Transcript Transformers

Transformers
What?
• Power stations produce high voltage
electricity about 25kV
• A transformer will ‘step up’ this voltage to
about 400kV before the electricity is put
through over head cables
Why?
• When a current passes through a wire,
friction causes the wire to get hot. The
more current passing through the wire the
hotter it gets.
• A transformer that has ‘stepped up’ the
voltage will also have ‘stepped down’ the
current.
How?
• Example. Drax power station produces a
given amount of energy. Lets estimate that
every second Drax is pumping out
4000,000,000J of energy
• Energy can not be created or destroyed
• All the energy that goes into a transformer
should come out (less any losses)
V
P = 450 000 000W
V = 25 000V
Using P = IV
I = P/V
I = 450000000
250000
I = 1800A
Transformers
What is a transformer?
A device used to increase or decrease voltage
Where are transformers used?
On the National Grid, household appliances
What do we call a transformer that
increases voltage?
STEP-UP Transformer
What do we call a transformer that
decreases voltage?
STEP-DOWN Transformer
How electricity gets to your home….
Power station
Step-up
transformer
National Grid
Step-down
transformer
Homes, businesses
and factories etc
Why bother with transformers?
riction in
When electrical current flows you get f_____
eat
the conductor. With friction you always get h___.
nergy You get more wasted
This heat is wasted e____.
oltages than high voltages. So the
energy at low v______
electricity is increased in voltage before it is
ational G__.
rid In this way less
transferred to the N_____
energy is lost. Then, when it gets to your home, a
own
school or a factory, the voltage is stepped d___.
Step-down
More/less turns on the primary coil than
the secondary coil.
Primary
Secondary
Step-up
More/less turns on the primary coil
than the secondary coil.
Primary
Secondary
Transformer calculations
The size of the output voltage depends upon the ratio of
the turns on the primary and secondary coils.
Guess what? There’s a formula (it is Physics after all!) -
V – voltage
V1 =
N1
V2 =
N2
N - number of turns
Transformer Question 1
A transformer has 200 turns on its primary coil
and 50 turns on its secondary coil. The input
voltage is 920V.
a) Is is a step-up or step-down transformer?
Step-down
a) What is the output voltage?
230V
Transformer Question 2
A transformer has 100 turns on its primary coil. It
has an input voltage of 35V and an output
voltage of 175V.
a) Is is a step-up or step-down transformer?
Step-up
a) How many turns are on the secondary coil?
500 turns