Industrial Power Systems

Evolutionary Aspects

Amitava Sil, Saikat Maity

• Publisher: CRC Press
• Year: 2022
• Print ISBN: 9781032138770
• eBook ISBN: 9781000567335
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Industrial Power Systems: Evolutionary Aspects provides evolutionary and integrated aspects of industrial power systems including review of development of modern power systems from DC to microgrid. Generation options of thermal and hydro power including nuclear and power from renewables are discussed along with concepts for single-line diagram, overhead transmission lines, concepts of corona, sag, overhead insulators and over voltage protective devices. Subsequent chapters cover analysis of power systems and power system protection with basic concept of power system planning and economic operations.

Features:

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• Covers the fundamentals of power systems, including its design, analysis, market structure and economic operations

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• Discusses performance of transmission lines with associated parameters, determination of performance and load flow analysis

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• Reviews residual generation/load imbalance as handled by the automatic generation control (AGC)

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• Includes different advanced technologies including HTLS overhead conductor, XLPE cable, vacuum/SF6 circuit breaker, solid state relays, among others

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• Explores practical aspects required for field level work such as installation of cable network for power distribution purposes, types of earthing and tariff mechanism

This book will be of interest to graduate students, researchers and professionals in power engineering, load flow and power systems protection.

1 Introduction

DOI: 10.1201/9781003231240-1

1.1 Evolution of Electrical Power System

Power systems have been operating for the last 100 years. All power systems have one or more sources of power. The history of power generation is long and convoluted, marked by myriad technological milestones, conceptual and technical, from hundreds of contributors. Coal has been used for power generation, and the first coal-fired steam generators provided low-pressure saturated or slightly superheated steam for steam engines driving direct current (DC) dynamos. Sir Charles Parsons, who built the first steam turbine generator (with a thermal efficiency of just 1.6%) in 1884, improved its efficiency 2 years later by introducing the first condensing turbine, which drove an Alternating Current (AC) generator. By the early 1900s, coal-fired power units featured outputs in the 1–10 MW range. By the 1910s, the coal-fired power plant cycle was improved which boosted net efficiency to about 15%. The demonstration of pulverized coal steam generators at the Oneida Street Station in Wisconsin in 1919 vastly improved coal combustion. Reheat steam turbines became the norm in the 1930s, when unit ratings soared to 300-MW output level. Main steam temperatures consistently increased through the 1940s, and the decade also ushered in the first attempts to clean flue gas with dust removal. The 1950s and 1960s were characterized by more technical achievements to improve efficiency with a supercritical main stream pressure. In 1878, the world’s first hydroelectric power project was created in the Cragside country house in Northumberland, England. Most large hydroelectric power plants generate electricity by water stored in vast reservoirs behind dams. Water from the reservoirs flows through turbines to generate electricity. Hydropower generations create difficult trade-offs when considering the impact on wildlife, climate change and other issues. In 1951, electricity generation using nuclear energy was started experimentally in Idaho, USA. The first commercial electricity-generating plant powered by nuclear energy was operated in Shippingport, Pennsylvania, in 1957 with a capacity of 60 MW. Nuclear plants are different from coal-based power generation as they do not burn anything to get the heat to generate steam. Instead, they split radioactive atoms like uranium by a process called fission to generate the necessary heat. As a result, unlike other coal-based energy sources, nuclear power plants do not release carbon or pollutants like nitrogen and sulfur oxides into the air.

The growing attention to the environmental impact and the consequent rise in new policies that support the usage of renewable energy sources, especially non-hydro sources such as wind and solar power, decentralized in nature, are real game changers. Three points can immediately make the difference clear: (i) renewable energy is derived from natural processes that are replenished constantly; (ii) generation from renewable energy sources is not perfectly predictable, and furthermore only in a limited sense controllable; and (iii) generation from renewable energy sources pushes to a more decentralized approach. The energy from renewable sources is generally located where the primary source (e.g., wind or solar irradiation) is maximum, which hardly ever matches the location of maximum load, resulting in a challenge for the transmission system, which is not developed to operate in this way. The volatility adds on the challenge, as it is not a good match for a system that was developed to operate “as planned” rather than “as it comes”, the latter requiring real-time monitoring and control. Due to co-existent traditional (nonrenewable) and renewable generating technologies, system operators have to coordinate the operation of the generation plants and ensure the stable and secure operation of the system. This has necessitated Wide-Area Measurement System enabled by communication technologies to control the operation of the generating stations and has created smart grids that enable bidirectional flows of energy and use two-way communication and control capabilities.

Smart grid is a large “System of Systems”, where each functional domain consists of three layers: (i) the power and energy layer, (ii) the communication layer and (iii) the IT/computer layer. Layers (ii) and (iii) are the enabling infrastructure that makes the existing power and energy infrastructure “smarter”. In smart grid domain energy-efficient transmission network will carry the power from the generation sites to the power distribution systems, which have communication interface between the transmission network and the generating stations, system operator, power market and the distribution system. The transmission network is monitored in real-time and protected against any potential disturbance. Further, substation automation and distribution automation are the key enablers for the smart distribution systems. There exists communication infrastructure to exchange information between the substations and a central distribution management system. Information exchange between the distribution system operator and the customers for better operation of the distribution system is a prime feature of the smart distribution systems. In smart grid domain building or home automation system monitors and controls the power consumption at the consumer premises in an intelligent way. In smart grids, customers play a supporting and pivotal role through demand response by peak-load shaving, valley-filling and emergency response for better operation of the distribution system.

Smart grid components include: (i) intelligent appliances capable of deciding when to consume power based on preset customer preferences, (ii) smart power meters featuring two-way communications between consumers and power providers to automate billing data collection, (iii) smart distribution that is self-healing, self-balancing and self-optimizing, (iv) smart generation capable of “learning” the unique behavior of power generation resources to optimize energy production and to automatically maintain voltage, frequency and power factor standards based on feedback from multiple points in the grid and (v) universal access to affordable, low-carbon electrical power generation (e.g., wind turbines, concentrating solar power systems, photovoltaic (PV) panels) and storage.

1.2 Thermal Power Plant

The location of thermal power plants depends on the following: (i) availability of cooling water, (ii) availability of fossil fuel in the command area, (iii) transport facilities, (iv) availability of land and its character, (v) ash disposal and (vi) availability of manpower and security considerations. Thermal power plants are of two types: (i) subcritical, where plants operate at a pressure around 170 bar and temperature around 550°C, and (ii) supercritical, where plants operate at very high temperature around 650°C and pressure around 300 bar which increase the efficiency (around 45%) in comparison to subcritical operation, where efficiency is around 38%. The increase in efficiency directly leads to reductions in unit cost of power and CO₂ emission. In the supercritical operation there is a significant reduction in NOx, SOx and particulate emissions. “Supercritical” is a thermodynamic expression describing the state of a substance where there is no clear distinction between the liquid and the gaseous phase (i.e., they are a homogeneous fluid). There are Ultra Supercritical plants where temperature is 593°C and efficiency is 42% and Advanced Supercritical thermal power plants where temperature is 700°C and efficiency is 49%.

Advantages of coal-based thermal power plants are as follows: they can respond to rapidly changing loads without difficulty, a portion of the steam generated can be used as a process steam in different industries (cogeneration plant), steam engines and turbines can work under 25% of overload continuously, the fuel used is cheaper, reliable – both as supply of power during peak demand as base power or as off peak power, high load factor and low capital cost. Disadvantages include the following: maintenance and operating costs are high, long time is required for erection and putting into action, a large quantity of water is required, great difficulty is experienced in coal handling, the presence of troubles due to smoke and heat in the plant, unavailability of good quality coal, maximum of heat energy is lost and the problems of ash removal.

Typical components of thermal power plants are water preparation system, coal preparation system, boiler and auxiliaries, air pre-heater, re-heater, turbine, generator, condenser, cooling tower, fan or draught system and ash handling system. A line diagram of thermal power plant is given in Figure 1.1.

FIGURE 1.1 Thermal power plant.

A thermal power plant has the following sections:

• Water Preparation – The total feed water in a thermal power plant consists of re-circulated condensate water and purified makeup water to replace water lost through sampling systems, steam losses, evaporation from cooling and blow-down. Water softeners and ion exchange demineralizers using membrane technology to remove dissolved impurities and produce ultra-high-pure makeup water that it coincidentally becomes an electrical insulator.
• Coal Preparation – Coal preparation is the removal of undesirable material from the Run-of-Mine coal by employing separation processes. Coal from the coal storage area is first crushed into small pieces and then conveyed to the coal feed hoppers at the boilers. Before entering the boiler, the coal is pulverized into a very fine powder, so that coal will undergo complete combustion during combustion process. Dryers are used in order to remove the excess moisture from coal that is mainly wetted during transport. The presence of moisture will result in fall of efficiency due to incomplete combustion and also result in CO emission. Magnetic separators are used to remove tramp iron pieces or separate iron particles from coal. Crushers are used for breaking coal into pieces of required feed size, which in pulverizing mill is 30 mm or below. The crushing is done in ring crusher and the hammer mill. Pulverizing of coal is done in either Ball and Tube Mill Pulverizer or Ring and Ball Pulverizer. Breaking a given mass of coal into smaller pieces in a pulverizer exposes more surface area for combustion, which allows faster combustion as more coal surface is exposed to heat and oxygen. This reduces the excess air required to ensure complete combustion and the required fan power also. A wide variety of low-grade coal can be burnt more easily when the coal is pulverized. Pulverized coal gives faster response to load changes as the rate of combustion can be controlled easily and immediately. Further, pulverized fuel systems are nowadays universally used for large capacity plants and use low-cost (low grade) fuel as it gives high thermal efficiency and better control as per the load demand.
• Boiler and Auxiliaries – Boilers may be of two types. (i) Fire Tube type where hot gases pass through the tubes and boiler feed water in the shell side is converted into steam and is generally used for relatively small steam capacities up to 12,000 kg/hour and low to medium steam pressures up to 18 kg/cm². Fire tube boilers are available for operation with oil, gas or solid fuels. (ii) Water Tube Boiler where boiler feed water flows through the tubes and enters the boiler drum. The circulated water is heated by the combustion gases (capacity range 4,500–120,000 kg/hour of steam) and converted into steam at the vapor space in the drum. These boilers are selected when the steam demand and steam pressure requirements are high as 125 kg/cm². Further boilers may be classified as: (i) Fluidized Bed Combustion type that has the advantages of high efficiency. Reduction in boiler size can be achieved due to high heat transfer rate over a small heat transfer area immersed in the bed with reduction in pollution control as SO₂ formation is greatly minimized by the addition of limestone or dolomite. Fluidized bed boilers have a wide capacity range of − 0.5 to over 100 T/hour. (ii) Atmospheric Fluidized Bed Combustion type, where atmospheric air, which acts as both the fluidization air and combustion air, is delivered at a pressure and flows through the bed after being preheated by the exhaust flue gases. (iii) Combined Fluidized Bed Combustion type, where coal is crushed to a size of 6–12 mm depending on the rank of coal and type of fuel feed fed into the combustion chamber. A Combined Fluidized Bed Combustion could be a good choice if the capacity of boiler is large to medium.
• In the steam-generating process, the furnace or burner systems provide controlled, efficient conversion of the chemical energy to heat energy, which in turn is transferred to the heat-absorbing surfaces of the steam generator. To do this, the firing system introduces fuel and air for combustion, mixes these reactants, ignites the combustible mixture and distributes the flame envelope and the products of combustion. Furnaces are of two types: (i) Grate-fired furnace is suitable for burning solid fuels like coal. Grate is provided for supporting the solid fuel and is so designed that it can also allow air to admit in the solid fuel for combustion. (ii) Fuel bed furnace is suitable for burning pulverized coal. Fluidization is a method of mixing fuel and air in a specific proportion, for obtaining combustion. A fluidized bed may be defined as the bed of solid particles behaving as a fluid. It operates on the principle that when an evenly distributed air is passed upward through a finely divided bed of solid particles at low velocity, the particles remain undisturbed, but if the velocity of air flow is steadily increased, a stage is reached when the individual particles are suspended in the air stream. If the air velocity is further increased, the bed becomes highly turbulent and rapid mixing of particles occurs which appears like formation of bubbles in a boiling liquid and thus the process of combustion as a result is known as fluidized bed combustion.

Stokers is a mechanical device which is used for supplying solid coal to furnace to maintain uniform operating condition, higher burning rate and greater efficiency. They may be of overfeed or underfeed type. It is determined by the feeding rate of coal below or above the level at which primary air is admitted.

The Rankine cycle is the fundamental operating cycle of all thermal power plants for steam generation. The operation of the cycle includes: (i) water from the condenser at low pressure is pumped into the boiler at high pressure, and this process is reversible adiabatic; (ii) water is converted into steam at constant pressure to the final (saturation) temperature by the addition of heat in the boiler; (iii) reversible adiabatic expansion of steam in the steam turbine; and (iv) constant pressure heat rejection in the condenser to convert condensate into water. By lowering the condenser pressure, superheating the steam to high temperatures and increasing the boiler pressure, the efficiency of the Rankine cycle can be increased.

Economizer is located in the boiler and above pre-heater to improve the efficiency of boiler by extracting heat from flue gases to heat the boiler feed water. In air pre-heater, the heat carried out with the flue gases that come out of economizer is further utilized for preheating the air before supplying to the combustion chamber. It is necessary equipment for supply of hot air for drying the coal in pulverized fuel systems to facilitate grinding and satisfactory combustion of fuel in the furnace.

From the boiler, steam goes to steam turbine. Turbines may be classified as non-condensing or backpressure type and condensing type. Backpressure turbines operate with an exhaust equal to or in excess of atmospheric pressure. The exhaust steam is used for lower pressure steam process applications. Condensing-type turbines operate with an exhaust pressure less than atmospheric pressure. It is costlier than the non-condensing type. The steam turbines are mainly divided into two groups: impulse turbine and impulse-reaction turbine. The turbine generator consists of a series of steam turbines interconnected to each other and a generator on a common shaft. There is a high-pressure turbine at one end, followed by an intermediate pressure turbine, two low-pressure turbines and the generator. The steam at high temperature (536°C–540°C) and pressure (140–170 kg/cm²) is expanded in the turbine.

The condenser condenses the steam from the exhaust of the...

Table of contents

• Cover
• Half Title Page
• Series Page
• Title Page
• Copyright Page
• Dedication Page
• Table of Contents
• Preface
• Authors
• Chapter 1 Introduction
• Chapter 2 Transmission and Distribution Systems
• Chapter 3 Overhead Transmission Line Constants
• Chapter 4 Corona and Sag
• Chapter 5 Cable
• Chapter 6 Characteristics and Performance of Transmission Line
• Chapter 7 Insulators for Overhead Lines
• Chapter 8 Overvoltages and Insulation Requirements
• Chapter 9 Electrical Fault Analysis
• Chapter 10 Load Flow Analysis
• Chapter 11 Stability Analysis
• Chapter 12 Fuses and Circuit Breakers
• Chapter 13 Power System Protection
• Chapter 14 DC Transmission
• Chapter 15 Electrical Power Distribution Substation
• Chapter 16 Power System Structure
• Chapter 17 Economic Operation of Energy Generating Systems
• Chapter 18 Automatic Generation and Control
• Chapter 19 Compensation in Power System
• Questions & Answers
• References
• Index