machine

1)    
Auto
Transformer

·       
Introduction:

Auto transformer is a that
with just a single twisting wound on a covered center. An auto transformer is similar to a two winding transformer however contrast in
the way the essential and auxiliary winding are interrelated. Both essential
side and optional side is regular to a piece of the winding. On stack
condition, a piece of the heap current is acquired straightforwardly from the
supply and the rest of the part is gotten by transformer activity. An Auto
transformer works as a voltage regulator.

 

·       Construction:

A variable auto
transformer

 

The
autotransformer has just a single winding. In this unique sort of transformer,
some portion of the winding is basic to both the essential and the optional
one.

The
guideline of operation of the transformer is the same as the one of the regular
transformer, at that point the connection amongst information and yield
voltages and info and yield streams and the proportion of number of turns
between the essential and the auxiliary winding is the same.

The
streams of the essential and optional windings are streaming on the contrary
headings, so the aggregate current moving through the regular piece of the
winding is equivalent to the contrast between the current on the low-voltage
winding and the current on the high-voltage winding. All together for an
autotransformer to work legitimately, the two windings ought to have a similar
winding sense.

At
the point when the essential current Ip, is moving through the single winding
toward the arrow as shown up, the secondary current, Is, streams in the
opposite direction. Along these lines, in the part of the winding that
generates the secondary voltage, Vs the present streaming out of the winding is
the difference of Ip and Is.

The autotransformer can
also be constructed with more than one single tapping point. Auto-transformers
can be utilized to provide different voltage points along its winding or
increase its supply voltage concerning its supply voltage VP as shown.

Autotransformer with multiple tapping
points

 

The standard procedure for denoting an auto transformer
winding is to name it with capital letters. Essentially the normal unbiased
association is set apart as N or (n). For the secondary tapping’s, suffix
numbers are utilized for all tapping points along the auto transformer
secondary winding. These number generally begin at number1 and continue in
ascending order for all tapping points as shown.

 

Auto transformer terminal
markings.

 An autotransformer is used principally for the
adjustments of line voltages to either change its value or to keep it
consistent. If the voltage modification is by a small amount, either up or
down, at that point the transformer ratio is small as Vp and Vs are almost
equal. Currents Ip and Is, are also nearly equivalent.

Along
these lines, the part of the windings passes on the contrast between the two
currents cab be made from a smaller conductor size, since the currents are much
smaller saving on the cost of an equivalent double wound transformer.

Principle
of working operation.

A.   
Step Up Transformer –At the point when
the number of secondary coil is higher than the primary coil, it will be called
as step up transformer. It converts low alternative voltage to high alternative
voltage.

Example
of step up transformer. The picture shows that Ns>Np.

B.   
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.

 

Example
of step down transformer. The picture shows that number of primary higher than
number of secondary coil.

Advantages
of auto transformer

1.    
smaller in size and cheaper.

2.     voltage
regulation as voltage drop in resistance 

3.     higher efficiency
than two winding transformer.

 

Disadvantages of auto transformer.

 

1.    
The auxiliary winding isn’t protected from the
essential winding. On the off chance that an auto transformer is utilized to
supply low voltage from a high voltage and there is a break in the auxiliary
winding, the full essential voltage comes across the optional terminal which is
risky to the operator and equipment.

2.     Used just in the
constrained places where a slight variation of the output voltage from input
voltage is required.

3.    
Absent of galvanic isolation.

2.
How copper is saving in autotransformer?

Presently we will examine the saving of copper in auto
transformer contrasted with two windings electrical power transformer. We
realize that weight of copper of any winding relies on its length and cross –
sectional zone. Again length of conductor in winding is corresponding to its
number of turns and cross – sectional area changes with evaluated current. So
weight of copper in winding is straightforwardly corresponding to result of
number of turns and evaluated current of the winding.

4.    
Three
phase transformer (operation and types)

 

The mixes of the three windings might
be with the essential delta-associated and the auxiliary star-associated, or
star-delta, star-star or delta-delta, contingent upon the transformers utilize.
At the point when transformers are utilized to give at least three stages they
are for the most part alluded to as a Polyphase Transformer.

The advancement of a centre kind
three phase transformer is as showed up in the figure. The core contains three
legs or limbs. Obviously, the centre is contained thin overlaid sheets to
diminish eddy current hardships. Each limb has fundamental and auxiliary
windings in cylindrical shape.

In a shell type three phase
transformer, three stages are more autonomous than they are in core type. Each
stage has its individual magnetic circuit. The development of shell type three
stage transformer is shown in the figure above. The advancement resembles that
of three single stage shell form transformers kept on the most noteworthy
purpose of each other.

Three
phase transformer connection

Star
or delta can be connected in the winding of primary or secondary windings. It
will provide a total of 4 possible connections for 3 phase transformer.

(star-star), (delta-delta), (star-delta), (delta-star), (open-delta
connection), (scott connection)

(i)   
Usually small, high voltage transformers
use Star-star connection. In star
connection number of required turn is reduced. Thus, reduction of the amount of
insulation also takes place.

 

(ii) 
Delta-delta
connection –Generally, large and low voltage transformer use this connection.
Number of required turns is decently greater than star-star association. This
connection can be used notwithstanding for unbalanced loading. Regardless of
whether one transformer is not balanced, system can keep on operating in open
delta association is one of the benefit of the connection

(iii) Star-delta connection-
The essential winding is star-star associated with grounded impartial and the
secondary winding is delta associated. Step down transformer at the substation
end of transmission line is mainly utilized for this connection.

 

(iv) Delta-star
connection- The essential
winding is related in delta and the optional winding is related in star with
unbiased grounded. This sort of connection is fundamentally used in step up
transformer toward the begin of transmission line.

(v)  
Open delta connection- Open
delta association can be used when one of the transformers in delta-delta is
incapacitated and the administration is to be continued until the point when
the defective transformers is repaired or supplanted.

 

 

 

(vi)  Scott
connection-  Two
transformers are utilized as a part of this sort of association. One of the
transformers has focus taps on both essential and auxiliary windings. Scott-association
can likewise be utilized for three stage to two stage change.

 

 

Three phase voltage and current.

 

 Where once more, VL is the line-to-line
voltage, and VP is the stage to-unbiased voltage on either the essential or the
optional side.

Three phase transformer
line and voltage current.

 

 

The
four fundamental setups of a three-stage transformer, we can list the
transformers optional voltages and streams as for the essential line voltage,
VL and its essential line current IL as appeared in the accompanying table.
Where: n breaks even with the transformers “turns proportion” (T.R.)
of the quantity of optional windings NS, partitioned by the quantity of
essential windings NP. (NS/NP) and VL is the line-to-fix voltage with VP being
the stage to-unbiased voltage.

                        5. Why transformer
rating specified in KVA?

Transformer rating indicated in (kVA)
in light of the fact that copper loss of a transformer relies upon current and
iron misfortune on voltage. Along these lines, add up to transformer relies
upon volt ampere (VA) and not on stage point amongst voltage and current. It is
free of load power factor. That is the reason rating of transformer in (kVA)
and not in KW(kilowatt).