Electrical Machines
Transformers, DC machines and induction motors look like three subjects and are one: a changing flux linking a coil. These topics animate the flux and the force rather than starting from the equivalent circuit.
Start from the beginning →8 topics you can watch now, 12 still to come.
Electromechanical energy conversion
The one principle the whole subject is an application of.
- How a Machine Converts EnergyStart here. Run one loop of wire as a generator, then reverse the arrow and run the identical hardware as a motor.
- Magnetic Circuits and ReluctanceOhm's law for magnetism — and the three places the analogy breaks, which are what actually size a machine.
- Faraday's and Lenz's laws in detail
- Force and torque from a field
Transformers
A machine with no moving parts, and the easiest one to reason about.
- The Ideal TransformerVoltage up, current down, power unchanged — and impedance transforming by the square, which is the property usually skipped.
- Losses, Regulation and EfficiencyOne loss follows the load and one ignores it, which is what puts the efficiency peak where it is.
- Equivalent circuit and referred quantities
- Autotransformers and three-phase connections
DC machines
Commutation: mechanically switching the current to keep torque up.
- EMF and Torque in a DC MachineThe raw output of every DC machine is alternating — watch the commutator reverse it at exactly the right instant.
- Shunt, Series and CompoundThree machines differing in one connection, and behaving nothing like each other. Includes the one that runs away.
- Construction and armature windings
- Armature reaction and commutation
Induction machines
The workhorse: no brushes, no supply to the rotor at all.
- The Rotating Magnetic FieldThree windings that never move produce a field that rotates — the most elegant result in the subject.
- Slip and the Torque-Slip CurveWalk the curve from standstill to synchronism and find that the useful part is a narrow sliver at the end.
- Speed control and single-phase motors
- Double-cage and deep-bar rotors
Synchronous machines
The machine that generates almost all the world's electricity.
- Alternator construction and EMF equation
- Voltage regulation methods
- Parallel operation and synchronisation
- Synchronous motor and V-curves
About Electrical Machines
Electrical machines are energy conversion made mechanical. Every motor and generator in the subject runs on the same two facts: a current in a magnetic field feels a force, and a conductor moving through a field has a voltage induced in it. Motors lean on the first, generators on the second, and every machine here does both at once.
The unifying object is the magnetic circuit, which is why it comes first. Once flux is something you can reason about like current in a network, transformers and rotating machines stop being separate topics and become the same analysis applied to a stationary and a moving geometry.
The rotating field is the concept that repays animation most. Three currents, spaced in time, producing a magnetic field that sweeps around a stator is nearly impossible to see in a still figure and obvious the moment it moves.
What to know first
- Electric Circuit Analysis
- Basic magnetism — flux, and the idea of a magnetic circuit
Where it gets used
- Choosing a motor with a torque-speed curve that suits the load
- Understanding transformer losses and why efficiency peaks where it does
- Reading a machine nameplate and knowing what each rating constrains