You have learnt about the power sector . The information is summarised in Fig.
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| Power Sector Scenario |
It is in this context that you have to learn about executing viable power distribution projects and schemes. In this section we sensitise you to the preparatory work that must be done for developing a project/scheme.
Considerations for Preparatory Work
There are many considerations that should be kept in mind while preparing a project/scheme.The project/scheme developer is expected to make site-specific decisions and plan to work out the scheme that proves acceptable and successful within the given situation, resources, data bank and utility. S/he is expected to obtain inputs from various hierarchical levels in the organisation at various stages of firming up the scheme. It is important that s/he has a fair idea of the market, regulatory regime and customer expectations.The following issues need to be addressed while developing a project/scheme for the power distribution sector:
•planning and design of the distribution system to meet load growth and to ensure that
− voltage conditions are within permissible levels;
− energy losses are minimal; and
− the system operates on least overall cost.
• improvement in reliability, security and quality of power supply;
• safety of operation;
• evolving a scientific automation and load management system;
• better customer service; and
• integration of distributed generation.
Recommended Strategy
The scheme for improvement and strengthening of the system should be based on a detailed study, which is unique to each site. The Indian conditions are diverse to such an extent that population density varies from just about a person per sq. km to about 30,000 people per sq. km (largest population density in the world). Planning for system improvement is data intensive. With the availability of computer based tools and software, it is now possible to study and compare a number of alternatives to evolve optimum system development plans.However, considering the present status of general data, it would be advisable to initially take the improvement and strengthening of system in two phases:Short-term and Long-term. During the implementation of short-term measures, database for long-term studies could be built up.
Short-term Planning
Short-term planning should accord maximum priority to loss reduction. The specific tasks to accomplish this objective are given in
Box.
Box : Tasks for Short-term Planning
• Energy accounting/energy audit;
• Network documentation – single line diagram/geographical map up to 11 kV level;
• Estimation of T&D losses/segregation of losses;
• Technical power loss reduction;
• Commercial power loss reduction;
• Improvement of voltage profile;
• Preparation of cost estimates;
• Financial analysis; and
• Preparation of short-term report.
Long-term Planning
While short-term measures are under implementation, long-term plans may be formulated for strengthening the system to meet future load demand. The tasks involved the long-term planning are:
• mapping of the system, data collection and validation of data;
• analysis of existing system;
• voltage variation/regulation study;
• reduction of technical losses in the system;
• load forecast;
• upgrading the network/expansion of the network;
• provisions for intake of power from Distributed Generation harnessing renewable energy sources; and
• technology options including integration of features of modernization of the system such as
− LT less system – High Voltage Distribution System (HVDS);
− installation of shunt capacitors;
− technologies for containing theft, e.g., Aerial Bunched Cables (ABCs), Automatic Meter Reading (AMR), Remote Meter Reading (RMR), etc.;
− Demand Side Management (DSM);
− communication facilities;
− Management Information System (MIS);
− consumer interface automation;
− distribution automation;
− customer relationship management systems;− reliability analysis; and
− training of personnel.
Note that these options are to be taken as recommendations rather than as being obligatory. Actually, the scheme developer has to judge the site-specific requirements and decide accordingly about which options to choose.However, we now discuss the features that should primarily be considered in the scheme formulation process.
Considerations for Scheme Formulation
You will agree that core competency test for distribution network operations lies in
A. Quality power delivery through proper voltage regulation;
B. Reliability in the power supply through network configuration that islands faults, finds alternate paths, and optimizes fault rectification time; and
C. Reactive power compensation for healthy operation.
We discuss each one of these aspects, in brief.
A. Quality Power Delivery through Proper Voltage Regulation As you know, the performance of electrical equipment is affected by variations in voltage, current and frequency of power supply. Many appliances in use today are very sensitive to these parameters and large variations can damage them. For example, the microwave oven is frequency sensitive whereas the tube-light is voltage sensitive and the filament bulb is current sensitive. In industry, the annealing process is a very precise current sensitive process whereas the performance of drive motors depends on the availability of voltage at their terminals and AC drives are frequency sensitive.
People consider voltage as the only important factor. (They quickly notice that a tube-light stops glowing when the voltage drops below a certain level.) Variations in frequency and current are the least recognised parameters. But these are equally important. You may recall several instances of grid failure due to drop in frequency engulfing vast areas in darkness. Among voltage, current and frequency, voltage is quantifiable and can be regulated by utilities. Controlling frequency variation is not in the hands of a power distribution company. This is why an electrical power supply network is designed and developed taking the voltage variation at different levels/sections. The process is going to be more intricate in the decades to come with intake from Distributed Generation to harness renewable energy resources.
BIS has specified the range of permissible/acceptable voltages at the consumer end. Today consumers/industries are using voltage sensitive electronic equipment in large numbers. So ensuring supply of quality power is absolutely necessary.
Box : Voltage Regulation Improvement Tools
•Bifurcation of lines: Long length transmission lines have more voltage drop due to I 2 R loss and resistance increases with increase in length.Therefore, it is preferable to have short transmission lines by bifurcating the existing long transmission lines or creating a new feeder from the primary substation.
•Reconductoring and Use of Higher Size Conductors: Another method of improving voltage regulation is by replacing old conductors with
one size higher new conductors. The main constraint in this method is that power has to be shut down to execute the work. So planning well in advance is essential before taking up reconductoring.
•Use of AAAC Conductor in place of ACSR Conductor: All aluminium alloy conductors (AAAC) have better conductivity than steel reinforced
aluminium conductors (ACSR) though these are costlier.
•Improving Power Factor: Voltage at receiving end bears less power due to use of induction motors in large numbers in industries as well as for pumps for irrigation purpose. This can be improved by using capacitors of proper rating near the load to compensate the reactive power requirement (see Appendix to this unit for an explanation of reactive power compensation).
•Diversifying the Load: Voltage regulation can improve if different categories of consumers use electrical power at different times. For example, industrial consumers can be asked to use power during night. PHED can use pumps in non-peak load hours. For this, the utility can fix differential tariff for different hours. Shaving off peak load helps considerably in reducing the cost of drawing peak load from hydro, ensures better grid management and network health besides preventing abuses to thermal generator.
•Setting of New Substation near Load Centre: Voltage regulation is improved if a PSS is set up instead of stretching 11 kV lines too long.With the increase in the number of consumers, the length of 11 kV lines also has to be increased. So through a proper survey of load, a new PSS can be installed near load centre that will provide better voltage to consumers.
B. Reliability in Power Supply through Network Configuration
The first and foremost important task for carrying out any distribution planning is to study the existing system. you have studied about the three types of networks (Fig.) normally available in the electrical distribution system: radial, loop, cross-loop network. You may like to read that section again.
Considerations for Preparatory Work
There are many considerations that should be kept in mind while preparing a project/scheme.The project/scheme developer is expected to make site-specific decisions and plan to work out the scheme that proves acceptable and successful within the given situation, resources, data bank and utility. S/he is expected to obtain inputs from various hierarchical levels in the organisation at various stages of firming up the scheme. It is important that s/he has a fair idea of the market, regulatory regime and customer expectations.The following issues need to be addressed while developing a project/scheme for the power distribution sector:
•planning and design of the distribution system to meet load growth and to ensure that
− voltage conditions are within permissible levels;
− energy losses are minimal; and
− the system operates on least overall cost.
• improvement in reliability, security and quality of power supply;
• safety of operation;
• evolving a scientific automation and load management system;
• better customer service; and
• integration of distributed generation.
Recommended Strategy
The scheme for improvement and strengthening of the system should be based on a detailed study, which is unique to each site. The Indian conditions are diverse to such an extent that population density varies from just about a person per sq. km to about 30,000 people per sq. km (largest population density in the world). Planning for system improvement is data intensive. With the availability of computer based tools and software, it is now possible to study and compare a number of alternatives to evolve optimum system development plans.However, considering the present status of general data, it would be advisable to initially take the improvement and strengthening of system in two phases:Short-term and Long-term. During the implementation of short-term measures, database for long-term studies could be built up.
Short-term Planning
Short-term planning should accord maximum priority to loss reduction. The specific tasks to accomplish this objective are given in
Box.
Box : Tasks for Short-term Planning
• Energy accounting/energy audit;
• Network documentation – single line diagram/geographical map up to 11 kV level;
• Estimation of T&D losses/segregation of losses;
• Technical power loss reduction;
• Commercial power loss reduction;
• Improvement of voltage profile;
• Preparation of cost estimates;
• Financial analysis; and
• Preparation of short-term report.
Long-term Planning
While short-term measures are under implementation, long-term plans may be formulated for strengthening the system to meet future load demand. The tasks involved the long-term planning are:
• mapping of the system, data collection and validation of data;
• analysis of existing system;
• voltage variation/regulation study;
• reduction of technical losses in the system;
• load forecast;
• upgrading the network/expansion of the network;
• provisions for intake of power from Distributed Generation harnessing renewable energy sources; and
• technology options including integration of features of modernization of the system such as
− LT less system – High Voltage Distribution System (HVDS);
− installation of shunt capacitors;
− technologies for containing theft, e.g., Aerial Bunched Cables (ABCs), Automatic Meter Reading (AMR), Remote Meter Reading (RMR), etc.;
− Demand Side Management (DSM);
− communication facilities;
− Management Information System (MIS);
− consumer interface automation;
− distribution automation;
− customer relationship management systems;− reliability analysis; and
− training of personnel.
Note that these options are to be taken as recommendations rather than as being obligatory. Actually, the scheme developer has to judge the site-specific requirements and decide accordingly about which options to choose.However, we now discuss the features that should primarily be considered in the scheme formulation process.
Considerations for Scheme Formulation
You will agree that core competency test for distribution network operations lies in
A. Quality power delivery through proper voltage regulation;
B. Reliability in the power supply through network configuration that islands faults, finds alternate paths, and optimizes fault rectification time; and
C. Reactive power compensation for healthy operation.
We discuss each one of these aspects, in brief.
A. Quality Power Delivery through Proper Voltage Regulation As you know, the performance of electrical equipment is affected by variations in voltage, current and frequency of power supply. Many appliances in use today are very sensitive to these parameters and large variations can damage them. For example, the microwave oven is frequency sensitive whereas the tube-light is voltage sensitive and the filament bulb is current sensitive. In industry, the annealing process is a very precise current sensitive process whereas the performance of drive motors depends on the availability of voltage at their terminals and AC drives are frequency sensitive.
People consider voltage as the only important factor. (They quickly notice that a tube-light stops glowing when the voltage drops below a certain level.) Variations in frequency and current are the least recognised parameters. But these are equally important. You may recall several instances of grid failure due to drop in frequency engulfing vast areas in darkness. Among voltage, current and frequency, voltage is quantifiable and can be regulated by utilities. Controlling frequency variation is not in the hands of a power distribution company. This is why an electrical power supply network is designed and developed taking the voltage variation at different levels/sections. The process is going to be more intricate in the decades to come with intake from Distributed Generation to harness renewable energy resources.
BIS has specified the range of permissible/acceptable voltages at the consumer end. Today consumers/industries are using voltage sensitive electronic equipment in large numbers. So ensuring supply of quality power is absolutely necessary.
Box : Voltage Regulation Improvement Tools
•Bifurcation of lines: Long length transmission lines have more voltage drop due to I 2 R loss and resistance increases with increase in length.Therefore, it is preferable to have short transmission lines by bifurcating the existing long transmission lines or creating a new feeder from the primary substation.
•Reconductoring and Use of Higher Size Conductors: Another method of improving voltage regulation is by replacing old conductors with
one size higher new conductors. The main constraint in this method is that power has to be shut down to execute the work. So planning well in advance is essential before taking up reconductoring.
•Use of AAAC Conductor in place of ACSR Conductor: All aluminium alloy conductors (AAAC) have better conductivity than steel reinforced
aluminium conductors (ACSR) though these are costlier.
•Improving Power Factor: Voltage at receiving end bears less power due to use of induction motors in large numbers in industries as well as for pumps for irrigation purpose. This can be improved by using capacitors of proper rating near the load to compensate the reactive power requirement (see Appendix to this unit for an explanation of reactive power compensation).
•Diversifying the Load: Voltage regulation can improve if different categories of consumers use electrical power at different times. For example, industrial consumers can be asked to use power during night. PHED can use pumps in non-peak load hours. For this, the utility can fix differential tariff for different hours. Shaving off peak load helps considerably in reducing the cost of drawing peak load from hydro, ensures better grid management and network health besides preventing abuses to thermal generator.
•Setting of New Substation near Load Centre: Voltage regulation is improved if a PSS is set up instead of stretching 11 kV lines too long.With the increase in the number of consumers, the length of 11 kV lines also has to be increased. So through a proper survey of load, a new PSS can be installed near load centre that will provide better voltage to consumers.
B. Reliability in Power Supply through Network Configuration
The first and foremost important task for carrying out any distribution planning is to study the existing system. you have studied about the three types of networks (Fig.) normally available in the electrical distribution system: radial, loop, cross-loop network. You may like to read that section again.
 |
| Radial, Loop and Cross-Loop Network Distribution Systems |
Network Documentation
This is an important prerequisite for network configuration, which involves preparing single line diagrams and the geographical map up to 11 kV. In case of low voltage network emanating from distribution transformers, the sample map for typical high, medium and low load density areas covering various categories of consumers should be prepared.The scheme should cover a brief description of the area covered under the circle. The various physical and demographic features, which could be included, are given in Box.
Box : Physical and Demographic Features to be Included in the Scheme
• Name of utility;
• Name of distribution circle;
• District/town(s)/village covered;
• Location, latitude and longitude;
• Total area and nature of population (urban and rural);
• Boundaries;
• Climatic conditions;
• Status of development;
• Access to electricity; and
• Economic structure – socio-economic features.
The existing organisational setup of the circle in respect of administration, planning, construction, operation and maintenance, etc. may be given.GIS,using GPS instruments, is a powerful tool to efficiently integrate the electrical distribution network with physical location of the consumers. You will study about these in Block 3 of the course BEE-002.
C. Reactive Power Compensation
Shunt capacitors provide the simplest and most economical way of managing reactive power. Agricultural pump sets and LT motive load
operate at very low power factor (0.6 to 0.7) and cause reactive power management and voltage profile problems in the system. These are responsible for increasing system losses. It has been realized that installation of LT capacitors close to the consumer load would reduce
• load current in the LT feeders; and
• overloading of distribution transformers, 11 kV lines and back-up system.
The reasons and proposed solutions are given below:
• Quite often LT consumers do not ensure that capacitors are working even if these are provided to them at the time of release of
connections. To overcome this problem, the power utilities should provide LT capacitors on distribution transformers.
• Changing load demand characteristics pose problems in deciding on the level of compensation. It would be worthwhile to provide minimum level of fixed compensation of LT level to meet the average demand conditions and prescribe higher nominal voltage (+10%) to ensure safe operation under possible adverse conditions. The balance requirement could be met by placing capacitors on 11 kV feeders wherever the site conditions permit.
While deciding the optimal location of capacitors, considerations such as their maintenance and feasibility of monitoring and maintaining should be kept in view. The requirement of additional switched reactive compensation at 66/33/11 kV level may be decided based on system studies. Adequate capacitors at 66/11 kV level may be provided on 220/66 kV and/or 132/33 kV substation.
This is an important prerequisite for network configuration, which involves preparing single line diagrams and the geographical map up to 11 kV. In case of low voltage network emanating from distribution transformers, the sample map for typical high, medium and low load density areas covering various categories of consumers should be prepared.The scheme should cover a brief description of the area covered under the circle. The various physical and demographic features, which could be included, are given in Box.
Box : Physical and Demographic Features to be Included in the Scheme
• Name of utility;
• Name of distribution circle;
• District/town(s)/village covered;
• Location, latitude and longitude;
• Total area and nature of population (urban and rural);
• Boundaries;
• Climatic conditions;
• Status of development;
• Access to electricity; and
• Economic structure – socio-economic features.
The existing organisational setup of the circle in respect of administration, planning, construction, operation and maintenance, etc. may be given.GIS,using GPS instruments, is a powerful tool to efficiently integrate the electrical distribution network with physical location of the consumers. You will study about these in Block 3 of the course BEE-002.
C. Reactive Power Compensation
Shunt capacitors provide the simplest and most economical way of managing reactive power. Agricultural pump sets and LT motive load
operate at very low power factor (0.6 to 0.7) and cause reactive power management and voltage profile problems in the system. These are responsible for increasing system losses. It has been realized that installation of LT capacitors close to the consumer load would reduce
• load current in the LT feeders; and
• overloading of distribution transformers, 11 kV lines and back-up system.
The reasons and proposed solutions are given below:
• Quite often LT consumers do not ensure that capacitors are working even if these are provided to them at the time of release of
connections. To overcome this problem, the power utilities should provide LT capacitors on distribution transformers.
• Changing load demand characteristics pose problems in deciding on the level of compensation. It would be worthwhile to provide minimum level of fixed compensation of LT level to meet the average demand conditions and prescribe higher nominal voltage (+10%) to ensure safe operation under possible adverse conditions. The balance requirement could be met by placing capacitors on 11 kV feeders wherever the site conditions permit.
While deciding the optimal location of capacitors, considerations such as their maintenance and feasibility of monitoring and maintaining should be kept in view. The requirement of additional switched reactive compensation at 66/33/11 kV level may be decided based on system studies. Adequate capacitors at 66/11 kV level may be provided on 220/66 kV and/or 132/33 kV substation.
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