11. In the case of lap winding resultant pitch is ___________
Multiplication of front and back pitches
Division of front pitch by back pitch
Sum of front and back pitches
Difference of front and back pitches
Answer: 4. Difference of front and back pitches
Explanation:
In lap winding, the conductors are joined in such a way that their parallel paths and poles are equal in number.
Back pitch (Yb): It is the span of the coil from the back end.
Front pitch (Yf): It is the span of the coil from the front end.
Resultant pitch (YR): Distance between the starts of two successive coils.
Formula:
YR = Yb – Yf = ± 2m
m = multiplicity factor
Yb = (2S / P) + 1
Yf = (2S / P) – 1
S = No. of slots
P = No. of poles
Yb ≠ Yf, Yf, and Yb are odd in successful winding design.
12. How many parallel paths are there in a 6-pole simplex lap-wound DC machine?
3
2
12
6
Answer:4. 6
Explanation:
The number of parallel paths in a 6 pole, simplex lap wound armature in a DC generator is 6.
A winding in which the number of parallel paths between the brushes is equal to the number of poles is called simplex lap winding.
In simplex lap winding, the terminating end of one coil is joined to the commutator segment and the starting end of the next coil is placed under the same pole. Also, the number of parallel paths is similar to the number of poles of the windings.
13. A 4 pole lap wound DC generator has a developed power of P watts and a voltage of E volts. Two adjacent brushes of the machines are removed as they are worn out. If the machine operates with the remaining brushes, the developed voltage and the power obtained in the machines are
E, P
E/2, P/2
E, P/4
E, P/2
Answer: 3. E, P/4
Explanation:
If the machine operates with the remaining brushes, the developed voltage and the power obtained in the machines are E, P/4.
14. In lap winding, the number of brushes is always _______ the number of poles.
Double
Same as
Half
None of these
Answer:2. Same as
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.
15. For a simplex wave wound generator, the emf generated path is given by _______.
(ΦPN)/120
(ΦZPN)/120
(ΦZPN)/180
(ΦZP)/N60
Answer:2. (ΦZPN)/120
Explanation:
The emf generated in DC machine is given by
$E = \frac{{NP\phi Z}}{{60A}}$
Where
Φ = Flux / pole in Weber
Z = Total number of armature conductors
P = Number of generator poles
n = Armature rotation in revolution per second (rps)
N = Armature rotation in revolution per minute (rpm)
A = Numbers of parallel path
Z / A = Number of armature conductors in series for each parallel path.
16. In DC generators, wave windings are preferred for
High current, low voltage
High current, high voltage
Low current, high voltage
Low current, low voltage
Answer: 3. Low current, high voltage
Explanation:
Wave Winding is an armature winding in which the coils are laid in two layers and follow each other on the surface of the armature in the form of waves with the coils being so connected in series that there are only two paths for the flow of current whatever the number of poles in the machine.
In wave winding, the number of parallel paths is two
This winding is mainly used for high voltage and low current applications
17. In DC generators, current to the external circuit from the armature is given through
Commutator
slip rings
Solid connections
Yoke
Answer: 1. Commutator
Explanation:
The commutator connects the rotating armature conductors to the stationary external circuit through brushes.
It converts the alternating current induced in the armature conductors into the unidirectional current in the external load circuit in generator action, whereas, it converts the alternating torque into unidirectional (continuous) torque produced in the armature in motor action.
18. A wave winding must go at least ______ around the armature before it closes back where it started.
Four times
Thrice
Twice
Once
Answer:3. Twice
Explanation:
In the wave winding, the end of one coil is connected to the starting of another coil of the same polarity as that of the first coil.
In simplex wave winding back pitch (YB) and front pitch (YF) are both odd and are of the same sign.
Back-pitch and front-pitch are nearly equal to the coil pitch and may be equal or differ by ± 2. Therefore, it must go at least twice around the armature before it closes back where it started.
+ For progressive winding, – for retrogressive winding.
19. A 4 pole generator with 16 coils has two-layer lap winding. The pole pitch is ________.
8
32
16
4
Answer: 1. 8
Explanation:
Given that,
Number of coils = 16
As the winding is two-layer winding
⇒ Total number of conductors = 2 × 16 = 32
Pole pitch = Number of conductors/number of poles = 32/4 = 8
20. Which one is not a valid condition for the wave winding?
Back pitch and front pitch are of the same sign
Back pitch and front pitch are odd numbers
Back pitch and front pitch may differ by two and maybe equal also
Commutator pitch is always unity
Answer: 4. Commutator pitch is always unity
Explanation:
Back pitch YB the distance between the top and bottom coil sides of a coil measured around the back of armature is called back pitch.
Front pitch YF the distance between the two coil sides connected to the same commutator segment is called front pitch.
Winding or resultant pitch YR the distance between the starts of the two consecutive coils measured in terms of coil sides is called resultant pitch.
Commutator pitch YC the distance between the two commutator segments to which the two ends of a coil are connected is called commutator pitch.
In wave winding back pitch and front pitch, both are odd and are of the same sign.
Back pitch and front pitch are nearly equal to pole pitch and may be equal or differ by ± 2, + for progressive winding, – for retrogressive winding.
