Vijay Kumar, Anjuli Chandra
Central Electricity Authority, New Delhi
Introduction
Sub- Transmission and Distribution systems constitute the link between electricity utilities and consumers, their revenue realization segment. For consumers, it represents the face of the utility. Efficient functioning of this segment of the utility is essential to sustain the growth of power sector and the economy. However, the present situation is characterised by unacceptably high losses (both technical and commercial), poor quality and reliability of supply, billing, revenue collection, frequent interruptions in supply and resultant consumer dis-satisfaction, etc. In this context, ST and segment of power sector needs immediate attention and action to achieve a turn around and self-sustenance of power sector.
Problems in Distribution Systems
The main issue in Distribution systems or rather more appropriately the issue confronting the power sector as a whole, is the reduction of Transmission & Distribution (T & D) losses to acceptable minimum levels. The all-India T & D losses, which were about 15% till 1966-67, increased gradually and are not at 24.79% (1997-98). During the last few years some of utilities variously estimated the losses in the range over 30% to 50% much higher than the preceding years. T & D losses in developed countries are around 7-8% only. Taking into consideration the Indian conditions such as far-flung rural areas, nature of loads, system configuration etc. the reasonable permissible (technical) energy losses should be 10%-15% in different states.
While the losses in Extra High Voltage (EHV) network are about 4%-5%, bulk of the losses occur in ST & D system. It is well known that these losses in Distribution systems include non-technical or commercial losses and that of power by various users with or without connivance of utility staff. These constitute a large component of overall losses. There are also losses on account of defective (slow) meters, stuck up/burnt meters etc. Further on account of estimation involved in agriculture sector consumption (30% of total), absence of adequate metering at the system level, deficiencies in consumer metering the validity of figure of T & D losses being reported become questionable. General conclusions are that the reported losses are under estimated and cover up large commercial losses (theft), actual figures are higher, technical losses are also high and bulk of the losses occur in Sub-Transmission and Distribution systems. Inefficiency, frequent interruptions, flickers and poor voltage also characterize distribution systems. In addition the billing and revenue collections are very poor leading to combined state utility financial losses of Rs. 26,0000 crores every year. If the current trend continues, in another three years, state utility financial losses will reach Rs. 45,000 crores a year. It is, therefore, necessary to bring about improvements in planning implementation and operation of ST & D systems in a scientific and efficient manner. The present traditional reactive and ad-hoc approach to network development should be replaced by an approach based on technical and reliability requirements, economic considerations of costs of energy loss and expansion of system to meet the growth of prospective demand with least cost.
Status of Data Doucmentation in Power Utilities
Reliable and sufficiently detailed data is required to facilitate decision making in all activities of Distribution System Management. Controlling costs improve efficiency and reducing down time has become essential for a utility in order to successful in the highly competitive environment of today where private utilities/distribution companies are coming into distribution. With the huge connected networks, number of spur lines and alternative feeds from different sources the creation, updation and management of distribution data is a Herculean task. Many studies conducted in the utilities of the country have indicated that the data documentation in most of the utilities is very poor. The data of distribution systems is maintained through hand-drawn maps with facilities data printed in text form on them and available with the JE/linesman in charge of the feeder. These maps are rarely updated.
Data Requirements
The data requirements for management of distribution systems are voluminous and varied. Some of them are indicated below: Consumer data
Category wise number of consumer and connected load including the Bulk Consumer’s details such as
- Contract demand
- Maximum demand
- Energy Consumption
- Supply Voltage
Demand data
- Peak demand MW/MVAR-simultaneous and non simultaneous
- Annual Energy Consumption data
Network data
- 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
- Existing Substation
- Existing lines
Sub-Transmission System
- Existing 66-33/11 kV Sub-Stations & Existing 66-33 kV LINES.
- Under Construction Sub-Station.
- Under Construction 66/33/11 kV lines.
Distribution System
- 11kV lines
- Distribution transformers
- LT lines.
Operational parameters
- Substation equipment status
- 66/33 kV Feeder breakdowns
- Failure of distribution transformers
- Tripping on 11 KV feeders/lines
- Consumer outages
Electrical network details
- Electrical network details – single line diagrams with conductor sizes, lengths, transformer locations, capacitors, capacitors, consumer location and load etc.
- Parameters of equipments, devices and conductors
- Load data-peak load, diversity factor, power factor etc.
LV Network
- Section length
- Conductor size of each section
- Connected load for each group of consumer
- Number of consumers in each group
- Total connected load on the transformer
Equipment Parameter Data
The Schematic diagram for existing sub-stations are to be prepared with information of power transformer rating and numbers, impedance values, bus bar scheme, isolators, circuit breakers type e.g. minimum oil/bulk oil/SF6/Vaccum and type of installation (indoor/outdoor), no of incoming and outgoing feeders, CTs and PTs, details of taps and normal tap position, spare bays etc.
Load Data
The load data covering the monthly, daily and yearly details of energy/peak power in the electrical system as well as information as below is required:
- Peak load on each transformer/feeder and corresponding actual voltage.
- Diversity factor at various voltage levels.
- Power factor at various voltage levels
- Load factor and loss load factor at various voltage levels.
Further data on billing, revenue collection, pending applications investment, material & manpower requirements etc are some of the other data required. As can be seen, the data requirement is very voluminous. These records have to be stored, retrieved and used by many different, people at different locations. If manual records are used, then there is every likely hood of these records getting displaced or destroyed. The use of advanced information technology tools for maintaining a coherent database becomes very essential.
Role of Information Technology in Distribution System Management
Initially, computers handled data only in alphanumeric form. GIS is an importantant tool in this area. Geographic Information Systems is a system of mapping of complete electrical network including low voltage system and customer supply points with latitude and longitudes overload on satellite imaging and/or survey of India maps. Layers of information are contained in these map representations. The first layer corresponds to the distribution network coverage. The second layer corresponds to the land background containing roads, landmarks, buildings, rivers, railway crossings etc. The next layer could contain information on the equipment viz poles, conductors transformers etc. Most of the electrical network/equipment have a geographical location and the full benefit of any network improvement can be had only if the work is carried out in the geographical context. Business processes such as network planning, repair operations and maintenance connection and reconnection has also to be based around the network model. Even while dong something as relatively simple as adding a new service connection, it is vital to know that users of the system are not affected by this addition. GIS in conjunction with system analysis tools helps to do just this.
For efficient and reliable operation of a distribution system, a reliable and well knit communication network is required to facilitate project coordination of the maintenance and fault activities of the distribution system. GIS when integrated with real time SCADA can help in sending the right signals to the communication network. Outages can be isolated faster than even before and maintenance crews dispatched with critical information including location of the fault.
GIS can be used in distribution systems management for:
- Handling customer inquiries
- Fault Management
- Routine maintenance can be planned.
- Network extensions and optimization
- What is analysis
- Network reconfiguration
- Improved revenue management
- SCADA can be integrated with GIS
- Rights of way and compensation
GIS environment hosts a wealth of presentation techniques that enable fast and accurate interpretation of results from power flow results to short circuit analysis.
Initiative by Government of India
For developing Sub-Transmission and Distribution schemes on a scientific basis with energy accounting and audit as an integral component, the Govt. of India has appointed a committee under the chairmanship of Member (PS), CEA to formulate guidelines/manuals on the various aspects of Sub-Transmission and Distribution development. The committee held discussion with various utilities in the country and has formulated the following manuals/guidelines. The above guidelines and manuals cover all the aspects and would provide guidance to the field level units to undertake ST & D development on a scientific approach to establish energy accounting and audit system etc. to achieve reduction of both commercial and technical losses and ensure quality and reliability of power supply to consumers.
- Guidelines for formulation of project report on upgradation of sub-transmission and distribution system;
- Guidelines for energy accounting and audit in power systems;
- Guidelines for project management, performance evaluation, operations and maintenance and renovation and modernization (R & M) of sub-transmission and distribution project;
- Manual on training of personnel deployed on sub-transmission and distribution and
- Technical specifications for equipment in ST & D: Conductors, Cables Distribution Transformers, Energy Meters and HT Shunt Capacitors and associated control equipment.
Conclusion
GIS integrate common database operations such as query and statistical analysis with the unique visualization and geographic analysis benefits offered by maps. These abilities distinguish GIS from other information systems and make it valuable from explaining events, predicting outcomes and planning strategies for Distribution System Management. With these modern information technology tools, the power utility can be proactive rather than reactive.
GIS systems have had the reputation of being great technology for patient people. Building a data base for Distribution systems on geographical systems is a time consuming and laborious task and would have to be carried out in a phased manner but ultimately the returns would be manifold.
