electrical base

Module Overview

  • This module covers the areas of:

    • Basic Electrical Theory

    • Transformers

    • Generators

    • Electrical Protection

Objectives

Basic Electrical Theory

  • Explain electrical terms including:

    • Current (I, Amps)

    • Potential (V, Volts)

    • Resistance (R, Ohms)

    • Capacitance (C, Farads)

    • Magnetic Flux (Webers)

    • Inductance (L, Henrys)

    • Frequency (f, Hertz)

    • Reactance (X, Ohms)

    • Impedance (Z, Ohms)

    • Active Power (P, Watts)

    • Reactive Power (Q, Vars)

    • Apparent Power (U, Volt Amps)

    • Power Factor (PF)

  • Identify the units of measurement of these electrical quantities.

  • Explain relationships among electrical quantities.

  • Describe the impact of moisture and temperature on electrical machines.

Transformers

  • Explain tap changers to adjust voltage ratio and their operational limitations.

  • Identify factors causing heating in transformers and their limitations on operations.

Generators

  • Explain the process of applying excitation near rated speed and its importance.

  • Identify parameters for generator connection to electrical systems.

  • Analyze generator responses when connected to inductive or capacitive loads.

  • Discuss control systems for generator terminal voltage and turbine governor functionalities.

Electrical Protection

  • Explain how differential protection operates in electrical systems.

  • Identify required protections for buses, transformers, and motors to ensure operational stability and safety.

Basic Electrical Theory

2.1 Introduction

  • Investigates definitions of basic electrical quantities, focusing on the movement of electrons.

2.2 Electrical Terms

  • Current (I, Amps): Flow of electrons, measured in Amperes (A).

  • Potential (V, Volts): Electric force driving current, measured in Volts (V).

  • Resistance (R, Ohms): Opposes current flow, measured in Ohms (Ω).

  • Capacitance (C, Farads): Ability to hold a charge, measured in Farads (F).

  • Magnetic Flux: Described by magnetic field lines surrounding a current-carrying conductor, measured in Webers (Wb).

  • Inductance (L, Henrys): Opposition to current change, measured in Henries (H).

  • Frequency (f, Hertz): Rate of alternating current, measured in Hertz (Hz).

  • Reactance (X, Ohms): Opposition to AC flow in capacitors/inductors, measured in Ohms.

  • Impedance (Z, Ohms): Total opposition to AC flow, combines resistance and reactance.

  • Active Power (P, Watts): Rate of energy used, measured in Watts (W).

  • Reactive Power (Q, Vars): Power flowing back and forth, necessary for inductors/capacitors.

  • Apparent Power (U, Volt Amps): Total power in the circuit, measured in Volt Amps (VA).

  • Power Factor (PF): Ratio of real power to apparent power; indicates efficiency.

2.3 Relationships of Basic Electrical Quantities

  • Voltage vs. Current in Resistors, Capacitors, Inductors: Different behaviors under direct and alternating current.

  • DC Circuit Components: Series (total resistance = R1 + R2 + ...) and Parallel configurations (total resistance = 1/(1/R1 + 1/R2 + ...)).

  • Transient Effects: Capacitors resist changes in voltage; Inductors resist changes in current.

  • Phasors: Used for representing AC voltages and currents in their varying forms.

Transformers

3.1 Introduction

  • Transformers enable voltage and current transformation in AC systems, aiding efficient power transmission.

3.2 Transformers - General

  • VA Rating: Maximum output current at standard voltage.

  • Cooling: Required for transformer operation, with various methods (ONAN, ONAF, etc.) indicated.

  • Frequency: Core losses increase at non-rated frequencies impacting efficiency.

3.3 Tap-Changers

  • Enable adjustment of voltage output by varying transformer turn ratios.

  • Types of tap-changers include Off-Load and On-Load.

Generators

4.1 Introduction

  • Describe significant aspects of turbine-generator operations and principles of electromagnetic induction.

4.2 Fundamentals of Generator Operation

  • Electric generation relies on DC supply to rotor windings facilitating voltage induction in copper coils.

  • Key components involve interaction between rotor's magnetic field and stator's three-phase windings.

4.3 Synchronous Operation

  • Explore load angle impacts, managing generator speed, and power output regulation.

Electrical Protection

5.1 Purpose of Electrical Protection

  • Fast intervention mitigates damage and assures stability in the electrical system during faults.

5.3 Essential Qualities of Electrical Protection

  • Protection systems must possess speed, reliability, security, and sensitivity.

5.6 Bus Protections

  • Utilize differential and over-current relay systems for bus fault detection.

5.7 Transformer Protection

  • Use differential protection and gas relays for complete coverage against transformer faults.

General Review Questions

  • Review objectives and key functions as defined in this module, focusing on relationships and operational limitations pertaining to electrical systems.