Hi..I have to give a current indication of a motor in a remote DCS panel.I already have measurements CTs used to indicate current in the panel itself.It will be right to connect the new CT having ratio 1/1A,in series with the existing 200/1A (window type CT) CT secondary,if burden is not a problem.???

Using a CT fed from secondary of another CT is commonly called an auxiliary CT and we have many like that in our plant.

As you said the burden of both CT circuits needs to be reviewed. The wiring and metering on the auxiliary CT secondary circuit adds to the burden on main CT circuit.

The ratio errors of the two CT's are cuumulative when viewed on the secondary of the auxiliary CT. If you wanted to improve accuracy at that point, I would think you could insert the extra relay and wiring directly in series with the secondary of the main CT (without any aux CT). Since you were planning on using 1:1 CT, the effect on burden of main CT would be the same and the calibration of your new devices would be the same. Less cost, better accuracy. I'm not sure why you would want a 1:1 auxiliary CT unless there is some need for isolation between the circuits.

Thank u for your quick reply....isolation was also one of the main purposes and we were not sure whether it would be correct to connect the remote indication in series with the existing one without ct...I would like to get clarified which one would be more accurate?

It would be more accurate to use only one CT. Less accurate to add a 1:1 CT to the secondary of existing CT (the error would almost double).

Really .. fantastic to see somebody replying to the queries....thank u....got clarified....