epe491_elements of power system
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Elements of Electrical Power and Machine SystemTRANSCRIPT
Electrical Power and Machines EPE491
D. Johari, FKE UiTM 1
Elements of Power System
Introduction
Electrical power system
o A network of components designed to transmit and distribute the energy produced by generators to locations where it is used.
o Required to generate and supply electrical energy to consumers.
Figure 1: A simple power system
The three main characteristics of electricity supply are as follows:
o Electricity cannot be stored in bulk form.
Thus, power must be generated continuously so that it meets the demand at a specific voltage and frequency.
o Increases in population, industrial expansion, housing areas and etc lead to the continuous increase in demand for power.
o Power station is located near to the resources location.
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Energy Resources
They are five main energy resources being used to generate electric energy
They are: coal, water, gas, oil and nuclear.
o Coal Most common source Relatively cheap fuel Unfortunately, the most polluting Antipollution features have to be included Non-renewable
o Water The best source Non-polluting
No cost for the ‘fuel’o Natural gas
Better and cleaner energy source than coal Principal disadvantage is hard to transport over long distance Non-renewable
o Oil A bit more polluting than natural gas but easy to transport over long distance However, much more expensive Non-renewable
o Nuclear energy Non-polluting
Extremely expensive to build Require elaborate safety system and expensive training Once built, the cost of the ‘fuel’ is low
Nowadays, active research and development has also been carried out for alternative renewable energy resources such as geo-thermal, wind, wave, solar, bio-mass and etc.
However, they are not yet economical
Figure 2: Coal Power Station
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Figure 3: Hydro Power Station
Figure 4: Wind Power Station
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Power System
Power system is usually divided into three parts: generation, transmission and distribution.
Figure 5: The three major components of power system
Generation System
Powers supplied by all power stations are based on power demand.
They are usually generated at a voltage between 11kV and 25kV
Figure 6 shows a typical load curve for 24 hours.
Total power depends on the time of the day and the daily activities of the consumers
Figure 6: Typical load curve
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There are 3 types of generating stations based on load demand:
1. Base-power station
o Base load is the minimum amount of power that a utility company must make available to its customers.
o Deliver full power continuously i.e. 24 hours a day and 365 days a year
o Most economical in terms of operating costs i.e. high efficiency output & most reliable
o Nuclear & coal-fired stations are suitable for this purpose
2. Intermediate-power station
o Can respond to changes in demand relatively quickly, usually by adding or removing one or more generating units
o Operate mainly during day time to complement the base stations
o The most economical in terms of production costs, although unreliable in terms of actual energy output
o Hydropower stations are suitable for this purpose
3. Peak-power station
o Generally run only when there is a high demand, known as peak demand
o Deliver power for short intervals during the day
o Able to respond very quickly because they can be started up in a few minutes
o Have high operating cost due to their idling-time and unutilized capital costs but necessary for optimal operation of power system
o Usually gas turbines are used for this purpose
Transmission System
Transmission system consists of transmission line and substations
Two types of transmission lines: overhead lines and buried cables
1. Overhead transmission line
Consist of three conductors suspended by towers or poles.
Generally the lowest-cost method (since most of the insulation is provided by air)
Classified according to the range of voltages:
o Low voltage: less than 1 kV (connection between residential or small commercial customer & the utility)
o Medium voltage: between 1 kV to ~ 33 kV (distribution in urban & rural areas)
o High voltage: between 33 kV to ~230 kV (for long distance transmission)
o Extra high voltage: over 230 kV up to ~ 800 kV (for long distance transmission)
o Ultra high voltage: higher than 800 kV
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2. Underground transmission line
These lines are designed to be buried underground or under water
Compared to overhead lines, buried cables are:
o More expensive (cost of burying cables is higher)
o Harder to maintain and repair
o Cannot be used for very long distances due to capacitance problems
Nevertheless, they are increasingly popular in new urban areas where overhead transmission lines are considered an eyesore.
Substation is a subsidiary station of power system where voltage is transformed from high to low or low to high using transformers.
There are three types of substation normally used:
1. Transmission substation
o Convert voltages to extremely high voltages for long distance transmission.
o Use high voltages in order to minimize losses and reduce cost
2. Distribution substation
o Step down the voltages to distribution level
3. Interconnecting substation
o Used to connect different power systems (e.g. between Malaysia and Thailand)
o Enable power exchange and increase in stability of the overall network
Distribution System
Distribute power to consumers by means of lower voltage networks
The medium voltage distribution is at 33kV and below i.e. 11kV, 6.6kV or 3.3kV.
The final consumer utilizes 415V three phase and 240V single phase.
The Grid System
Grid system is an overall network that consists of many interconnected power system.
The advantages of grid systems are:
o Stability in operation
The system has greater reserve power through their combined resources than a system working in isolation.
Therefore, the system would be able to withstand a large disturbance and is more stable. Stability will increase with an increase in number of stations.
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o Service continuity
If one of the generating stations should break down or to closed for inspection and repair, energy could be supplied by the remaining stations.
o Economy
In this system, the load can be shared among various generating station so that the overall operating cost is minimized.
Thus, we can shut down a number of stations when demand is low.
In Peninsular Malaysia, the power grid is known as the National Grid.
o It is operated and owned by Tenaga Nasional Berhad (TNB).
o The system spans the whole of Peninsular Malaysia, connecting electricity generating stations owned by TNB and Independent Power Producers (IPPs).
o IPPs are privately owned power producers
Generate and sell power to TNB
Examples of IPPs:
1. YTL Generation Sdn Bhd
Paka, Pasir Gudang
2. Malakoff Berhad
Lumut Power Sattion, Segari
Prai Power Station, Butterworth
Tanjung Bin Power Station, Johor
3. Genting Sanyen Power Sdn Bhd
Kuala Langat Power Station
There are also two other electrical grids in East Malaysia:
o In Sabah: Sabah Electricity Sdn. Bhd. (SESB)
o In Sarawak: Sarawak Electricity Supply Corporation (SESCO)