Chapter 2 The Transformer Flashcards
Parts of the transformer
In which part of the transformer does the magnetic field oscillate?
The core which is made of iron or steel
_____________ is the ease at which soft iron conducts the magnetic lines of force.
“Permeability”
When a voltage is applied to the primary coil a magnetic field is induced in the core. What in turn happens to the secondary coil?
A voltage is induced in the secondary coil.
What is the purpose of making the core out of 0.014 inch thick steel sheets coated with insulating material?
It reduces the core loss and heating produced in the core by insulating each sheet from the other.
What is the turns ratio in a transformer?
The ratio of turns in the primary coil to turns in the secondsry coil.
How is the KVA of a transformer calculated?
KVA = volts × amps ÷ 1000
Which coil of a transformer has the most turns?
The primary. The secondary coil has less turns, larger wire, and higher insulation.
What are the different ways of cooling transformers?
Air - The core and coils are mounted in a metal case with ventilators at the top and bottom. These are called dry type transformers.
Askarel - A heavy sticky substance used as a coolant.
Oil - Used as insulating material, and as a medium for carrying heat in the core and coils to the outer tank wall.
The two main losses of the transformer are called _________ and __________ losses.
“Iron” and “Copper”
The amount of current to fully magnetize the iron core is sometimes known as the _______________ or ____________________.
exciting current or charging current.
Without ________ losses and ___________ losses or I2R loss, the transformer would be 100% efficient.
“Core” and “Copper”
What is the industry standard for subtractive transformers?
Industry standard states that transformers rated at 200 KVA and above or having a primary voltage over 8600 volts are subtractive.
Which transformer will carry the greater load when transformers are banked or paralleled?
The transformer with the lower impedance.
What is the advantage of having a high impedance on a transformer.
It limits the amount of short circuit current through the windings, causing less mechanical stress.
Can transformers of diff. KVA ratings be paralleled?
Yes. Transformers of diff. KVA ratings can be paralleled; if the impedances are nearly the same, the load will split proportionally.
