AHMEDABAD INSTITUTE OF TECHNOLOGY

DC MACHINE WINDING TERMS & DESIGN Prepared By, (1) 130020109048 (2) 130023109003 (3) 140023109001 (4) 140023109002 (5) 140023109003 (6) 140023109004 (7) 140023109005 (8) 140023109006 MR URVISH MEVADA JIGNESH PATEL GUIDED BY HOD

DC machine winding terms & design Basically Armature winding of a Dc machine is wound by one of the two methods, Lap winding and lap winding The difference between these two is merely due to the end connections and commutator connections of the conductor.

DC machine winding terms & design Terms related to DC winding: Pole pitch: It is defined as number of armature slots per pole. For example, if there are 36 conductors and 4 poles, then the pole pitch is 36/4=9. Coil span or coil pitch (Ys): It is the distance between the two sides of a coil measured in terms of armature slots. Front pitch (Yf): It is the distance, in terms of  armature conductors, between  the second conductor of one coil and the first conductor of the next coil. OR it is the distance between two coil sides that are connected to the same commutator segment. 

DC machine winding terms & design Back pitch (Yb): The distance by which a coil advances on the back of the armature is called as back pitch of the coil. It is measured in terms of armature conductors. Z = the number conductors P = number of poles YB = Back pitch YF = Front pitch YC = Commutator pitch YA = Average pole pitch YP = Pole pitch YR = Resultant pitch

DC machine winding terms & design Resultant pitch (Yr): The distance, in terms of armature conductor, between the beginning of one coil and the beginning of the next coil is called as resultant pitch of the coil. Armature winding can be done as single layer or double layer. It may be simplex, duplex or multiplex, and this multiplicity increases the number of parallel paths. The induced emfs in the different paths tend to differ slightly due to the non- uniformities in the magnetic circuit.

D.C machine winding terms & design Lap winding: Then, the back and front pitches are of opposite sign and they cannot be equal. YB = YF ± 2m m = multiplicity of the winding. m = 1 for Simplex Lap winding m = 2 for Duplex Lap winding When, The commutator pitch for the lap windings is given by yc = ±m, m = 1,2, The increase in the number of parallel paths in the armature winding brings about a problem of circulating current. One method commonly adopted in d.c. machines to reduce this problem is to provide equalizer connection.

D.C machine winding terms & design The number of parallel paths formed by the winding equals the number of poles. The number of conductors that are connected in series between the brushes therefore becomes equal to Z/2b Thus the lap winding is well suited for high current generators. In a symmetrical winding the parallel paths share the total line current Equally

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.

Duplex Lap Winding A winding in which the number of parallel path between the brushes is twice the number of poles is called duplex lap winding.

Disadvantages of Lap Winding This winding is necessarily required for large current application because it has more parallel paths. It is suitable for low voltage and high current generators. Disadvantages of Lap Winding It gives less emf compared to wave winding. This winding is required more no. of conductors for giving the same emf, it results high winding cost. 2. It has less efficient utilization of space in the armature slots.

Simplex wave winding In this type of winding finish F1 of the coil 1 is connected to the start sx of coil x starting s1 of coil 1. 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: 1. Yb (Back pitch) and Yf (Front pitch) must be approximately equal to Yp (Pole pitch) 2. Yb and Yf must be odd. 3. Yb and Yf may be equal or differ by ±2. + for progressive winding, - for retrogressive winding 4. Yc = (Yb + Yf ) / 2 and should be a whole number.

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.: 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 (Yb + Yf) = 14 (Yb - Yf ) = 2 Solving above equations Yb = 8 and Yf = 6 back pitch yb = 2c/p ± k For lap winding both Yb and Yf must be odd and differ by 2 Satisfying the above condition Yb = 7 and Yf = 5 (Winding diagram and ring diagrams are shown below)

At the back Yb = 7 coil connected side to coil side At the front yf =5 coil connected side to coil side At the back yb =7 coil connected side to coil side At the front yf = 5 Coil connected side to coil side 1+7=8 3+7=10 5+7=12 7+7=14 9+7=16 11+7=18 13+7=20 15+7=22 8-5=3 10-5=5 12-5=7 14-5=9 16-5=11 18-5=13 20-5=15 22-5=17 17+7=24 19+7=26 21+7=28 23+7=30 25+7=32 27+7=34 26-5=21 28-5=23 30-5=25 32-5=27 34-5=29

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