measurements. The most common form is the bar primary type
(Diagram 70).
It is clearly impracticable to construct an instrument to measure
currents as high as say 200-300 A, so a current transformer is used to
step down the secondary current to a value which can be measured on a
standard instrument.
Example 4.3
A current of 300 A flowing in a bus-bar needs to be measured. The
ammeter available has a maximum rating of 0.5 A. How many turns on
the secondary of a current transformer would be required to measure the
primary current? where N
p
=
1
(single bus-bar); I
p
= 300 A ...
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