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Current Transformer Rated primary current vs Max. Primary current

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Sultanpepper123:
I've been reading up alot on how to work with a CT. Basicly you have a primary current (eg: 100A) and a turns ratio (eg:1:2500) and a load resistance (eg:5 ohms) so now things are straight forward we can calculate the secondary current (40mA) and let's put a burden resistor 3 ohms to get 120mV while not exceeding the maximum power the CT can deliver. Now I'm currently working on an energy meter design, and while looking for the suppliers i'm getting these specs.



As you can tell the supplier is giving out " Rated primary current " and " Max primary current". I've opened a 80A rated energy meter and found out the CT's have a writing " 5 (80)A / 2.5mA/0.1 " , is it 5A or 80A ?

My questions :

1. On an absolute maximum load 100A will this CT not saturate ?

2. How can i work with this thing ? is it supposed to be saturated somehow and still work on both spectrums ?

UPDATE:

Finally got a reply from a supplier. The response is in the attachments below.

edpalmer42:
You should go to the manufacturer for clarification.  But I would interpret these specs as meaning that your circuit should remain below <Rated Primary Current> during normal operation.  However, under fault conditions, current levels up to <Maximum Primary Current> won't damage the transformer.

Notice that Is * N = Ip .  So that confirms that these values are the normal operating mode.

Ed

Sultanpepper123:

--- Quote from: edpalmer42 on September 19, 2019, 03:31:36 pm ---You should go to the manufacturer for clarification.  But I would interpret these specs as meaning that your circuit should remain below <Rated Primary Current> during normal operation.  However, under fault conditions, current levels up to <Maximum Primary Current> won't damage the transformer.

Notice that Is * N = Ip .  So that confirms that these values are the normal operating mode.

Ed


--- End quote ---

I've sent an email to several manufacturers, if i find anything i'll post an update for anybody who may fall in my situation. Thanks for your help BTW.

soldar:

--- Quote from: Sultanpepper123 on September 19, 2019, 02:03:54 pm --- 1. On an absolute maximum load 100A will this CT not saturate ?

2. How can i work with this thing ? is it supposed to be saturated somehow and still work on both spectrums ?
--- End quote ---

You have a serious misconception. Flux from the primary is instantly counteracted by flux from the secondary. Current is not limited by core saturation. It is limited by copper resistance. That is the way forward power transformers work as well. Only flyback transformers store energy. Forward transformers do not saturate because you add load.

MagicSmoker:

--- Quote from: soldar on September 21, 2019, 09:35:32 pm ---
--- Quote from: Sultanpepper123 on September 19, 2019, 02:03:54 pm --- 1. On an absolute maximum load 100A will this CT not saturate ?

2. How can i work with this thing ? is it supposed to be saturated somehow and still work on both spectrums ?
--- End quote ---

You have a serious misconception. Flux from the primary is instantly counteracted by flux from the secondary. Current is not limited by core saturation. It is limited by copper resistance. That is the way forward power transformers work as well. Only flyback transformers store energy. Forward transformers do not saturate because you add load.

--- End quote ---

Forward transformers will saturate from too many Volt*Seconds (Et), however, and this is what limits the maximum output voltage from a conventional CT. This basically means there is an upper limit to the value of the burden resistor for a given primary current. The CT datasheet will almost certainly give the Et rating; if it doesn't then find another CT vendor.

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