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Theory of Alternating-Current Machinery by Alexander S. Langsdorf is a seminal engineering text that remains highly regarded for its rigorous mathematical depth and clarity in explaining electromagnetic principles. First published in 1937 as part of the McGraw-Hill "Electrical Engineering Texts" series, this comprehensive volume spans nearly 800 pages, focusing on the steady-state theory of AC machinery. Overview and Academic Significance

Unlike many modern texts that simplify complex derivations, Langsdorf’s work is known for making "no compromise" on mathematical explanations. It serves as a bridge between pure physics and applied engineering, often preceding vector diagrams and complex algebra with deep discussions of physical relations.

Author Profile: Alexander S. Langsdorf (1877–1973) was the Dean Emeritus of the Schools of Engineering and Architecture at Washington University and a Fellow of the American Institute of Electrical Engineers.

Key Distinctions: Reviewers frequently cite his remarkable treatment of transformer phasor diagrams as a standout feature. Core Topics and Chapter Structure

The text is designed for senior electrical engineering students and covers the following major areas of AC theory:

Transformers: Detailed analysis of fundamental principles, connections, insulation, heating, and load stresses.

Synchronous Generators: Deep dives into the operation and resultant fields of synchronous machines.

Induction Motors: Theoretical treatment of asynchronous machines, which can be studied independently from other sections.

Mercury Arc Rectifiers: Inclusion of electronic devices that were cutting-edge at the time of publication. Theory-alternating-current-machines-alexander-langsdorf-pdf

Analysis Tools: Extensive use of circle diagrams, phasor diagrams, and complex algebra to model machine performance. Accessing the Text Engineering - Nature

Introduction to AC Machines

Alternating Current (AC) machines are a type of electric machine that uses alternating current to produce mechanical energy. They are widely used in industrial, commercial, and residential applications due to their high efficiency, reliability, and flexibility.

Key Concepts

  1. Alternating Current (AC): An electric current that periodically reverses direction, oscillating at a specific frequency.
  2. Synchronous Speed: The speed at which an AC machine operates when its rotor is synchronized with the rotating magnetic field produced by the stator.
  3. Polyphase: A system of multiple AC currents, typically 3-phase, used to improve efficiency and reduce voltage drops.

AC Machine Types

  1. Synchronous Machines: Machines that operate at synchronous speed, typically used for applications requiring constant speed, such as generators and motors.
  2. Induction Machines (Asynchronous Machines): Machines that operate at a speed less than synchronous speed, commonly used for applications such as pumps, fans, and conveyor belts.

Theory of AC Machines

  1. Rotating Magnetic Field: A magnetic field produced by the stator windings that rotates at synchronous speed.
  2. Induced EMF: The electromotive force (EMF) induced in the rotor windings due to the rotating magnetic field.
  3. Torque Production: The interaction between the stator and rotor magnetic fields produces torque, causing the rotor to rotate.

AC Machine Design and Construction

  1. Stator Design: The stator consists of a laminated steel core with copper windings embedded in slots.
  2. Rotor Design: The rotor consists of a laminated steel core with copper windings (synchronous machines) or aluminum/copper bars (induction machines).

Performance Analysis

  1. Equivalent Circuit: A simplified circuit representation of an AC machine, used to analyze performance and predict behavior.
  2. Power Flow: The flow of power through an AC machine, including input power, output power, and losses.

Control and Applications

  1. Speed Control: Methods used to control the speed of AC machines, such as varying the frequency or voltage.
  2. Applications: AC machines are used in a wide range of applications, including industrial drives, power generation, and transportation.

References

For a more in-depth understanding of AC machines, I recommend consulting the textbook "Alternating-Current Machines" by Alexander and Langsdorf, as well as other reputable resources.

Theory of Alternating-Current Machinery by Alexander S. Langsdorf is a classic engineering textbook that provides a comprehensive analysis of the construction and operation of AC machines. Key Information

Alexander S. Langsdorf, former Professor of Electrical Engineering and Dean at Washington University. Subject Matter:

The principles and theory underlying alternating-current machines, including transformers, synchronous generators, and various types of AC motors. First Edition: Published in 1937. Second Edition:

Released around 1955, including updates for the m.k.s. system. Publisher: Originally published by McGraw-Hill Book Company Core Topics Covered

The textbook is widely cited in electrical engineering syllabi for its detailed treatment of: Principles of alternating current machinery - djm.cc Theory of Alternating-Current Machinery by Alexander S

3. Induction Motors (The Induction Principal)

Langsdorf explains the induction motor as a "transformer with a rotating secondary." He meticulously covers:

4. Key Equations (selected)

  1. Air‑gap MMF (fundamental component):
    [ \mathcalF_g(\theta) = \fracN_s I_s\sqrt2 , k_w , \cos(p\theta - \omega t) ]
    where ( N_s ) = turns per phase, ( I_s ) = rms current, ( k_w ) = winding factor, ( p ) = pole pairs.

  2. Electromagnetic Torque (general form):
    [ T_em = \frac32 p , \frac\partial \lambda_sr\partial \theta_r ]
    with ( \lambda_sr ) = mutual flux linkage between stator and rotor.

  3. Induced EMF (E) for a synchronous machine:
    [ E = 4.44 f N_s \Phi_m k_w ]
    where ( f ) = supply frequency, ( \Phi_m ) = peak flux per pole.

  4. Induction Machine Slip:
    [ s = \fracn_s - nn_s,\quad n_s = \frac120 fp ]

  5. Torque‑Speed Characteristic (induction):
    [ T(s) = \frac3 V^2 R_r / s\omega_s \big[ (R_s + R_r/s)^2 + (X_s + X_r)^2 \big] ]

Why Engineers Still Seek the PDF Version

Given that the book is out of print in physical form (original hardcovers now fetch collector’s prices), the digital route is logical. Here is why the search for a Theory-alternating-current-machines-alexander-langsdorf-pdf persists: