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Test: DC Motor Starting - Electrical Engineering (EE) MCQ


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10 Questions MCQ Test Electrical Machines - Test: DC Motor Starting

Test: DC Motor Starting for Electrical Engineering (EE) 2024 is part of Electrical Machines preparation. The Test: DC Motor Starting questions and answers have been prepared according to the Electrical Engineering (EE) exam syllabus.The Test: DC Motor Starting MCQs are made for Electrical Engineering (EE) 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Test: DC Motor Starting below.
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Test: DC Motor Starting - Question 1

A starting resistance is inserted at the starting in an induction motor as well as dc motor.

Detailed Solution for Test: DC Motor Starting - Question 1

For both the machines the purpose is different.

Test: DC Motor Starting - Question 2

Considering a human handed control system for the dc motor speed control, if the resistance wire cut out too slowly, then

Detailed Solution for Test: DC Motor Starting - Question 2

Due to the slow cut off the resistance the current will be high for a large amount of time and it will cause the machine to burn.

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Test: DC Motor Starting - Question 3

A 100 hp, 250 V, 350 A shunt dc motor with an armature resistance of 0.05 ohms. To limit maximum starting current to twice the rated of its value, what will be the number of stages of starting resistances?

Detailed Solution for Test: DC Motor Starting - Question 3

n= log(Ra/Rt)/log(Imin/Imax) ; Rt = Vt/Imax= 250/700 = 0.357 ohms
= log(0.05/0.357)/log(350/700)
= 2.84
= 3 (approx).

Test: DC Motor Starting - Question 4

Following are the observations due to large starting current in dc motor.
(i) Sparking at brushes
(ii) Mechanical shock at shaft
(iii) Source current fluctuations
(iv) Burning of the field winding

Detailed Solution for Test: DC Motor Starting - Question 4

All the observations can be seen due to large starting current in dc motor.

Test: DC Motor Starting - Question 5

The shunt motor starters that can be used is/are

Detailed Solution for Test: DC Motor Starting - Question 5

Both 3-point and 4-point starters can be used.

Test: DC Motor Starting - Question 6

The direct-on-line starter is used to start a small dc motor because it limits initial current drawn by armature circuit. 

Detailed Solution for Test: DC Motor Starting - Question 6

The direct-on-line starter can not limit the speed by limiting the current.

Test: DC Motor Starting - Question 7

Thyristor controlled starter is preferred over DOL starter due to

Detailed Solution for Test: DC Motor Starting - Question 7

A thyristor controlled method is more efficient as it has lesser resistance and losses while operating.

Test: DC Motor Starting - Question 8

For a 7.46 kW, 200 V dc shunt motor with full load efficiency of 85% has armature resistance of 0.25 ohms. Calculate the value of starting resistance in ohms for a current 1.5 times of the full load current.

Detailed Solution for Test: DC Motor Starting - Question 8

Full load current = 7460/(200*0.85) = 43.88 A
Starting current = 1.5*43.88 = 65.883 A
R = V/I = 200/65.883
= 3.038 ohms
Starting resistance = 3.038 – 0.25 = 2.788 ohms.

Test: DC Motor Starting - Question 9

The effect of fringing increases as we

Detailed Solution for Test: DC Motor Starting - Question 9

Fringing is the effect in which the magnetic flux lines bulge out of the the flux. and it is introduced at the air gaps.

Test: DC Motor Starting - Question 10

The post effects of the armature reaction is

Detailed Solution for Test: DC Motor Starting - Question 10

There is no such post effect of armature reaction . The armature reaction phenomena affects the working condition only.

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