dc generator

By shyamlal • 07:32

Calculation of Generated EMF in a DC Generator

Problem Statement

Determine the generated EMF in a lap-wound, \(4\)-pole DC generator having a useful flux per pole of \(0.07\text{ Wb}\), \(220\) armature turns, and running at a speed of \(900\text{ rpm}\).

Given Data

  • Number of poles (\(P\)) = \(4\)
  • Useful flux per pole (\(\Phi\)) = \(0.07\text{ Wb}\)
  • Number of armature turns = \(220\)
  • Speed of the armature (\(N\)) = \(900\text{ rpm}\)
  • Winding type = Lap-wound

Step-by-Step Solution

Step 1: Determine Total Number of Armature Conductors (\(Z\))

Since each turn consists of two active coil sides (conductors):

$$Z = 2 \times \text{Number of turns} = 2 \times 220 = \mathbf{440\text{ conductors}}$$

Step 2: Determine Number of Parallel Paths (\(A\))

For a lap-wound armature, the number of parallel paths equals the number of poles:

$$A = P = \mathbf{4}$$

Step 3: Calculate the Generated EMF (\(E_g\))

The standard EMF equation of a DC generator is:

$$E_g = \frac{\Phi \cdot Z \cdot N \cdot P}{60 \cdot A}$$

Since \(A = P\) for a lap winding, the terms cancel out:

$$E_g = \frac{\Phi \cdot Z \cdot N}{60}$$

Substituting the given numerical values:

$$E_g = \frac{0.07 \times 440 \times 900}{60}$$

$$E_g = \frac{27720}{60} = \mathbf{462\text{ V}}$$

Final Result:

The generated EMF of the DC generator is \(462\text{ V}\).

Show the classification of dc generator on the basis of field winding in a schematic diagram

DC generators are broadly classified based on how their field windings are energized and connected with respect to the armature circuit into two primary groups:

  • Separately Excited DC Generators: Field winding is energized by an independent external DC source.
  • Self-Excited DC Generators: Field winding is energized by the current produced by the generator's own armature.

1. Classification Tree Hierarchy

DC GENERATORS Separately Excited Self-Excited Shunt Wound Series Wound Compound Wound Short-Shunt Long-Shunt Cumulative Compound Differential Compound Field winding energized by Independent External DC Source

2. Circuit Connections of Field Windings

Shunt Generator A R_sh + (V) - Field in Parallel Series Generator A R_se + (V) - Field in Series Short-Shunt Compound A R_sh R_se + - Both Shunt & Series Fields

3. Field Winding Details & Applications

Type Field Winding Construction Connection Manner Typical Application
Separately Excited Many turns of thin wire (High \(R\)) Connected to external battery/DC source Ward-Leonard speed control, laboratory testing
Shunt Wound Many turns of thin wire (High resistance, \(R_{sh}\)) Connected in parallel with armature Battery charging, general constant-voltage lighting
Series Wound Few turns of thick copper conductor (Low resistance, \(R_{se}\)) Connected in series with armature Line drop compensator (boosters) in DC feeders
Compound Wound Contains two sets of windings: one shunt coil and one series coil Short-shunt: Shunt coil across armature only.
Long-shunt: Shunt coil across armature + series coil. 		Cumulative: Arc welding, elevators, heavy power supply.
Differential: Rarely used.
Flux Action in Compound Generators:
  • Cumulative Compound: Series field flux aids the shunt field flux (\(\Phi_{\text{net}} = \Phi_{sh} + \Phi_{se}\)).
  • Differential Compound: Series field flux opposes the shunt field flux (\(\Phi_{\text{net}} = \Phi_{sh} - \Phi_{se}\)).