Answer / madhusudhan

inorder to produce constant magneticfield we required to
apply D.C rather than A.C. which gives variable magnetic
field

Answer / shantanu mishra

The DC current also called field current or excitation
current is given to produce magnetic field in which rotor of
the generator rotates and produces EMF. the EMF can be
varied by regulating field current.

Answer / mahesh

we need a rotational magnetic field of sine wave for the
emf to be induced . if dc is given, the field that is
produced in the air gap is almost a sine wave with constant
magnitude. for ac excitation the air gap flux is not a sine
wave .

Answer / u.vijay bhaskar reddy

for producing constant flux on the rotor

Answer / nagarjunacharya

to produce emf in the stator either we should apply
alternating flux or dynamic(rotating) conductor.as already
we are rotating rotar by prime mover ,wewe have to apply.

Answer / venkatrao chowdary

the dc current produce constant magnetic field.when rotor
conductors are rotated this conductors cuts the magnetic
lines of flux than emf is induced.this emf is called
dynamically induced emf.when ac is given to the alternater
it induces statically induced emf.the operation of
alternater we need dynamically induced emf.so ac is not
given to the alternater.

Answer / u.v.subhashreddy

alternator is an speeed machine. the dc current gives
exication current is given to produce a magnetic field so
giving d.c supply to field of an alternator.

Answer / y.srinath

dynamically induced e.m.f requires fixed polarity& magnetic flux .if we given a.c to field the polarity of a particular pole is not fixed .if one pole behaves as north pole for +ve half cycle & same behaves as north pole for negative half cycle to.that's why we are using d.c supply for alternator.

Answer / b madhu sudhan reddy

alternator is a constant speed machine.i.e it always runs
at synchronus speed.so,for producing constant speed we
require constant excitation.so,for the constant excitation
we require constant supplly.i.e d.c supply

Answer / pravallika

for magnetising poles in rotor

what is effect of reverse c.t connection on metering.

4 Answers   Cushman Wakefield,

Do you have any P.L.C in your organization?

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HOW TO CALCULATE THE SIZE OF CABLE COPPER & ALUMINIUM

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An 11kv system consisting of an underground cable to a sub station about 300 meters away was shut down for about 10 hrs. On energising, it tripped off on earth fault about 10---20 mins later 6 times but since than it is not tripping.its already 3 weeks now. The SPAJ was found to be fine. what could be the cause.No test had been done to determine the cause of the trippings till now because of demand.

2 Answers