Before the field study is commenced, it is prudent to study the existing databank on the power distribution network in place. In our institutions, it is a general tendency that wherever data is not subjected to internal or external audit, figures are estimated. Though data about material in stores, customer bills, etc., are dependable but the length of 11 kV feeders may be based on estimates as it gets extended by site conditions and may not be properly recorded. We have examples of 11 kV feeders running over 150 km whereas the normal length of a feeder should be less than 15 km.
Therefore, intensive field study is required and the local substation officials should be informed before it is undertaken. If you wish to use GPS instruments, etc., your field work should be well planned. Interaction with development agencies, Municipal Corporation, etc., could also be firmed up for network expansion plans. All preparatory work should be taken up so that theexpensive and difficult field visits could bring in the best information bank that would form the backbone for developing and analyzing the schemes. In the following subsections, we present the information that is useful in this regard.It could be further enriched by the officials undertaking the field visit.
Brief Description of the Circle/Project Area
The scheme should describe the area covered under the circle (Box).
Box: Physical and Demographic Features to be Included in the DPR
• Name of Utility
• Name of Distribution Circle
• District/Town(s)/Village covered
• Location : Latitude and Longitude
• Area
• Population
• Boundaries
• Climatic Conditions
• Status of Development
• Access to Electricity
• Economic Structure – Socio-economic features
• Predominantly Urban/Rural
The existing organisational setup of the circle in respect of administration, planning, construction, operation and maintenance, etc. may be given.
Data Collection/Compilation of Existing System
For convenience in operation and administration, the area covered by a circle is divided into divisions and sub-divisions while the electrical network in the circle remains one single connected entity. It is likely that some feeder(s)/ substation(s) may get interconnected to other circles through switch(es)/metered point(s) that may be provided for the purpose. Detailed data about the existing power system should be collected in respect of the following:
− Contract Demand;
− Maximum Demand;
− Energy Consumption; and
− Supply Voltage.
• Peak demand MW/ MVAR – simultaneous and non simultaneous
• Annual Energy Consumption – Energy balance sheet
• Geographical Map (to scale) of the area depicting Transmission and Sub-transmission System.
• Source(s) of power supply/Grid substation(s) supplying power to the area
•Category-wise number of consumers and connected load, including the bulk consumer details such as
− Existing substations;
− Existing lines.
•Sub-transmission System
− Existing 66-33/11 kV substations and existing 66-33 kV lines;
− Under construction substations;
− Under construction 66/33/11 kV lines.
•Distribution System
− 11 kV lines;
− Distribution transformers; and − LT lines.
•Operational Parameters
− Substation equipment status;
− 66/33 kV feeder breakdowns;
− Failure of distribution transformers;
− Tripping on 11 kV feeders/ lines; and
− Consumer outages.
•Electrical Network Details
For carrying out studies, the sub-transmission and distribution system and its backup system from Grid substations to the consumers’ level should bedetailed. The data requirements for analysis of the existing power system are:
− Electrical network details: single line diagrams with conductor sizes, lengths, transformer locations, transformation capacities, capacitors,consumer location and load, etc.;
− Parameters of equipment, devices and conductors; and
− Load data: peak load, diversity factor and power factor.
•Sub-transmission and Distribution Network
Electrical network mapping should, in the first phase, be prepared as single line diagram showing the network layout. The network diagrams should be prepared for each and every substation and line section up to LV bus of the distribution transformer.
•LV Network
The LV network starts from the low voltage terminals of the distribution transformer. The following information is essential for modelling of the low-voltage network;
− section length;
− conductor size of each section;
− connected load for each group of consumers;
− number of consumers in each group; and
− total connected load on the transformer.
Sample LV network emanating from distribution transformer located in high, medium and low load density pockets of the circle and covering different categories of consumers should be modelled to form the basis for determining the improvement in the entire LV network.
•Equipment Parameter Data
The schematic diagrams for existing substations should be prepared with information of power transformer ratings and numbers, impedance values,bus-bar scheme, isolators, circuit breakers, minimum oil/ bulk oil/ SF6/ vacuum and type of installation (indoor/ outdoor), number of incoming and outgoing feeders, CTs and PTs, details of taps and normal tap position, spare bays, etc.
•Load Data
The load data should cover the monthly, daily and hourly details of energy/ peak power in the electrical system of the circle. The various operational and load data required are :
− peak load on each transformer/ feeder and corresponding actual voltage;
− diversity factor at various voltage levels;
− power factor at various voltage levels; and
− load factor and loss load factor at various voltage levels.
The load data could be obtained from the log sheets maintained at each 33/11 kV substation. The data could also be obtained more accurately from logging type electronic energy meters, if available in the system.The planning studies should be based on actual feeder load conditions and measurements taken at various points in the system. Load data in respect of distribution transformers may be compiled by using tong-tester and/ or by installing meters on LT side of distribution transformer.The 33/11 kV and 66/11 kV substations and 11 kV feeders are to be fitted with electrostatic meters with data logging facilities. The daily, monthly and annual load curves considering the seasonal variation will have to be analysed from the logged data on these meters to compute the system peak and average demands.
•System Load Factor and Loss Load Factor (LF and LLF)
The annual load duration curve for the circle may be derived by aggregating the typical hourly spot reading of system power demand at grid substation(s) feeding the Distribution circle for typical working days and holidays in each month during the year. This would take into account the seasonal variations as well.The system power losses are proportional to the square of the system load. An annual loss load duration curve may accordingly be derived from the load duration curve by squaring the ordinates. The load factor and loss load factor for the system may be computed from load duration and loss load duration curve, respectively
•Data Validation
The data compiled for the existing system has to be validated for correctness and consistency, especially in respect of load and network data. In the case of meter supplies, metering deficiencies in the form of non-functioning/defective meters have an impact on the correctness of loading/consumption figures. The proportion of non-working and defective meters should be identified. Check metering has to be done periodically on random sample basis. In case of un-metered supplies, the data would have to be worked out by sample metering and field studies. These measures would help in evolving suitable mechanisms for data validation.
Therefore, intensive field study is required and the local substation officials should be informed before it is undertaken. If you wish to use GPS instruments, etc., your field work should be well planned. Interaction with development agencies, Municipal Corporation, etc., could also be firmed up for network expansion plans. All preparatory work should be taken up so that theexpensive and difficult field visits could bring in the best information bank that would form the backbone for developing and analyzing the schemes. In the following subsections, we present the information that is useful in this regard.It could be further enriched by the officials undertaking the field visit.
Brief Description of the Circle/Project Area
The scheme should describe the area covered under the circle (Box).
Box: Physical and Demographic Features to be Included in the DPR
• Name of Utility
• Name of Distribution Circle
• District/Town(s)/Village covered
• Location : Latitude and Longitude
• Area
• Population
• Boundaries
• Climatic Conditions
• Status of Development
• Access to Electricity
• Economic Structure – Socio-economic features
• Predominantly Urban/Rural
The existing organisational setup of the circle in respect of administration, planning, construction, operation and maintenance, etc. may be given.
Data Collection/Compilation of Existing System
For convenience in operation and administration, the area covered by a circle is divided into divisions and sub-divisions while the electrical network in the circle remains one single connected entity. It is likely that some feeder(s)/ substation(s) may get interconnected to other circles through switch(es)/metered point(s) that may be provided for the purpose. Detailed data about the existing power system should be collected in respect of the following:
− Contract Demand;
− Maximum Demand;
− Energy Consumption; and
− Supply Voltage.
• Peak demand MW/ MVAR – simultaneous and non simultaneous
• Annual Energy Consumption – Energy balance sheet
• Geographical Map (to scale) of the area depicting Transmission and Sub-transmission System.
• Source(s) of power supply/Grid substation(s) supplying power to the area
•Category-wise number of consumers and connected load, including the bulk consumer details such as
− Existing substations;
− Existing lines.
•Sub-transmission System
− Existing 66-33/11 kV substations and existing 66-33 kV lines;
− Under construction substations;
− Under construction 66/33/11 kV lines.
•Distribution System
− 11 kV lines;
− Distribution transformers; and − LT lines.
•Operational Parameters
− Substation equipment status;
− 66/33 kV feeder breakdowns;
− Failure of distribution transformers;
− Tripping on 11 kV feeders/ lines; and
− Consumer outages.
•Electrical Network Details
For carrying out studies, the sub-transmission and distribution system and its backup system from Grid substations to the consumers’ level should bedetailed. The data requirements for analysis of the existing power system are:
− Electrical network details: single line diagrams with conductor sizes, lengths, transformer locations, transformation capacities, capacitors,consumer location and load, etc.;
− Parameters of equipment, devices and conductors; and
− Load data: peak load, diversity factor and power factor.
•Sub-transmission and Distribution Network
Electrical network mapping should, in the first phase, be prepared as single line diagram showing the network layout. The network diagrams should be prepared for each and every substation and line section up to LV bus of the distribution transformer.
•LV Network
The LV network starts from the low voltage terminals of the distribution transformer. The following information is essential for modelling of the low-voltage network;
− section length;
− conductor size of each section;
− connected load for each group of consumers;
− number of consumers in each group; and
− total connected load on the transformer.
Sample LV network emanating from distribution transformer located in high, medium and low load density pockets of the circle and covering different categories of consumers should be modelled to form the basis for determining the improvement in the entire LV network.
•Equipment Parameter Data
The schematic diagrams for existing substations should be prepared with information of power transformer ratings and numbers, impedance values,bus-bar scheme, isolators, circuit breakers, minimum oil/ bulk oil/ SF6/ vacuum and type of installation (indoor/ outdoor), number of incoming and outgoing feeders, CTs and PTs, details of taps and normal tap position, spare bays, etc.
•Load Data
The load data should cover the monthly, daily and hourly details of energy/ peak power in the electrical system of the circle. The various operational and load data required are :
− peak load on each transformer/ feeder and corresponding actual voltage;
− diversity factor at various voltage levels;
− power factor at various voltage levels; and
− load factor and loss load factor at various voltage levels.
The load data could be obtained from the log sheets maintained at each 33/11 kV substation. The data could also be obtained more accurately from logging type electronic energy meters, if available in the system.The planning studies should be based on actual feeder load conditions and measurements taken at various points in the system. Load data in respect of distribution transformers may be compiled by using tong-tester and/ or by installing meters on LT side of distribution transformer.The 33/11 kV and 66/11 kV substations and 11 kV feeders are to be fitted with electrostatic meters with data logging facilities. The daily, monthly and annual load curves considering the seasonal variation will have to be analysed from the logged data on these meters to compute the system peak and average demands.
•System Load Factor and Loss Load Factor (LF and LLF)
The annual load duration curve for the circle may be derived by aggregating the typical hourly spot reading of system power demand at grid substation(s) feeding the Distribution circle for typical working days and holidays in each month during the year. This would take into account the seasonal variations as well.The system power losses are proportional to the square of the system load. An annual loss load duration curve may accordingly be derived from the load duration curve by squaring the ordinates. The load factor and loss load factor for the system may be computed from load duration and loss load duration curve, respectively
•Data Validation
The data compiled for the existing system has to be validated for correctness and consistency, especially in respect of load and network data. In the case of meter supplies, metering deficiencies in the form of non-functioning/defective meters have an impact on the correctness of loading/consumption figures. The proportion of non-working and defective meters should be identified. Check metering has to be done periodically on random sample basis. In case of un-metered supplies, the data would have to be worked out by sample metering and field studies. These measures would help in evolving suitable mechanisms for data validation.
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