Answer / mahesh

Metering ct needs high accuracy(ie,value of metering ct should be small 0.1,0.2,etc.,) than protection ct ie, metering ct accuracy class will be=0.1,0.2,0.5,1,3 and 5
eg;
The accuracy class of measuring or metering CT is 0.1, means the maximum permissible limit of error is 0.1%, more clearly, if we try to measure 100 A with a 0.1 class CT, the measured value may be either 100.1 or 99.9 A or anything in between these range.

for protection CT the accuracy class is low (ie, value of protection ct should be high 5P,10P,15P)

Answer / raja

Protection CT will be more sensible then Metering CT

Answer / mulengal

by design protection cts have lower burden which allows for
higher fault currents while metering cts have higher burden
which allows for accuracy

Answer / kadiresan.k

Generally CT is used to measure higher currents, We need
both Metering and Protection CTs seperately with different
class of accuracy. The purpose of metering CT is to read
the actual current, so it has less class of accuracy.
Whereas in case of protection CT, The measured value of
current is used to protect the equipment by identifying the
abnormalities at the initial stage itself, (provided the
protection relay is tuned perfectly)and protects the
equipment(motors/transformers/transmission and distribution
systems)So it needs high accuracy than metering CTs.

Answer / minal

ct for protection means that current transformer is used to
step down the higher values of current to lower values
which is to be measured by the instruments.Thus it protects
the equipment from damages.
ct is also used to measure the low values of current.This
is how it is used for metering.

Answer / infodoss

CT is used to measure the transmission current.
Transmission currents are very high so cannot messure
directly.first to step down the current and then measure
the current using some ratio.CT protection is used to
avoide the aceident and eleminating losses.

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