Electrical Safety and Relay Basics

Jadeer Learning Manual - Electrical Area 2

• This manual covers plant electrical installation at level 1
• The document's issue date is November 6, 2024
• The next review date is October 1, 2027
• The discipline is electrical technician
• The job/area is area 2
• The learning module is JAD-LC-A2-YP-EMT-LM
• The revision date is 2024.01

Basics of Electricity

• Electrical hazards are dangerous
• Between 1992 and 2001, 4309 individuals lost time at work due to electrical injuries
• In 1992-2001, there were an average of 4,309 work-related electrical deaths
• Electrical injuries cost workers time away from work and can be long and painful
• The goal is worker health and quality of work life
• 3 milliamperes of current through the body can lead to injuries

Learning content

• Table of contents
• Learning objectives
• Basic introduction to electricity
• DC and magnetism
• Understanding of AC circuits
• Series parallel circuits
• Understanding of electrical formulas
• Understanding of the power triangle

Objectives

• Basic understanding of DC and magnetism
• Basic understanding of AC Circuits & Series Parallel Circuits
• Understanding of Power Triangle

Basic Introduction of Electricity

• All matter is made up of molecules composed of atoms
• Atoms have a nucleus with electrons orbiting around it
• The nucleus is made up of positively charged protons and neutral neutrons
• Electrons are negatively charged

Additional information

• Conductors permit electrons to flow freely
• Conductors: copper, gold, silver, aluminum
• Insulators oppose current flow
• Insulators: plastic, rubber, glass, mica, ceramic
• Semiconductors exhibit qualities of both conductors and insulators

Electric Charge

• Elements are defined by the number of electrons in orbit around the nucleus and by the number of protons in the nucleus
• An atom with an equal number of electrons and protons is electrically neutral
• Electrons which leave their orbits due to external force create positive and negative charges

Attraction and Repulsion of Electric Charges

• Opposite charges attract
• Like charges repel
• Invisible lines of force are in the fields surrounding objects with charges, causing attraction or repulsion

Current

• Electricity is the flow of electrons through a conductor
• Current is measured in amperes (amps)
• Direct Current (DC) flows consistently in one direction
• Alternating Current (AC) reverses its direction periodically

Voltage

• Voltage (or potential difference) is the force that drives current
• Voltage is measured in volts
• A difference in potential between two points is referred to as voltage

Resistance

• Resistance (opposition to current flow) is a circuit, component, or material property
• Resistance is dependent on composition, length, cross-section, and temperature of the resistive material
• Resistance is measured in ohms

Ohm's Law Triangle

• Simplifies calculations involving voltage, current, and resistance in a circuit.
• Using the triangle you can quickly determine the correct formula

Basics of Electrical (DC and Magnetism)

• Magnetism is integral to electricity - producing electricity
• Permanent magnets are characterized by attracting iron and assuming a north-south orientation
• Invisible magnetic lines of flux leave the north pole and enter the south pole.

Interaction between magnets

• Similar poles repel and opposing poles attract

Electromagnetism

• Electric current produces a magnetic field
• The direction of current flow and the direction of the magnetic field are related.
• The relationship can be visualized using the left-hand rule.
• Electrical devices such as motors, circuit breakers, and contactors utilize electromagnetic principles

Electromagnets

• A coil of wire carrying a current acts as a magnet
• The strength of the field is increased by adding more turns, increasing the current or using a core of soft iron
• Electromagnets are used in various electrical devices (e.g., motors, circuit breakers).

Understanding of AC Circuits (AC Current)

• Current changes direction periodically
• Sine waved are used to represent AC Voltage and Current

Basic AC Generator

• Consist of a magnetic field, an armature, slip rings, and brushes.
• The armature is a number of conductive wires wound in loops that rotate through the magnetic field
• When a conductor moves through a magnetic field, a voltage is generated.
• The process continuous as long as the generator is running.

Frequency

• Frequency is the number of cycles per second of voltage
• Measured in Hertz (Hz).
• The standard power line frequency in many countries is 60 Hz.

Four-pole AC Generator

• The frequency is the same as the number of rotations per second with a magnetic field.
• An increase in the number of poles causes an increase in the number of cycles completed in a revolution

Amplitude

• The peak or maximum value for each half of the sine wave
• The peak-to-peak value is the range of positive and negative peaks
• The effective value is also referred to as RMS
• Instruments are designed to measure AC voltages/currents that mostly display the effective value.

Inductive Reactance

• The opposition to current flow is called inductive reactance
• It is proportional to both inductance and frequency

Current and Voltage Phases

• In purely resistive circuits, current and voltage are in phase.
• Current lags the voltage in an Inductive circuit by 90 degrees.
• Current leads the voltage in a capacitive circuit by 90 degrees.

Capacitive Reactance

• Capacitors also oppose current flow in AC circuits by capacitive reactance,
• It is inversely proportional to the frequency and capacitance.

Calculating Impedance

• Impedance (Z) is the total opposition to current flow in an AC circuit
• Impedance is represented as a vector with magnitude and direction.
• Resistance, inductive reactance, and capacitive reactance are at right angles to each other
• Reactance is plotted at 90 degrees

RLC Circuits

• Circuits that contain resistance, inductance, and capacitance
• Calculating total impedance- use formula with resistance and reactance.
• The resistance, inductance, and capacitance are in series
• The values of resistance, inductance, and capacitance change when the frequency changes

Parallel Circuit Resistance/Current

• The total resistance is found by adding all the current in a series configuration
• The total current is found adding the current in a parallel configuration

Transformer

• A device which steps up or down voltage
• Uses mutual induction to transfer energy between electrical circuits
• Composed of primary and secondary coils
• Coils are frequently wound on the same iron core

Residential Transformer Applications

• Single-phase, three-wire supply is common
• Voltage between either hot wire and neutral is 120V
• Voltage between two hot wires is 240V
• 120V - general purpose and lighting
• 240V - heating, cooling, cooking

Three-Phase Power

• Used when power requirements are higher than in single phase applications
• Three overlapping AC cycles are used
• Each wave represents a phase
• Each phase is offset by 120 degrees

Three-Phase Transformers

• Have three interconnected coils in both the primary and secondary
• Connected in either wye or delta configuration

Power in AC Circuits

• The force required to make electricity flow through a conductor is called a difference in potential, electromotive force (emf) or voltage
• Voltage is measured in volts
• A difference in potential between two points is referred to as voltage.
• The vector sum of true power and reactive power is known as apparent power.
• Apparent power (S) is measured in volt-amperes (VA).
• True power is sometimes called effective power, and is equal to the current squared times the resistance(I2x R)
• Measured in Watts (W)

Power Factor (PF)

• The power factor is the ratio of true power to apparent power.
• It is also equal to the cosine of the phase angle

Introduction to Electrical Switches

• An electrical switch is used to interrupt electron flow.
• Switches are binary devices (either fully on or off)
• Different types of switches exist
• Process switches are designed for machine control rather than manual operation
• Various mechanical, electronic, and optical switch types

List of Switch Types

• Hand Switches: Toggle, Pushbutton, Selector
• Process Switches: Limit, Proximity, Speed, Pressure, Temperature, Level, Flow, Nuclear

Contact "normal" state and make/break sequence

• Normal position of the switch is when there is no influence or force on the switch.

Generic Symbology

• Normally Open (NO) contacts are open when unactuated
• Normally Closed (NC) contacts are closed when unactuated

Electro-mechanical Switches

• Introduces contactors, relays
• Lists types of contactors and relays

Test your knowledge on electrical safety measures and relay operations. This quiz covers typical voltage ratings, coil currents, mounting methods, and essential concepts of electricity. Perfect for students in electrical engineering or related fields.