Current Transformer

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mjc1060

Senior Member
I have to remove and replace a protective relay for a 4160V circuit breaker. When I remove the protective relay is the CT secondary considered open? Do I need to short the CT before the relay is removed?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I have to remove and replace a protective relay for a 4160V circuit breaker. When I remove the protective relay is the CT secondary considered open? Do I need to short the CT before the relay is removed?
if the primary side is still energized you definitely want to short out the secondary side or you will get an infinite voltage there. the CT should be wired to a shorting block anyway. Just short it out before you mess with it any.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
If the CT wires are ran through a test switch it should shunt when you open them.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
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Retired PV System Designer
if the primary side is still energized you definitely want to short out the secondary side or you will get an infinite voltage there. the CT should be wired to a shorting block anyway. Just short it out before you mess with it any.
The voltage may seem infinite, but it is finite and predicted by the turns ratio of the CT and the load impedance on the primary side, as well as the saturation characteristics of the CT core.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
if the primary side is still energized you definitely want to short out the secondary side or you will get an infinite voltage there. the CT should be wired to a shorting block anyway. Just short it out before you mess with it any.
The voltage may seem infinite, but it is finite and predicted by the turns ratio of the CT and the load impedance on the primary side, as well as the saturation characteristics of the CT core.
And also possibly limited by whatever is the weakest link in the insulation breakdown voltage on the secondary side.
 

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
Here’s what happens when one goes open! LOL! The meter failed on this one, mucho dinero to fix!
 

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hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
How long did that take to occur? Looks like it burned up.
Don’t know how long it took, customer owned meter/transformer/high line from street. I just walked into the store about 15 minutes after it blew a pole fuse. Melted the secondary feeds to the store. The poco went ahead and upgraded their metering at the street. Store was on generator for about two weeks.
 
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