Difference between Closed loop hall effect sensor and toroidal CT?

https://i.stack.imgur.com/H3u6Y.jpg https://i.stack.imgur.com/aIF19.jpg

Attached are image of CTs used in an overload relay. My major was in Power System Protection so don't know much about electronics. On an internet search there came out to be two kind of CTs; toroidal and closed loop hall effect sensors that resemble these CTs. Can someone please help me out with these CTs. Which kind of CT are these? and how can I get one? What I know is that they operate at 50 Hz and have primary at 60A.

by abdulmunim
October 03, 2017

I would suspect those to be just two terminal current transformers with associated measurement circuitry. Hall effect types have more contacts. The part in your photo appears to come from an obsolete Schneider Electric S50. To buy small quantities of CT go to Farnell or Digikey, for large quantities go to AMGIS.

by mikerogerswsm
October 03, 2017

its EOCR SSD 60 from Samwha. Thanks a lot for the answer. There's a [DEC] M7 diode rectifier taking input from each CT core via a Capacitor.

by abdulmunim
October 03, 2017

That sounds right. The CT should have a load resistor across its secondary. For example a 1:1000 transformer with a 10k load presents 10k/N-squared ohms, ie 0.01 ohms at the primary (the single-turn conductor). The secondary voltage is converted to dc by the diode and compared with a reference voltage. When it is greater than the reference, overcurrent shutdown is triggered. Very crude, but good enough to stop a stalled motor from burning out. Other systems use a combination of peak, average, and true rms processing. There is a delay to permit the motor to draw high starting current briefly.

by mikerogerswsm
October 03, 2017
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