Electrical Relays and Control Circuits Quiz

Jadeer Learning Manual - Electrical Area 2

• This manual is for general business use.
• It covers the subject of Plant Electrical Installation Level-1
• The document's revision number is 2024.01
• The issue date is 6 Nov 2024
• Electrical technician Area 2 is covered in this manual
• Subject matter experts, Marwan Owaidhah, Ali Fallatah, Bandar Al-Mesawi, and Ahmed Haresi developed the manual
• Area Owners/Leaders approved the manual.

Basics of Electricity

• All matter is composed of atoms
• Atoms have a nucleus with electrons orbiting around it.
• The nucleus is composed of protons and neutrons.
• A negative charge of electrons is balanced by a positive charge of protons.
• Electrons are bound in their orbit by attraction to protons.
• Free electrons are electrons in the outer band that can become free of their orbit by external forces.
• Current is produced when free electrons move to the next atoms.
• Materials that permit many electrons to move freely are called conductors. (Copper, gold, silver, and aluminum)
• Copper is widely used as a conductor due to being relatively inexpensive and one of the best conductors.
• Materials that allow few free electrons are called insulators. (Plastic, rubber, glass, mica, and ceramic)
• Electrical cables combine conductors and insulators.
• Semiconductors have characteristics of both conductors and insulators. (Silicon)
• Electrons moving from one atom to another produce electron flow.
• The basis of electricity is electron flow.
• Electrical charges are defined by the number of electrons in orbit around the nucleus and the number of protons in the nucleus.
• An atom with an equal number of electrons and protons is electrically neutral.
• Atoms with an excess of electrons have a negative charge.
• Atoms with a deficiency of electrons have a positive charge.
• Opposite charges attract; like charges repel. (Coulomb's Law)

Attraction and Repulsion of Electric Charges

• Charged bodies create an invisible electric field.
• Like charges repel, and unlike charges attract.
• Electric fields create invisible lines of force.

Current

• Electricity is the flow of electrons in a conductor.
• Measured in amperes (amps).
• Direct current (DC) flows consistently in one direction.
• Alternating current (AC) changes direction periodically.

Voltage

• Voltage is the force that pushes electricity through a conductor.
• Designated by the letter "E" or "V."
• Measured in volts (V).
• Voltage sources (e.g., batteries, alternators, generators) have an excess of electrons at one terminal and a shortage at the other.

Resistance

• Resistance opposes current flow in a circuit.
• Varies based on material composition, length, cross-section, and temperature.
• Measured in ohms (Ω).
• Ohm's Law relates Current, Voltage, and Resistance.

Ohm's Law Triangle & Examples

• Formula for determining current, voltage, and resistance.

Basics of Electricity (DC and Magnetism)

• Magnetism:
• Permanent magnets have two poles (north and south).
• Magnetic lines of force (flux) emanate from the north pole and enter the south pole.
• Magnets interact, with like poles repelling and unlike poles attracting.

Electromagnetism

• A magnetic field is generated by current flow in a conductor.
• A relationship exists between current flow and the direction of the magnetic field.

Electromagnetism

• A coil of wire carrying a current acts like a magnet. The strength can be increased by: adding more turns, increasing current, or winding the coil around iron.

Understanding of AC Circuits AC Current

• Alternating Current(AC):
• AC power sources' voltage polarity changes.
• Represent graphically as a Sine wave.
• Vertical axis represents amplitude, horizontal axis time.
• Positive direction is when waveform is above time axis, negative direction when waveform is below time axis.

Basies AC generator

• A basic generator has a magnetic field, an armature, slip rings, and brushes connecting to a load.
• A magnetic field is created by an electromagnet, or in simple generators permanent magnets.

Frequency

• Measured in Hertz (Hz). One Hz equals one cycle per second.
• The number of cycles per second of voltage induced in the armature is the generator's frequency.
• Typical power line frequency: 50 Hz in some countries and 60 Hz in the US and others.

Four pole AC Generator

• Frequency is same as number of rotations per second.
• Number of poles affecting the cycles in a single revolution.

Amplitude

• Maximum voltage or current value for each half cycle of a sine wave.
• Peak-to-peak value is twice the peak value.

Instantaneous Value

• The value of current or voltage at a specific point in time.

Inductive reactance

• Opposes changes in current in AC circuits
• X_L = 2πfL (X_L - Inductive Reactance, f - Frequency, L - Inductance)

Capacitive reactance

• Opposes changes in current in AC Circuits,
• X_C = 1/(2πfC), (X_C - Capacitive Reactance, f - Frequency, C - Capacitance)

Current and Voltage Phases

• In resistive circuits, current and voltage are in phase.
• In inductive circuits, voltage leads current by 90°
• In capacitive circuits, current leads voltage by 90°
• In a mixed (R, X) circuit, phase difference between current and voltage varies.

Series R-L-C Circuits

• Total Impedance calculates using given formula.

Parallel R-L-C Circuits

• Total circuit current calculated by adding current values of parallel branches or by dividing circuit voltage.

Transformers

• Transfer electrical energy between circuits.
• Mutual induction.
• Primary and secondary coils. Transformers may step-up or step-down the voltage.

Residential Transformer Applications

• Single phase, 3-wire supply system.
• 120 volts between hot and neutral wire, and 240 between hot wires.

Three Phase Power

• Three overlapping AC cycles in power distribution systems.

Power in AC Circuits

• True power (P), calculated as I²R
• Apparent power (S), calculated as IE.
• Reactive power (Q): Not used in work, but accounted for in AC power calculations.
• Voltage, current, and power factor are related using a triangle. (Power Triangle).

Power Factor

• Ratio of true power to apparent power.

Series Circuit Resistance

• Resistances are added together to determine total resistance.

Series Circuit Voltage and Current

• The total voltage is the sum of the voltage drops across each resistor. Current flowing in a series is the same everywhere.

Parallel Circuit Resistance

• Total resistance is calculated using a formula that includes the value of each resistance in the circuit.

Parallel Circuit Current

• Circuit current is the sum of branch currents or total voltage divided by the overall resistance.

Series-Parallel Circuit

• Combination of series and parallel resistor circuits. Total resistance calculated by adding series resistances and taking reciprocals to determine parallel resistances.

Understanding of Electrical Formulas

• Ohm's Law (E = IR)
• Power formula

Kirchhoff's Laws

• First law ( Current law): Sum of currents entering a junction is equal to the sum leaving a junction.
• Second law ( Voltage law): Sum of voltage drops around a complete path equals the source voltage.

Ohm's Law and Impedance

• Relates voltage, current, and impedance. Impedance is a measure of total opposition to AC current in a circuit.

Electromechanical Switches

• Introduction
• Contactor
• Construction
• Operating Principle
• Relay
• Basic Design and Operation
• Applications and Types
• Relay Application Considerations
• Timers
• Review

Digital Logic Functions

• Introduction
• Digital logic functions
• Permissive and Interlock Circuits
• Motor control circuits

Test your knowledge on electrical relays, their voltage ratings, and key characteristics in control circuits. This quiz covers various aspects of relays used in machine tools and aerospace applications, along with fundamental concepts in inductance and current flow. Perfect for students and professionals in electrical engineering.