Introduction
Electrical energy is a special type of energy because it possesses unique characteristics that make it highly valuable and in demand:
- It can be generated in one location and transmitted to distant locations almost instantly.
- It can be easily converted into other forms of energy, such as heat, light, or mechanical energy, with high efficiency.
- It can be distributed and transmitted through relatively simple and scalable systems, making it accessible to a wide range of applications.
- Electrical energy can be generated, transmitted, and used with minimal energy loss, especially when compared to other forms like heat or mechanical energy. This makes it an efficient choice for a wide range of applications.
- Electrical energy is easily controlled and can be precisely regulated, allowing for the accurate operation of everything from small devices to large industrial machinery.
An additional important characteristic of electrical energy is that it must be generated in the exact amount as it is consumed, as electrical energy still can not be easily stored in large quantities (except in specific cases like batteries or pumped hydro storage). This makes the balance between supply and demand important for maintaining a stable and reliable power system.
Planing and Operation of Power Systems
The primary objective of a Power System is to provide electrical energy to consumers with the required quality and stability, while ensuring it is ecologically sustainable and economically feasible. This is why the planning and operation of electrical systems are one of the most important and interesting branches of study and practice.
The electrical energy system is a complex techno-economic system, integrating both technical and economic activities. On the technical side, it involves the generation, transmission, distribution, and management of electrical power. On the economic side, it focuses on optimizing costs, maximizing efficiency, and ensuring that energy production and distribution are cost effective, while also meeting regulatory, environmental, and consumer demands. The combination of these two fields ensures that electrical systems operate smoothly, efficiently, and sustainably.
Power system planning involves creating development strategies, designing projects, and constructing system components to ensure the power system can meet future demand, starting from its current condition.
Power system operation aims to make the best possible use of the existing facilities and components within the system.
While the commercial and economic aspects of power systems are governed by agreements and market rules, it is essential to emphasize that the actual functioning of power systems is fundamentally based on the unchangeable laws of physics. Therefore, all commercial regulations and operational agreements must operate within the boundaries set by these physical laws.
Physical Laws that Govern Operation of Electric Power Systems
The most important physical laws that govern the operation of electric power systems come from electromagnetism and thermodynamics, with a bit of mechanics:
- Ohm's Law: V = I x R which defines the relationship between voltage, current, and resistance.
- Kirchhoff's Laws:
- Kirchhoff's Current Law (KCL): The total current entering a node equals the total current leaving it.
- Kirchhoff's Voltage Law (KVL): The sum of all voltages around a closed loop is zero.
- Faraday's Law of Electromagnetic Induction: A changing magnetic field induces an electric current - essential for generators and transformers.
- Lenz's Law: The direction of induced current opposes the change that caused it - important in magnetic effects and inductance.
- First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed - used in energy balance of power systems.
- Second Law of Thermodynamics: No energy conversion is 100% efficient; some energy is always lost as heat - defines efficiency limits.
- Third Law of Thermodynamics: As temperature approaches absolute zero, entropy approaches a constant minimum - relevant in extreme low-temperature applications.
- Newton's Laws of Motion: Important in the design and analysis of rotating machinery like turbines and generators.
- Maxwell's Equations: The foundation of electromagnetism – used in advanced design of electrical components and transmission systems.
In this article, the focus is on the first and second thermodynamic laws that govern the transformation and flow of energy within power systems.These principles help define the physical boundaries within which all power generation must operate.
Thermodynamic Laws
In a thermal power plants, the process of electricity generation involves converting thermal energy (usually from burning fossil fuels like coal, natural gas, or from nuclear reactions) into mechanical energy, which is then converted into electrical energy. This process uses the principles of thermodynamics, specifically the First Law of Thermodynamics.
Thermodynamic laws are fundamental laws of nature and they tell us what can and cannot happen when it comes to energy conversion. Without them, we wouldn't know the limits of how efficiently we can turn fuel into electricity.
First Law of Thermodynamics
Have you ever wondered how electricity is generated in a thermal power plant? The process begins with the burning of fuel (such as coal or natural gas) in a boiler, which produces heat. This heat is transferred to water, turning it into steam. The steam is then directed to a turbine, where its thermal energy is converted into mechanical energy by causing the turbine blades to spin. This rotating turbine is connected to a generator, which transforms the mechanical energy into electrical energy. As the turbine spins, the generator produces electricity. Once the steam has passed through the turbine, it is cooled in a condenser, where it returns to water form, ready to be reheated and reused.
The entire process is explained by the First Law of Thermodynamics. In a thermal power plant, this law governs the energy transformations as follows:
- The chemical energy in the fuel is converted into thermal energy (heat).
- This thermal energy is then transformed into mechanical energy by the steam turbine.
- Finally, the mechanical energy is converted into electrical energy by the generator, which powers our homes and industries.
The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed from one form to another. This means that the total energy of an isolated system remains constant, though energy can change between heat, work, and internal energy.
The formula for the First Law of Thermodynamics is:
ΔU = Q - W
- ΔU = Change in internal energy of the system
- Q = Heat added to the system
- W = Work done by the system
In a thermal power plant, the process begins by burning fuel (such as coal, natural gas, or oil) in a boiler to produce heat. The chemical energy stored in the fuel is released as thermal energy (heat). The chemical energy stored in the fuel is released as thermal energy (heat). The First Law of Thermodynamics is essentially the law of energy conservation and looking at the formula:
Energy Input (Q): The fuel burned in the boiler provides thermal energy. This is the heat that is transferred to the water to convert it into steam. At this point, no work is done directly by the fuel, as the energy is initially stored as heat. The work will happen later when the steam moves the turbine. But for now, the energy is in the form of heat.
The internal energy of the system increases because the heat energy is added to the water (making the water hotter, and eventually turning it into steam). So, Q represents the heat transferred from the fuel to the water, and ΔU represents the increase in the internal energy of the water as it absorbs heat.
In this first step, the equation looks like:
ΔU = Q
After the water is heated in the boiler, it turns into steam. This steam now contains thermal internal energy in the form of high-pressure, high-temperature steam. The steam moves to the turbine, where its thermal energy is converted into mechanical energy. The steam then expands in the turbine, causing the turbine blades to spin. As the steam moves through the turbine, it loses some of its thermal energy, and this energy is converted into mechanical work (motion).
As the steam expands in the turbine, work is done on the turbine blades. This is the key moment where thermal energy is converted into mechanical energy. The energy in the steam is now being used to spin the turbine and perform mechanical work. As the steam expands and loses energy while performing work on the turbine, the internal energy of the steam decreases. When the steam expands in the turbine, heat (Q) is no longer being added to the system, but instead, internal energy from the steam is converted into mechanical work.
Heat (Q) = 0: At this point, no additional heat is being added to the steam in the turbine. The steam has already absorbed heat in the boiler, and now it is expanding and doing work. Therefore, Q = 0 during the turbine's expansion.
Change in Internal Energy (ΔU): As the steam expands and does work, its internal energy decreases because some of that internal energy (heat) is now being converted into mechanical work. This is where ΔU becomes important. The steam loses internal energy because it is performing work.
Work (W): The mechanical work (W) done by the expanding steam is the energy converted from the internal energy of the steam. The turbine converts this thermal (internal) energy into mechanical energy, which is used to rotate the turbine blades and generate electricity.
The First Law of Thermodynamics in this case can be written as:
ΔU = W
The work (W) done by the steam is equal to the decrease in the internal energy ΔU. At the end, the mechanical work done by the turbine blades is transmitted to the generator, which converts the mechanical energy into electrical energy.
In thermodynamics, the expansion can be modeled as either an adiabatic (no heat exchange) or isentropic (constant entropy) process, where the pressure continuously drops as the gas does work.
The work done in the turbine by the expansion of the gas is typically calculated using the formula:
W = ∫ P dV
Where:
- W is the work done by the gas.
- P is the pressure of the gas.
- dV is the change in volume.
- V1 and V2 are the initial and final volumes of the gas during expansion.
This formula comes from the First Law of Thermodynamics, which relates the work done by a gas to the change in its volume.
In this case: When a gas expands, it does work on the turbine blades by pushing them. This is the mechanical work (W) done by the steam or gas. The pressure (P) of the gas decreases as it expands, and the volume (V) increases. This is why the integral is used to account for the continuous change in pressure and volume during the expansion process.
Conclusion
Heat (Q) is the energy transferred between a system and its surroundings due to a temperature difference. It flows from high to low temperature and is not stored in the system. Instead, it alters the system's internal energy or performs work.
