Answer / ashim kumar das

Its basically depends on the circuitry, whether you are
using it as a metering CT or a Protection CT.
For metering purpose generally 5A CT is used, because the
VA drop occurd in the cable between CT and the metering
instrument doesn't much harmfull for the system.

But for protection purpose 1A CT is recommended, because if
the distance between the CT and the protection relay is
very large, the VA drop occurd in the cable can give
reduced current reading to the instrument and this will be
a thread to the machine.

Answer / shekhar

it is because that secondary of c.t is connected to relay
to trigger it when any fault occurs.
primary of c.t carries fault current so very high value so
to protect the equipment the secondary is low.
it is in the range 0-10A

Answer / rahul

more of our meter & relay are of 1A to 5A range to operate
because the accuracy,loss & stability factor so alwayes the
CT O/P is 1A to 5A

Answer / rajiv

what is the maximum rating of ct can we measure below 1 amps

Answer / eng . ammar al-qudah

it depends on the purpose of the CT , when we install the CT before a protection device , a 5A CT will be installed for the most protection device , and when the CT are needed for measurement system the choice will be 1A for more accuracy , so we can't give a certain answer for this , it depends where we use it .

Answer / mahamuni raja

this is not a standard case the CT secondary shall be 5A.
moreover it depends upon the purpose,for protection
generallly will use 5A and for metering 1A. however while
selecting 5A the voltage drop will occur also didtance
between the metering and the protection relay.

Answer / puneet kumar

because current is measure by ammeter whose rating is up to
5 amp.(at secondry side of CT - CT is used only to reduce
the level of current at the measurable and safety level)
since we konw that CT has only 1 turn at primary
side becuase current is at higher value, to reducing it we
provide more turns at secondry side.. and this value can
measure by 5 amp. ammeter easily.
In power system, CT is used as protection device
also, which give signal to relay for operate under when
current become more than 5 amp.(at secondry side)

Therefore, CT secondry are rated 5A generally.

Answer / anthony

relays are connected to the sec. of a ct . If a large
rating is proposed for the sec. of the ct then it would
mean that the magnetising current (emag. relays) would be
high too, since on the sec. side you have an inductive
relay. This would actually present itself as a load on the
sec.of the ct .

Answer / karthik

#it is depent up on the round value for our calculation.
# the relay specification
# standrd form

Answer / arun

The CT has separate primary and secondary windings. The
primary winding which consists of few turns of heavy wire,
wound on a laminated iron core is connected in series with
one of the line wires. The secondary winding consists of a
greater number of turns of a smaller size of wire. The
primary and secondary windings are wound on the same core.
The current rating of the primary winding of a CT is 100 A.
The primary winding has three turns and the secondary
winding has 60 turns. The secondary winding has the
standard current rating of 5A;therefore the ratio between
the primary and secondary current is 100/5 or 20/1.The
primary current is 20 times greater than the secondary
current. Since the secondary windings 60 turns and the
primary winding has 3 turns, the secondary winding has 20
times as many turns as the primary winding. For a CT the
ratio of primary to secondary currents is inversely
proportional to the ratio of primary to secondary
turns..this 5A s the standard fixed by the electricity
corporation and they folow t..so its a convention to follow
this standarrdd

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