transformer

1. • Cooling systems :
1- Air
2- Oil
• Air use in Dry Transformer

2. • Disadvantage :
1- Not allowed to download transformers except
for a small period of time
2
- Low durability insulation
3
- The windings effect Dust and dirt
4
- Increasing the size of the windings to
follow the air

3. • Oil filled transformer in power Tr:
• The basic elements:
1-Oil
2- Radiators
3-Fans
4-Pumps
5-Cooling pipes

4. • Transformer Oil :
• Function:
• 1- Cooling
• 2- Insulation
• The Properties Transformer Oil:
1-Dielectric strength
2-Viscoisty
3-Flash Point(145 c)
4-denisty (.88/cm3 at 15 c),the efficiency of
transfer the temperature about 21 times
of Air

5. •Radiators:

7. •Fans:
• Increase the efficiency of cooling
( Forced Circulation)
Note:
1- Small Fans put in the front the Radiators
cause Vibration
2- Large Fans put Under the Radiators

8. • Cooling Class :
• The Characterization IEC:
1 2 3 4
internal
cooling
type
Circulation
type
External
cooling
type
Circulation
type

9. O N A N
Oil Natural Air Natural

11. •ONAN:

12. • Use in Small Transformer
• Advantages :
1-Simple
2-low cost
3-High Reliability
4-low noise
Disadvantages:
1-Large Radiators and high cost
2- Limited in small transformer

13. •ONAF:
• Use in High power Tr
• Use two fans groups and work automatic
• Distribution fans regularly

14. •OFAF :

15. ODAF:

16. •Multi-stage cooling:
• Change in rating value with Cooling

17. • What's the meaning :
ONAN/OFAF/OFAF cooling class
transformer with”45/60/75 MVA
continuous at 65 c Temperature rise:

18. Inactive parts auxiliary parts
• Functions of transformer oil :
1- Cooling

19. 2- Insulation between the windings and
core and tank
• Breakdown voltage for Air up to 30kv/cm
• Breakdown voltage for Oil up to 80kv/cm
3
- Covers all metal parts to prevent
oxidation where effect on conductor
condictivity
4
- Identifies many of the faults (take sample
of the oil )

20. • Tank :
Types :
1-plain tank in small power Tr under 50 KVA
2-Tubed tank in medium power Tr
3-Tank with Radiators in High power Tr

21. • Function of Tank :
1. core and windings protection
2. Carry conductors out lines
3. Keep up transformer oil
4. Carry Radiators tubes

22. • Explosion vet

23. • Conservator Tank :
 Absorption any Expansion or contraction in
oil
 Increase oil to main tank

24.  The volume of Conservator Tank about 1/10
to main transformer
 At full load increase oil volume about 8%
therefore hieght oil about 30% of Conservator
Tank hieght
 increase Conservator Tank (oil level tube)
to show oil vapor color :

25. White Burn in insulation paper
Yellow Burn in insulation fibber and wood
Black
decomposition and burn
Oil

26. • Bochholz Relay:

27. • Breather unit :
 Contain on silica gel: crystalline salt
absorb moisture in air during entry to the
transformer

28. Silica gel colors:
•
color Case
Blue normal
Wardy Moisture saturation and must
change or drying in furnace
(150:200 c)
White Moisture saturation and must
change
Black Oil saturation and must change

29. • Oil protection system :
 The sealing in small transformer:
1- by conservator tank

30. 2- Nitrogen-positive pressure :
- Use compressed Nitrogen about 10%
above oil in main tank

31. • Tap Changer :

32. • Tap Changer Values:

33. •The idea of Tap Changer :

34. • Example 2:

35. • Example 3:

36. • Comparison between on load and off load Tab
Changer:
On load Off load
Tr type Power Tr Distribution Tr
Points 17 point or more 3 or 5
Surrounded
condition
Cylinder filled oil Transformer oil
Change
method
Auto manual
Place Cylinder with
parallel with
coils

37. • HV and LV bushing (isolators) :

38. • Function of Skirts :
Using Corona Rings :

39. • Flange :

40. • Rod gap :

41. • Accessories :
1- Pressure Relief Valve:

42. 2- Dial transformer capillary tube

44. 3- Liquid Level Gauge:
• indicates the level of the insulating liquid in the
main transformer tank.
• The standard gage has a center marking
indicating the level at 25 C. Dial markings are
minimum -25 C - maximum.

45. 4- Pressure-Vacuum Gauge:
• Gage readings vary with transformer temperature
changes and would normally indicate a positive
pressure.
• The gage may indicate a vacuum within the tank
when the transformer is de-energized or is
operating under light or no-load conditions in
allow ambient temperature.
• Any change in temperature indication of a leak in
the transformer seal and should be investigated

46. 5- Oil temperature indicator :

47. 6- Winding temperature indicator :

49. • K- Factor :
The ratio between the additional losses in
the energy of harmonics and eddy current
losses (4,7,13,20,30)
• K=4 (50 % non linear loads)
• K= 13 (100% non linear loads)

50. • Effect harmonics on connection of
windings :

51. • Flux on magnetizing current:

53. • Filter for preventing third harmonic:

54. • Relation between magnetizing current and
output voltage :

55. • Effect harmonics on Star connection

56. • Effect harmonics on Delta connection :

58. • Effect the earthing on transformer :
1- Ungrounded System:

59. Advantages :
1-Short circuit current very low
2- KVA SC during short very low (Short circuit level
)
Disadvantages :
1-S.c between phase and ground ,voltage increase
on other two phases
2-Short circuit current very low, protection device
not work
3-Arcing voltage occurs between phase and
ground during S.C

60. • Earthing System:
Solution problem Ungrounded System
• Connection methods :
1- Star Star: Y-Y

61. • Advantages :
1-Vp and Vs in phase where not phase
Displacement
2- low turns in phase Vp=57% of Vline
Disadvantages :
1- Vs is distorted wave
2-un balance load
3-third harmonic causes over voltage
4-

62. • Delta –Star :

63. •Advantages :
1- low current in each phase
2- third harmonic circulate in delta
3-earth fault current follow in Neutral for
star
4- Zero sequence current circulate in delta

64. • Delta-Delta:

65. •Advantages :
1-use in low voltage and high current where
Iph=57%of Iline sothat winding Tr is low in
cross section area and copper
2-third harmonic circulate in delta
Disadvantages :
1-Weak for mechanical stress and electrical
stress
2- Not neutral (N) ,if occurs fault increase
voltage on three phase

66. • Earthing faults in Delta-Delta connection :

67. • Interconnected star: (Zig Zag)

68. Rt
Zig Zag transformer in the earthling

69. • Delta-Zig Zag Connection:

70. • Example 1:
This number 925554 on transformer body:
Example 2 :
75554 or 025554
1 50 KVA
2 100
3 200
4 300
5 500
6 800
7 1000
8 1500

71. • What “s the meaning:

72. • BIL ( Basic impulse level :
Ability insulators inside Tr to increase in
voltage result surge or opening and
closing