DC Generator

Electrician Trade Theory, Module-1

Posted May 15, 2025 Updated Dec 11, 2025

By Roni

9 min read

DC Generator

⭕️ Show all Answers

Q1: What is the name of the part marked as 'X' in DC generator?

Armature core
Brush
Commutator raiser
Commutator segment

Q2: What is the name of D.C generator?

Differential long shunt compound
Differential short shunt compound
Cumulative long shunt compound
Cumulative short shunt compound

Q3: Which rule is used to find the direction of induced emf in D.C generator?

Cork screw rule
Right hand palm rule
Fleming's left hand rule
Fleming's right hand rule

Q4: Which formula is used to calculate the generated emf in D.C generator?

$\frac{\phi ZN}{60}$ volts
$\frac{\phi ZNP}{60}$ volts
$\frac{\phi ZNP}{60A}$ volts
$\frac{\phi ZNPA}{60}$ volts

Q5: What is the formula to calculate back emf of a D.C motor?

$E_b = \frac{V}{I_aR_a}$ Volts
$E_b = V \times I_aR_a$ Volts
$E_b = V - I_aR_a$ Volts
$E_b = V + I_aR_a$ Volts

Q6: What is the name of the part marked 'X' in DC generator?

Pole tip
Pole coil
Pole core
Pole shoe

Q7: What is the name of the D.C generator?

Shunt generator
Series generator
Compound generator
Separately excited generator

Q8: Which energy is converted into electrical energy by generator?

Heat
Kinetic
Chemical
Mechanical

Q9: What is the name of D.C generator's field?

Short shunt compound generator
Long shunt compound generator
Differential compound generator
Cumulative compound generator

Q10: What is the principle of D.C generator?

Cork screw rule
Fleming's left hand rule
Fleming's right hand rule
Faraday's laws of electromagnetic induction

Q11: What is the formula for dynamically induced emf?

BLV volts
BL sin$\theta$ volts
BLV sin$\theta$ volts
BLV cos$\theta$ volts

Q12: Which rule is used to find direction of magnetic field?

Cork screw rule
Right hand palm rule
Fleming's left hand rule
Fleming's right hand rule

Q13: What is the name of the part of DC generator?

Stator
Pole core
Pole shoes
Yoke (or) frame

Q14: How many parallel paths in duplex lap winding of a 4 pole DC generator?

Q15: Name the part of DC generator?

Side end plates
Pole shoe lamination
Commutator segment
Armature core lamination

Q16: How interpoles are connected in a DC generator?

In series with armature
In parallel with armature
In series with shunt field
In parallel with shunt field

Q17: What is the necessity of residual magnetism in a self excited DC generator?

Build up the voltage
Reduce the field current
Reduce armature current
Maintain constant output voltage

Q18: Which are the two points that the brush contact resistance measured in D.C machines?

Resistance between the opposite brushes
Resistance between brush and commutator raiser
Resistance between brush and commutator
Resistance between brush and armature conductors

Q19: Which voltage drop is indicated in the portion marked as 'X'?

Full load voltage drop
Armature voltage drop
Armature reaction drop
Shunt field voltage drop

Q20: What is the name of the compound generator, if the shunt field is connected in parallel with armature?

Cumulative compound
Long shunt compound
Differential compound
Short shunt compound

Q21: Why the armature core of a DC generator is laminated?

Reduce the copper loss
Reduce the friction loss
Reduce the hysteresis loss
Reduce the eddy current loss

Q22: Why armature resistance of a D.C generator is very low?

Reduce armature current
Reduce armature voltage drop
Run armature with less weight
Reduce the temperature of armature

Q23: Why the D.C generator should run in clockwise direction only?

Protect brushes from damage
Protect the residual magnetism
Avoid short circuit in armature
Avoid over loading of generator

Q24: Why compensating winding is provided in large DC generators?

Connect more loads
Reduce commutation effect
Neutralize armature reaction effect
Increase the efficiency of generator

Q25: What is the reason for DC generator fails to build up voltage?

Loose brush contact
Armature resistance is more
Field resistance is above critical resistance
Prime mover is running at above rated speed

Q26: What is the name of generator, if its field is connected in parallel with armature?

Shunt generator
Series generator
Compound generator
Self excited generator

Q27: What is the purpose of pole shoe in DC generator?

Reduce the air gap
Increase the field strength
Minimize the magnetic losses
Spread out flux uniformly in the air gap

Q28: What is the function of split rings in DC generator?

Collects the current unidirectionally
Maintain constant voltage
Reduces the voltage drop at brushes
Increases the terminal voltage than rated

Q29: Which material is used to make brush in generator?

Carbon and graphite
Steel and graphite
Cast iron and graphite
Aluminium and graphite

Q30: Why DC generators are loosing their residual magnetism?

Running without load continuously
Heavy short circuit in load
Continuous running without break
Change of direction of rotation very often

Q31: How does the magnetic circuit complete through the yoke and poles in a generator?

Field coils
Armature core
Laminated pole core
Winding conductors in armature

Q32: Why the terminal voltage decreases if load increases in DC shunt generator?

Because of armature reaction effect
Due to increased in armature resistance
Because of brush voltage drop decreases
Due to increased in shunt field inductance

Q33: Which type of DC generator is used for long distance distribution lines?

Shunt generator
Series generator
Differential compound generator
Cumulative compound generator

Q34: Which method is used to improve the insulation resistance in DC generator?

Replacing the brushes frequently
Heating the machine by running periodically
Cleaning the commutator segments regularly
Blowing hot air in to the machine during maintenance

Q35: Which type of D.C Generator works in absence of residual magnetism?

Shunt generator
Series generator
Compound generator
Separately excited generator

Q36: Which type of D.C generator is used for arc welding?

Shunt generator
Series generator
Differential compound generator
Cumulative compound generator

Q37: What is the property of wave winding in D.C generator?

Low current low voltage
High current low voltage
Low current high voltage
High current high voltage

Q38: What is the purpose of resistance wire used in the commutator connection in D.C. generator?

Maintain constant voltage
Nullifying statically induced emf
Increasing statically induced emf
Smooth reversal of current direction

Q39: Why solid pole shoes are used in D.C generator?

To reduce the copper loss
To increase the residual magnetism
To decrease the residual magnetism
To reduce the reluctance of magnetic path

Q40: Which metal is used to make large capacity DC generator yoke?

Cast iron
Soft iron
Aluminium
Rolled Steel

Q41: What is the function of split rings in a D.C generator?

Supplies output continuously
Makes output in the uni direction
Makes output in the opposite direction
Collects the output from alternate conductors

Q42: Which type of voltage is induced dynamically in a D.C generator?

Pulsating voltage
Oscillating voltage
Alternating voltage
Direct current voltage

Q43: What is the purpose of slot marked as 'X'?

To fix the key way
To make air circulation
For lubrication purpose
For easy removal from shaft

Q44: What is the purpose of field coils in D.C generator?

To increase the flux in air gap
To decrease the magnetizing current
To magnetize the poles to produce coil flux
To increase the reluctance of magnetic path

Q45: Which metal is used to make pole core of large DC generator machines?

Soft iron
Cast iron
Cast steel
Stainless steel

Q46: Why the pole core stampings are laminated in DC generator?

Reduce the friction loss
Reduce the windage loss
Reduce the hysteresis loss
Reduce the eddy current loss

Q47: Which type of DC generator is used for electroplating process?

Shunt generator
Series generator
Differential compound generator
Cumulative compound generator

Q48: What is the purpose of compensating winding in DC generator?

Minimizes rough commutation
Maintain constant output voltage
Neutralizes the demagnetizing effect
Decreases the excitation current of field coils

Q49: What is the effect if the shunt field resistance is above critical resistance value in a D.C generator?

Output voltage is pulsating
Output voltage is above normal
Generator fails to build up voltage
Generator builds up voltage normally

Q50: What is the effect of armature reaction in DC generator?

Output voltage increases
Output voltage decreases
Output voltage is pulsating
Output voltage will become zero

Q51: Calculate the emf generated in a 4 pole DC generator with simplex wave wound armature has 1020 conductors and driven at a speed of 1500 rpm, the flux/pole is 0.007 webers?

178 V
243 V
357 V
428 V

Show Calculation

* Number of poles ($P$) = $4$ * Number of conductors ($Z$) = $1020$ * Speed ($N$) = $1500 \text{ rpm}$ * Flux per pole ($\phi$) = $0.007 \text{ Wb}$ * Winding type = Simplex Wave Wound The generated EMF ($E_g$) in a DC generator is calculated using the formula: $$E_g = \frac{\phi Z N P}{60 A}$$ For a **Wave Wound** armature, the number of parallel paths ($A$) is always equal to 2, regardless of the number of poles. $$E_g = \frac{0.007 \times 1020 \times 1500 \times 4}{60 \times 2}$$ $$E_g = 357 \text{ Volts}$$

Q52: How the effect of armature reaction can be neutralized in large DC generators?

Using compensating winding
Providing additional inter poles
Increasing brush contact resistance
Adding resistance wires with winding

Q53: What is the effect in D.C generator, if it is kept ideal for long time?

Field coil resistance increases
Armature resistance Increases
Increase the armature reaction
Looses its residual magnetism

Q54: Calculate the induced emf of 4 pole dynamo having 1000 rpm lap wound and total number of conductors is 600, the flux/ pole is 0.064 wb?

160V
320V
480V
640V