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difference between ct current ratio to turns ratio

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raman00084

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can any one explain the ct current ratio and turns ratio. in my ct the name plate is as follows ratio 10/5 what it is current are turns ratio.
 

a 10/5 ct will have 10 secondary turns and 5 primary turns?
 

or any other number of turns resulting in a 2:1 ratio

It forgot to mention that current ratio is the inverse of turns ratio. The winding with higher current has less turns.
 

i am having a toroidal ct of 10/5 rating, how much primary turns i must loop 1 are 5?
 

I1/I2=N2/N1=10/5=2/1

You can make as much windings as you want but keeping the ratio.
 

A 10/5 current transformer is rarely designed in single turn toroid core "through" technology. In so far it may be an unsuitable example.
 

raman00084, i looked up several 10/5A current transformers and there are differences.

If they have a molded in stud for the primary 10A connection then it would be 10A in and 5A out.

If it has a open hole so you can add more primary winding's then it may be designed for more primary winding's. In one example i found the 10/5A transformer requires 10 primary turns to be added. See last page PDF, FCT29-10/5.

I do not know if 10 turns is a standard for this size CT or if it is manufacture specific.
 

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  • wide range of current transformers and through hole turns datasheet_20.pdf
    207.1 KB · Views: 57

if i make 2 primary turns then what happens?
 

Well i am guessing here. If your CT needs 10 primary turns to meet the nameplate spec of 10/5A, then just two turns would try to make it a 50/5A.

If you used 20 turns then you would have a 5/5A.

Did you look up the exact model you have on the internet to see what the mfg says.
 

I think you need to measure the secondary winding inductance. Then measure the inductance of one primary turn.
Then do NS/NP = SQRT(LS/LP)

However, if there are so few secondary turns that you can physically count them, then just count them..but I would be surprised, since the whole idea of CT (other than isolation) is to make the secondary current much smaller than the primary current.

You usually only ever do one primary turn with a Current transformer.
 

You usually only ever do one primary turn with a Current transformer.
Click to expand...
As shown in the datasheet linked by FlapJack in post #9, this isn't always the case, particularly for CTs with low primary current and 5A output (to be connected to energy meters etc.). But we can presume that the intended operation, including the number of primary turns is clearly indicated in the mounting instructions. In so far there should be no need to count secondary turns, which is a bit difficult with molded windings. Measuring inductance or current ratios is a last resort of course.
 
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