Hello,

I have a Toroid core Current transformer(for protective inst) whose current range is 1- 100 A rms with turns ratio of 1:2500 (Datasheet says). I have only 30 Amp current source to test the CT. If I inject 20 Amp thru the primary wire by looping it around the core 4 times (primary turns become 5) I get the approx equivalent current (as with direct injection of 100 Amp) at secondary. My question is that conclusive that the CT core will behave same if i could have passed 100 Amp current thru' primary wire (instead looping). Is there any better way to test it ??

Regards,
tech77

 

Tech787... there is a simple way to test it, but the data you presented is conflicting!

If the CT turns-ratio is 2500:1, then passing 2,500 A in a single conductor thru the window, produces an mmf of 2500 AT. Thus, a circuit connected to its secondary terminals will carry 1 Ampere.

For the case you cited, 20-A looped 5-times thru the window, yields an mmf equal to 5x100 or 100-AT, and the corresponding secondary will carry 100/2500 or 40 mA.

My question to you is, "What does a range of 1-300A mean?"

Regards, Phil Corso

 

Hi Phil,

CT is 1 - 100 Amp current range & turns ratio 1 : 2500. The CT is Toroid core & it has only 2 secondary terminals and the wire i will insert (pass thru) the core will act as Primary wire. If 100 Amp flows thru' primary , 40 mA will flow at secondary. Now if i increase the primary turns to 5 and flow 20 Amp thru' primary the same 40 mA will flow thru secondary. Now i wanted to know the effect of Primary current on the core in the above 2 cases? will they be same? By flowing 20 Amp and increasing primary loop can i be sure to have seen the effect of 100 Amp flowing thru single primary wire??

Regards,
tech77

 

Tech77...

A) Range: The 1 to 100A range you have identified is the range of current normally expected in the protection circuit!

B) Turns-Ratio: Because the ratio is 2500:1, then, any ampere-turns (ATs) produced in the primary, whether 2500-A in a bus passed thru the CT 'window' or 1-A in a single conductor looped 2500 times around the toroid, will produce an mmf of 2500 ATs.

C) Reur Question: Yes! Unless there is a defect the current in the secondary will always be primary ATs divided by 2500! At least until saturation of the CT occurs.

Phil Corso