The document provides an extensive overview of transformer design, focusing on core and shell types along with their respective advantages and disadvantages related to construction, cooling, and repair accessibility. It discusses various classifications of transformers based on service type, power utility, and the significance of core material, dimensions, and design considerations for enhancing performance while minimizing losses. Additionally, it highlights factors such as flux density, window design, and overall dimensions that influence transformer efficiency and functionality.

1. DESIGN OF TRANSFORMER

2. Classification of transformer
• Depending upon the type of construction used:
• I. Core type
• II. Shell type

3. Classification of transformer
• Depending upon the type of construction used:
• I. Core type
• II. Shell type

4. Classification of transformer
• Depending upon the type of construction used:
• I. Core type
• II. Shell type

5. Classification of transformer
• Depending upon the type of construction used:
• I. Core type
• II. Shell type

6. Comparison of core type and shell type transformers
core type shell type
Construction simpler in design and permit easier
assembly and insulation of winding
Design – complex
Assembly - complicated
Mechanical
forces-
The forces produced between windings is
proportional to the product of the currents
carried by them.
Since the windings carry currents in
opposite direction, there exists a force of
repulsion between them.
Hence, the inner winding experiences a
compressive force and outer winding
experiences a tensile force.
In a shell type transformer,
windings have greater
capability of withstanding
forces produced under short
circuit as these windings are
surrounded and supported by
the core.
mechanical strength- high

7. Comparison of core type and shell type transformers
core type shell type
Leakage
reactance:-
 Large space required between the high
and low voltage winding,
 Leakage reactance - high
The windings can be easily
subdivided by using sandwich
coil.
 leakage reactance - low
Repairs The winding of core type transformer is
completely accessible so coils can be easily
inspected. And also core type transformer is
easy to dismantle for repair
In shell type transformer, the
coils are surrounded by core,
therefore difficulty in
inspection and repair of coils.

8. Comparison of core type and shell type transformers
core type shell type
Cooling In core type transformer windings are exposed
and therefore the cooling is better in winding
than core.
In case of shell type
transformer core is exposed
therefore cooling is better
than winding.

9. Classification of transformer
 Classification on the basis of type of service:
 I. Distribution transformer
 II. Power transformer
 Classification on the basis of power utility:
I. Single phase transformer
II. Three phase transformer

10. Construction of transformer
1. Transformer core
2. Winding
3. Insulation
4. Tank
5. Bushings
6. Conservator
7. Buchholz Relay
8. Explosion vent
9. Transformer oil

11. Design detail
Output of transformer: let

12. Design detail
Output of transformer: let

13. Design detail
• Output equation of transformer
• Single phase transformer :-
• Three Phase Transformer :-

14. Design detail
• Optimum design
• Transformer may be designed to make one of the following
quantity as minimum
• i. Total volume
• ii. Total weight
• iii. Total cost
• iv. Total loss

15. Design detail
• Optimum design
• All these quantities vary with ratio r = фm/ AT.
• If high value of ‘r’ then flux will be high, so large cross
section is required which will increase volume, weight and
cost of iron and also give higher iron loss.
• Also due to decrease in value of ‘AT’ the volume, weight
and cost of copper decreased and also decrease in copper
losses.
• Thus ‘r’ is a controlling factor for above mention quantities.

16. Design detail - Core
 Purpose of Transformer Core
• In an electrical power transformer, there are primary, secondary
and may be tertiary windings.
• The performance of a transformer mainly depends upon the flux
linkages between these windings.
• For efficient flux linking between these windings, one low
reluctance magnetic path common to all windings should be
provided in the transformer.
• This low reluctance magnetic path in transformer is known as core
of transformer

17. Design detail - Core
 Types of core
1. Rectangularcore: It is used for core type distribution transformer
and small power transformer for moderate and low voltage and
shell type transformer.
• In core type transformer, the ratio of depth to width of core vaies
between 1.4 to 2
• In shell type transformer width of central limb is 2 to 3 times the
depth of core.
• Square and stepped cores: For high voltage transformers, where
circular coils are required, square and stepped cores are used.

18. Design detail
2. Square and stepped core
Square core Stepped Core

19. Design detail
2. Cross-section and dimensions of Stepped cores

20. Design detail- Core
Choice of flux density
• The value of flux density in the core determines the core area.
• High value of flux density give smaller core area, so saving in iron
cost.
• Small core are a provides reduced mean turn of winding which
gives reduction in copper cost. But higher flux density increase
iron losses resulting high temperature rise.
• The value of flux density also depends upon service conditions of
transformer. A distribution transformer design with low value of
flux density to keep down the iron losses.

21. Design detail- Core

22. Design detail- Core
• Material for Transformer Core
• Main problem with transformer core is, its hysteresis loss and eddy current loss
in transformer.
• Hysteresis loss in transformer mainly depends upon its core materials.
• A small quantity of silicon alloyed with low carbon content steel produces
material for transformer core, which has low hysteresis loss and high
permeability.
• For increasing demand of power, it is required to further reduce the core losses
and for that, another technique is employed on steel, which is known as cold
rollingg.

23. Design detail- Core
• The core steel which has under gone through both the silicon alloying and cold
rolling treatments is commonly known as CRGOS or Cold Rolled Grain Oriented
Silicon Steel.
• This material is now universally used for manufacturing transformer core.
Although this material has low specific iron loss but still; it has some
disadvantages,
• it is susceptible to increase loss due to flux flow in direction other than grain
orientation and it also susceptible to impaired performance due to impact of
bending and blanking the cutting CRGOS sheet. Both the surfaces of the sheet
are provided with an insulating of oxide coating.

24. Design detail- Core
• Influence of Diameter of Transformer Core
• Let us consider, the diameter of transformer core be ′D′. Then,
cross-sectional area of the core,
• (1)
• Voltage per turn, (2)
• Where, Bm is the maximum flux density of the core.
• (3)

25. Design detail- Core
• E is proportional to D2. Therefore voltage per turn is increased with
increase in diameter of transformer core. Again if voltage across the
winding of transformer is V. Then V = eN, where N is the number of
turns in winding. If V is constant, e is inversely proportional to N.
And hence, D2 is inversely proportional to N. So, diameter of the
core is increased, the number of turns in the transformer winding
reduced. Reduction of number of turns, reduction in height of the
core legs in-spite of reduction of core legs height increased in core
diameter, results increase in overall diameter of magnetic core of
transformer. This increased steel weight ultimately leads to
increased core losses in transformer. Increased diameter of the core
leads to increase in the main diameter on the winding. In – spite of
increased diameter of the winding turns, reduced number of turns
in the windings, leads to less copper loss in transformer.

26. Design detail- Core
• Window in a single phase transformer contains one primary winding
and one secondary winding
• Total copper area in window Ac = Tp ap + Ts as
• Tp - turns in primary winding , ap area of primary turn
• ap =Ip/delta , delta = current density
• Total conductor area – Ac = TpIp/delta + TsIs/delta = (TpIp+TsIs)/delta
• = 2AT/delta
• Window space factor –
• Kw = Conductor area in window/ Total area of window
• Kw = Ac/Aw
• Ac = KwAw , AT = KwAw.delta /2

27. Design detail- Core
• Rating of 1phase tfr =
• Q = Vp Ip x1000 = EpIp x 1000
• Et.Tp.Ip.1000 = Et. AT x 1000

28. Design of insulation
• Electrical considerations
 Eddy current losses
 Leakage reactance
• Mechanical considerations
• Thermal consideration
• Window Space Factor: It is the ratio of copper area in the window
to the total window area.
• Kw = 10/(30+kV) for transformer rating 50 to 200kVA
• Kw = 12/(30+kV) for rating about 1000 kVA
• Kw = 8/(30+kV) for rating about 20 kVA

29. Design of Window
• Window dimensions:
• The area of window depend upon total conductor area and
window space factor.
• Area of window
• Aw = total conductor area/ window space factor
• = 2.ap Tp/Kwfor 1-ph transformer
• = 4.ap Tp/Kwfor 3-ph transformer
• Aw = height of window x width of window = Hw x Ww
• The ratio of height to width of window, Hw /Wwis b/w 2 to 4.

30. Design of Yoke
• Design of Yoke:
• The section of yoke can either be taken as rectangular or it
may be stepped.
• In rectangular section yokes,
• depth of the yoke = depth of core area of yoke
• Ay = Dy x Hy
• Dy = depth of yoke= width of largest core stamping = a
• Ay = 1.15 to 1.25 of Agi for hot rolled steel = Agi for CRGO

31. Overall dimensions
• Overall dimensions Single Phase Transformer
• d= diameter of circumscribing circle
• D= distance b/w centers of adjacent limbs
• H= overall height W= length of yoke
• D = d + Ww,
• Dy = a
• H = Hw + 2Hy
• W = D + a
• Width over two limbs = D + outer diameter of hv winding Width over
one limb = outer diameter of hv winding

32. Three Phase Transformer
• Three Phase Transformer D = d + Ww, Dy = a H = Hw + 2Hy
• W = 2D + a, Width over two limbs = D + outer diameter of hv
winding Width over one limb = outer diameter of hv winding