Answer / p.raju

yes , There is difference between the protection ct and
metering CT in operating conditions

*The CT using for protection will have to carry the fault
currents which are 10 times the normal full load current
thats why it is designed at much bellow the saturation point
(knee)inorder to aviod saturation.

*The CT used for metering will have to carry only full load
current thats why it is designed near to knee point.
as per accuracy concern the metering Ct should be more
accurate under normal operating condition.....i.e under
normal operating condition the pretection CT accuracy not
imp..........

Answer / avdhesh

Metering CT : It will function up to full load current only
then it will be saturated. It will not follow the CTR Above
the full load curent. Take the example of a train, if
boggies are connected to engine it will follow the speed of
engine but if coupling is broken boggies will not follow
the engine.

Protection CT : These CTs have to protect against fault
hence these CTs are not supposed to saturate during fault
current and they should transform secondary current exectly
replica of fault current. For example class 5P20 means 5 =
% error, P = protection class, 20 means = 20 times of rated
current means when 20 times of rated current is flowing
through CT the error in sec. current may be +/- 5%.

Never connect metering CT for protection purpose as it will
saturate during fault and will not provide any protection
at all.

Answer / debashisdb

Two major differences:

1. Accuracy class: Metering needs high accuracy at load
current while Protection need not have that high accuracy.

2. Safety Factor: It determines the multiplicity of load
current at which the CT saturates. Metering ct should have
lesser value so that it saturates before the meters can get
damaged due to some abnormality. Protection should have
high value since its main purpose desires the ct to
withstand high fault currents to be sensed back to the
relays.

There is another special class ct that combines the
features of both the above used for differential protection.

Answer / rahul

The diferrence is of accuracy class. for measuring more
accuracy is desiered

Answer / amir

Metering CT: Designed at a point not far from knee point on
the CT saturation curve.
Protection CT: Designed at much lower point on the curve.

Answer / john bosco

METERING CT:
these types CT are construction wise Different from
Protection CTs. Generally the Core material used will be
different and Core area will be very less compared to
protection Cts. since the application/Requirement of
metering CT is to provide Accurate current for measuremet
at normal loading condition also should saturate for
fault/abnormal condition to prevent Meters connected to
metering CTs from damages resulting from high secondary
currents on fault condition. because meters cannot
withstand for such amount secondary current.

Protection CT:
CT used for protection relays are required to provide
accurate secondary current to relay measurement for
satisfactory operation on faults.

so these CTs should not saturate on fault conditions.

Answer / a.k.tiwari

metering cts are used for the urpose of measuring the current and thus recording the consumption when secondary is connected to the metering terminals.
protection cts are used for protection against over current or faulty current, their secondary is thus connected to the protection relays and the to the tripping coil. there may be series or shunt trip mechanism, thus the burden(VA) of protection ct is more as compared to metering cts.
however the accuracy class of measuring ct is of more significance as they are used for measurment.

Answer / 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

Answer / arif shah

There is a very important difference between a metering CT and a protection CT. A metering CT is so designed that in case of faults, it will saturate and thus save the instrument connected to its secondary from damage due to excessive current. On the other hand, a protective CT is designed to faithfully reproduce the largest fault current.

Answer / thiru

Protection ct: It is used for protection against fault in power system and also secondary connection connected to protective relay.
Metering ct: It's measure the actual current of the system and also secondary connection connected to meters.

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