Working and Different types of Current Transformers with its Characteristics.

1. CURRENT TRANSFORMER
PREPARED BY:
MAYURSINH RATHOD

2. CONSTRUCTION
 Current Transformer is Instrument transformer which is used for measure
high current of transmission line.
 By using C.T. we can measure high current from normal rating Ammeter(0-
5 A).
 C.T. have primary winding of few turns of thick copper conductor which is
connected to series with heavy current carrying conductor.
 The secondary winding is made of more number of turns of thin copper
conductor.
 The secondary winding is connected to coil of normal rating ammeter.

3. CONSTRUCTION
 The following figure shows construction of C.T.

4. WORKING
 The C.T. is step up transformer which step up the voltage of primary side
to secondary side.
 From current point of view, C.T. is step down transformer which step down
current of primary to secondary.
 Its depends of following equation,
𝐼1
𝐼2
=
𝑁2
𝑁1
where, 𝐼1= primary current
𝐼2= secondary current
𝑁1= number of primary turns
𝑁2= number of secondary turns

5. WORKING
The following figure shows measurement of line current

6. CORE DESIGN
 Amount of exciting current dawn by C.T. depends on material of core and
flux developed in it.
 The appropriate current ma be obtained directly from exciting
characteristic of C.T. The general shape of characteristic is as shown below.

7. CORE DESIGN
 The characteristic is divided into two region which are ANKLE POINT and
KNEE POINT.
 The working current extends between this two region and measuring
current operates only in ANKLE POINT.
 KNEE POINT is define as 10% increase in sec. voltage produces 50%
increase in exciting current.
 Beyond the KNEE POINT C.T. is said in ENTER region in this major of
primary current is utilize to maintain flux in core.

8. TYPES
 Types of C.T. is depends on current ratings as following…
Secondary current rating:
 Generally it should be 1 or 5 ampere. For following reason it would be 2
ampere also…
 Not possible to add or remove turn to adjust ratio of primary and secondary.
 Some times load is high so 5 A is very much current, then 2 A is suitable.
 Cost will increase as secondary turn will increase.
 If some reason secondary is opened, very high voltage is produced. It will
damage the C.T. and also trouble for operator.

9. TYPES
Primary current rating:
 It is need to ratio
𝐸𝑥𝑐𝑖𝑡𝑎𝑡𝑖𝑜𝑛 𝑀𝑀𝐹
𝑃𝑖𝑚𝑎𝑟𝑦 𝑀𝑀𝐹
should be low. For this primary current
should be at least 500 A.
 For small side and economically we need to reduce primary current below
500 A by providing multiple turns.
 Following figure shows different types of C.T.s,

10. VECTOR DIAGRAM

11. APPLICATION
 To measure high current by medium range of ammeter
 Small current requirement from high current conductor
 Very high voltage requirement