Answer / iamdon

CT is used mainly for Instrumentation(Measurement and
protection system) purposes thats why it is also termed as
instrument transformer.The measuring and protecting devices
are not rated to sustain high currents.What a CT does is,
it lowers the current in secondary side so that measurement
as well protection can be done at a reduced level of
current.

The digit in CT ratio of secondary side is IS standard for
rated secondary current so that uniformity among manufactures
be established.
The various values of secondary currents are
1)in the range of 0-5 amp e.g, 1A,5A
2)in the order of mA(particularly 40mA)in case of digital
devices for measurements and protection.


Perhaps Shayam had ingnored this fact.It cann't be any
number.

Author:arbelectbit@yahoo.com

Answer / nagesh

the first part will show the primary current eg 75/5 75 amp
will be your primary current and 5amp represents the
secondary current, but its not always 5, even in market
30/1 and 50/1 etc is also avaiable, but true there is an
standard. Rest all what Iamdon said perfectly ok.

Answer / k.prakashchandra

Secondary 5 A was used earlier.Now with electronic relays
and meters ,the secondary is 1 A

Answer / vinod g

Purpose of INSTRUMENT TRANSFORMER (CT & PT) is to reduce
the voltage and current respectievly.In EHV/HV/MV voltage
and current for the protection/metering canot be taken
directly as its voltage is very high and required huge
insulation and cost, so PT & CT is using to stepdown
voltage and current. Protection CT and measuring CT are
different class of manufaturing and secondary current
normally one amps but it can be manufactured as per
customer requirement. in 415 V also CT is using if current
is high.

Answer / dipak

ct secondary current is always 1 or 5 amp . i think 1 amp where the current path is short and less relay are installed. and where the current path is long it is 5 amp to avoid loading.

Answer / shyam

hear 5 is primary winding turns of the CT .it can be any
number not only 5

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