Why CT secondary should not be kept open?



CTs are used for the measurement of high currents as a 

primary sensor. The output of the CT is normally connected 

to the relevant ammeter which has very low impendence and 

secondary remains almost short circuited. The secondary 

current has no control over primary current in a CT. If 

secondary is open circuited two things will happen :
1. Due to absence of secondary current no counter magnetic 
field is produced and flux in core of CT rises to 
saturation level which can change the charateristics of CT 
and damage it permanently 
2. since number of turns in secondary is very high (1: 
1000) for , a very high voltage may be induced in secondary 
that can harm the persons working on the instruments panel.
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