CT - Measurement + post "CT Sizing" 10/02/10 by jwparker

[trbartlett]

I have some questions around the same guys...
Retrofitting power monitoring to a sub-station which only has protection ct's fitted. It has been decided that 3 measurment ct's will be installed. Substation 66/11kV. Going on tx size, 400Amps seems to be max constant secondary. Protection CT's are 600:1 and the guy asking me to sort this for him has asked me to try and find 600:5 split core measuring ct since the sub will only be down for a short time - i am not sure if such a beast exists.
He is hoping to hook it to a satec PM175. (the existing protection ct's are hooked to a satec PM171E - off drawing)The PM175 specifies a burden of 0.1VA. I was wondering what voltage the PM175 would see at its input if 600:5 ct hooked up assuming primary current did get as high as 600amps? 20mV?
The other thing is i have had some guy tell me that a split core is available but isolation level is only 7kV - can someone guide me here - the cable it is going around is insulated etc photo attached
Thanks in advance ...

 

[rcw retired EE]

Here's one source. Check opening dimensions.

Many others are available from other suppliers.

http://www.electroind.com/ct-split.html

 

[jghrist]

I was wondering what voltage the PM175 would see at its input if 600:5 ct hooked up assuming primary current did get as high as 600amps? 20mV?

Yes. V = VA/A = 0.1/5 = 0.02

 

[trbartlett]

Me again...with another question. I was thinking about a 400:5 ct's rather than 600:5 for the power monitoring application since i believe the acuracy would be little better however, I was questioned as to whether short time peaks would be captured such as motor starts etc. My immediate thoughts were that this sub supplies a whole mine site and if there were questions as to a motor start 'seen' at 11kV at the substation causing values outside of the CT's specified paramenters then perhaps the whole electrical infastructure was about to collaps in a heap. So i dismissed it as not a problem. However, i have been thinking about the starting of a 4000hp sync motor (3.3kV) sometimes carried out DOL. I am sure that would be notable at the 11kV sub but then it gets back to the question of durations, connection agreements, electrical regulations and moreso what is being done with the monitored information. As there will always be instantanious and very short time peaks which may be outside the parameters of the CT's, I am not quite sure where the boundaries of power monitoring are. How much is supposed to be recorded? Thanks in advance for any guidence and comments on this topic...