Electrical Circuits and Machines

Electrical Circuits and Machines

• 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).

AC Power System Components

• 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.

Electric Machines (Motors and Generators)

• 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.

Electromagnetic Fields

• 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)

Other Concepts

• 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.