The windings used in rotating electrical machines can be classified as D Concentrated ; All the winding turns are wound together in series to form one multi-turn coil ; All the turns have the same magnetic axis ; Examples of concentrated winding are - field windings for salient-pole synchronous machines.

C. Machines - Primary and secondary windings of a transformer 0 Distributed Windings All the winding turns are arranged in several full-pitch or fractional-pitch coils ; These coils are then housed in the slots spread around the air-gap periphery to form phase or commutate winding ; Examples of distributed winding are - Stator and rotor of induction machines - The armatures of both synchronous and D. C. Canines Armature windings, in general, are classified under two main heads, namely, 0 Closed Windings ; There is a closed path in the sense that if one starts from any point on the winding and traverses it, one again reaches the starting point from where one had started Used only for D. C. Machines and A. C. commutate machines 0 Open Windings ; Open windings terminate at suitable number of slip-rings or terminals ; Used only for A. C. Machines, like synchronous machines, induction machines, etc Some of the terms common to armature windings are described below: 1 .

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Conductor. A length of wire which takes active part in the energy-conversion process is a called a conductor. 2. Turn. One turn consists of two conductors. 3. Coil. One coil may consist of any number of turns. 4. Coil -side. One coil with any number of turns has two coil-sides. Introduction to AC Machines DRP. Sad Abraham Shall 4 The number of conductors (C) in any coil-side is equal to the number of turns (N) in that coil. One-turn coil two-turn coil multi-turn coil 5. Single- layer and double layer windings. Single- layer winding ; One coil-side occupies the total slot area ; Used only in small AC machines one coil-side per slot 0 Double- layer winding ; Slot contains even number (may be 2,4,6 etc. ) of coil-sides in two layers ; Double- layer winding is more common above about cow machines Two coil -sides per slot 4-coil-sides per slot Coil-sides Coil -sides Overhang Top layer Bottom layer 5 The advantages of double-layer winding over single layer winding are as follows: a. Easier to manufacture and lower cost of the coils b. Fractional-slot winding can be used c. Chorded-winding is possible d.

Lower-leakage reactant and therefore , better performance of the machine e. Better Neff waveform in case of generators 6. Pole - pitch. A pole pitch is defined as the peripheral distance between identical points on two adjacent poles. Pole pitch is always equal to 180 0 7. Coil-span or coil-pitch. The distance between the two coil-sides off coil is called coil-span or coil-pitch. It is usually measured in terms of teeth, slots or electrical degrees. Electrical. 8. Chorded-coil. 0 If the coil-span (or coil-pitch) is equal 0 in case the coil-pitch is to the pole-pitch, then the coil is termed a full-pitch coil.