Jadeer Learning Manual - Electrical Basics

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Questions and Answers

What is the primary function of the iron yoke in an electromagnetic relay?

To act as a spring and return the armature to its relaxed state.

To house the relay system.

To provide a low reluctance path for magnetic flux. (correct)

To provide a mechanical link between the armature and the contacts.

What causes the armature to move when a current is applied to the coil of an electromagnetic relay?

The electric current directly moving the armature.

The spring force pushing it towards the coil.

The magnetic field attracting it towards the coil. (correct)

Gravity pulling it downward.

What is the typical role of a diode placed across the coil in a DC-powered electromagnetic relay?

To dissipate energy from the collapsing magnetic field. (correct)

To provide a backup power source for the relay.

To protect the contacts from corrosion.

To increase the strength of the magnetic field.

In a typical electromagnetic relay, what is the purpose of the spring connected to the armature?

To return the armature to its original de-energized position. Signup and view all the answers

Why do electromagnetic relays need to operate quickly in high voltage/high current applications?

To minimize the risk of arcing between contacts. Signup and view all the answers

In an AC circuit containing both resistance and capacitive reactance, what is the phase relationship between current and voltage?

Current leads voltage by more than 0 degrees and less than 90 degrees Signup and view all the answers

What effect does inductance have on current in an AC circuit?

It causes a continuous opposition to current flow Signup and view all the answers

What does impedance represent in an AC circuit?

The total opposition to current flow in the circuit Signup and view all the answers

In an impedance vector diagram, at what angle is capacitive reactance plotted?

-90 degrees Signup and view all the answers

In a series RLC circuit, how does current relate to voltage in the inductance component?

Current lags voltage by 90 degrees Signup and view all the answers

How is the magnitude of an impedance vector calculated?

By taking the square root of the sum of the squares of the reactance and resistance vectors Signup and view all the answers

If a circuits impedance vector has an angle of -45 degrees, what does this indicate?

The circuit contains equal amounts of resistance and capacitive reactance Signup and view all the answers

What is the 'normal' condition of a speed switch, as described in the text?

Shaft not turning Signup and view all the answers

What is the 'normal' condition of a pressure switch?

Zero applied pressure Signup and view all the answers

What is the 'normal' condition for a temperature switch, according to the examples provided?

Ambient (room) temperature Signup and view all the answers

What is considered the 'normal' state of a level switch, according to the text?

An empty tank or bin Signup and view all the answers

What is the described 'normal' condition for a flow switch?

Zero liquid flow Signup and view all the answers

If a flow switch is used as a low-flow alarm, what contact configuration would typically be used so that the alarm activates when flow is lost?

Normally-closed Signup and view all the answers

In generic switch symbology, how are normally-open contacts depicted?

Two vertical lines that do not touch. Signup and view all the answers

How are normally-closed contacts designated in generic switch symbology?

Two vertical lines with a diagonal line between them Signup and view all the answers

In the context of a switch, what is 'normal' state?

The state of the switch as it's stored on a shelf, unactuated. Signup and view all the answers

In control logic schematics, how is a capacitor typically represented to distinguish it from a normally-open switch contact?

A symbol with two parallel plates, one of which is curved, as for a polarity sensitive capacitor. Signup and view all the answers

What design factor must be considered when using multiple position selector switches?

The sequence of breaking and making connections. Signup and view all the answers

In a 'break-before-make' switch configuration, what happens when the switch is moved from one position to the next?

The old contact is broken before the new contact is made. Signup and view all the answers

What is a key characteristic of a 'make-before-break' switch design?

It momentarily allows both circuits to be connected together when switching between positions. Signup and view all the answers

What potential issue must be considered when using a 'make-before-break' switch?

The circuit must be able to tolerate connections between adjacent positions. Signup and view all the answers

In the context of selector switches, what does the term 'throws' refer to?

The stationary contact positions. Signup and view all the answers

What does the term 'poles' refer to when describing selector switches?

The number of moving contacts. Signup and view all the answers

A switch with one moving contact and five stationary contacts is designated as what?

Single pole, five-throw. Signup and view all the answers

If a control system uses a single symbol to represent a capacitor, even if it is not polarity sensitive, why is this done?

To differentiate it from a normally open-switch contact. Signup and view all the answers

What is the primary difference between a break-before-make and make-before-break switch?

Whether the circuit is momentarily opened or bridged during switching. Signup and view all the answers

What is a double-pole, five-throw switch composed of?

Two single-pole, five-throw switches mechanically linked. Signup and view all the answers

According to the table of contents, on what page does the 'Basic Design and Operation' of relays start?

95 Signup and view all the answers

Which of the following best defines an electrical contactor?

An electromechanical switching device used for remote power or control circuit switching Signup and view all the answers

What is the primary function of a contactor?

To remotely switch a power or control circuit. Signup and view all the answers

What activates a contactor?

A control input with lower voltage/current. Signup and view all the answers

In the semiconductor industry, what does 'contactor' refer to?

A specialized socket that connects the device under test. Signup and view all the answers

According to the provided table of contents, on what page can we find information about contactor ratings?

88 Signup and view all the answers

What is an electromechanical switch?

A switch that is actuated by a solenoid. Signup and view all the answers

What is NOT a typical application for contactors?

Interrupting a short circuit Signup and view all the answers

What does the term 'ganged' mean in the context of switches?

Switches actuated by a common mechanism. Signup and view all the answers

Study Notes

Jadeer Learning Manual - Electrical Area 2

This manual covers plant electrical installation - level 1
Date of issue: 6 November 2024
Next review date: 1 October 2027
Document reference: JAD-LC-A2-YP-EMT-LM
Module: 2024
Revision: 2024.01

Basics of Electricity

Elements of an Atom: All matter is composed of molecules, which are made up of a combination of atoms. Atoms have a nucleus with electrons orbiting around it. The nucleus is composed of protons and neutrons. Most atoms have an equal number of electrons and protons. Electrons have a negative charge (-). Protons have a positive charge (+). Neutrons are neutral.
Free Electrons: Electrons in the outer band can become free of their orbit by external forces (magnetic fields, friction, or chemical action). These "free electrons" move from one atom to the next, creating electron flow which is the basis of electricity.
Conductors: Materials that allow many free electrons to move freely are called conductors. Copper, gold, silver, and aluminum are examples of good conductors. Copper is widely used due to its relative low cost.
Insulators: Materials that allow few free electrons are called insulators. Plastic, rubber, glass, mica, and ceramic are examples of good insulators. Insulators are used to prevent electrons from flowing outside the conductor pathways.
Semiconductors: Materials exhibiting characteristics of both conductors and insulators, such as silicon. Semiconductors are used to create transistors, diodes, and other solid state electronic devices.

Basic of Electricity Learning Content

Table of Contents (page 5)
Learning Objectives (page 6)
Basic Introduction of Electricity (page 8)
DC and Magnetism (page 8)
Understanding of AC Circuits (page 8)
Series and Parallel Circuits (page 8)
Understanding of Electrical Formulas (page 8)
Understanding of Power Triangle (page 8)

Objectives

Basic understanding of DC and Magnetism (page 5)
Basic understanding of AC Circuits and Series/Parallel Circuits (page 5)
Understanding of Power Triangle (page 5)

Common Electrical Hazards

Electrical injuries are a serious concern, with 4,309 employees on average taking time off work for injuries between 1992 and 2001
Electricity can cause both immediate and secondary effects including: tingling sensations, muscle contractions, respiratory paralysis, heart clamps, tissue and organ burns.
Exposure even at low levels (3 milliamperes) can injure.

Preventing Workplace Hazards

Electrocution is a leading cause of workplace fatalities
Younger workers have a higher risk of death from electrical shock.
Many workplace electrocutions involve contact with power lines while handling equipment.

Basic Introduction of Electricity

Atoms are the basic building blocks of all matter
Atoms have nuclei with electrons orbiting around them
Atoms have equal numbers of protons and electrons.
Electrons carry a negative charge ( - ) and protons carry a positive charge (+)
Electrons being attracted to protons, are bound in their orbit

Attraction and Repulsion of Electric Charges

Opposite charges attract, and similar charges repel
Charged bodies create an invisible electric field
Coulomb's Law: The force of attraction or repulsion depends on the strength of charges and the distance between them

Current

Electricity is the flow of electrons in a conductor
Current is measured in amperes (amps), denoted by the symbol "A".
Direct current (DC) flows in one direction consistently.
Alternating current (AC) periodically changes direction.

Voltage

Voltage, electromotive force (emf), or potential difference is the force required to make electricity flow through a conductor
It is measured in volts, represented by the letter “V”.
A difference in potential exists between the terminals of a voltage source.
For DC, voltage polarity remains unchanged, while AC polarity alternates.

Resistance

Resistance in an electrical circuit opposes the flow of current
Resistance depends on material composition, length, cross-section and temperature
The unit of measurement for resistance is ohms (Ω).

Ohms Law Triangle

Ohm's law relates current (I), voltage (E), and resistance (R)
The illustration shows how to calculate any unknown value using the appropriate formula: E = I xR; I = E / R; R = E / I

Basics of Electricity (DC and Magnetism)

Principles of magnetism are important to electricity, and vice-versa
All magnets have two poles: north and south.
Invisible magnetic flux lines emanate from the north pole and enter the south pole.
Magnetic fields can be shown visually using iron filings.
Like poles repel, and unlike poles attract.

Electromagnetism

Electric currents generate a magnetic field.
A relationship exists between the direction of current flow and the direction of the magnetic field (left-hand rule).

Electromagnets

A coil of wire carrying current acts like a magnet.
Increasing the number of turns in a coil, current, or having the coil around a conductive material as a core increases the strength of the magnetic field generated.
Used in many electrical devices as motors, circuit breakers, and relays

Understanding of AC Circuits AC Current

The supply of current for electrical devices may come from a direct current (DC) source or an alternating current (AC) source.
In a direct current (DC) circuit, electrons flow continuously in one direction from the power source through a conductor to a load and back to the power source.
In an alternating current (AC) circuit, the flow direction reverses many times a second reversing (changing) polarity.
AC is represented graphically as a sine wave.
The vertical axis represents the magnitude of current or voltage.

Basic AC Generator

Includes a magnetic field, an armature (consisting of conductive wires in loops), slip rings, and brushes.
A voltage is induced in the conductor as the armature rotates through a magnetic field.
The current flows from the armature to the load via the slip rings and the carbon brushes.
This process continues as long as the generator is in operation.

Frequency

Frequency is the number of cycles per second of voltage induced in the armature.
The unit of frequency is Hertz (Hz), with a cycle per second being equal to 1 Hz.
Common power line frequencies in many countries are 50 and 60 Hz.

Four-pole AC Generator

A two-pole AC generator completes one cycle for each revolution.
A four-pole AC generator completes two cycles per revolution
Increased poles increase frequency

Amplitude

Amplitude in AC current or voltage is variation in value.
Three ways to express or measure amplitude: peak value, peak-to-peak value, and effective value.
Peak is the maximum value on one-half cycle
Peak-to-peak is from +peak to -peak
The effective value is also known as the RMS value, approximately 70.7% of the peak value.

Calculating Impedance

Impedance is the total opposition to current flow in an AC circuit
It's represented as a vector with both magnitude and direction
Impedance vector angle corresponds to phase relationship between voltage and current.

Series RLC Circuits

RLC circuits have resistance, inductance, and capacitance in series
Calculated using Ohm's Law for current
Inductance and capacitance add to total opposition, called reactance, in opposing current directions.

Parallel RLC Circuits

Parallel circuits have resistance, inductance, and capacitance in parallel, and increase circuit capacitance.
Total capacitance is the sum of each capacitor value
The total resistance value is inversely proportional to the individual resistance values in the parallel circuit

Capacitors

Capacitance is a measure of a circuit's ability to store an electrical charge
Capacitance is a function of the plate area, distance between plates, and type/material of the dielectric between the plates
Farad (F) is the standard unit of measurement for capacitance.
Microfarads (µF) and picofarads (pF) are frequently used smaller units of measurement for capacitance.

Capacitance in Series/Parallel

Connecting capacitors in series decreases the total capacitance
Connecting capacitors in parallel increases the total capacitance

Inductive Reactance

Inductive reactance is the opposition to changing currents in AC circuits
Inductive reactance varies with both frequency (f) and inductance (L) values.

Current and Voltage Phases

Resistance circuits have current/voltage in phase.
Inductive circuits have current lagging the voltage by 90°
Capacitive circuits have current leading the voltage by 90°
Circuits with resistance and reactance (inductive or capacitive) fall somewhere in the in-between.

Transformers

Transformers transfer electrical energy from one circuit to another via mutual induction.
A single-phase transformer has a primary and secondary coil.
Transformers are rated in kilovolt-amps (kVA) which determines the current and voltage that can be delivered to the load (motor, appliances etc.) without overheating
Transformers can be used to step up or down voltage.

Residential Transformer Applications

A typical residential system uses 120V to outlets and 240V for high loads (heat, air, cooking)

Three-Phase Power

A three-phase system provides improved voltage and current outputs over single-phase systems.
Three-phase systems are common in industrial settings.

Power in AC Circuits

In resistive circuits, power is dissipated as heat.
True power is the actual power consumed by the circuit and is the current squared times resistance.
Reactive power is related to the inductance/capacitance causing power to return to the source.
Apparent power is total power delivered, is the sum of true power and reactive power.

Power Factor

Power factor is a ratio expressing how efficient power is used.
It is calculated using the cosine of the angle between voltage and current.
A power factor of 1.0 means all the delivered power is consumed while a value of 0 means no power is consumed, (lost).

Series Circuit Resistance

Resistances are added together to find the total resistance in a series circuit arrangement

Series Circuit Voltage and Current

Total circuit current is determined by dividing the source voltage by the total circuit resistance
Voltage drop across each resistor is the current flow times its circuit resistance; (sum of all resistor voltage drops = source voltage)

Parallel Circuit Resistance

The total resistance of a series circuit is the reciprocal of the sum of the reciprocals of the individual resistances.

Parallel Circuit Current

Total current is the sum of individual currents flowing through each component/resistor.
Current in each parallel component/resistor is equal to the total circuit voltage divided by the individual component/resistor resistance.

Contact 'normal' state and break sequence

The 'normal' state is when a switch or a relay is not influenced by any outside processes.
'normally open' contacts are open when the contact is not activated, while 'normally closed' contacts are closed when the contact is not activated

Generic Symbology

Normally-open contacts are denoted by two unconnected parallel vertical lines
Normally-closed contacts are denoted by two parallel vertical lines connected by a diagonal

Electro-mechanical Switches

Introduction (page 84)
Contactor (page 84)
Construction (page 85)
Operating Principle (page 87)
Rating (page 88)
Basic Design and Operation (page 95)
Types of Relay (page 97)
Applications (page 108)
Relay Application Considerations (page 109)

Time Delay Relays

Introduction (page 115)
Normally-Open, Timed-Closed (page 116)
Normally-Open, Timed-Open (page 117)
Normally-Closed, Timed-Open (page 118)
Normally-Closed, Timed-Closed (page 119)
Time-Delay and Logic Circuits (page 120)

Digital Logic Functions

Introduction (page 128)
Digital Logic Functions (page 128)
Permissive and Interlock Circuits (page 138)
Motor Control Circuits (page 142)

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This quiz covers the fundamentals of electricity, including the structure of atoms, free electrons, and conductors. It is essential for individuals studying electrical installation at a foundational level. Understanding these concepts is crucial for further exploration in the electrical field.