Engineering Finding the Armature Resistance from winding/coil resistance

AI Thread Summary
The discussion focuses on calculating armature resistance in a lap wound generator using coil resistance and the number of poles. The initial calculation of total resistance from 16 coils at 0.3 ohms each resulted in 4.8 ohms, which was deemed too high. By recognizing that the coils are in parallel across the 4 poles, the effective resistance was recalculated to 1.2 ohms. The final formula confirms that the number of parallel paths equals the number of poles, leading to a correct solution of 0.3 ohms for armature resistance. This method effectively simplifies the calculation without needing back e.m.f. data.
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Homework Statement
The Blades of a 20kW, 400V machine rotate at 2 revs per second at rated wind speed.

This four pole machine has a lap wound armature consisting of 16 coils each with a resistance of 0.3ohms. calculate the resistance of the armature.
Relevant Equations
V=E - Ia*Ra
I'm struggling to find the exact way to do this and think that I am overthinking the equation,

all of my lesson notes tend to explain how to find the armature resistance using the back e.m.f and the armature current, we can figure out the armature current but do not have enough information to work out the back e.m.f. so that means that the simplest way to do this is using the coil resistance and number of poles.

So the first instinct would be to do 16 coils with 0.3 ohm resistance each so 16*0.3 = 4.8 - which seems high for the armature resistance.

that being said as it is a lap wound machine the 16 coils would be in parallel across the 4 poles so 16/4 = 4 which gives the 4 parallel resistances

so 4*0.3 = 1.2

1/R = (1/1.2)*4

R=1/3.334 = 0.3
 
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In a lap wound generator number of parallel paths = number of poles.
So, your solution, seems to me, is correct.
 

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