Generation,Transmission and distribution of power

Generation,Transmission and distribution of power

How power is generated?

Genrally, in india 3phase-220volt is generated in power stations. after generating it is transmitting through wires(transmission cables) to the sub-stations . And From the sub-stations this power is again transmitted to the distributor or electricity company. and this companies further transmit this power to your home at some cost. 
Electricity generation is the process of generating electric power from with the help of prime movers .It is the first stage of electricity to end users, the other stages being transmission, distribution energy stored and recovery, using pumped-storage methods.

A characteristic of electricity is that it is not a primary energy freely present in nature in remarkable amounts and it must be produced. Production is carried out in power stations Electricity is most often generated at a power stations by Electromechanical generators, primarily driven by heat engines fueled by combustion or nuclear fission but also by other means such as the kinetic energy of flowing water and wind.

 Other energy sources like solar phtovoltaic cell(solar cell) and Geo-thermal energy,wind energy,wave energy,Tidal energy,bio-energy also available. but they all are renewabl energy sources which are widely used in future instead of these methods ,we discussed above. 
I will post another blog on this topic of renewable sources of energy.but in this blog we discussed only generation,transmission,and distribution of power. 

Types of power plants

Thermal power plant- A thermal power station or a coal fired Thermal power plant is by far, the most conventional method of generating electrc power with reasonably high efficiency. It uses coal as the primary fuel to boil the water available to super heated stream for driving the steam turbine. The steam turbine is then mechanically coupled to an alternator rotor, the rotation of which results in the generation of electric power. Generally in India, bituminous coal or brown coal are used as fuel of boiler which has volatile content ranging from 8 to 33% and ash content 5 to 16 %. To enhance the thermal efficiency of the plant, the coal is used in the boiler in its pulverized form.
In coal fired thermal power plant, steam is obtained in very high pressure inside the steam boiler by burning the pulverized coal. This steam is then super heated in the super heater to extreme high temperature. This super heated steam is then allowed to enter into the turbine, as the turbine blades are rotated by the pressure of the steam. The turbine is mechanically coupled with alternator in a way that its rotor will rotate with the rotation of turbine blades. After entering into the turbine, the steam pressure suddenly falls leading to corresponding increase in the steam volume. After having imparted energy into the turbine rotors, the steam is made to pass out of the turbine blades into the steam condenser of turbine In the condenser, cold water at ambient temperature is circulated with the help of pump which leads to the condensation of the low pressure wet steam. Then this condensed water is further supplied to low pressure water heater where the low pressure steam increases the temperature of this feed water, it is again heated in high pressure. This outlines the basic working methodology of a thermal power plant.

Advantages of Thermal Power Plants

• Fuel used i.e coal is quite cheaper.
• Initial cost is less as compared to other generating stations.
• It requires less space as compared to hydro-electric power stations.

Disadvantages of Thermal Power Plants

• It pollutes atmosphere due to production of smoke & fumes.
• Running cost of the power plant is more than hydro electric plant.

Hydro power plant -In Hydro-electric plants the energy of the falling water is utilized to drive the turbine which in turn runs the generator to produce electricity. Rain falling upon the earth’s surface has potential energy relative to the oceans towards which it flows. This energy is converted to shaft work where the water falls through an appreciable vertical distance. The hydraulic power is therefore a naturally available renewable energy given by the eqn:
P = gρ QH
Where, g = acceleration due to gravity = 9.81 m/sec ²
ρ = density of water = 1000 kg/m ³
H = height of fall of water.
This power is utilized for rotating the alternator shaft, to convert it to equivalent electrical energy. 
An important point to be noted is that, the hydro-electric plants are of much lower capacity compared to their thermal or nuclear counterpart. For this reason hydro plants are generally used in scheduling with thermal stations, to serve the load during peak hours. They in a way assist the thermal or the nuclear plant to deliver power efficiently during periods of peak hours.

Advantages of Hydro Electric Power Station

• It requires no fuel , water is used for generation of electrical energy.
• It is neat and clean energy generation.
• Construction is simple , less maintenance is required.
• It helps in irrigation and flood control also.

Disadvantages Hydro Electric Power Station

• It involves high capital cost due to dam construction.
• Availability of water depends upon weather conditions.
• It requires high transmission cost as the plant is located in hilly areas.

Nuclear power plant-The nuclear power generating stations are similar to the thermal stations in more ways than one. How ever, the exception here is that, radioactive elements like uranium and thorium are used as the primary fuel in place of coal. Also in a Nuclear station the furnace and the boiler are replaced by the Nuclear reactor and the heat exchanger tubes.
For the process of nuclear power generation, the radioactive fuels are made to undergo fission reaction within the nuclear reactors. The fission reaction, propagates like a controlled chain reaction and is accompanied by unprecedented amount of energy produced, which is manifested in the form of heat. This heat is then transferred to the water present in the heat exchanger tubes. As a result, super heated steam at very high temperature is produced. Once the process of steam formation is accomplished, the remaining process is exactly similar to a thermal power plant, as this steam will further drive the turbine blades to generate electricity.

Advantages of nuclear power

1. The generation of electricity through nuclear energy reduces the amount of energy generated from fossil fuels (coal and oil). Less use of fossil fuelsmeans lowering greenhouse gas emissions (CO² and others).
2. Currently, fossil fuels are consumed faster than they are produced, so in the next future these resources may be reduced or the price may increase becoming inaccessible for most of the population.
3. Another advantage is the required amount of fuel: less fuel offers more energy. It represents a significant save on raw materials but also in transport, handling and extraction of nuclear fuel. The cost of nuclear fuel (overall uranium) is 20% of the cost of energy generated.
4. The production of electric energy is continuous. A nuclear power plant is generating electricity for almost 90% of annual time. It reduces the price volatility of other fuels such as petrol.
5. This continuity benefits the electrical planning. Nuclear power does not depends on natural aspects. It's a solutions for the main disadvantage of renewable energy, like solar energy or eolic energy, because the hours of sun or wind does not always coincide with the hours with more energy demand.
6. It's an alternative to fossil fuels, so the consumption of fuels such as coal or oil is reduced. This reduction of coal and oil consumption benefits the situation of global warming and global climate change. By reducing the consumption of fossil fuels we also improve the quality of the air affecting the disease and quality of life.

Disadvantages of nuclear power

We've previously discussed the advantage of using nuclear energy to reduce fossil fuel consumption. Organizations often use this argument in favor of nuclear energy but it's a partial truth. Much of the consumption of fossil fuels is due to road transport, used in heat engines(cars, trucks, etc.). Savings in fossil fuel for power generation is fairly low.

1. Despite the high level of sophistication of the safety systems of nuclear power plants the human aspect has always an impact. Facing an unexpected event or managing a nuclear accident we don't have any guarantee that decisions we took are always the best. Two good examples are Chernobyl and Fukushima.
2. The Chernobyl nuclear accident is, by far, the worst nuclear accident in the history. Different wrong decisions during the management of the nuclear plant caused a big nuclear explosion.
3. Referring to the Fukushima nuclear accident, the operations done by the staff were highly questionable. Fukushima nuclear accident is the second worst accident in the history.
4. One of the main disadvantages is the difficulty in the management of nuclear waste. It takes many years to eliminate its radioactivity and risks.
5. The constructed nuclear reactors have an expiration date. Then, they've to be dismantled, so that main countries producing nuclear energy could maintain a regular number of operating reactors. They've to built about 80 new nuclear reactors during the next ten years.
6. Nuclear plants have a limited life. The investment for the construction of a nuclear plant is very high and must be recovered as soon as possible, so it raises the cost of electricity generated. In other words, the energy generated is cheap compared to the cost of fuel, but the recovery of its construction is much more expensive.
7. Nuclear power plants are objectives of terrorist organizations.
8. Nuclear power plants generate external dependence. Not many countries have uranium mines and not all the countries have nuclear technology, so they have to hire both things overseas.
9. Current nuclear reactors work by fission nuclear reactions. These chain reactions is generated in case control systems fail, generating continous reactions causing a radioactive explosion that would be virtually impossible to contain.
10. Probably the most alarming disadvantage is the use of the nuclear power in the military industry. The first use of nuclear power was the creation of two nuclear bombs dropped on Japan during World War II. This was the first and the last time that nuclear power was used in a military attack. Later, several countries signed the Nuclear Non-Proliferation Treaty, but the risk that nuclear weapons could be used in the future will always exist.

How to transmit 

Generally, there are two systems by which electrical energy can be transmitted.

1. High voltage DC electrical transmission system.
2. High voltage AC electrical transmission system.

There are some advantages in using DC transmission system 

Advantages:

1. There are two conductors used in DC transmission while three conductors required in AC transmission.
2. There are no Inductance and Surges (High Voltage waves for very short time) in DC transmission.
3. Due to absence of inductance, there are very low voltage drop in DC transmission lines comparing with AC (if both Load and sending end voltage is same)
4. There is no concept of Skin effect in DC transmission. Therefore, small cross sectional area conductor required.
5. A DC System has a less potential stress over AC system for same Voltage level. Therefore, a DC line requires less insulation.
6. In DC System, There is no interference with communication system.
7. in DC Line, Corona losses are very low.
8. In High Voltage DC Transmission lines, there are no Dielectric losses.
9. In DC Transmission system, there are no difficulties in synchronizing and stability problems.
10. DC system is more efficient than AC, therefore, the rate of price of Towers, Poles, Insulators, and conductor are low so the system is economical.
11. In DC System, the speed control range is greater than AC System.
12. There is low insulation required in DC system (about 70%).
13. The price of DC cables is low (Due to Low insulation)
14. In DC Supply System, the Sheath losses in underground cables are low.
15. DC system is suitable for High Power Transmission based on High Current transmission.
16. In DC System, The Value of charging current is quite low, there fore, the length DC Transmission lines is greater than AC lines.

Disadvantages:

1. Due to commutation problem, Electric power can’t be produce at High (DC) Voltage.
2. For High Voltage transmission, we can not step the level of DC Voltage (As Transformer can not work on DC)
3. There is a limit of DC Switches and Circuit breakers (and costly too)
4. Motor generator set is used for step down the level of DC voltage and the efficiency of Motor-generator set is low than transformer.
5. The system makes complex and costly.
6. The level of DC Voltage can not be change easily. So we can not get desire voltage for Electrical and electronics appliances (such as 5 Volts, 9 Volts 15 Volts, 20 and 22 Volts etc) directly from Transmission system.

AC Transmission:

Nowadays, the generation, transmission and distribution mostly is in AC.

Advantages:

1. AC Circuit breakers is cheap than DC Circuit breakers.
2. The repairing and maintenance of AC sub station is easy and inexpensive than DC Substation.
3. The Level of AC voltage may be increased or decreased step up and Step down transformers.

Disadvantages:

1. In AC line, the size of conductor is grater than DC Line.
2. The Cost of AC Transmission lines are greater than DC Transmission lines.
3. Due to Skin effect, the losses in AC system are more.
4. In AC Lines, there is Capacitance, so continuously power loss when no load on lines or Line is open.
5. Other line losses are due to inductance.
6. More insulation required in AC System
7. Also corona Losses occur In AC System,  
8. There is telecommunication interference in AC System.
9. There are stability and synchronizing problems in AC System.
10. DC System is more efficient than AC System.
11. There are also re-active power controlling problems in AC System.

Note: Nowadays, it is possible to step up or step down the level of DC Voltages by Choppers and Boosters. Also there is no commutation problem and we can use rectifier units for that purpose.

Types of pole

.Now let us discuss about the electric poles used in overhead transmission lines.The supporting structures for overhead line conductors are various types of poles and towers called line supports.In general, the line supports should have the following properties :

(i) High mechanical strength to withstand the weight of conductors and wind loads etc.

(ii) Light in weight without the loss of mechanical strength.

(iii) Cheap in cost and economical to maintain.

(iv) Longer life.

(v) Easy accessibility of conductors for maintenance.

The line supports used for transmission and distribution of electric power are of various types including wooden poles, steel poles, R.C.C. poles and lattice steel towers.The choice of supporting structure for a particular case depends upon the line span, X-sectional area, line voltage, cost and local conditions.

1. Wooden poles : These are made of seasoned wood (sal or chir) and are suitable for lines of moderate X-sectional area and of relatively shorter spans, say upto 50 metres.Such supports are cheap, easily available, provide insulating properties and, therefore, are widely used for distribution purposes in rural areas as an economical proposition.The wooden poles generally tend to rot below the ground level, causing foundation failure.In order to prevent this, the portion of the pole below the ground level is impregnated with preservative compounds like creosote oil.Double pole structures of the ‘A’ or ‘H’ type are often used to obtain a higher transverse strength than could be economically provided by means of single poles.
The main objections to wooden supports are : 

(i) tendency to rot below the ground level

(ii) comparatively smaller life (20-25 years) 

(iii) cannot be used for voltages higher than 20 kV

(iv) less mechanical strength and 

(v)  require periodical inspection.

                        

2. Steel poles : The steel poles are often used as a substitute for wooden poles.They possess greater mechanical strength, longer life and permit longer spans to be used.Such poles are generally used for distribution purposes in the cities.This type of supports need to be galvanised or painted in order to prolong its life.The steel poles are of three types (i) rail poles (ii) tubular poles and (iii) rolled steel joints.

3. RCC poles : The reinforced concrete poles have become very popular as line supports in recent years.They have greater mechanical strength, longer life and permit longer spans than steel poles.Moreover, they give good outlook, require little maintenance and have good insulating properties.Figure shows R.C.C. poles for single and double circuit.The holes in the poles facilitate the

climbing of poles and at the same time reduce the weight of line supports.The main difficulty with the use of these poles is the high cost of transport owing to their heavy weight.Therefore, such poles are often manufactured at the site in order to avoid heavy cost of transportation.

                             

4. Steel towers : In practice, wooden, steel and reinforced concrete poles are used for distribution purposes at low voltages, say upto 11 kV.However, for long distance transmission at higher voltage, steel towers are invariably employed.Steel towers have greater mechanical strength, longer life, can withstand most severe climatic conditions and permit the use of longer spans. The risk of interrupted service due to broken or punctured insulation is considerably reduced owing to longer spans.Tower footings are usually grounded by driving rods into the earth.This minimises the lightning troubles as each tower acts as a lightning conductor.Figure below shows a single circuit tower.However, at a moderate additional cost, double circuit tower can be provided as shown in Figure below.The double circuit has the advantage that it ensures continuity of supply.It case there is breakdown of one circuit, the continuity of supply can be maintained by the other circuit.

                            

Two ways of Transmit power

• Overhead
• Underground

Overhead Transmission-An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy along large distances. It consists of one or more conductors(commonly multiples of three) suspended by towers or poles. Since most of the insulation is provided by air, overhead power lines are generally the lowest-cost method of power transmission for large quantities of electric energy.

 Advantages:  

1. The main advantage is that they are easier to repair if damaged (Usually just go up a ladder and do the necessary work) 
2.  They are not restricted by the landscape that they are in e.g. you can easily suspend them over a motorway or river 
3.  Also they have a less chance of electrocuting people as they are so high up
4.   Lose less energy then if they were underground as they do not have any good conductors near them to transfer energy away as easily 
5.  Cheaper to set up and maintain than if they were underground

Disadvantages: 

1. Main problem is that they visually pollute the areas they are set up in 
2. Suffer from problems like vandalism, assisting terrorism (Easy access), and lightning strikes 
3.  Birds and low flying aircrafts can sometimes fly into them

undergound transmission-Undergrounding is the replacement of overhead cables providing electrical power or telecommunications, with underground cables. This is typically performed for aesthetic purposes, but also serves the additional significant purpose of making the power lines less susceptible to outages during high wind thunderstorms or heavy snow or ice storms. Undergrounding can increase the initial costs of electric power transmission and distribution but may decrease operational costs over the lifetime of the cables.

Advantages:

1.  Reduced visual impact. 
2. Reduction or elimination of electrical and magnetic fields above ground, and hence elimination of potential health concerns. 
3. Reduced transmission losses. 
4.  Reduced planning delays.  
5. Increased security of supply, with elimination of disruption due to extreme weather. 
6.  Road side developments can be made without Section 37 application.

Disadvantage

1.  Undergrounding is more expensive, since the cost of burying cables at transmission voltages is several times greater than overhead power lines, and the life-cycle cost of an underground power cable is two to four times the cost of an overhead power line. 
2.  Whereas finding and repairing overhead wire breaks can be accomplished in hours, underground repairs can take days or weeks, and for this reason redundant lines are run. 
3.  Underground cable locations are not always obvious, which can lead to unwary diggers damaging cables or being electrocuted. 
4.  Operations are more difficult since the high reactive power of underground cables produces large charging currents and so makes voltage control more difficult.
5.  Whereas overhead lines can easily be uprated by modifying line clearances and power poles to carry more power, underground cables cannot be uprated and must be supplemented or replaced to increase capacity. Transmission and distribution companies generally future-proof underground lines by installing the highest-rated cables while being still cost-effective. 
6. Underground cables are more subject to damage by ground movement. The 2011 Christchurch earthquake in New Zealand caused damage to 360 kilometres (220 mi) of high voltage underground cables and subsequently cut power to large parts of Christchurch city, whereas only a few kilometres of overhead lines were damaged, largely due to pole foundations being compromised by liquefaction.

How to distribute

Electricity is generated at power plants and moves through a complex system, sometimes called the grid, of electricity substations, transformers, and power lines that connect electricity producers and consumers. Most local grids are interconnected for reliability and commercial purposes, forming larger, more dependable networks that enhance the coordination and planning of electricity supply.

In the United States, the entire electricity grid consists of hundreds of thousands of miles of high-voltage power lines and millions of miles of low-voltage power lines with distribution transformers that connect thousands of power plants to hundreds of millions of electricity customers all across the country.

The stability of the electricity grid requires the electricity supply to constantly meet electricity demand, which in turn requires coordination of numerous entities that operate different components of the grid. The U.S. electricity grid consists of three large interconnected systems that operate to ensure its stability and reliability. To ensure coordination of electric system operations, the north american electric Realibility corporation developed and enforces mandatory grid reliability standards that the Federal energy Regulatory COMISSION (FERC) approved