Answer / venkat iyer

Selection of CTs depends upon its usage, whether for
metering or protection. Class of accuracy, VA burden and
palatability to instrument safety factors need to be
considered incase of metering CTs. In case of protection
CTs, linearity factor w.r.t its primary current and
accuracy factors need to be considered. Metering CTs are
expressed in terms of Class 1 or Class 3 where as
protection cts are expressed as 5P10 or 5P15 or 5P20 or
10P10 etc. The first digit stands for the class of accuracy
and P stands for protection and the last two digits stands
for linearity.

Answer / mervin

A CT used for Instrumentation is required to be accurate
over a normal working range , whereas CT for protection is
required to five a correct CT ratio several times the rated
current . Cores made using Nicel-Iron alloy gives accuracy
upto 5 times the rated current n suitable for
Instrumentation . Cores made using Cold rolled silicon
steel are accurate upto 15 times the rated current and
suitable for protection .An accuracy of about 2-3% is
desirable for distance and differential relays .CT burden
and CT linearity should also be considered during selection
of a CT .

Answer / ramakrishna m

The selection of CT depends on the current ratings of relays
those are used in the protecting circuitry and also depends
on accuracy that circuitry requires.

Answer / kapil

it depends on the protection circuitary ratings and the
accuracy u desire for the application. it must supply the
rated current to the relays with the accuracy u desire for
ur purpose,and also copper losses in the CTs should be
minimum so it also depends on the laminations and conductor
material u choose.

in india single phase is 230v and three phase is 440v but in other countries single phase is 110v and three phase is 380v why..?

2 Answers  

---

watt meter have 4 terminals what there name??? and what theses 4 terminals indicates ?? and why 2 terminals are short circuited??

1 Answers  

---

why humming sound occured in h HT transmission line

3 Answers  

---

what is the electricity

3 Answers  

---

can we install LT panel & HT panel in one room?

1 Answers  

---

In three phase supply why we use R Y B Colour not other.

4 Answers  

---

Why does curving the pole faces in a dc machine contributes to a smoother dc output voltage from it?

0 Answers  

---

What is the difference between Neutral and Earth

6 Answers   Bhel,

---

What do you mean by Stimulastion Test in Diesel Genarator / Why & when it's conducted ?

0 Answers   JLL,

---

how many safety really of DG sets.

0 Answers   MBD, Nerolac,

---

How to calculate the Harmonics losses in terms of cost/unit.

0 Answers  

---

For a 6.6kV Motor it is recommended to do megger test with 500 V d.c and not more than 5kV d.c but the Hi voltage withstand test should be performed by 12kV AC. Why the dc voltage test should be limited but AC voltage withstand test could be with such a high voltage?

0 Answers   Hormozgan Steel,

---