Skip to content
Solved Assignments

Analysis and Calculations of Resistances, Wire Sizes, and Magnetomotive Force in DC Machine Field Windings

Analysis and calculations related to DC machine field windings.

Preview 2 of 2 pages

See the first 2 pages exactly as they appear in the document.

  1. Page 1
    Read page 1 as text

    Analysis and Calculations of Resistances, Wire Sizes, and Magnetomotive Force in DC Machine Field Windings Measurements taken on a DC Machine during a lab: Rated at 125V, 2.4A 1. Shunt Field = .57A, 125.3V, 219.82 Ohms. 2. Series Field = 2.4 A, 19.008V, 7.92 Ohms. 3. Armature = 2.97 A, 21.48 V, 8.95 Ohms. Explain the difference in the resistances found for the shunt field, series field, and armature circuits. In particular, why is the resistance of the shunt field so different from the resistances of the armature and series field? What would I expect the relative wire size to be (heavy or light gauge) and why, and the number of turns (many or few) on each of the three windings? Answer: - series field and armature resistances need to be as minimum as possible because to minimize the Ia^2 R loss due to armature current Ia whereas in the case of shunt field, the value of resistance must be largest so that we can reduce V^2/Rf losses. Relative wire size should be very light gauge for the shunt field and heavy gauge for the other two i.e. series field and armature. Number of turns is more in shunt field due to high resistance and less in other two. 2. If the values obtained were taken at a temperature of 20 C, what would the resistance values above be at 55 C? could you please show the calculation, and how to do it. ( I researched and found that copper wire increases in resistance by .0039% for e ach degree rise in temperature, in Celsius. Answer: - R = R1[1+ ⍺ (T2 - T1) ] , R1is initial resistance as 20 C Here T1 = 20 Celsius, T2 = 55Celsius and ⍺ = 0.0039 % = 0.000039 On setting these values, we get R = R1[1+0.000039(55 - 20)] = R1(1.001365) So the new resistance at 55C will be 1.001365 times of the initial resistance R1 which is measured at 20C 4. If the shunt field windings are composed of #34 AWG copper wire, and each turn is approximately 12 inches long, how many turns of wire are there on the shunt field of the DC machine? (I looked this up and found the resistance coefficient of #34 copper wir e to be 260.9 Ohms. Area = 0.0201 mm^2 0.129mm

  2. Page 2

More Engineering study materials

See all

Study this document with CramX

Once it is in your library, every tool can work from it.