What is the difference between CT for protection and Ct for
metering?

Answer Posted / shashi kant

PROTECTION CT CORE is different as compare to Metering CT,
as metering CT SECONDARY is connected to meter to measure
so accuracy is needed ,so the core of Metering CT is
designed or made in such that its core gets saturated on
enmourse increase of primary current, for ex CT with
accuracy of 125% of rated current of ratio400:1, means its
seconary current will never go beyond 1.25amp i.e if the
primary current is 1000 amp,as by the above ratio the
secondary current should be 2.5amp, but in the case of
protection CT as its secondary is connected to relay to
sense the fault current so accuracy is not so important ,
if metering CT IS placed in place of protection ct, then in
case of any fault a heavy fault current in primary of
Metering CT the secoundary output current will be limited
to its rated current (generally 125%) which will be normal
and so the relay may not able to sense the fault

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