COMPUTER AIDED ELECTRICAL DRAWING (CAED) 10EE65 part1

COMPUTER AIDED ELECTRICAL DRAWING (CAED) 10EE65

Winding Diagrams: (i) DC Winding diagrams (ii) AC Winding Diagrams Terminologies used in winding diagrams:

Conductor: An individual piece of wire placed in the slots in the machine in the magnetic field.

Turn: Two conductors connected in series and separated from each other by a pole pitch so that the emf induced will be additive.

Coil: When one or more turns are connected in series and placed in almost similar magnetic positions. Coils may be single turn or multi turn coils.

Coil group: One or more coil single coils formed in a group forms the coil group.

Winding: Number of coils arranged in coil group is said to be a winding.

Pole Pitch: Distance between the poles in terms of slots is called pole pitch.

Fig. 2 Single and Multi turn coils

Full Pitch winding: If the coil pitch for a winding is equal to pole pitch the winding is called full pitch winding Fig .

Chorded winding: When the pitch of the winding is less than the full pitch or pole pitch then the winding is called short pitch winding or chorded winding.

Fig. 3 Full pitched and short pitched coils

Single layer winding: Only one coil side placed in one slot.

Double layer winding: Two coil sides are placed in a single slot. Single and double layer windings are shown in Fig 4

Classification of windings: Closed type and open type winding

Closed type windings: In this type of winding there is a closed path around the armature or stator. Starting from any point, the winding path can be followed through all the turns and starting point can be reached. Such windings are used in DC machines.

Open windings: There is no closed path in the windings. Such windings are used in AC machines.

DC Windings: Two types of windings (a) Lap winding (b) Wave winding

These two types of windings differ in two ways (i) number of circuits between positive and negative brushes, (ii) the manner in which the coil ends are connected. However the coils of both lap and wave windings are identically formed.

TYPES AND SHAPES OF WINDING WIRES: The winding wires used in electrical motors are classified as follows. 1) Round wires 2) Rectangular straps 3) Stranded wires

1. Round Wires: It has thin and thick conductors and are used in semi-closed slot type motors and mush winding rotors. It is wounded in reels and available in Kilograms.

2. Rectangular straps: It is used in open type slot motors. These conductors are available as long straps in

meters. They are used in the following places. 1) Low voltage motor windings. 2) Used as conductor in high current motor. 3) Series field motor winding coils.

Winding Pitches:

Back Pitch: The distance between top and bottom coil sides of a coil measured around the back of the armature is called back pitch and is designated as yb. Back pitch is approximately equal to number of coil sides per layer. Generally back pitch is an odd integer.

Front Pitch: The distance between two coil sides connected to the same commutator segment is called the front pitch and is designated as yf.

Winding Pitch: The distance between the starts of two consecutive coils measured in terms of coil sides is

called winding pitch and is designated as Y.

Y = yb – yf for lap winding Y = yb + yf for wave winding

Commutator pitch: The distance between the two commutator segments to which the two ends of a coil are connected is called commutator pitch and is designated as yc and is measured in terms of commutator segments.

Lap Winding: The winding in which successive coils overlap each other hence it is called lap winding. In this winding end of one coil is connected to the commutator segment and start of the adjacent coil situated under the same pole as shown in fig. 6. Lap winding is further divided as simplex and Duplex lap winding.

Simplex lap winding: In this type of winding finish F1 of the coil 1 is connected to the start S2 of coil 2 starting under the same pole as start s1 of coil 1.

We have back pitch yb = 2c/p ± k where c = number of coils in the armature, p = number of poles, k = an integer to make yb an odd integer.

8. Number of parallel paths = mp = number of brushes.

Simplex wave winding: In this type of winding finish F1 of the coil 1 is connected to the start Sx of coil x starting under the same pole as start s1 of coil 1.

Fig. 7 wave windings

Wave winding: In wave winding the end of one coil is not connected to the beginning of the same coil but is connected to the beginning of another coil of the same polarity as that of the first coil as shown in fig. 7. Important rules for Wave winding:

Dummy coils: The wave winding is possible only with particular number of conductors and poles and slots combinations. Some times the standard stampings do not consist of the number of slots according to the design requirements and hence the slots and conductor combination will not produce a mechanically balanced winding. Under such conditions some coils are placed in the slots, not connected to the remaining part of the winding but only for mechanical balance. Such windings are called dummy coils.

Equalizer rings or Equalizer connections in Lap winding: This is the thick copper conductor connecting the equipotential points of lap winding for equalizing the potential of different parallel paths.

Sequence diagram or ring Diagram: The diagram obtained by connecting the conductors together with their respective numbers. This diagram is used for finding the direction of induced emf and the position of brushes.

Ex.1 Draw the winding diagram of a D C Machine with 4 poles, 14 slots, progressive, double layer lap winding. Show the position of brushes and direction of induced emf.

Soln: Number of poles = 4 ; Number of slots = 14, Number of conductors = 14 x 2 = 28 Pole pitch = Number of conductors/pole = 28/4 = 7

We have pole pitch = (Yb + Yf ) / 2 = Yp Hence

AC Windings:

Generally open windings except when delta connected

Classification: Based on : Supply: 1Φ & 3 Φ

Placing: Concentrated and Distributed

No. of layers: Single and Double layer End connection: Lap, wave and concentric The pitch: Full pitched and short pitched

Terms Used in AC windings:

Balanced winding: If the number of coils per pole per phase is same and a whole number then the winding is balanced winding.

Unbalanced winding: If the number of coils per pole per phase is not a whole number then the winding is balanced winding.

Slot angle: Slot angle = 1800/ pole pitch (electrical degrees)

Full pitched winding: The pitch of the coil is equal to full pitch or equal to 1800 then the coil is called the full pitched winding.

Short pitched winding or short chorded winding: If the pitch of the coil is less than 1800 or less than the full pitch then the coil is called short pitched coil.

Coil span: Coil span is the distance between two coil sides measured in terms of slots. Coil span = winding pitch/slot angle; For full pitched winding 180/slot angle

Ex.1: Draw the developed winding diagram of a 3 phase induction motor with 18 slots, 2 poles, single layer, full pitched winding with delta connection.

Soln: No. of slots per pole per phase = 18/(2 x 3) = 3 Pole pitch = no. of conductor / pole = 18/2 = 9

Slot angle = 180/ pole pitch = 180/9 = 200 Full pitched winding = coil span = 180

Coil span = winding pitch/slot angle = 180/20 = 9 slots

Winding Table:

Ex.2. Develop the winding diagram of a 5 HP, 440 volts, 3phase 4 pole induction motor with 24 slots, double layer full pitched lap winding.

Soln: No of poles = 4, No. of slots = 24, Phases = 3 No. of slots per pole per phase = 24/(2 x 4) = 2 Pole pitch = No. of slot/pole = 24/4 = 6

Winding pitch = full pitch =1800

Slot angle = 180/pole pitch = 180/6 = 300

Starting of phases: Rs = 1 (00) Ys = 5 (1200) Bs = 9 (2400)

Winding Diagram

Ex. 3. Design and draw the developed winding diagram of an alternator with following details: No of poles

= 2 no. of phases = 3, No. of slots = 24, single layer lap winding, short pitched by one slot.

Soln:

No. of poles = 2; No. of conductors = 24;

Pole pitch = 24/2 = 12; no of slots/pole /phase =24/ (2x3) = 4 No. of coils = 24/2 = 12

No of coils/pole/phase = 12/(2x3) = 2

Slot angle = 180/pole pitch = 180/12 = 150

Winding pitch = 180 – (slot angle x no of slots shorted) = 180 – 1 x15 = 165 Hence coil span = 1650 = 11 slots

Connections: Rs = 1, Ys = 1 + 120/15 = 9; Bs = 1 + 240/15 = 17

Ex. 4. Design and draw the developed winding diagram of an alternator with following details: No of poles = 4 no. of phases = 3, No. of slots = 24, single layer wave winding, delta connected.

Soln: