By Noel M. Morris (auth.)
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U. output power -losses The per cent efficiency is one hundred times greater than the per unit efficiency. The losses in an electrical machine include copper losses (/2 R losses) in the electrical circuit as well as iron losses in the magnetic circuit. Additional losses also occur due to bearing friction and windage, the latter being due to the power absorbed in circulating air through the machine (this may be large if the machine is fitted with a cooling fan). The efficiency of an electrical machine is a function of the loading conditions.
C. C. 5 If Armature reaction is the expression used to describe the effect that the magnetic field produced by the armature current has on the magnetic field produced by the field system. 4a shows the magnetic field produced by the main field system of a two-pole machine when the armature current is zero. mJ. 4b. mJ. mJ. m.! 4b) opposes the main flux at Wand Z, and assists the main flux at X and Y. 9) = pZ t C7t = kt ....... N ~ ,,- \ y \ \ I / \. 5). 8 are constants in a given machine. 4 Armature reaction: (a) main (or direct axis) magnetic field, (b) armature field, (c) combined fields 48 ELECTRICAL PRINCIPLES '" produced by the main field system alone, and is increased above it at X' and Y'.
Per conductor = rate of change of flux d4> dt Types of Commutator Winding If the machine has p pole-pairs and if the flux per pole is 4>, then in There are two types of commutator winding, namely one revolution each conductor cuts 2p4> Wb. The time taken for the armature to complete one revolution at a speed of n rev Is is lin s. mJ. per conductor is (1) lap winding (frequently used in high-current machines), which provides as many parallel paths through the armature as there are poles (e = 2p) on the machine.