A "Primary Turn" is the number of times the
primary conductor passes through the CT’s window.
The main advantage of this
ratio modification is you maintain the accuracy and burden capabilities of
the higher ratio. The higher the primary rating the better the CT accuracy
and burden rating.
You can make smaller ratio modification
adjustment by using additive or subtractive
"Secondary Turns". Example: A CT
with a ratio of 100:5A, by adding 1 additive "Secondary
Turn" the ratio
modification is 105:5A. By adding one "Subtractive "Secondary Turn" the
ratio
modification is 95:5A. Subtractive secondary turns are achieved by
placing the X1 lead through
the window from the H1 side and out the H2 side.
Additive "Secondary Turns" are achieved by
placing the X1 lead through the window fromH2
and out the H1 side. So when
there is only 1 primary turn each secondary turn modifies the ratio by 5
amperes. If there is more than 1 primary turn each secondary turn value is
changed (i.e. 5A divided by 2 primary turns= 2.5A) The following table
illustrates the effects of different combinations of primary and secondary
turns.
