safe output of its ________ winding.
If exceeded, what may occur?
hint: insulation, winding
maximum; secondary
If exceeded, the transformer may overheat causing breakdown in insulation or burning out of the winding
Name 3 things the rating of a high tension transformer in a diagnostic X-ray unit should include.
- The maximum current which may flow continuously.
- The percentage permissible overload.
- The maximum voltage that can safely deliver under no load condition
