Download step-up transformer

GOVERNMENT ENGINEERING COLLEGE
RAJKOT
Electrical Machine
Kumbhani Akshay
Kavathiya Vishal
Faldu Sachin
Gevariya Sagar
(130200117048)
(130200117046)
(130200117024)
(130200117032)
A transformer is a device for increasing or decreasing
an a.c. voltage.
STRUCTURE OF TRANSFORMER
CIRCUIT SYMBOL FOR TRANSFORMER
HOW TRANSFORMER WORKS
Laminated soft
iron core
Input voltage
Output voltage
(a.c.)
(a.c.)
Primary coil
Secondary coil
All transformers have three parts:
1. Primary coil – the incoming voltage Vp (voltage
across primary coil) is connected across this
coil.
2. Secondary coil – this provides the output
voltage Vs (voltage across the secondary coil)
to the external circuit.
3. Laminated iron core – this links the two coils
magnetically.
Notice that there is no electrical connection between the two coils,
which are constructed using insulated wire.
TWO T YPES OF TRANSFORMER
A step-up transformer increases the voltage there are more turns on the secondary than on the
primary.
A step-down transformer decreases the voltage
- there are fewer turns on the secondary than on
the primary.
To step up the voltage by a factor of 10, there
must be 10 times as many turns on the secondary
coil as on the primary. The turns ratio tells us
the factor by which the voltage will be changed.
FORMULA FOR TRANSFORMER
voltage across the primary coil
number of turns on primary

voltage across the secondary coil number of turns on secondary
Vp
Vs

Np
Ns
Where Vp = primary voltage
Vs = secondary voltage
Np= Number of turns in primary coil
Ns = Number of turns in a secondary coil.
WORKED EXAMPLE NO. 1
THE DIAGRAM SHOWS A TRANSFORMER.
CALCULATE THE VOLTAGE ACROSS THE SECONDARY
COIL OF THIS TRANSFORMER.
Step-up transformer!
SOLUTION
VP N P

VS N S
Substituting
12 180

VS 540
Crossmultiplying
180.VS  12 x 540
12 x 540
 VS 
180
 VS  36 V
WORKED EXAMPLE NO. 2
A T R A N S FO R M E R W H I C H H A S 1 3 8 0 T U R N S I N I T S P R I M A RY C O I L I S
T O B E U S E D T O C O N V E R T T H E M A I N S VO LTAG E O F 2 3 0 V T O
O P E R AT E A 6 V B U L B . H O W M A N Y T U R N S S H O U L D T H E S E C O N DA RY
C O I L O F T H I S T R A N S FO R M E R H AV E ?
VP = 230 V
NP = 1380
Obviously, a Step-down transformer!!
VS = 6 V
NS = ?
SOLUTION
VP N P

VS N S
Substituting
230 1380

6
NS
Crossmultiplying
2300.N S  6 x 13800
6 x 1380
 NS 
230
 N S  36 turns
Transformer Equivalent circuit (1)
I2
I1
INL
E1
Transformer
E2
13
Transformer Equivalent circuit (2)
I2
I1
INL
Transformer
14
Transformer Equivalent circuit (3)
I1
I2
INL
Transformer
15
Transformer Equivalent circuit (4)
I1
INL
I2'
Transformer
16
Open circuit Test
•It is used to determine Lm1 (Xm1)and Rc1
•Usually performed on the low voltage side
•The test is performed at rated voltage and frequency under
no load
Transformer
17
Short circuit Test
•It is used to determine Llp (Xeq) and Rp(Req)
•Usually performed on the high voltage side
•This test is performed at reduced voltage and rated frequency
with the output of the low voltage winding short circuited such
that rated current flows on the high voltage side.
Transformer
18
Transformer Construction
Transformer
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Transformer Construction(2)
Left: Windings shown only on one leg
Right: Note the thin laminations
Transformer
20
3- Transformer Construction (3)
Transformer
21
3- Transformer Construction(4)
Left: A 1300 MVA, 24.5/345 kV, 60Hz transformer with forced oil
and air (fan) cooling.
Right: A 60 MVA, 225/26.4 kV, 60 Hz showing the conservator.
Transformer
22