insulator, conductors and transformers

1. Chapter 1
Winding insulating material

2. Winding insulating materials
• Insulating materials:
Offers very high resistance to the flow of current
Used to keep the current in its proper path along the conductor

3. Electrical properties
• Electrical resistivity : the value must be very high
• Dielectric strength : it is the maximum voltage gradient the material
withstand before electrical break down occurs.

4. Classification of insulating materials
1. Classification according to substances and materials.
• Solid Insulating Materials [Inorganic and organic]
• Mica, wood, slate, glass, porcelain, rubber, cotton, silk, rayon, terylene, paper and
cellulose materials etc
• Liquid Insulating Materials [Oils and Varnishes]
• Refined hydrocarbon minerals oils, Linseed oil, spirit and synthetic varnishes, etc.
• Gaseous Insulating Materials
• Dry air, carbon dioxide, argon, nitrogen, etc.

5. 2. Classification according to temperature.

6. • Class Y : 900C: Paper, cotton, silk, natural rubber, polyvinyl chloride
• Class A : 1050C: Same as class Y but impregnated, plus nylon.
• Class E : 1200C: Polyethylene terephthalate (terylene fibre, melinex film), cellulose
triacetate,polyvinyl acetate enamel.
• Class B : 1300
C: Mica, fiberglass (alkali free alumino borosilicate), bituminized asbestos,bakelite,
polyester enamel.
• Class F : 1500 C: As class B but with alkyd and epoxy based resins, polyurethane.
• Class H : 1800C: As class B with silicone resin binder, silicone rubber, aromatic polyamide (nomex
paper and fiber), polyamide film (enamel, varnish and film) and estermide enamel.
• Class C : Above 1800
C: As class B but with suitable non-organic binders; (Teflon, Mica,Micanite,
Glass, Ceramics, Polytetrafluoroethylene).

7. CHARACTERISTICS OF A GOOD INSULATING MATERIAL
• Very high insulation resistance.
• High dielectric strength.
• Low thermal expansion.
• Non-inflammable when exposed to arcing.
• Resistant to oils or liquids, gas fumes, acids and alkalies.
• Should have no deteriorating effect on the material, in contact with it.
• Good thermal conductivity.
• High mechanical strength
• High thermal strength.
• Should be resistant to thermal and chemical deterioration.
• Should be resistant to moisture absorption.

8. Insulation application area
• between conductor /coils and earth (phase-to-earth),
• between conductor /coils of different phases (phase-to-phase),
• between turns in a coil (inter-turn) and
• between the coils of the same phase (inter-coil).

9. INSULATING MATERIALS - FORMS
• Insulation Tapes and sleeves
• Insulation paper
• Insulation cloth

10. Insulating materials
• Leathroid paper
• NOMEX
• Triflexil
• Film paper
• Press Board
• Bamboo stick
• Etc..

11. Insulating varnishes
• Increased mechanical bonding to the winding wires
• Improved dielectric properties
• Improved thermal conductivity
• Protection to the winding against moisture and chemically corrosive
environment

12. Winding wires

13. Winding wires
• They are solid wires
• Insulated with varnish*
• Used in transformer, inductor, motor, generator, speaker
wires and etc
Wire
• May be cylindrical or rectangular cross-section
• Used to carry electricity and telecommunication signals
• Sizes are determined by standard gauge values

14. Suitable metal wires*
• Platinum
• Silver
• Gold
• Copper
• Aluminum
• Iron
• And some alloys of this metal are used
• Brass and bronze *

15. PROPERTIES OF CONDUCTORS
• Electrical properties
• Highly conductive
• Low Resistivity
• Electrical Energy dissipated as heat must be low
• Temperature to resistance ratio must be low
• Mechanical properties
• high ductility
• High tensile strength(withstand stress and strain)
• Solderability – the joint should have low contact resistance
• Resistance to corrosion*
• Easy to fabricate

16. Cont …
• Economical property
• Low cost
• Easily available
• Easy to manufacture
• ***

17. THE CHOICE OF A CONDUCTOR MATERIAL
• Resistivity of the materials
• Temperature coefficient of resistance
• Resistance against corrosion
• Oxidation characteristics
• Ease of soldering and welding
• Ductility
• Mechanical strength
• Flexibility and abundance
• Durability and low cost
• Resistance to chemicals and weather

18. • Commonly Used Conductor Materials:
Copper &
Aluminum

19. Comparison of Copper and Aluminium as conductors for Power Transmission Lines:
Copper Aluminum
1. Metal is costly
2. 100 per cent conductivity
3. Good resistance to corrosion
4. Heavier as compared to aluminium
5. Good ductility and malleability
6. Excellent soldering and welding capacity
7. Less suited for low temperature
8. Very small cross-section can carry heavy
current
9. Because of softness and flexibility, it can easily
be twisted repeatedly
10. The wind pressure and weight of snow is less
because of smaller cross-section
11. widely used in wires, cables, windings of
generators and transformers, overhead
conductors, busbars.
Metal is cheap
75 per cent conductivity
Good resistance to corrosion
Lighter as compared to copper
Good ductility and malleability
Poor solderability and weldability
Well suited to cold climate
Cross-section should be 50 percent more to carry
the same current as that of
copper.
Due to brittleness, cannot be twisted.
The wind pressure and weight of snow is more
because of higher cross-section
most often used as overhead transmission
conductors, busbars, ACSR
conductors.

20. Enameled wire
• Enameled wire is a wire coated with a very thin insulating layer
• Core materials are copper or aluminum
• The coatings are polyurethane, polyamide, or polyester resin - called as
“enamel”.
• This tin covering(enamels) helps to avoid short circuit from the surface of the
conductor when wounded in to coils. *

21. Enameled wires classification
• Classification based on insulation class
• Grade 1
• Grade 2
• Grade 3
• Classification based on temperature class*
• Common classes are 120 ,155 , 1800
c *
• Classification based on gauge value or area (square
millimeter)
• Cylindrical
• Rectangular*

24. Properties of enameled wires
• High dielectric strength
• Very low dissipation factor
• remaining reasonably constant at high frequencies or
under humid conditions
• No mechanical or chemical stripping required.
• Good resistance to abrasion.
• Good flexibility and adhesion to the conductor Smaller
coefficient of friction,
• Higher mechanical intensity, Excellent heat resistance.
• Good solderability.

25. TYPES AND SHAPES OF WINDING WIRES:
• Winding wires used in electrical motors can be classified as:
• Round wires
• Rectangular wires
• Stranded wires

26. Usage of alternate sizes
Resistance of winding is measured in two methods.
(i) By using multimeter, the resistance of the winding is directly measured in ohms or kilo
ohms.
(ii) 15 to 20% value of the rated voltage is applied by using auto transformer to each
phase of three phase winding. Then current in each phase is measured and then
the resistance of the winding is calculated.

27. 2. Area of Cross-section of one particular wire gauge number is two times
more than that of gauge number, when increased by three. For example
area of cross-section for 17 gauge wire is approximately two times more
than that of 20 gauge wires. If 17 gauge wire is not available then we use
two 20 gauge wires.
• 3. When 20 gauge and 17 gauge wires are used for particular length, then
the weight of17 gauge wire is double as that of the weight of the 20 gauge
wire, because weight isdirectly proportional to the area of cross-section of
the wire.
• 4. Resistance of the winding wire is indirectly proportional to the cross-
sectional area ofthe wire. Therefore, the resistance of 17 gauge wire is half
of the resistance value of 20gauge wire.

28. GAUGE PLATE
• Is a device used to find the gauge value of wires

29. Chapter 3
Transformers

30.  A TRANSFORMER is a device that transfers electrical
energy from one circuit to another by electromagnetic
induction (transformer action).
 Power is transferred:
 With out change in frequency
 With a change of magnitude of current and voltage

31. example
 Load = 2A , 10V
 Source =1A, 20V
 P=VI
 So we need transformer in between to connect them.

32. BASIC OPERATION OF A TRANSFORMER
 In its most basic form a transformer consists of:
• A primary coil or winding.
• A secondary coil or winding.
• A core that supports the coils or windings

33. Cont…
 The varying current passing through the primary winding
creates varying magnetic flux in the primary winding which
expands and cut through the secondary winding which in
turn induce emf(voltage) in the secondary winding.
 Then when load is connected to the secondary winding the
secondary current will flow through the load.

34. Core characteristics
 Air (above 20KHz)
 Soft iron(less than 20KHz)
 Steal sheet

35. Types of construction
 Hollow core transformer

36.  Shell-core transformer
 Have E and I section of metal

37. TRANSFORMER WINDINGS

38. TRANSFORMER LOSSES
 Copper Loss
 Eddy current loss
 Hysteresis loss

39. Transformer ratings
 Not only turn ratio
 voltage, current, and power-handling capabilities of the primary and
secondary windings must also be considered.
 Frequency consideration of transformer:
 Above operating frequency
 Below operating frequency

40. Design of Transformer