Chapter 3 Flashcards
Theory
What is a transformer in its simplest form referred to as?
Nothing more than two coils of wire placed very close to each other (but not touching)
What happens if you place the two coils of wire around an iron core?
Induction will be maximized, and higher voltages will be obtained
What happens to a coil of wire that is placed next to another coil of wire that is attached to a source of AC Power?
It will become energized
How can the amount of induced voltage be transformed?
By changing the number of turns in the secondary coil.
What do transformers directly out of the generating station do?
Step-Up Voltage
What do transformers located at distribution substations and on distribution poles?
Step-Down Voltage
What is turns ratio?
A comparison of the number of turns of wire in each coil.
How is the turns ratio calculated?
By dividing the primary voltage rating by the secondary voltage rating
What is polarity?
The direction flow through the two coils.
Where is polarity set?
During the manufacturing process and cannot be changed in the field.
How is polarity determined?
By the direction the secondary coil is wrapped in relation to the direction the primary coil is wrapped
What can the polarity of a transformer be?
Additive or Subtractive
If it is additive, what side will the X1 Bushing be on?
Right-Hand Side
If it is subtractive, what side will the X1 Bushing be on?
Left-Hand Side
What is very important to know when banking and paralleling transformers?
Polarity
By industry standards, what will transformers 200kVA and smaller, with a primary rating of 8660 volts and below be rated?
Additive
What will all other transformers be rated?
Subtractive
What are the two main losses of the transformer?
Iron and Copper Losses
What is an Iron Loss known as?
No-Load Loss and they’re created by the oscillation of the magnetic field in respect to the core
What is a Copper Loss known as?
Load Loss caused when a current flows in a conductor
What does heat limit?
Current flow and is referred to as I2R loss
If a transformer didn’t have these two losses how efficient would it be?
100% Efficient
What is impedance?
Total opposition to current flow caused by the transformer
What is impedance made up of?
Resistance and Inductive Reactance
