I-II - Ee105_els - Unit-III - Question Bank

7/25/2019 I-II - Ee105_els - Unit-III - Question Bank

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VIGNANS UNIVERSITY :: VADLAMUDI

EE105 Electrical Science

UNIT III

(D.. Mac!ine" # Tran"$%r&er"'

1 Mar )*e"ti%n"

1. The armature of D.C. generator is laminated to

(a) Reduce the bulk (b) provide flux (c) insulate the core (d) reduce eddy current loss

. !ccording to "leming#s right$hand rule for finding the direction of induced e.m.f.% &hen

middle finger points in the direction of induced e.m.f.% forefinger &ill point in the

direction of

(a) motion of conductor (b) lines of force (c) either of the above (d) none of the above

'. n lap &inding% the number of parallel paths is al&ays

(a) double the number of poles (b) same as the number of poles

(c) half the number of poles (d) t&o

. n *ave &inding% the number of parallel paths brushes is al&ays

(a) double the number of poles (b) same as the number of poles

(c) half the number of poles (d) t&o

+. +. n a four$pole D.C. machine

(a) all the four poles are north poles (b) alternate poles are north and south

(c) all the four poles are south poles (d) t&o north poles follo& t&o south poles


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,. n D.C. generators% current to the external circuit from armature is given through

(a) Commutator-rush (b) solid connection (c) slip rings (d) none of above

/. rushes of D.C. machines are made of

(a) carbon (b) soft copper (c) hard copper (d) all of above

0. The material for commutator brushes is generally

(a) mica (b) copper (c) cast iron (d) carbon

. The insulating material used bet&een the commutator segments is normally

(a) graphite (b) paper (c) mica (d) insulating varnish

12. The armature core of a D.C. generator is usually made of

(a) silicon steel (b) copper (c) non$ferrous material (d) !luminium

11. The sole purpose of a commutator in a dc generator is to

(a) increase output voltage (b) reduce sparking at brushes

(c) provide smoother output (d) convert the induced ac into dc

1. The e.m.f. generated in a D.C. generator is directly proportional to

(a) flux3pole (b) speed of armature

(c) number of poles (d) all of the above

1'. *rite 45" e6uation of DC 7enerator.

1. *rite Tor6ue e6uation of DC motor.

1+. *rite the types of DC 7enerator

1,. *rite the types of DC motor.

1/. *hat are the types of transformers8


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1. Dra& the circuit diagrams of a shunt motor and shunt generator

. Dra& the circuit diagrams of a series motor and series generator

'. 122? transformer has 02 turns and is fed from a ,22:

supply and the secondary &inding has 2 turns. "ind the peak value of flux in the core

and secondary voltage.

,. The e.m.f. induced in the armature of a shunt generator is ,22 :. The armature resistance

is 2.1 ohm. f the armature current is 22 !% Determinethe terminal voltage if the rush

contact drop is 1: per brush.

10 Mar )*e"ti%n"

1. 4xplain the construction of DC machine &ith neat diagram.

. (a) Derive the 45" e6uation of a DC generator

(b) ! ,$pole &ave &inded DC 7enerator has ,22 armature conductors% a flux of 2.2*b.

Calculate the speed at &hich the generator must run to generate 22:.

'. (a) Derive the tor6ue e6uation of a DC motor

(b) ! ,$pole DC 5otor takes ,2! armature current% the armature has &ave connected +02

conductors. The flux per pole is 12m*b. Calculate the tor6ue developed by the

armature of the DC motor.

. (a) Derive the 45" e6uation of a transformer


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(b) ! 122?% 1$ phase transformer is built on core having a cross sectional

area of 1+Cmand /2 turns on =: side Calculate

(i) The value of peak flux density

(ii) @o of turns on >: Aide.

0. The maximum flux density of a +23''22:% +2>?% 1$ phase transformer is 1. Tesla.

f the emf per turn is 0:.Determine the area of the transformer core% primary and

secondary turns.

. !n 0$pole lap &inded DC 7enerator has ,2 armature conductors% a flux of 2m*b.

CalculateB

(i) The speed at &hich the generator must run to generate '22:.

(ii) The nduced emf if generator is &ave &inded and driven at 22rpm.

12. ! $pole &ave &ounded DC 7enerator has +1 slots and each slot has 2 armature

conductors.

(i) *hat &ill be the 45" generated in the machine &hen driven at 1+22 rpm

assuming flux per pole to be / m*b.

(ii) f the generator has lap connected armature &inding% &hat &ill be the 45"

generated.

11. ! ,$pole &ave &inded DC 7enerator has ,22 armature conductors% a flux of 2.2*b.

CalculateB

(i) The speed at &hich the generator must run to generate '22:.


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(ii) *hat &ould be the speed if the generator is lap connected8

I-II - Ee105_els - Unit-III - Question Bank

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