CT, PT And CVT It help in measurement of high voltage And current. * It provide low voltage and current to the electrical device. * It’s measure application is in the protection system where relay is work on low amount of voltage and current.

1. ”INSTRUMENT
TRANSFORMER”
Presented by :
*Nishant kumar
Reg. No. 0701209350
Electrical & Electronics Engineering
Silicon institute of technology , Bhubaneswar

2. [ Contents ]
▪Instrument transformer
 Introduction
 Classification
▪Current transformer
Principle of Operation
Construction & Classification
 Application & Specification
2

3. ▪ Potential Transformer
Principle of operation
Construction ,Classification & Application
▪Electromotive voltage
transformer
Introduction
Construction & Application
▪ Capacitive voltage transformer
Introduction
Construction & Application 3

4. [ Introduction of instrument
transformer ]A electrical device which help in measurement
of high voltage or current.
It provide low range current and voltage to the
protection system.
By using low range ammeter can measure
high current.
By using low range voltmeter can measure
high voltage.
4

5. [ Types of instrument transformer ]
Instrument transformer has two type
1) Current transformer
2)Potential transformer
5

6. [ current transformer ]
 It is normally known as CT.
This is a type of step up transformer.
This is step up transformer because when
we step up, the voltage increases and
current decrease.
 The current is step down in a known ratio
called current ratio.
6

7. [Construction of current transformer]
7
The current transformer has primary coil
of one or less no. of turns of thick wire
which is connected in series with the
transmission line.
It’s core is made of by rolled steel.
The secondary consist of large number of
turns of fine wire.
The secondary and primary winding are
insulated to each other and oil immersed.

8. Current transformer
8

9. CURRENT TRANSFORMER
9

10. [classification of current transformer]
On the basis of primary winding
1) Wound type
2) Bar type
On the basis of secondary winding
1) Ring type
2) Stadium type
3) Rectangular type
On the basis of working
1) Summation CT.
2) Core balance CT.
3) Interposing CT. 10

11. [ Standards ]
The Indian and international standard for CT
o Standard Standard no. Year⁞ ⁞
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
British BS 3938 1973⁞ ⁞
 American ANSI C.57.13 1978⁞ ⁞
 Australian AS 1675 1986⁞ ⁞
 India IS 2705 1992⁞ ⁞
 IEC IEC 60044-1 1996⁞ ⁞
(International electro technical commission)
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Manufacturing company
 BHEL,CGL,ABB,Joti,Siemens… Etc.
11

12. [ Testing of current transformer ]
Different type of test :
 Accuracy test
 Dielectric insulation test
 Temperature rise test
 Verification of polarity test
Different method of testing
 Mutual induction method
 Silsbee’s method 12

13. [ Specification ]
 For a 11 kv CT.--------------------------------------------------------------------------------------------
 System voltage : 11 kv
 Insulation level voltage : 12/28/75 kv
 Ratio : 200/1-1-0.577 A
 Core 1 : 1 A metering
 Core 2 : 1 A protection
 Core 3 : 0.577 A, Class power supply
 Short time rating 20 kA for 1 sec
 Insulation security factor : ISF<10 13

14. [ POTENTIAL
TRANSFORMER ]Potential transformer normally known as
PT.
That is a type of step down transformer.
Step down transformer ,step down the
voltage and rise the current.
The voltage is step down in the known
ratio called voltage ratio.
14

15. [ principle of operation ]
It is always connected in parallel to the
transmission line.
It’s secondary winding is very low with
respect to the primary.
The secondary winding is designed so
that a voltage of 100 to 150 v is delivered
to the instrument load.
Line voltage =voltmeter reading/Ratio
Ratio=no. of turn in secondary/no.of turn in primary
15

16. POTENTIAL TRANSFORMER
16

17. POTENTIAL TRANSFORMER
17

18. [ construction of potential
transformer ]
Core size is large and made of by steel.
Primary side large no. of turn.
Secondary side only few no. of turn.
Secondary and primary winding are
insulated to each other and oil immersed.
18

19. [ classification of potential
transformer ]
Types of potential transformer
1) Shell type
2) Dry type
3) Oil type
-----------------------------------------------------------------------------------------------------------------------------------------
Rating Type
------------------------------------------------------------------------------------------------------------------------------------------
Below 5000 v Shell type
5000 – 138000 v Dry or oil type
Above 138000 v Only Oil type
--------------------------------------------------------------------------------------------------------------------------------------------
19

20. [ Standards ]
The Indian and international standard for PT
o Standard Standard no. Year⁞ ⁞
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 British BS 3841 1973⁞ ⁞
 American ANSI C.57.13 1978⁞ ⁞
 Australian AS 1243 1982⁞ ⁞
 India IS 3156 1992⁞ ⁞
 IEC IEC 186 1987⁞ ⁞
(International electro technical commission)
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Manufacturing company
 BHEL,CGL,ABB,Joti,Siemens… Etc. 20

21. [ Testing of Potential transformer ]
Different type of test :
 Accuracy test
 Dielectric insulation test
 Temperature rise test
 Verification of polarity test
Different method of testing
 Absolute null method
 Employing capacitance divider method
21

22. [ specification ]
For a 11 kv VT :
System voltage : 11kv
Insulation level voltage : 12/28/75 kv
Number of phase : Three
Vector Group : star/star
Ratio : 11 kv/ 110 kv
Burden : 100 VA
22

23. [ Electro motive voltage
transformer ]
o Why not conventional type potential
transformer.
Above 100 kv , size are very large.
Insulation problem
High heating effect
Costly to build
23

24. [ designs ]
1. Insulated casing
 Use high voltage insulated oil
2. Moulded rubber potential transformer
 Replace oil and porcelain bushing to
the synthetic rubber.
3. Cascaded transformer
 For voltage divider cascaded n no. of
transformer.
24

25. [ capacitive voltage
transformer ]
A less expensive alternative of electro
magnetic voltage transformer.
Use no. of capacitor as a voltage
divider.
Less insulation problem.
Very cheaper.
Simple circuit.
25

26. CAPACITIVE VOLTAGE
TRANSFORMER
26

27. [ Design ]
 Use capacitor band.
Use an Auxiliary transformer.
Secondary have very low voltage.
Any bus bar protection system or any
measuring device connect to the
secondary of the auxiliary transformer.
27

28. CAPACITIVE VOLTAGE
TRANSFORMER
28

29. Application of instrument transformer
* It help in measurement of high voltage or current.
* It provide low voltage and current to the electrical
device.
* It’s measure application is in the protection system
where relay is work on low amount of voltage and current
29

30. REFERENCES :
• Introduction to the electrical machines.
Macmillan.
• Hand book of transformer design and
applications. McGraw-Hill.
• IEEE Transactions on power Apparatus
And System.
30

31. ANY
Query ???
31

32. Thank You !