Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
Saturation occurs, if the voltage drop at transformer (or more exactly the voltage integral) exceeds a certain value and should be surely avoided, if the transformer is intended for measurment purposes.
Apart from that, it is ruled by usual transformer properties as winding ratio, main an stray inductance, winding resistance and core dependant things. General literature regarding transformers could be found in heaps at the forum.
You need to provide more information on what you want to do.
Current transformers are widely used in electrical power engineering, that is to measure mains current (60Hz or 50Hz). In this case, they use silicon steel cores, not ferrite.
Now, you want to use ferrite core. What frequency range and what current level
do you want to measure? If possible, provide information on the ferrie core you have. This is important because you may not be able to build the transformer if you can not get the specified core, even if someone's recommendation is very good technically.
S. H.
You need to provide more information on what you want to do.
Current transformers are widely used in electrical power engineering, that is to measure mains current (60Hz or 50Hz). In this case, they use silicon steel cores, not ferrite.
Now, you want to use ferrite core. What frequency range and what current level
do you want to measure? If possible, provide information on the ferrie core you have. This is important because you may not be able to build the transformer if you can not get the specified core, even if someone's recommendation is very good technically.
S. H.
Thanks for replay shwoo !
Yes i need it to measure mains current (50Hz).
Actually I need it for UPS out put current over load Protection.
If you want to do calculations, you need at least an inductance factor (AL value) for the core. Although ferrite torroids are not optimal suited for LF current transformer, they may be used, even with a low permeability (≈ AL value) core, possibly with less performance.
Typical current transformer could be 100:1 up 1000:1, implying a 100 to 1000 turns secondary winding. The secondary winding could either be connected to a load resistor or a current amplifier with virtually zero ohms input impedance. The latter would give better accuracy but most likely isn't necessary for this application.
With increasing load resistance, the transformer LF cut-off frequency will rise. It should be, however considerably below your 50 Hz operating frequency. A too high load resistance could also cause core saturation, possibly excessive core heating and high voltages a the secondary. If have no core data, you can start with a resistance that would result in e. g. 100 mV secondary voltage (Uload=Iprim/n*Rload).
Useful number of turns depend on primary current and intended secondary signal and circuit. You should also try to understand the basic behavior of the current transformer. Ignoring stray inductance, you have a secondary current I2 = I1/n^2.
It's a current source in parallel with the transformers main inductance as seen at the secondary,
L2 = AL*n^2
You get a high pass with a cut off frequency fhp = R/(L*6.28), R is the sum of secondary winding resistance and load resistance. With a low permeability core, both windings and load resistance should be low respectively number of turns high to achieve a suitable behaviour. I assume also, you have no torroid core winding maschine, which limits number of turns to a few hundred anyway.
Ziau...
As I said earlier, please be specific.
What kind of current level are you trying to measure?
Are you looking for 1 to 3A? Or 100A?
As you are talking about UPS, I assume the voltage level is a few hundred
volts, for which insulation may not be big issue for professionals.
Why are you stuck with ferrite for 50Hz?
Any reason?
S. H.
Zia dont give me that tired old story about how good I have it living in the United States because its just a way for you to tell yourself its ok to not make the effort needed.
Just because you dont live in the US does not mean that you cant find the information you need to learn about a topic of your choice.
The fact that you have access to the internet tells me that where you live is not all that bad. It could most likely be better but at least you can search for and find the information to gain the knowledge you want.
There are many people on this board that live in places similar to yours or even in places worse off that still manage to locate the information about a given topic and learn what they want. It may take them longer then others but they still learn.
I dont know where you live since you did not put that information on your avatar block but like I said if you have access to the internet you have access to the information you need. Just search for it.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
