University of Zakho
College of Engineering
Mechanical Engineering Department
Electrical engineering
( auto transformers )
Name : Badirkhan tayib rashid
Stage : 3rd
February
2020
Content:
1. Introduction:
2. Theory of autotransformer:
3. How dose to autotransformer work?
4. Type of transformer:
5. Example:
6. Application:
7. Advantage and disadvantage:
8. Conclusion:
9. Reference:
Introduction:
High voltage autotransformers are one of the most
important and expensive devices in the power system.
Hence, it is important to remotely control and monitor
their condition. To meet current requirements of power
companies it is essential to constantly improve
functionality of autotransformer monitoring systems. The
main aim in using such systems is to ensure continuity
and reliability of the operation of autotransformers,
reducing costs and economic losses associated with
possible failures.
This article concerns the system which collects data from
autotransformers. The
system was realized in the
Theory of autotransformer:
How dose to autotransformer work?
Autotransformers transform voltage and current in much the same
way that conventional transformers do, but with the important
difference that they only have one winding,
The single winding is provided with a tap which can be used as the
output (for voltage step-down) or as the input (in voltage step-up
applications). One end of the winding is a common point for both
input and output, and the other end fills the remaining role.
Importantly, an autotransformer provides no isolation which is something
that is often essential in transformer applications, so this more often than
not precludes their use. A common application of autotransformers is the
Variac, which is supplied mains voltage to the ends of the windings and
has a continuously adjustable tap with a large knob to provide a variable
output voltage.
Type of transformer:
Step UP Transformer :
A transformer in which Ns>Np is called a step up transformer. A step up
transformer is a transformer which converts low alternate
voltage to high alternate voltage.
Step DOWN Transformer :
A transformer in which Np>Ns is called a step down transformer. A step
down transformer is a transformer which converts high alternating voltage
to low alternating voltage.
N1=primary turn(1-3)
N2=secondary turn(2-3)
I1 [l=primary current
I2=secondary current
Vl=primary voltage
V2=secondary voltage
From the above fig. We get
V2 N2
=
V 1−V 2 N 1−N 2
V2 (N1−¿N2)=N2(V1−¿V2)
V2N2−¿V2N2=N2V1−¿N2V1
V2N1=N2V1
V2 N2
=
V1 N1
=K
Example:
An autotransformer is required to step-up a voltage from 220 volts to 250
volts. The total number of coil turns on the transformer main winding is
2000. Determine the position of the primary tapping point, the primary
and secondary currents when the output is rated at 10KVA and the
economy of copper saved.
N1 V 1 N 2∗V 1
=
N2 V2
N1= V2
2000∗220
= 250
=1760 Turns
VA 10.000
I2= V 2 = 250 =40A
P1=P2=V1I1=V2I2
N 2∗I 2 250∗40
I= V1 220
=45.4 A
Application:
Used in both Synchronous motors and induction motors.
Used in electrical apparatus testing labs since the voltage can be
smoothly and continuously varied.
They find application as boosters in AC feeders to increase the
voltage levels.
Used in HV Substation due to following reasons.
1. If we use normal transformer the size of transformer will be very
high which leads to heavy weight, more copper and high cost.
2. The tertiary winding used in Auto transformer balances single
phase unbalanced loads connected to secondary and it does not
pass on these unbalanced currents to Primary side. Hence
Harmonics and voltage unbalance are eliminated.
3. Tertiary winding in the Auto Transformer balances amp turns so
that Auto transformer achieves magnetic separation like two
winding transformers.
Advantage and disadvantage:
Advantage:
There are considerable savings in size and weight
There are decreased losses for a given KVA capacity .
Using an autotransformer connection provides an
opportunity for achieving lower series impedances and
better regulation. Its efficiency is more when compared with
the conventional one .
Its size is relatively very smaller .
Voltage regulation of autotransformer is much better .
Lower cost
Low requirements of excitation current .
Less copper is used in its design and construction .In
conventional transformer the voltage step up or step down
value is fixed while in autotransformer, we can vary the
output voltage as per out requirements and can smoothly
increase or decrease its value as per our requirement.
Disadvantage:
The autotransformer connection is not available with certain three-
phase connections.
Higher (and possibly more damaging) short-circuit currents can
result from a lower series impedance.
Short circuits can impress voltages significantly higher than
operating voltages across the windings of an autotransformer.
For the same voltage surge at the line terminals, the impressed and
induced voltages are greater for an autotransformer than for a two-
winding transformer.
Autotransformer consists of a single winding around an iron core,
which creates a change in voltage from one end to the other. In
other words, the self-inductance of the winding around the core
changes the voltage potential, but there is no isolation of the high
and low voltage ends of the winding.
CONCLUSION
A new approach to teaching the principles of auto transformers and their
main applications in power engineering was presented in this paper. The
approach will provide the students with more comprehensive information
about the equipment. In addition, a strong connection between the
theoretical aspects and the engineer’s every day practice is emphasized. A
number
Reference:
1. https://m.monografias.com/trabajos93/ensayo-
autotransformadores/ensayo-
autotransformadores.shtml
2. Auto transformer design _a practical handbook for
manufacturers
3. https://www.quora.com/What-are-the-advantages-of-
an-autotransformer-and-why-is-it-used-in-a-substation
4. The adaptation of the multi tapped auto transformer to
dimming of incandescent lamps
5. Design optimization and implementation of a single
phase Auto-Transformer with OLTC,Voltage and Over
Current protection. By Mohsin Waqar&Asad Ismail
6. https://www.mepits.com/tutorial/426/electrical/how-to-
design-a-step-up-and-step-down-auto-transformer
