Open CT
Open CT
(OP)
I recently found arcing/melting on shorting terminal block for a set of 2000:5 ct for some 480v gear.The terminal block is melting and it would not be possible to tighten the screws. Obviously, the CT's are open and I don't want to touch it. Unfortunately I have to shut the entire plant down to fix this - very, very painful. What will happen if the CT goes fully open? Could this cause a fault in the gear?






RE: Open CT
If the CT terminals are open, then there will probably be some flashovers between the terminals, depending on how close the are. If they are not sparking, then there is probably some internal flashing, and eventually there will be a short in the secondary winding. This causes high current flow and potentially high temperatures.
It's hard to say if the gear will fail or not, without more detail on the installation.
My advise.....take the outage. Besides equipment damage, it is a definate safety hazard!
RE: Open CT
Discuss the financial effects and safety aspects of a forced/unscheduled outage with your managers.
RE: Open CT
Can you verify which phase CT conection is shorting?
I would expect that if you said that the shorting block 'is melting' that you have a continuing problem(i.e. it hasn't burned itself closed or open). You might be able to verify this with an IR scan.
Bottom line, schedule a shutdown ASAP, but make sure you have replacement CTs(and a shorting block) on hand.
RE: Open CT
A problem may be the internal-CT activity externally propagating to melt larger pieces of copper.
RE: Open CT
I don't follow your last comment. Can you please offer more detail?
Unless there is enough primary current in the CT to drive the secondary current higher, the secondary current should not be at a level to melt any suitable copper connection. If the primary current is high enough to drive high currents through the secondary, then he's got a bigger problem!
RE: Open CT
RE: Open CT
Had an x000:5 C200 CT "drool" and track across a Glastic bus support, faulting at 277V and tripping a unit-sub hi-side (12kV) 50/51. About a dozen local ACBs had working 'LSIG' protection, but they were downstream of the failed CT. CT "singing" had been noticed, but its meaning was not understood, and didn't get reported in time.
IIRC, the gear builder submitted 2-element watt and watthour meters in as-builts, but 2½- or 3-element components were installed.
RE: Open CT
http://www.insulatedtools.com/
for high voltage insulated tools and cloth. The CT secondary voltage against ground should be measured first.
RE: Open CT
http://www.ee.uidaho.edu/ee/power/EE525/lectures/L16-17/plots.pdf
for Open CT Secondary Voltage plot, ~40000VAC