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Questions and Answers
Materials that allow many electrons to move freely are called insulators.
Materials that allow many electrons to move freely are called insulators.
False
Plastic, rubber, and glass are examples of good conductors.
Plastic, rubber, and glass are examples of good conductors.
False
Semiconductors act like a conductor when an external force is applied and like an insulator when an external force is not applied.
Semiconductors act like a conductor when an external force is applied and like an insulator when an external force is not applied.
False
A material with more electrons than protons has a net positive charge.
A material with more electrons than protons has a net positive charge.
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When two like-charged bodies are brought together, their electric fields attract each other.
When two like-charged bodies are brought together, their electric fields attract each other.
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If two identical single-pole, five-throw switches are ganged together, the assembly is called a 'single-pole, five-throw' switch.
If two identical single-pole, five-throw switches are ganged together, the assembly is called a 'single-pole, five-throw' switch.
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A level switch will have a normal condition of a full tank or bin.
A level switch will have a normal condition of a full tank or bin.
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A contactor can interrupt a short circuit current like a circuit breaker.
A contactor can interrupt a short circuit current like a circuit breaker.
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Contactors can range from devices that can be held in one hand to large devices approximately a meter on a side.
Contactors can range from devices that can be held in one hand to large devices approximately a meter on a side.
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A normally-closed switch is depicted with a diagonal line between two vertical lines, indicating the connection.
A normally-closed switch is depicted with a diagonal line between two vertical lines, indicating the connection.
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An electromechanical switch is always operated by a manual lever.
An electromechanical switch is always operated by a manual lever.
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A flow switch's normally-open contacts will close when there is adequate flow through the pipe.
A flow switch's normally-open contacts will close when there is adequate flow through the pipe.
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Contactors are used to control electric motors, lighting, and heating.
Contactors are used to control electric motors, lighting, and heating.
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A temperature switch will have a normal condition of absolute zero temperature.
A temperature switch will have a normal condition of absolute zero temperature.
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A speed switch will not be turning, when the condition is normal.
A speed switch will not be turning, when the condition is normal.
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A transformer with more turns in the primary coil than in the secondary coil steps up the voltage.
A transformer with more turns in the primary coil than in the secondary coil steps up the voltage.
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In a residential supply system, the voltage between one hot wire and neutral is 240 volts.
In a residential supply system, the voltage between one hot wire and neutral is 240 volts.
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The kVA rating of a transformer indicates the amount of volt-amps it can safely deliver to its load.
The kVA rating of a transformer indicates the amount of volt-amps it can safely deliver to its load.
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In a step-up transformer, the current is increased while the voltage is decreased.
In a step-up transformer, the current is increased while the voltage is decreased.
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Maximum coupling in a transformer occurs when all flux lines from the primary coil pass through the secondary coil.
Maximum coupling in a transformer occurs when all flux lines from the primary coil pass through the secondary coil.
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Study Notes
Jadeer Learning Manual - Electrical Area 2
- This is a learning manual for electrical technicians
- The document covers the basics of plant electrical installation, level 1
- The manual was developed by Marwan Owaidhah (12943), Ali Fallatah (12610), Bandar Al-Mesawi (13107) and Ahmed Haresi (33423)
Control Page
- Discipline: Electrical Technician
- Job/Area #: Area 2
- Reference #: JAD-LC-A2-YP-EMT-LM
- Module #: 2024
- Revision #: 2024.01
- Issue Date: 6 Nov 2024
- Next Review Date: 01 Oct 2027
- Approvers: XXXXXXXXXXXXXXX
Basics of Electricity
- The manual covers basic electrical concepts
- The manual includes topics like Table of contents, Learning Objectives, Basic Introduction of Electricity, DC and Magnetism, Understanding of AC Circuits, Series Parallels Circuits, Understanding Of Electrical Formulas, Understanding of Power Triangle
Objectives
- Basic understanding of DC and Magnetism
- Basic understanding of AC Circuits & Series Parallel Circuits
- Understanding of Power Triangle
Common Electrical Hazards
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Electricity can be dangerous and lead to worksite fatalities
-
Electrical injuries are a costly and time-consuming problem
-
Electrical exposure can cause tingles, muscle contractions, falls and other injuries
-
The risk of fatalities and injury increases with the current passing through the body
-
Muscle reactions can cause falls and potential fatal injuries
Basic Introduction of Electricity
-
Matter is composed of atoms
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Atoms have a nucleus with electrons orbiting around it
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The nucleus is composed of protons and neutrons
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Electrons have a negative charge, protons have a positive charge, neutrons are neutral
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Electrons in the outer band can become free and move from one atom to another
-
This electron flow is the basis of electricity
Conductors
- Materials that permit electron movement are called conductors (e.g., copper, gold, silver, aluminum)
- Copper is a common conductor due to its conductivity and relatively low cost
Insulators
- Materials that resist electron flow are called insulators (e.g., plastic, rubber, glass, mica, ceramics)
- Insulators are used to prevent unwanted electron flow in electronic devices
Semiconductors
- Semiconductors have characteristics of both conductors and insulators
- A semiconductor conducts when an external force is applied, and acts as an insulator when an external force is in the opposite direction
- Transistors, diodes, and other solid-state electronic devices use semiconductor properties
Electric Charges
- Atoms are defined by the number of electrons orbiting the nucleus and protons in the nucleus
- Atoms with equal number of electrons and protons are electrically neutral
- Excessive electrons create a negative charge
- Excessive protons create a positive charge
Attraction and Repulsion of Electric Charges
- Opposites attract, likes repel
- Charged bodies have an invisible electric field
- The strength of the attraction or repulsion depends on the strength of the charges and the distance between them
Current
- The flow of electrons in the same general direction is called current
- Current is measured in amperes (amps)
- Constant current flow in the same direction is called direct current (DC)
- Current that changes direction periodically is called alternating current (AC)
Voltage
- The force that makes electrons flow is called potential difference, electromotive force, or voltage
- Voltage is measured in volts
- Voltage sources have a difference in potential between the terminals (excess of electrons at one terminal, shortage at the other)
Resistance
- Resistance is the opposition to current flow in an electrical circuit
- The amount of resistance depends on the material's composition, length, cross-section and temperature.
- Resistance is measured in ohms (Ω)
- A resistor is a component to provide a particular amount of resistance
Ohms Law Triangle
- A simple way to remember Ohm's Law formulas
- If two values are known, the third can be easily calculated using the appropriate Ohm's law formula
Basics of Electricity (DC and Magnetism)
- Magnetism is related to electricity
- Magnets have two poles (north and south)
- Magnetic lines of force run from the north pole to the south pole
- Magnets attract or repel each other depending on the polarity of the poles involved
Electromagnetism
- An electromagnetic field is a magnetic field generated by current flow in a conductor.
- A relationship exists between the direction of current flow and the direction of the magnetic field
- The left-hand rule for conductors demonstrates this relationship
Electromagnets
- A coil of wire carrying current acts like a magnet
- The strength of the field can be increased by adding more turns to the coil or increasing the amount of current
- Electromagnets are used in various electrical devices like motors, circuit breakers, contactors, relays and starters
Understanding of AC Circuits - AC Current
- AC current flows in one direction, then the other periodically
- AC current is represented by a sine wave
- The vertical axis represents current/ voltage magnitude and direction, horizontal axis represents time
Basic AC Generator
- A generator consists of a magnetic field, an armature, slip rings, and brushes (which connect to the load)
- The armature rotates in the magnetic field
- A voltage is induced in the armature, causing current to flow
Frequency
- The number of cycles per second of voltage in the armature is the frequency of the generator
- Frequency is measured in hertz (Hz)
- The standard power line frequency in most countries is 60 Hz
Four Pole AC Generator
- The generator has four poles, which increases the number of cycles completed per revolution
Amplitude
- The range of variation (rise and fall) of the voltage or current in an AC circuit is called amplitude
- Amplitude is specified as peak value, peak-to-peak value and effective value
Instantaneous Values
- Instantaneous value is the value of voltage or current at any point on the sine wave
- This is equal to the peak value times sin of the angle
Inductive Reactance
- Opposition to current flow caused by changes in current in an AC circuit is called inductive reactance
- Measured in ohms (Ω)
- Inductive reactance is proportional to both the inductance and the applied frequency
Current and Voltage Phases
- In a purely resistive circuit current and voltage rise and fall at the same time.
- In a purely inductive circuit voltage leads current by 90 degrees
- In a circuit with both resistance and inductive reactance the voltage leads current by more than zero degrees and less than 90 degrees
Capacitive Reactance
Opposition to current flow in an AC circuit is called capacitive reactance. Measured in ohms (Ω) Capacitive reactance is inversely proportional to frequency and capacitance
Capacitance in Series
- Connecting capacitors in series decreases total capacitance
- The formula for series capacitors is similar to the formula for parallel resistors
Capacitors in Parallel
- Adding capacitors in parallel increases circuit capacitance
- Total capacitance determined by adding the capacitor values
RLC Circuits
- Many circuits contain resistance, inductance, and capacitance
- In an inductive AC circuit, current lags voltage by 90 degrees
- In a capacitive AC circuit, current leads voltage by 90 degrees
Calculating Impedance
Impedance (Z) is the total opposition to current flow in an AC circuit
Series-Parallel Circuits
- A series circuit has one path for current flow
- A parallel circuit has multiple paths for current flow
Series-Circuit Voltage and Current
- The current in a series circuit is determined by dividing the source voltage by the total resistance
- The sum of the voltage drops across each resistor equals the source voltage
Parallel-Circuit Resistance
- Total resistance for a parallel circuit is determined by adding the reciprocal of the resistance values of the individual resistors
Parallel-Circuit Current
- The current in each branch of a parallel circuit is calculated by dividing the circuit voltage by the resistance of the branch
- Total circuit current is calculated by adding the current in all branches or can be found by dividing the circuit voltage by the total resistance
Transformers
- A transformer transfers electrical energy between two circuits using mutual induction.
- Transformers may be used for stepping the voltage up or down
Transformer Turns Ratio
- The turns ratio of a transformer affects voltage and current
- The relationship between primary and secondary voltage affects the current and impedance levels of the transformer (higher turns mean higher impedance)
Residential Transformer Applications
- The most common power supply system in residential applications in the United States is a single-phase, three-wire supply system
Three-Phase Power
- Used in commercial and industrial applications where power requirements are higher than those of a typical residence
Three-Phase Transformers
- Transformers use three interconnected coils for three-phase power
- Transformers can be a "Wye" or a "Delta" configuration
Understanding of AC Circuits - Power and PF
- True power (P) is the power consumed by the resistive loads in an electrical circuit.
- Apparent power (S) is the power delivered to an electrical circuit.
- Reactive power(Q) is the power consumed by inductors and capacitors
Power Factor
- Power factor is the ratio of true power to apparent power in an AC circuit.
- A purely resistive circuit has a power factor of unity (1)
- In purely reactive circuits, the power factor is zero
Electrical Switches
- A switch is an electrical device to interrupt the flow of electrons in a circuit.
- Hand switches are operated by a person, like a toggle switch, pushbutton, or selector switch
- Process switches are activated by machine motion rather than through human interaction, as a limit switch
Table of Contents (Electrical Switches)
- Introduction
- Switch Types
- Process Switches
- Pole and Throw
- Contact ''normal'' state
- Generic Symbology
- Review
Objectives (Electrical Switches)
- Understand switch types, processes, and contacts
Electromechanical Switches
- Introduction
- Construction
- Operating Principle
- Rating
- Basic Design and Operation
- Types of Relay
- Applications
- Relay Application Considerations
Time-Delay Relays
- Introduction
- normally-open, timed-closed
- normally-open, timed-open
- normally-closed, timed-open
- normally-closed, timed-close
- Time Delay and Logic Circuits
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Description
This manual serves as a foundational guide for electrical technicians, focusing on plant electrical installation at level 1. Covering essential topics such as DC, magnetism, AC circuits, and electrical formulas, it aims to equip learners with a solid understanding of electrical concepts.
