- #1
HomeExperiement
- 55
- 5
Hi!
I have question about current transformers (CT). I have BH-0.66 class 0.5 20/5 current transformer. According to my understanding 20/5 means 4 times current reduction. For some reason I get about 20 times current reduction. Now I am curious if the factory managed to label 100/5 CT as 20/5 CT or if those integrated CTs have some specific needs in order to work correctly that I am not aware of.
I know that it measures about 20 times less current because I compared it with multimeter. And also tried clamp meter. At least with clamp meter I get correct reading easily. And polarity or cable angle doesn't seem to affect reading too much - maybe +/- 10%. But with CT looks like no matter how I wire it the reading is always about 20 times less, not 5 like I would expect. It happened with both small and large loads. And that is why I was wondering if there is something specific that I need to know about CTs in order to get correct reading that normal clamp meter hasn't require me to learn yet.
Also I got one more question when I was reading about CTs from interenet:
https://testguy.net/content/190-Current-Transformer-Basics-Understanding-Ratio-Polarity-and-Class
Here it says that
I have question about current transformers (CT). I have BH-0.66 class 0.5 20/5 current transformer. According to my understanding 20/5 means 4 times current reduction. For some reason I get about 20 times current reduction. Now I am curious if the factory managed to label 100/5 CT as 20/5 CT or if those integrated CTs have some specific needs in order to work correctly that I am not aware of.
I know that it measures about 20 times less current because I compared it with multimeter. And also tried clamp meter. At least with clamp meter I get correct reading easily. And polarity or cable angle doesn't seem to affect reading too much - maybe +/- 10%. But with CT looks like no matter how I wire it the reading is always about 20 times less, not 5 like I would expect. It happened with both small and large loads. And that is why I was wondering if there is something specific that I need to know about CTs in order to get correct reading that normal clamp meter hasn't require me to learn yet.
Also I got one more question when I was reading about CTs from interenet:
https://testguy.net/content/190-Current-Transformer-Basics-Understanding-Ratio-Polarity-and-Class
Here it says that
I was wondering if there is any reason why it should be important in my case where I only have single phase AC and one meter? At least the clamp meter doesn't seem to care.It is very important to observe correct polarity when installing and connecting current transformers to power metering and protective relays.