a) A triplex lap-wound armature is use in a 14 poles machine with 14 brushes sets, each spanning three commutator bars. Calculate the number of parallel paths in the armature. b) Repeat a) for a triplex wave-wound armature having two such brush sets and 14 poles. c) Calculate the generated emf in each of the above problems, if the flux per pole is 4.2x106 lines, the generated speed is 60rpm, and there are 420 coils in the armature, each coil having 20 turns.

An electromagnet has a movable iron part and dimensions of magnetic circuit with uniform cross section as shown in figure. The core is made of ferromagnetic material with relative permeability of 3000: a) b) c) Calculate the magnetic reluctance of the circuit and the inductance of the main winding. Determine the air-gap flux, the flux density and the field intensity of the core and gap. Because of a fault in the power supply, the exciting current is increased to 8 A causing the mobile element of the iron core to move to a zero gap position as a result of the excessive electromagnetic force action. If this movement occurs in 0.01 s, find the transient voltage induced in the test coil having two turns. 0.5 mm air-gap 2 cm 2 A 3 cm 2 cm 60 turns 18 cm test coil 24 cm 0.5 mm air-gap

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