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