Constructional Features of DC M
-
Upload
pradeepsambangi -
Category
Documents
-
view
231 -
download
0
Transcript of Constructional Features of DC M
-
8/13/2019 Constructional Features of DC M
1/28
Constructional Features of DC M/C
-
8/13/2019 Constructional Features of DC M
2/28
-
8/13/2019 Constructional Features of DC M
3/28
-
8/13/2019 Constructional Features of DC M
4/28
Essential Parts of DC M/C
1. Field System2. Armature
3. Commutator4. Brushes5. Bearings & Shaft
-
8/13/2019 Constructional Features of DC M
5/28
Field System Purpose To create a uniform magnetic field. Permanent Magnet/ Electromagnet Field system consists of 4 parts
i. Yoke or Frame Used as frame of the machine and
carries the flux produced by poles. Not laminated.Made of cast steel / cast iron.
ii. Pole cores Used to carry the coils of insulatedwires carrying the field/exiting current. Usually of
circular cross section. Made of cast steel.iii. Pole shoes Support for the field coils. To spread
out the flux more uniformly. To reduce reluctance.iv. Magnetizing coils
-
8/13/2019 Constructional Features of DC M
6/28
-
8/13/2019 Constructional Features of DC M
7/28
Armature Rotating part of the dc m/c Purpose Rotate the conductors in the
Magnetic field Made of highly permeable silicon-steel. Laminated. There are slots over the periphery of the
armature Slot Used to house the armature windings
-
8/13/2019 Constructional Features of DC M
8/28
-
8/13/2019 Constructional Features of DC M
9/28
-
8/13/2019 Constructional Features of DC M
10/28
-
8/13/2019 Constructional Features of DC M
11/28
Commutator
Important part of DC M/C Functions:
Provides electrical connection b/w rotating
armature and stationary electric circuit. Performs mechanical rectification. Keeps rotor magnetic axis stationary in space.
Cylindrical Structure Made of Cu. Commutator segments are insulated from
each other by mica
-
8/13/2019 Constructional Features of DC M
12/28
-
8/13/2019 Constructional Features of DC M
13/28
Brushes
Purpose Collect current from thecommutator and supply it to external electriccircuit or vice versa.
Brushes are rectangular in shape and rest onthe commutator.
Made of carbon graphite / metal graphite /Cu. Wear out rapidly. Hence constant lubrication is required.
-
8/13/2019 Constructional Features of DC M
14/28
-
8/13/2019 Constructional Features of DC M
15/28
Bearings & Shaft
Bearings are used to reduce friction. Ball bearings/ Pedestal bearings/ Roller
bearings are generally used. Shaft is used to transfer mech. Power from or
to m/c. The shaft is made of mild steel.
-
8/13/2019 Constructional Features of DC M
16/28
DC M/C Armature Winding
-
8/13/2019 Constructional Features of DC M
17/28
Armature Winding
It is an arrangement of conductors to developa desired emf.
Improve the quality of voltage (similar tobattery voltage).
Depending upon the rating of the m/carmature winding are of different types.
Two common types of Armature winding: Lap winding Wave winging
-
8/13/2019 Constructional Features of DC M
18/28
Terminology Conductor- Each individual length of wire lying
in MF. Coil Conductors with one or more turns and
with two terminals. Coil side- Each coil has two coil sides. Overhang
-
8/13/2019 Constructional Features of DC M
19/28
Winding Arrangement of coils is calledwinding.
Slot (S) Coil pitch/ coil span Distance between the
coil side of a coil in terms of number of slots is
called coil pitch. Pole pitch Number of slots per pole. Commutator segment Commutator Pitch Separation of coil sides of
coil in terms of in terms of commutatorsegments is called commutator pitch
i di
-
8/13/2019 Constructional Features of DC M
20/28
Lap winding : Y c = 1 Wave winding : Y c= 2* Yp Single layer winding : Only one coil side is
place per slot.Therefore total no. of coils = S/2
Double layer winding : Each slot will housetwo coil sides. Physically one coil side is placedin the lower portion of slot while other placedabove it.
Therefore total no. of coils = S In nth slot coil side placed in upper deck is
numbered as n and coil side placed in lowerdeck is numbered as n
-
8/13/2019 Constructional Features of DC M
21/28
General Procedure
Given : Slots and Poles. Calculate coil span ( = S/P) Calculate commutator pitch Y c. (Decide lap or
wave winding) Complete the winding and connect the coil
side terminals to commutator segment. Finally decide and place the stationary
brushes on the correct commutator segments.
-
8/13/2019 Constructional Features of DC M
22/28
Developed Diagram
-
8/13/2019 Constructional Features of DC M
23/28
Lap Winding
Yc = 1 If Yc = +1 => Progressive lap winding If Yc = -1 => Retrogressive lap winding
-
8/13/2019 Constructional Features of DC M
24/28
Lap winding in practical dc m/c Given : S = 16 & P = 4
-
8/13/2019 Constructional Features of DC M
25/28
-
8/13/2019 Constructional Features of DC M
26/28
-
8/13/2019 Constructional Features of DC M
27/28
-
8/13/2019 Constructional Features of DC M
28/28
For LAP Winding: No. of commutator segments = S. No. of parallel paths = P. No. of Brushes = P.
Lap winding is adopted for low voltages, high
current DC machines
1. Slots = 8 and P = 4. Draw the complete lap
winding diagram.