Math Problem Statement

A 10 kW, 250 v, d.c., 6 - pole shunt generator runs at 1000 r.p.m when delivering full-load. The armature has 534 lap-connected conductors. Full load copper loss is 0.64 kW. The total brush drop is 1 volt. Determine the flux per pole. Neglect the shunt current.

Solution

To determine the flux per pole for the given DC shunt generator, we'll use the following steps and formulas:


1. Key Data Provided:

  • Power output (PoutP_{\text{out}}) = 10kW=10,000W10 \, \text{kW} = 10,000 \, \text{W}
  • Terminal voltage (VV) = 250V250 \, \text{V}
  • Speed (NN) = 1000r.p.m.1000 \, \text{r.p.m.}
  • Poles (PP) = 66
  • Armature conductors (ZZ) = 534534
  • Lap connection: Number of parallel paths (AA) = P=6P = 6 (since lap winding has A=PA = P)
  • Full-load armature copper loss (PcuP_{\text{cu}}) = 0.64kW=640W0.64 \, \text{kW} = 640 \, \text{W}
  • Total brush drop = 1V1 \, \text{V}
  • Neglecting shunt current (Ish=0I_{\text{sh}} = 0).

2. Calculate Armature Current:

The total output power of the generator is:

Pout=VIaP_{\text{out}} = V \cdot I_{\text{a}}

Rearranging for IaI_{\text{a}} (the armature current):

Ia=PoutV=10,000250=40AI_{\text{a}} = \frac{P_{\text{out}}}{V} = \frac{10,000}{250} = 40 \, \text{A}


3. Determine the Generated Voltage EgE_{\text{g}}:

The generated voltage EgE_{\text{g}} is related to the terminal voltage VV, brush drop, and armature resistance (RaR_{\text{a}}). Using:

Eg=V+Brush Drop+IaRaE_{\text{g}} = V + \text{Brush Drop} + I_{\text{a}} R_{\text{a}}

However, since the armature copper loss is given (Pcu=Ia2RaP_{\text{cu}} = I_{\text{a}}^2 R_{\text{a}}), we can find RaR_{\text{a}}:

Ra=PcuIa2=640402=0.4ΩR_{\text{a}} = \frac{P_{\text{cu}}}{I_{\text{a}}^2} = \frac{640}{40^2} = 0.4 \, \Omega

Now substitute into EgE_{\text{g}}:

Eg=V+1+(40)(0.4)=250+1+16=267VE_{\text{g}} = V + 1 + (40)(0.4) = 250 + 1 + 16 = 267 \, \text{V}


4. Use the EMF Equation to Find Flux Per Pole:

The EMF equation for a DC generator is:

Eg=NPϕZ60AE_{\text{g}} = \frac{N \cdot P \cdot \phi \cdot Z}{60 \cdot A}

Rearranging for flux per pole (ϕ\phi):

ϕ=Eg60ANPZ\phi = \frac{E_{\text{g}} \cdot 60 \cdot A}{N \cdot P \cdot Z}

Substitute the known values:

  • Eg=267VE_{\text{g}} = 267 \, \text{V},
  • N=1000r.p.m.N = 1000 \, \text{r.p.m.},
  • P=6P = 6,
  • Z=534Z = 534,
  • A=6A = 6 (lap winding).

ϕ=26760610006534\phi = \frac{267 \cdot 60 \cdot 6}{1000 \cdot 6 \cdot 534}

Simplify:

ϕ=961203204000=0.03Wb\phi = \frac{96120}{3204000} = 0.03 \, \text{Wb}


Final Answer:

The flux per pole is:

ϕ=0.03Wb\phi = 0.03 \, \text{Wb}


Would you like a breakdown of any part of the solution or further related questions answered? Here are some related problems to consider:

  1. How would the flux per pole change if the generator speed increased to 1200 r.p.m.?
  2. What happens to the generated voltage EgE_{\text{g}} if the armature resistance is halved?
  3. How does the number of poles affect the flux per pole calculation?
  4. What would be the effect of shunt current on the calculation?
  5. How is the efficiency of the generator calculated in this scenario?

Tip: Always check the generator's operating speed and connection type (lap or wave) when using the EMF equation.

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Math Problem Analysis

Mathematical Concepts

Electromagnetism
DC Machines
Electrical Engineering Calculations

Formulas

Armature Current: I_a = P_out / V
Generated Voltage: E_g = V + Brush Drop + I_a * R_a
Resistance: R_a = P_cu / I_a^2
EMF Equation: E_g = (N * P * φ * Z) / (60 * A)

Theorems

Electromagnetic Induction in DC Machines

Suitable Grade Level

Undergraduate (Electrical Engineering)