CT (flux) saturation

just learned about saturation the hard way:

i play with current measurement, CT N ( turns) and burden resistor and i run into that problem.


Background: for a given current transformer if the burden resistor is to high and the primary current to high

the CT goes into saturation. ( can find lots of references here too, but interesting to read www.idc-online.com/technical_references/pdfs/electrical_engineering/current_transformer_concepts.pdf )


Symtoms for CT in saturation:

 - for calibrating EMON by a low current get a ICAL factor.

   but when you test it with a high current need a ICAL factor twice or more

 - when calibrating PhaseCAL to get p=1.0  with a OHM LOAD need high values ( 4..) instead the default 1.7


and that is how my arduino inputs looked like ( Ain range 0 .. 1023 for 0 .. 5V with 2V5 AC offset)

volt current


here i exceeded the prim. AC current (1.7A)

for the CT ( N = 1000 )  and used burden resistor (470ohm) measuring range is only about 1A.


Robert Wall's picture

Re: CT (flux) saturation

kllsamui's picture

Re: CT (flux) saturation

thanks, very good link.


only using arduino and no scope available it was very interesting for me to see that current plot.

as the CT is less 1$ i still think its worth the extra work.


a combination of range adjustment by burdenresistors

 - one big soldered to CT  ( low ampere range )

 - one small parallel to it by jumper ( high ampere range )

+ using the trick to loop the primary current 2..3 times through the CT  for increase sensitivity for low currents

gives many possible configurations.

but just lookout for that saturation trap.


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