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Transcript
Ahmedabad Institute of
Technology
1
SUB-DC MACHINES AND TRANSFORMER
TOPIC-CONSTRUCTION OF SINGLE AND
THREE PHASE TRANSFORMER
GUIDED BY-PROF.MAYALAKSHMI PILLAI
MADE BY-GROUP 3
SEM-3
Made by
2
 140020109017
 140020109019
 140020109020
 140020109021
 140020109022
 140020109023
 140020109025
Makvana Mitesh
Makvana shivam
Urvish maru
Dinesh matalani
Parmeshwar meena
Ronak mishra
Nikhil pansuria
Introduction
3
 Transformer is an electrical device that transfers
electrical power from one circuit to another
by magnetic coupling.
 It does so without change of frequency
and without any moving parts.
 Transformer works only with AC supply
Construction of transformer
4
The transformer is very simple in construction
It consists of magnetic circuit linking with two
windings.
Continue…
5
 The simple element of transformer consist of two coil






having mutual inductance and laminated steel core.
The two coils insulated from each other and steel
core.
Other necessary parts are:
A suitable container
Suitable bushing
suitable medium
breathers
Practical transformer
6
Continue…
7
 In all types of transformer the core is constructed of
transformer sheet steel lamination assembled to
provide a continuous magnetic path within a
minimum of air gap included.
 The steel used is of high silicon content.
 The eddy current loss is minimized by laminating the
core.
 The lamination being insulated from each other by
alight coat of varnish.
Continue…
8
The thickness of lamination varies from 0.35 to 0.5 mm .
Continue…
9
 Constructional transformer are of two types:
 Core type
 Shell type
Continue..
10
 The transformer called core type because the
winding surrounds considerable part of core.
 The transformer called shell type because core
surrounds a considerable part of winding.
 In diagram of core type transformers the primary
and secondary winding are shown located on
opposite legs of core but in actual these are
interleaved to reduce leakage flux.
Continue…
11
Core type transformer
12
 The coil used are form wound and are of cylindrical
types.
 But for large size transformers round coils are used.
 Circular cylindrical coils are used because of their
mechanical strength these are wound in helical
layers with different layer insulated from each other
by paper.
 Since low voltage winding is easiest to insulate it is
placed nearest to core.
Continue…
13
Continue…
14
 Because of lamination and insulation, the effective
core area is reduced.
 For large size transformer it is wasteful to use
rectangular cylindrical coils so circular cylindrical
coils are preferred .
 A common improvement on square core is to
employ cruciform core which demand at least two
size of core stripes.
Cruciform core
15
Shell type
16
 In this the winding are put around the central limb&






the flux path is completed through two side limbs.
The coils are form wound but are multi layer disc
type usually wound I the form of pancakes.
Advantages of such construction.
A relatively more rigid core
Lesser weight and size per kVA rating
Low iron losses at higher operating flux densities
Low cost of manufacture.
Shell type transformer
17
Three phase transformer
18
Three phase transformer
19
 Large scale generation of electric power is usually 3-
phase at generated voltage of 13.2kV or higher.
 For transmission purpose 3 phase transformer are
necessary to step up generated voltage to
transmission line.
 In olden days for this purpose 3 single-phase
transformer are interconnected.
 But nowadays due to improvement in design 3 phase
transformer are used.
Continue…
20
 Advantage of 3phase over single phase transformer
 It occupies less floor space for same rating.
 Weight less, cost about 15%less.
 Only one unit is to be handled and connected.
 Disadvantage:
 If any one phase become disabled then whole
transformer has to be removed for service.
Continue…
21
Cooling in transformer
22
 Voltage below 25000V transformer are cooled by air
blast no need of oil.
 For large transformer core and winding are
immersed in insulating oil and conservative tank is
placed above it.
 For very large transformer the oil is regulated by
means of pump and heat is carried out by water
which is flowing in pipes.
Breathers
23
 In large transformers where complete air tight
construction is impossible, chambers are known as
breathers are provided to permit thee oil inside the
tank to expand and contracts temperature changes.
 The atmospheric moisture is entrapped in these
breathers & is not allowed to pass in oil.
Bushings
24
 All transformer leads are carried out by suitable
bushing.
 For moderate voltage porcelain bushing are used to
insulate the leads as they come out of the tank.
 They are look like insulators on transmission lines.
 In high voltage installation oil filled type bushing are
used.
Conservator tank
25
 It is the most important part of transformer for
cooling purpose.
 Its size is depends on the type of transformer and
power specification.
 Insulating mineral oil is filled in the conservative
tank.
 The mineral is used for insulation purpose and for
providing cooling in transformer
References
26
 1.A textbook of electrical technology, volume 2 AC
and DC machine, B.L. theraja A.K. theraja, S.chand
and company pvt.ltd.
 2.DC machine and transformer , Dr J.G. Jamnani,
Mahajan publishing house