Contents:
Importance of electricity
AC & DC, Ampere, Volt, Watt, Resistance, Power, Calculation of unit, Live (phase) & Neutral, Three phase, Earthing,
Fuse, Circuit breaker, Distribution, Transformer
Safety precaution
Symbols of electrical engineering
Basic electronics and communication system
Introduction to Electricity
Electricity can be defined as the flow of electric power or charge.
- Electricity is a secondary energy which means it is obtained from the conversion of other sources of energy, such as coal, natural gas, nuclear power, and other natural sources which are called primary sources.
- Electricity itself is neither renewable nor non-renewable but energy sources we use to make electricity can be renewable or non-renewable sources.
Whenever electric charges moves or flows, that is an electric current.
| Current can be defined as the free flow of electrons (negative charge) in any conductor. |
Whenever two points having electrical potential difference are connected by a conductor (a continuous material which can carry electrons for its flow), electricity flows.
Note: Electric current flows from positive to negative and electron flows from negative to positive.
Importance of Electricity
The importance of electricity are very wide. It includes:
- Powering Daily Life: Electricity is essential for powering household appliances, lighting, heating, and cooling systems, enabling daily activities in homes, schools, and workplaces.
- Industrial and Economic Growth: Factories, industries, and businesses rely on electricity to run machinery, production lines, and IT systems, driving economic growth and development.
- Communication and Connectivity: Modern communication systems, including the internet, phones, and satellite networks, depend on electricity for operation, facilitating global connectivity.
- Healthcare Advancements: Hospitals and healthcare facilities rely on electricity to power medical equipment, support life-saving devices, and maintain 24/7 operations.
- Transportation: Electricity powers various modes of transport, including electric trains, subways, and electric vehicles, contributing to sustainable and efficient transportation systems.
- Entertainment and Comfort: From television and computers to air conditioning and gaming consoles, electricity enhances comfort and entertainment, improving quality of life.
- Education and Research: Schools, universities, and research institutions depend on electricity for lighting, computers, laboratory equipment, and digital learning platforms.
- Public Safety: Streetlights, traffic signals, surveillance systems, and emergency services all rely on electricity to ensure public safety and efficient urban management.
- Renewable Energy Integration: Electricity enables the integration of renewable energy sources like solar and wind, contributing to sustainable and environmentally friendly energy systems.
Terminology related to Electricity
- Current: It is free flow of electrons in any conductor. It is represented by the symbol ɪ. Ampere is the SI unit of current and it is represented by Amps.
- Volts: It is the force or pressure (potential difference) that causes the flow of electrons in any closed circuit. The unit of this force is Volt and is represented by V.
- Resistance: Any electrical appliance connected in an electric circuit is a load or resistance for the circuit against which the current has to flow, thereby consuming electric power.
| Resistance can be defined as that property of a substance which opposes the flow of electricity through it. |
Resistance is represented by R. The unit of resistance is ohm ( or Ω).
Ω symbol is pronounced as “Omega”.
- Live or Phase: In a single-phase AC system, Live (Phase) refers to the wire that carries the voltage from the power source to the load. It is the “active” conductor that provides the current to power devices. (current आउने बाटो)
- Neutral is the return path for the current back to the power source. It is usually grounded to ensure safety, and it completes the electrical circuit by balancing the flow of electricity. (Current जाने बाटो)
- Earthing (Grounding): It is the process of connecting the electrical installation or equipment to the earth using a conductor. The purpose of earthing is to provide a safe path for fault current to flow into the ground, protecting people from electric shocks due to electric leakage and ensuring the safety of electrical systems.
- Three Phase System: A three-phase system consists of three live (phase) wires and sometimes a neutral wire. In this system, each phase carries alternating current that is out of sync with the others by 120 degrees, providing a more consistent and balanced power flow.
Three-phase power is more efficient for transmitting large amounts of electricity, making it suitable for industrial applications, factories, and heavy machinery. It can deliver more power and has a smoother energy flow compared to single-phase systems.
Types of Circuit
Open Circuit:
An open circuit is a circuit where the path for the flow of electric current is interrupted or broken. As a result, no current flows through the circuit because there is a gap or disconnection in the wiring, switch, or component.
Example: A light switch in the “off” position creates an open circuit, stopping electricity from reaching the light bulb.
Closed Circuit:
A closed circuit is a complete electrical loop where the path for current flow is continuous, allowing electricity to travel through the circuit. All components are connected, and there is no break in the circuit, enabling the current to flow.
Example: A light switch in the “on” position creates a closed circuit, allowing electricity to flow and power the light bulb.
Fundamentals of AC and DC system of Electricity
There are two systems of electric generation and supply, namely
- Direct Current (DC)
- Alternating Current (AC)
Fundamentals of DC
Direct current is produced by sources such as batteries, solar cells generator, etc. Direct current does not change its direction, i.e. electrons flows through the circuit in one direction only. This is because the polarities of terminals of the voltage foes not change. The positive polarity of the voltage source remains positive and negative polarity remains negative always, so that the current at all time flows in the same direction.
Advantages of DC:
- DC series motors are most suitable for traction purposes in tram cars, railways carriages, and lifts.
- DC is required for electroplating, electrolytic, and electrochemical processes.
- Arc lamps for search lights and cinema projectors work in DC.
- Arc welding is better in DC than AC.
- DC works more efficiently in circuit breakers.
- In rolling mills, DC supply is used for speed control in both forward and reverse directions.
- Semiconductors electronics require low voltage DC supply.
- Solar cells and hydrogen fuel cells all produce DC.
- Stable Voltage: DC provides a constant voltage level, making it ideal for sensitive electronic devices like computers and mobile phones.
- Efficient for Short Distances: DC power is more efficient for transmission over short distances, with minimal power loss.
- Better for Batteries: DC is the type of current stored in batteries, making it ideal for portable devices and electric vehicles.
- Simpler Circuit Design: DC systems have simpler and more straightforward circuit designs, which are easier to manage and maintain.
- Less Noise in Electronics: DC power tends to generate less electrical noise, which is crucial for high-precision electronics.
- Compatibility with Renewable Energy: Many renewable energy sources, like solar panels, produce DC power directly, reducing the need for conversion to AC.
- Safe at Low Voltages: DC at low voltages is safer to handle than AC in certain applications.
Fundamentals of AC
The other type of electricity is called ‘Alternating Current’. This is the electricity that we get electricity from the wall plug base on our homes daily.
The electricity is not provided as a single, constant voltage, but rather as a sinusoidal (sine) wave that varies in magnitude as well as polarity (+ve to -ve and so on) thus changing direction over time. It starts at zero, increases to a maximum value and then decreases to a minimum negative value; the cycle repeats itself like in below figure:
Advantages of AC:
- Efficient Long-Distance Transmission: AC can be transmitted over long distances with minimal power loss, thanks to its ability to be easily transformed to higher voltages.
- Easily Transformed: AC voltage can be increased or decreased using transformers, which is crucial for efficient power distribution and utilization.
- Widespread Use: AC is the standard form of electricity supplied to homes, industries, and businesses, making it compatible with most appliances and infrastructure.
- Cost-Effective: AC generation and transmission are generally more cost-effective, especially over large-scale power grids.
- Reliable for Heavy Machinery: AC is commonly used for running heavy machinery and industrial equipment due to its stability and ability to provide large amounts of power.
- Less Maintenance: AC generators and motors tend to have simpler designs and require less maintenance compared to DC equipment.
- Standard for Electric Grids: AC is the preferred choice for national power grids worldwide, due to its advantages in efficient generation, distribution, and control.
Fuse
Fuse is a device which cuts off the circuits when more than predetermined value of current flows in a circuit. It is the weakest point of the circuit, which breaks when more than normal current flows in a circuit.
Materials for Fuse Wire:
- Fuse wire must be able to carry the normal current without much heating but should efficiently melt when normal working current is exceeded.
- Either copper or lead-tin alloy is mostly used as a material for an ordinary fuse wire. Lead-tin allow with 37 % lead and 67 % tin is best suited for the purposes as it is very hard.
- Minimum length of a fuse wire should be between 65mm to 100 mm.
Types of Fuse Holders:
There are many types of fuse holders inside which the fuse wires are housed and which are finally placed in a the circuit. They are:
- Semi-enclosed fuse or re-wirable fuse or Kit Kat fuse unit:
It is commonly found in our homes for domestic purposes. This type of fuse has a simple design where a fuse wire is manually replaced when it blows due to a fault. The wire is placed between two terminals, and it can be re-wired after melting. These fuses are commonly used in domestic applications for low-voltage protection. - Totally enclosed or cartridge fuse:
A cartridge fuse is a fully enclosed fuse where the fuse element is encased in a tube, typically made of ceramic or glass, and the entire unit is replaced when it blows. It is widely used in household appliances and industrial equipment for better safety and protection. - High rupturing capacity fuse or HRC type fuse:
An HRC fuse is designed to handle high fault currents and ruptures safely without causing damage to the system. It has a high breaking capacity and consists of a fuse element in a sealed enclosure, which can withstand high temperatures. It is commonly used in industrial circuits and heavy electrical applications. - Miniature Circuit Breaker (MCB):
While technically not a fuse, an MCB is a modern alternative to fuses. MCBs are widely used in residential and commercial electrical installations for their convenience and reliability, as they can be reset after tripping, unlike fuses which need to be replaced.
A MCB automatically switches off the current instantly if there is a short circuit or power overload. It thus prevents damage to expensive wiring and the risk of fire. Supply is restored by manually switching ‘ON’ again after the fault is rectified. There is no fuse to replace or rewire.