Facts OF Transformers & Termonolegy The Presentation Covers clear understanding for students and fresh engineers

1. WELCOME

2. TRANSFORMERS
Facts/features/terminology
By
K.R.Suri
Retd. General Manager,
PGCIL

3. TOPICS FOR DISCUSSION
POWER Xmers Vs Distt. Xmers
Functions of Radiators/Cooling
Types of Xmers.
Capacity
Flux Density

4. TOPICS FOR DISCUSSION CONTD.
Vector Group
Harmonics
%age Impedance
Parallel Operations.
OLTC
Protective equipments in Xmers.

5. POWER VS DISTRUBTION XMERS
No description available to
distinguish.
However Xmers upto 10 MVA, 33/11
Kv are Distribution Xmers. Beyond
that all are Power Xmers.
Available Power Xmers
 3 Phase,400Kv, 315/500 MVA
 1 Phase, 400kv, 105MVA
 1 Phase 765/800Kv, 500MVA

6. POWER VS DISTRUBTION XMERS CONTD.
Distribution Power
Designed for
maximum Efficiency at
around 75% of rated
capacity
Designed for
maximum Efficiency at
full load at its rating.
Designed for low flux
density i.e. 1- 1.2
Tesla. As they are
subjected to low
Voltage conditions.
Designed for high flux
density i.e. up to 1.7
Tesla. As they are
subjected to high
voltages under light
load conditions.

7. POLE MOUNTED XMER

8. 33/11 KV XMER

9. 400KV, 500 MVA XMER

10. 1PHASE 765 KV XMER

11. 1PHASE 765 KV XMER

12. FUNCTION OF RADIATORS OR COOLING
Radiators cool the Xmers indirectly
through Xmer oil.
Xmer oil when gets heated up has a
tendency to rise up and thus
automatically circulates within the
Xmers for cooling

13. RADIATOR COOLING PRINCIPLE
TRANSFORMER
Radiator
Bank
Heated oil Goes Up

14. TYPE OF COOLING
ON – Oil and Natural.
ONAF– Oil natural Air Forced.
AFOF – Air forced Oil Forced.

15. OIL & NATURAL [ON] COOLING

16. FORCED AIR COOLING

17. FORCED AIR COOLING

18. OFAF COOLING
TRANSFORM
ER
Radiator
Bank
Heated oil Goes Up
M

19. OIL PUMP

20. EFFECTS OF COOLING
 500MVA – 400KV
 Max. Temp. Rise Allowed 50˚ Above
Ambient.
 However while designing Techno -
Economical Factors are considered.
ONAN ONAF OFAF
MVA 300 400 500
Current 433 578 725

21. TYPES BASED ON WINDINGS
2 Winding Xmers
3 Winding Xmers
Multi Winding Xmers
Auto Xmers

22. 2 WINDING XMER

23. 3 WINDING XMER

24. MULTI WINDING XMER

25. AUTO XMER

26. TYPES BASED ON OUTPUT PHASES
3 Phase to 3 Phase
3 Phase to 1 Phase
3 Phase to 2 Phase
3 Phase to Multi Phase

27. 3PHASE TO SINGLE PHASE XMER.
127*1.732 = 230 V
127V
127V
127V
230
V
230
V
230
V

28. 3 PHASE TO 2 PHASE XMER

29. SCOT/T CONNECTED XMERS.
120°
90°

30. BENEFITS OF MULTI CIRCUIT XMERS
Mostly incoming supply is
unbalanced magnitude wise
as well as vectorally.
Hence output voltage is
regulated and gives balance
loading to primary.

31. UNBALANCE LOADING

32. LIMITATIONS OF MULTI CIRCUIT XMERS
Not Rated so Far more than
10 MVA and high Voltages
upto 33 KV.

33. TYPE OF XMER CONSTRUCTION WISE
Dry / Resign Bonded
Oil Type

34. DRY/RESIGN XMER

35. RATING WISE TYPES
Continuous Rating
•POWER XMERS
•DISTRIBUTION XMERS
Short time rated
•TRACTIONS XMERS
•ARC FURNACE XMERS
•MINING XMERS

36. OTHER TYPES XMERS
High Impedance / Neutral
Grounding.
Isolation
Special type Traction

37. SPECIAL TRACTION XMER FOR
INDIAN RAILWAYS

38. VECTOR GROUP
Δ ↔Υ ↔ Υ
Δ ↔ Δ

39. VECTOR DIAGRAM

40. VECTOR DIAGRAM

41. TESTING FOR VECTOR GROUP

42. VECTOR GROUP OF AUTO XMERS

43. HARMONICS
Xmers of High Capacity
beyond 250 MVA have
tendency to generate 3rd
harmonics.
3rd Harmonics -- ?

44. HARMONICS

45. HARMONICS

46. REASONS OF HARMONICS
Inherent design of Xmer
Developed due to characteristics of
Load i.e. Induction Motors.
CFL/Tube Lights, Neutral Unbalance,
Quality of CRGO, Arc Furnaces
Out of Which third harmonic is more
prominent.

47. REASONS OF HARMONICS CONTD.
To suppress 3rd harmonics within
the Xmer and not to travel in power
system they are allowed to circulate
with in 3rd winding i.e. Territory
Winding.

48. TERRITORY WINDING
R
Y
B
3rd Harmonics
Circulates within
Delta

49. CAPACITY
315 MVA 300+15*MVA
500 MVA 470+30*MVA
 * Rated for this capacity,
However Not used.

50. TERRITORY WINDING - 1 PHASE

51. TERRITORY WINDING - 3 PHASE

52. %AGE IMPEDANCE
It is called as Voltage drop in
transformer due to winding
resistance and leakage
reactance.
It is also called as voltage
required on one side to
calculate full load current under
short circuit condition of other
side.

53. %AGE IMPEDANCE CONTD.
Has a major effect on symmetrical
faults and determines maximum
current flow through transformer under
fault condition.
Xmer with Low %age impedance will
have to face more fault current.
V=ZI , I= V/Z Hence I is inversely
proportnal to Z
Low Impedance More current

54. However High Impedance means
increase voltage drop increases Xmer
losses, Decreases Short Circuit
Current, Big Size of Xmer
Which in other mean in techno -
economical way
Normally Power Xmer are designed a
range from 9% to 12%
Distribution Xmer are designed 5% to
8%
%AGE IMPEDANCE CONTD.

55. IMPEDANCE CHECK AT SITE

56. SIGNIFICANCE OF %AGE IMPEDANCE
It has a major role to Play
in Parallel operation of
Xmers.

57. WHY %AGE IMPEDANCE SHOULD
BE SAME
Xmer having different %age
Impedance i.e. Internal Drop will not
share load in equal proportion.
Effective Impedance (Z) of Xmer is
 %age Impedance*V2/MVA

58. PARALLEL OPERATION OF XMERS
CB
T1 T2

59. CONDITIONS OF PARALLEL OPERATION
Voltage & Ratio should be same
Vector Group / Phase Sequence
should be same.
%age impedance should be same.
Tap Changer Ratio should be same.

60. XMERS HAVING DIFFERENT
IMPEDANCE/CAPACITY
 Xmer %age Imp. Capacity Voltage Effective Imp
 A 12.5 315 400 63.5 Ohm
 B 10.5 315 400 53.35 Ohm
 C 12.5 500 400 40 Ohm

61. CASE I --- EQUAL %AGE IMPEDANCE
ASSUMING TOTAL LOAD 800 MVA
63.5
Ohm
63.5
Ohm
40 Ohm,
500 MVA
315
MVA
220 Kv
400 KV
223
MVA
223
MVA
354
MVA
I = 800*1000/400*1.73
=1155 A

62. Effective Impedance
1/R = 1/R1 + 1/R2 + 1/R3 = 17.7 Ohm
Current Through 500 MVA Xmer =
511 Amp. = 354 MVA
Current Through 315 MVA Xmer =
321.5 Amp. = 231MVA
Total load 816 MVA

63. Load on each Xmer shall be in the
ratio of
500/315 =1.58 MVA Ratio
511/321.5 =1.58 Current Ratio
Hence Each Xmer share load
according to its capacity

64. CASE II – UNEQUAL %AGE IMPEDANCE
ASSUMING TOTAL LOAD 800 MVA
63.5O
hm
63.5
Ohm
315
MVA
220 Kv
400 KV
251
MVA
251
MVA
290
MVA
I = 800*1000/400*1.73
=1155 A
315
MVA
53.3
Ohm
500
MVA

65. Effective Impedance
1/R = 1/R1 + 1/R2 + 1/R3 = 19.90 Ohm.
Current Through 500 MVA Xmer =
431 Amp. = 298 MVA
Current Through 315 MVA Xmer =
361 Amp. = 251MVA
Total load 800 MVA

66. Load ratio on each Xmer is
500/315 = 1.58 MVA Ratio
431/361 = 1.19 Current Ratio
Hence Each Xmer is not sharing load
according to its capacity.

67. CONCLUSION
600 MVA = X+X*1.19
600 MVA = 2.19*X
X = 274 MVA
600 = 274+1.19*326
Hence Load can only be allowed
between 550 to 600MVA.

68. TAP CHANGERS
Types
Off Load
On Load

69. OFF LOAD TAP CHANGER

70. ON LOAD
TAP
CHANGERS

71. ON LOAD TAP CHANGER

73. OLTC
 Always installed on HV Side to reduce
Rupturing current to avoid damage.
 Windings are added when input Voltage gets
Reduced.
 Windings are reduced when Input Voltage is
high.
 V1N1 = V2N2
 V2 = V1/N2*N1 = K*N1

74. TRANSFORMER OIL
 TYPES
 NAPTHELENE BASE
 PARAFFIN BASE

75.  NAPTHA BASE
 EASILY OXIDISED------ HENCE SLUDGE FORMATION
IS MORE. SLUDGE CIRCULATES WITH OIL AND
DOES NOT HINDER COOLING
 PARAFFIN BASE
 SLOW OXIDATION RATE, IT IS INSOLUBLE THUS
RESTS AT BOTTOM OF TANK & EFFECTS
COOLING
 INDIAN CONTEXT ---- PARAFFIN IS USED,
AS EASILY AVAILABLE

76. PROTECTIVE EQUIPMENTS
Buchhloz Relay
PRV
MOG
Silica Gel Breather
Fire Fighting System
 Water Spray System
 Nitrogen Fire Extinguish System.

77. BUCHHLOZ RELAY

78. PRV
Transformer

79. MOG

80. SILICA GEL BREATHER

81. HIGH VELOCITY WATER SPRAY FIRE
EXTINGUISH SYSTEM

82. TEMP. SENSORS
Sensors

83. NITROGEN FIRE EXTINGUISH SYSTEM

85. NITROGEN CYLINDER

86. Than
k
you