Blue Circuit Board

download report

Transcript Blue Circuit Board

Transformers
A transformer changes the intensity of
alternating voltage and current.
Mutual Induction
Transformers
A device in which two coils are placed near one another without electrical
connection. The number of turns in the coils differs, causing a change in currnet
in the secondary coil; this serves to either increase or decrease the voltage.
http://harphys.com/wp-content/uploads/2010/10/transformermovie-clip.swf
Types of transformers
•
•
•
•
Air core
Open core
Closed core
Shell type
Air core transformer
Open core transformer
Closed core transformer
Shell type transformer
Step up vs Step-down
If you increase the number of turns on the right, the voltage coming off the
transformer will increase in proportion.
Using the numbers in the example above, you can see that the right side has
four times more turns. As a result, the voltage on the right has increased
four times (from 100 V to 400 V). The voltage has been stepped up by a factor
of four.
Because current is inversely proportional to voltage, you can see that stepping
up the voltage pays a price ... the current on the right is only a quarter of what it
was on the left. Step-up transformers increase the voltage, but decrease the
current. In our example above, the current went from 10 A to 2.5 A, a reduction
of by a factor of four
If you decrease the number of turns on the right, the voltage coming off the
transformer will decrease in proportion.
Using the numbers in the example above, you can see that the right side has
one fifth the number of turns. As a result, the voltage on the right is only
one-fifth as large. The voltage has been stepped down by a factor of five (1000
V down to 200 V).
Because current is inversely proportional to voltage, you can see that stepping
down the voltage gives a bonus ... the current on the right is five times what it
was on the left. Step-down transformers decrease the voltage, but increase the
current. In our example above, the current went from 2 A to 10 A, an increase by
a factor of five.
Transformer law
Ns
Np
If the turns ratio is greater than 1 the transformer is a step-up transformer.
If the turns ratio is less than 1 the transformer is a step-down transformer
Autotransformer (kVp selector)
self-induction