ARMATURE
WINDING
Introduction
Armature winding is a fundamental topic in the study of DC
machines, particularly DC generators and DC motors. The
armature winding is responsible for generating electromotive
force (e.m.f.) in a DC generator and for carrying current in a DC
motor. The arrangement of conductors in the armature
determines the electrical performance, voltage level, and
current capacity of the machine.
Definition of Armature Winding
• Armature winding refers to the arrangement
and interconnection of conductors placed
in the slots of the armature core of a DC
machine. These conductors are connected
to commutator segments in such a way that
the alternating e.m.f. induced in the
armature conductors is converted into
unidirectional (DC) output at the terminals.
Purpose of Armature Winding
• The main purposes of armature winding are: - To generate
electrical energy in a DC generator by electromagnetic induction
- To ensure continuous and smooth DC output through proper
commutation - To provide the required voltage and current rating
of the machine
Types of Armature Windings
• For drum-type armatures, two types of windings are
commonly used:
1. Lap Winding
2. Wave Winding
The difference between these windings lies mainly in
the way the coil ends are connected to the commutator
segments.
General Rules for Armature Windings
• The following rules apply to both lap and wave windings:
1. The back pitch (YB) and front pitch (YF) are approximately equal to the
pole pitch to obtain full-pitched winding.
2. Both YB and YF must be odd numbers to allow proper placement of coil
sides in the armature slots.
3. The number of commutator segments is equal to the number of coils.
4. The winding must be a closed winding, meaning all conductors are
included and the path returns to the starting point.
Lap Winding
Description
In lap winding, the finishing end of one coil is connected to the starting end of the
adjacent coil under the same pole. The winding laps back on itself, which is why it
is called lap winding.
Types of Lap Winding
• Simplex Lap Winding – one winding per pole
• Duplex Lap Winding – two windings per pole
• Triplex Lap Winding – three windings per pole
Characteristics of Simplex Lap Winding
• Back pitch (YB) and front pitch (YF) are odd and differ by 2
• Average pitch (YA) is equal to pole pitch
• Commutator pitch (YC) is ±1
• Number of parallel paths (A) = P, where P is the number of poles
• Suitable for low-voltage, high-current applications
Wave Winding
Description
In wave winding, the coils are connected in such a way that the winding
progresses in a wave-like pattern around the armature. The winding passes under
successive poles of opposite polarity before returning to a nearby commutator
segment.
Characteristics of Simplex Wave Winding
· Back pitch (YB) and front pitch (YF) are equal and odd
· Average pitch (YA) is approximately equal to pole pitch
· Number of parallel paths (A) = 2, regardless of the number of poles
· Requires only two brushes
Suitable for high-voltage, low-current applications
Comparison of Lap and Wave Windings
Commutation in Armature Windings
Commutation is the process by which the alternating current induced in the
armature conductors is converted into direct current at the terminals. Proper
armature winding ensures smooth commutation, reduced sparking at the
brushes, and efficient operation of the DC machine.
Importance of Armature Winding Selection
The choice between lap winding and wave winding depends on: - Required
voltage level - Required current output - Number of poles - Application of the DC
machine
Correct selection improves efficiency, reliability, and performance of the machine.
Computation of Generated E.M.F. in DC
Generator (Related to Armature Winding)
The type of armature winding directly affects the generated electromotive force
(e.m.f.) of a DC generator because it determines the number of parallel paths in
the armature.
E.M.F. Equation of a DC Generator
The general equation for the generated e.m.f. of a DC generator is:
Eg = (Φ Z N / 60) × (P / A) volts
Where:
Φ = Flux per pole (weber)
Z = Total number of armature conductors
N = Speed of armature (rpm)
P = Number of poles
A = Number of parallel paths
For different windings: - Simplex Lap Winding: A = P - Simplex Wave Winding: A = 2
Sample Computation – Lap Wound Generator
Given: - Number of poles, P = 4 - Total armature conductors, Z = 800 - Flux per
pole, Φ = 0.02 Wb - Speed, N = 1000 rpm - Type of winding: Simplex Lap
Solution:
For simplex lap winding: A = P = 4
Substitute into the e.m.f. equation:
Eg = (Φ Z N / 60) × (P / A) Eg = (0.02 × 800 × 1000 / 60) × (4 / 4) Eg = (16,000 / 60)
Eg = 266.67 V
Sample Computation – Wave Wound Generator
Using the same machine data but with simplex wave winding:
For simplex wave winding: A = 2
Eg = (Φ Z N / 60) × (P / A) Eg = (0.02 × 800 × 1000 / 60) × (4 / 2)
Eg = (16,000 / 60) × 2 Eg = 533.33 V
Effect of Armature Winding
on Voltage and Current
From the computations: - Wave winding produces higher
voltage because it has fewer parallel paths - Lap winding
produces lower voltage but higher current capacity due to more
parallel paths
This demonstrates why lap windings are used for low-voltage,
high-current machines, while wave windings are used for highvoltage, low-current machines.
Summary
Armature winding is a vital component of DC machines that
determines the electrical characteristics of the generator or
motor. Lap winding provides multiple parallel paths and is
suitable for high-current applications, while wave winding
offers fewer parallel paths and is ideal for high-voltage
applications. Understanding the construction rules and
characteristics of each type of winding is essential for
analyzing and designing DC machines.
References
·
Hernandez, C. L. DC and AC Machinery Module, Laguna
University
·
Theraja, A. K., & Theraja, B. L. (2005). A Textbook of
Electrical Technology, Vol. II: DC and AC Machines
·
DOE Fundamentals Handbook (1992). Electrical Science
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