Question { 5020 }

Electrical Diagram of Electric Arc Furance from transformer
to Furances

Answer

The cuurrent in the secondary of the arc furnace will be
very high i.e. in kA. Hence the secondary will be devided
into no. of small bus bars and will be connected to the 3
electrodes to form a Delta, using copper hollow tubes and
flexible hoses. Water will be circulating in the copper
tubes for providing cooling. There will be a provision to
change the primary connection either in star or in delta.
Three single phase transformers can also be used instead of
only one 3 phase transformer.

Question { 6529 }

What is the secondry voltage of 420kV Current Transformer ,
the rated current is 2600A

Answer

If the rated current of the CT is 2600/5 amps, then the
secondary voltage will be (420000x2600)/5= 218400000
(i.e.218400kv)

Question { 6529 }

What is the secondry voltage of 420kV Current Transformer ,
the rated current is 2600A

Answer

Correction to answer: If the secondary is open voltage will
be 218400 kv and it will be '0', if it is shortcircuited

Question { TCS, 16181 }

7/20,3/20 electrical wire is specified as stated.Why?

Answer

7/20 means 7 is no. of conductors and 20 is the gauge of
each conductor. It is old way of expressing the size of the
conductor.

Question { 5792 }

How to calculate the current rating of power cables ?

Answer

You need to know the distace between source of supply and
the load. consider a voltagedrop of 5%. i.e. 5V for a 440v
system. use the formula V=IR from this you will know the
resistance required for your requirement. (I is the load
that you want to connect). Use R=Pl/a to find the correct
cross section of the cable. (P is resistivity of either
copper or Aluminium, l is the distance).

Question { 6361 }

We have a bank capacitor rating of 60 KVAR for a overall
load of 160 KVA and we have connected three loads of 50KVA
each. We would like to auto matically correct PF using APFC.
How do we design it?

Answer

APFC panel should be connected to main incoming busbar i.e.
from where 160 kva load was fed. 60 kvar capacitors should
be devided into smaller capacities i.e you have to use
either 6x10 kvar or 4x 15kvar or 10x6kvar. I will consider
6x10 kvar. in APFC you have to programe each stage
capacity. here the value is 10 kavar. You have to take 6
no. of capcitor switching duty contactros and to be wired
as per the APFC. It also requires one CT signal and voltage
signal(any one of the three phases of main busbar). You can
program s/on and s/off time in APFC. and also you can
program target power factor. EPCOS apfc is the best
controller I have used.

Question { 4721 }

what is different between DIGITAL and ANALOG?

Answer

Digital signal means either True or False. Only 2 states
will be there. Example for this is pushbutton,Hot metal
detector,proxy etc.
Analog means the signal will vary with conditions. out put
may be 4-20mA, 0-20mA,0-10V,0-5V etc. examples are
pressure,flow transducers,RTD,Thermocouple etc

Question { 9966 }

4-Why we measure the insulation resistance of main core and
frame in spite of that must be connected with ground

before energize the transformer?

Answer

If there is any fault in the winding or core, the fault
current should be grounded and transoformer should be
tripped on on earth fault. If the transformer is healthy
the insulation resistance measured will be with in the
permisible value.

Question { Nalco, 6941 }

How power factor of electric system improved?

Answer

Normal way of improving power factor is by connecting shunt
capacitors. Because they supply leading Kvar which
nutralises the reactive kvar present in the system.