Answer / minu

no u cannot. this is because the metering and protection CT
cores are differently designed and r made up of different
materials. A Protection CT core is designed so as not to
get saturated at very high fault currents which can cause
mal-operation of the relay connected to that CT. Also, the
accuracy required in the metering CTs is higher than that
required in the protection CTs.

Answer / ramesh kumar k

Mr.Mohit & Ms. Minnu...

both of u be cool specially... it is not a war field
yaar... ha.. ha...

What ms.minnu said is correct...

u cant use the measuring CT for protection purpose...and
protection ct also can't be used for measuring purpose...
it is not safe...

So Mr. Mohit, from my point of view what you have might
done is.. u have used a CT which u have purchased for
measuring purpose, but still having a additional core for
protection and u might have shorted the metering core
terminals and used the protection core only.. if you have
not used so... I think your system is still safe because
there is not shortcircuit fault tilltime... its very
dangerous if any short circuit occurs... because a metering
CT core is designed in such a way that if there is any
shortcircuit.. it gets saturated and doesnot deliver any
output... if u use this for protection purpose your relay
will not get current(i.e. it gets 0 A which is nothing but
no load condition..). But your relay is set to operate only
in over current conditions... so now what happend.. even in
over current condition, your relay is not getting over
currents hence it will not send any signal to the circuit
breaker...

I suggest, in this regards, u please consult ur higher
authorities...

Ms. minnu, i think we have not studied enough on CTs & PTs
n our basic engineering study...

P.S:
I welcome u both for further clarifications, mail me at
rammy_233@yahoo.com

Answer / minu

Mr. Mohit,
i am working as a power system protection engineer in one
of India's biggest consultancy firms. wat u said abt
increasing the no. of cores of a ct does not mean that the
metering n protection cts are same. n i think u've
forgotten ur basic engineering study wherein we were taught
abt the basic differences in metering and protection cts. u
can still find them in any gud power system book.

p.s. its Miss Minu, not Mr. Minu

Answer / sangram

you can use a single CT but they have enclosed two
different cores which is desired one for metering & other
for Protection. the meaning of both words are very
different, we want to consider ISF( Instrument Security
Factor) for Metering & ALF( Accuracy Limit Factor) for
protection CT.

Answer / j.karthik(cce)

Mr.Ramesh kumar said answer is very correct..

We cannot use the Measuring C.T. for the protection
purpose.and we also cannot use the protection C.T. for
Measuring purpose.

Protection C.T Classes are:
CL 5P20
CL 5P10
CL PS

Measuring C.T Classes are:
CL 0.2
CL 0.5
CL 1.0

Generally the Measuring C.T's and Protection C.T's are
differentiate by using the C.T Classes..

Answer / mohit varshney

Mr. Minu.....
I am working as a commissioning engineer in in switchyard
in 2x600 MW thermal powerplant. i have myself done the ct
commissioning here. if u want i can send u proof of wht i
have answered to this question...so better check ur
credentials and dont mislead ppl.

Answer / mohit varshney

Yes u can....
u can increase the number of secondary cores....
for e.g. u can use 5 core CT in which 4 are used for
protection purpose and one is used for metering(measuring)
purpose.

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