[SOLVED] Current Transformer. Help!

Hello Everyone,

I am currently working on a Energy Meter project and I will be purchasing a Current Transformer. Before I will purchase I wanted to make sure that my understanding is correct, so please help me out.

With my type of project, I would be needing a Current Transformer that has more Primary winding than Secondary winding ratio (Ex. 200:1), right?

I based my assumption that a current transformer ratio means I primary : I secondary?

I am confused with the Idea that if the ratio is referring to voltage (V primary : V secondary) and just calculate the corresponding current, it could make me buy the opposite kind of Current Transformer I need for my project.

Looking forward of hearing from you guys. Thanks

I would be needing a Current Transformer that has more Primary winding than Secondary winding ratio (Ex. 200:1), right?

Click to expand...

Surely wrong. To get a lower current "copy" of the primary current, the secondary winding needs more turns than the primary. Review transformer equations https://en.wikipedia.org/wiki/Transformer

Thank you for your answer, what confused me though is my idea of a current transformer where it only has 1 Coil around a circular magnetic core. And the wire to be measured should pass through the magnetic core. In other words, i cant picture out why the current transformer has two coils to begin with.

My understanding about transformer ratio is that Power (P) is just Pprimary = Psecondary. V*I (primary) = V*I (secondary), P/Vprimary = P/Vsecondary.

Sir if you may, please suggest a current transformer ratio that I can look into, so it could narrow down my research to understanding why that particular ratio is applicable to my purpose. Thank you so much for your time.

eebhoi01 said:

I based my assumption that a current transformer ratio means I primary : I secondary?

Click to expand...

I beg to differ. Please consider the basic principles of operation. Current transformers are just regular transformers...

The basic cause is the oscillating magnetic field- that is produced by an alternating current. The magnitude of the oscillating magnetic field is proportional to the magnitude of the current and the number of turns which in turn depends on the applied voltage and the impedance of the transformer primary.

The oscillating magnetic field produces a voltage in the secondary that depends on the number of turns in the secondary. If some current is allowed in the secondary that will in turn oppose the magnetic field (the cause).

In real life current transformers you will have one or two turns for the primary and the secondary will be much larger. The secondary produces a voltage which is often loaded with a resistor and filtered to get a final voltage that is proportional to the primary current.

eebhoi01 said:

Sir if you may, please suggest a current transformer ratio that I can look into, so it could narrow down my research to understanding why that particular ratio is applicable to my purpose. Thank you so much for your time.

Click to expand...

That depends on how much current you wish to measure in the primary.
0.1amp, 10 amps, 10,000 amps ?

And what you plan to connect to the secondary.
Is it an analog ac amp or milliamp meter.
Or do you require just a low voltage as an input for an electronic measurement circuit ?

Also.....all current transformers must have a burden resistor in parallel with its secondary.

The value of the required burden resistor is given on the datasheet.
For instance, for the Coilcraft CS60-010, a 50 ohm resistor is required: