DC Generator Winding MCQ || DC Generator Winding Questions and Answers

1. In lap winding of a P pole dc machine, the number of brushes are equal to

1. 2
2. 4
3. P
4. 2P

Explanation:

Lap Winding is a form of two-layer winding for electric machines in which each coil is connected in series with the one adjacent to it. lap winding is used for high current and low voltage machines.

• In lap winding, the number of parallel paths is equal to the number of Pole (P).
• Therefore the number of brushes is also equal to P

2. The winding where dummy coils are used is sometimes called as

1. Duplex winding
2. Triplex winding
3. Forced winding
4. None of these

Explanation:

• Wave winding is actually called incomplete winding because after completion of winding some slots are left empty.
• These empty slots are generally filled with some extra coils namely called dummy coils.
• Windings employing dummy coils are sometimes known as ‘ forced ‘ windings.
• These dummy coils are used for providing mechanical balance for the rotor only.
• Dummy coils are similar to other coils and are insulated from other coils.
• They physically exist but are not electrically connected.

3. In armature winding the distance between the segments to which the ends of coils are connected is?

1. Resultant pitch
2. Front pitch
3. Commutator pitch
4. Back pitch

Explanation:

Commutator pitch YC the distance between the two commutator segments to which the two ends of a coil are connected is called commutator pitch. We measure commutator pitch in terms of commutator bars or segments.

Commutator pitch = average pitch = (YB + YF)/2.

Where

YB = Back Pitch

YF = Front Pitch

4. A 4 – pole, separately excited, wave wound DC machine with negligible armature resistance is rated for 230 V and 5 kW at a speed of 1200 rpm. If the same armature coils are reconnected to form a lap winding, what is the rated voltage (in volts) and power (in kW) respectively at 1200 rpm of the reconnected machine if the field circuit is left unchanged?

1. 230 and 5
2. 115 and 5
3. 115 and 2.5
4. 230 and 2.5

Explanation:

For wave wound, number of parallel pat (A1) = 2

${E_1} = \frac{{p\phi Nz}}{{60{\rm{\;}}{A_1}}}$

E1 ∝ 1/A1

Lap wound

for lap wound,

Number of parallel path = Number of poles

i.e., A2 = P = 4

E2 ∝ 1/A2

E2/E1 = A2/A1

E2= E1/2

It is given that armature resistance (Ra) = 0

so, E ∝ V

E2/E1 = V1/V2

V2 = V1 E2/E1

V2 = V1/2

so, power (p) = V Ia

Ia = P/V

Ia = 1/V

so,

$\dfrac{{{I_{{a_2}}}}}{{{I_{{a_1}}}}} = \dfrac{{{V_1}}}{{{V_2}}}{\rm{\;}}\{ {V_2} = \dfrac{{{V_1}}}{2}\}$

Ia2 = 2Ia1

The power of the machine will remain same as Plap = Pwave

The machine with lap wound armature coils will have rated voltage.

V2 = V1/2 = 230/2 = 115

∴ Plap = Pwave = p = 5 kW

5. The commutator pitch for simplex wave winding is equal to _______.

1. Half pitch
2. Average pitch
3. Full pitch
4. Quarter pitch

Explanation:

The commutator pitch for simplex wave winding is equal to the average pitch.

Average pitch (YAmust be an integer number, because it may close itself. We take ± 2 (two) because after one round of the armature the winding falls sort of two conductors.

In Simplex lap winding there are as many parallel paths as there are field poles on the machine.

• In this winding, we connect the end of one coil to the starting of another coil of the same polarity as that of the first coil.
• In this type of winding the coil, side progresses forward around the armature to another coil side and goes on successively passing through N and S poles till it returns to a conductor lying under the starting pole.

6. The number of armature parallel paths in a two-pole D. C. generator having duplex lap winding is

1. 2
2. 4
3. 6
4. 8

Explanation:

Lap winding is the winding in which successive coils overlap each other. It is named “Lap” winding because it doubles or laps back with its succeeding coils.

Duplex lap winding: A winding in which the number of parallel paths between the brushes is twice the number of poles is called duplex lap winding.

Number of parallel paths (A) = 2P

Given DC machine is duplex lap wound.

Number of poles (P) = 2

The number of parallel paths (A) = 2P = 4

7. The material used for generator, motor winding and field windings are ______.

1. Enamelled copper wire
2. Super enameled copper wire
3. Rolled copper bars
4. Silver

Explanation:

Enameled copper wire is used for generator, motor winding, and field windings.

• Coils are typically wound with enameled copper wire, sometimes termed magnet wire.
• The winding material must have a low resistance, to reduce the power consumed by the field coil, but more importantly to reduce the waste heat produced by ohmic heating.
• The enameled wire basically refers to an aluminum or copper wire which has been given a coating.
• The enameled copper wire is used to convert electrical energy to mechanical energy for making motors, office HVAC, etc.
• The main reason for using copper is its high electrical conductivity.
• So the use of this metal (Cu) as compared to other types of metals is more because it improves energy efficiency for motors.

8. For a Lap wound generator, the number of parallel paths in the armature is taken to be:

1. 4
2. 2
3. Number of poles / 2
4. Number of poles

Explanation:

Lap winding is the winding in which successive coils overlap each other. It is named “Lap” winding because it doubles or laps back with its succeeding coils.

• A winding in which the number of parallel paths between the brushes is equal to the number of poles is called simplex lap winding.
• A winding in which the number of parallel paths between the brushes is twice the number of poles is called duplex lap winding.
• In this winding number of parallel paths between the brushes is always 2.

9. A 6-pole lap-connected DC generator has 480 conductors and armature circuit resistance is 0.06 ohm. If the conductors are reconnected to form wave winding, other things remaining unchanged, the value of armature circuit resistance will be

1. 0.01 Ω
2. 0.08 Ω
3. 0.36 Ω
4. 0.54 Ω

Explanation:

A2lap × Rlap = A2wave × Rwave

In lap winding A = P = 6

Rlap = 0.06 Ω

In wave winding A = 2

62 × 0.06 = 22 × Rwave

Rwave = (36 × 0.06) / 4

Rwave = 9 × 0.06 = 0.54 Ω

10. In case of DC generators, lap winding is suitable for:

1. High current and low voltage ratings
2. Low current and low voltage ratings
3. High current and high voltage ratings
4. Low current and high voltage ratings

Answer: 1. High current and low voltage ratings

Explanation:

Lap Winding is one type of winding with two layers, and it is used in electric machines. Every coil in the machine is allied in series with the one nearby coil to it. The applications of lap winding mainly include low voltage as well as high current machines.

• In lap winding, the number of parallel paths (A) is the same as the number of brushes and poles
• This winding is mainly used for low voltage and high current applications.

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