Electrical Circuits and Machines

Study Notes

Transformers: Devices that change AC voltage levels. They are used to increase or decrease voltage levels in electrical power systems. Transformers have a primary and secondary coil and operate based on electromagnetic induction.
Types of transformers: Step-up transformers increase voltage, while step-down transformers decrease voltage. Autotransformers have a common winding for both primary and secondary coils.
Transformer Tap Changers: Mechanisms that adjust transformer voltage levels. There are manual (non-automatic) and automatic types (OLTC).

Power Generation: Power plants generate electricity. Common types include hydro, thermal (fossil fuel, nuclear), and renewable sources.
Power Transmission: High-voltage lines transmit electricity over long distances. High voltage is used to minimize transmission losses.
Power Distribution: Lower voltage lines distribute electricity to consumers.

Motors: Convert electrical energy to mechanical energy. They use electromagnetic forces to create rotation. Motors have stator (stationary part) and rotor (rotating part).
Generators: Convert mechanical energy to electrical energy. They employ electromagnetic induction to generate voltage. Common types include DC and AC Generators (alternators).
Components Stator, Rotor, windings, brushes, commutator, and the magnetic field.

Magnetic Fields: Generated by electric currents. Defined by the magnetic flux density (B) and magnetic field intensity (H).
Magnetic Flux: Measured in webers (Wb).
Magnetic Field Intensity H: Measured in ampere-turns per meter (At/m).
Magnetic Flux Density B: Measured in teslas (T).
Relationship: B = μH. μ is the permeability of the material.
Force on a current-carrying conductor in a magnetic field: F = iL x B (vector product)

Load (in Power Systems): The electrical demand placed on a power system by consumers. Load is often expressed in units like kilowatts (kW).
Load Factor: The ratio of the average load to the maximum load over a given period. It indicates how efficiently a power system is utilized.
Power Factor: The cosine of the phase angle between voltage and current in an AC circuit. It shows the proportion of apparent power that is contributing to useful work (active power).
Active Power (P): The power that performs useful work (e.g., heating a resistor). It is measured in watts (W)
Reactive power (Q): Power used for storing energy in the electric and magnetic fields of inductors or capacitors. It does not perform useful work. It's measured in volt-amperes reactive (VAR).
Apparent Power (S): The total power in an AC circuit. It is the product of voltage and current. It's measured in volt-amperes (VA).
Relationship: S² = P² + Q².