Basic Electrical Engineering: DC Circuits and Transformers

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Questions and Answers

What are the three fundamental passive electrical circuit elements mentioned for DC circuits?

Resistor (R), Inductor (L), and Capacitor (C)

State Kirchhoff's Current Law (KCL).

Kirchhoff's Current Law states that the algebraic sum of currents entering a node (or junction) in an electrical circuit is equal to zero, or equivalently, the sum of currents entering a node equals the sum of currents leaving the node.

State Kirchhoff's Voltage Law (KVL).

Kirchhoff's Voltage Law states that the algebraic sum of all the voltages around any closed loop in an electrical circuit is equal to zero.

Which circuit analysis theorems are mentioned for DC circuit analysis?

<p>Superposition, Thevenin, and Norton Theorems (C)</p> Signup and view all the answers

What is the difference between peak and RMS values for a sinusoidal waveform?

<p>The peak value is the maximum instantaneous value of the waveform. The RMS (Root Mean Square) value is the effective value, representing the equivalent DC value that would produce the same heating effect. For a sinusoid, RMS value = Peak value / √2.</p> Signup and view all the answers

Define power factor in AC circuits.

<p>Power factor is the ratio of real power (doing useful work) to apparent power (total power flowing in the circuit). It is also equal to the cosine of the phase angle difference between the voltage and current waveforms.</p> Signup and view all the answers

What phenomenon occurs in series and parallel RLC circuits at a specific frequency where inductive and capacitive reactances cancel each other out?

<p>Resonance</p> Signup and view all the answers

What are the two common connection types for three-phase balanced circuits?

<p>Star (Wye) and Delta (D)</p> Signup and view all the answers

What information does a BH characteristic curve provide about a magnetic material?

<p>The BH characteristic curve shows the relationship between the magnetic flux density (B) induced in a material and the magnetizing force (H) applied to it. It illustrates properties like saturation, retentivity, and coercivity.</p> Signup and view all the answers

What are the main components of losses in a practical transformer?

<p>Transformer losses primarily consist of core losses (hysteresis and eddy current losses) and copper losses (I²R losses in the windings).</p> Signup and view all the answers

What does the 'regulation' of a transformer signify?

<p>Voltage regulation of a transformer is a measure of the change in its secondary terminal voltage when the load changes from no load to full load, at a specified power factor, with the primary voltage held constant. It is usually expressed as a percentage of the full load voltage.</p> Signup and view all the answers

How is a rotating magnetic field typically generated in electrical machines?

<p>A rotating magnetic field is typically generated by supplying three-phase AC currents, which are 120 degrees out of phase with each other, to a set of stator windings that are physically displaced by 120 degrees around the stator.</p> Signup and view all the answers

What is the significance of the torque-slip characteristic for a three-phase induction motor?

<p>The torque-slip characteristic describes how the motor's output torque varies with its slip (the difference between synchronous speed and actual rotor speed). It determines the motor's starting torque, breakdown (maximum) torque, and operating performance under different loads.</p> Signup and view all the answers

Synchronous generators are primarily used to convert mechanical energy into AC electrical energy.

<p>True (A)</p> Signup and view all the answers

Identify four components of LT (Low Tension) Switchgear mentioned.

<p>Switch Fuse Unit (SFU), Miniature Circuit Breaker (MCB), Earth Leakage Circuit Breaker (ELCB), Moulded Case Circuit Breaker (MCCB).</p> Signup and view all the answers

What is the primary purpose of earthing in electrical installations?

<p>The primary purpose of earthing (grounding) is safety. It provides a low-resistance path for fault currents to flow to the ground, preventing dangerous voltages from appearing on equipment casings and minimizing the risk of electric shock.</p> Signup and view all the answers

Flashcards

Electrical Circuit Elements

Electrical circuit components including Resistors (R), Inductors (L), and Capacitors (C).

Kirchhoff's Current Law (KCL)

States that the sum of currents entering a node is equal to the sum of currents leaving the node.

Kirchhoff's Voltage Law (KVL)

States that the sum of voltage drops around any closed loop in a circuit is equal to zero.

Superposition Theorem

A method to simplify circuits by considering the effects of each independent source separately.

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Thevenin's Theorem

States that any linear circuit can be replaced by an equivalent circuit consisting of a voltage source and a series resistance.

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BH Characteristics

Deals with magnetic domains and behaviors of magnetic materials.

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Transformer Equivalent Circuit

A transformer model representing the actual transformer with ideal components and added impedances to account for losses.

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Torque-Slip Characteristic

Three-phase induction motor's speed compared to synchronous speed.

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Miniature Circuit Breaker (MCB)

A protective device that opens a circuit when excessive current flows through it.

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Earth Leakage Circuit Breaker (ELCB)

A safety device used to protect against electrical shock by detecting leakage currents.

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MCCB

Molded Case Circuit Breaker. Another type of protective device used in electrical installations.

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Power Factor

The ratio of real power to apparent power.

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RMS value

Peak value divided by the square root of 2 for sinusoidal waveforms.

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Star connection

Voltage and current relationship in a star connected circuit.

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Delta connection

Voltage and current relationship in a delta connected circuit.

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Real Power

Power that performs actual work.

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Reactive Power

Power that oscillates between the source and load, required for reactive components.

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Apparent Power

The product of voltage and current, without considering the phase angle.

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Switch Fuse Unit (SFU)

SFU is High Rupturing Capacity fuse switch disconnector

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Earthing

Process of connecting electrical equipment to the earth for safety purposes.

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Study Notes

  • Course: Basic Electrical Engineering
  • Course Code: ELE150C
  • Credits: 3
  • Regulation: 2020

DC Circuits

  • Focus on electrical circuit elements (R, L, and C), voltage and current sources
  • Kirchhoff's current and voltage laws are important
  • Analysis of simple circuits with DC excitation should be performed
  • Superposition, Thevenin, and Norton Theorems are key

AC Circuits

  • Cover representation of sinusoidal waveforms, peak and RMS values, and phasor representation
  • Real power, reactive power, apparent power, and power factor are important concepts
  • Analysis of single-phase AC circuits and resonance in series and parallel RLC circuits is necessary
  • Three-phase balanced circuits, voltage, and current relations in star and delta connections are included

Transformers

  • Focus on magnetic materials, BH characteristics, and ideal and practical transformers
  • Equivalent circuits and losses in transformers should be covered
  • Regulation and efficiency, along with three-phase transformer connections, are important

Electrical Machines

  • Generation of rotating magnetic fields should be understood
  • Construction and working of a three-phase induction motor is included
  • Significance of torque-slip characteristic should be considered
  • Starting of induction motors and torque-speed characteristic of separately excited DC motors are covered
  • Construction and working of synchronous generators are also included

Electrical Installations

  • Focus on components of LT Switchgear, including Switch Fuse Unit (SFU), MCB, ELCB, and MCCB
  • Types of wires and cables and earthing practices should be covered
  • Types of batteries and their important characteristics are included

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