Many advanced countries have achieved industrial and social progress by ensuring uniform development in all spheres. India, as a developing nation, has achieved great progress in many spheres of scientific and technological fields including atomic energy, and currently has forayed into information technology also. However, India lags behind in modernising infrastructure industries. This fact has been realised, and recently a lot of stress is being laid on improving and modernising the infrastructure industries. Automation is the key to modernisation and has now been conceptually understood as a way to increase efficiency and improve productivity. Consequently, automation is becoming an integral part of most of the process industries including the power generation process. However, in India, automation remains a far cry in the field of electrical power transmission and distribution. This has naturally resulted in reduced efficiency and productivity in the core sector of our infrastructure. With quality awareness becoming the watchword all over, consumers demand better quality and they are willing to pay for the same. With this development in consumers preferences, quality improvement in the power supply industry has become absolutely essential. In this article, an attempt is made to review the recent advances in substations control and automation. Efficient operation and monitoring of high voltage and low voltage substations is very important for the improvement of power quality, which means ensuring power supply at the proper voltage and frequency with the least number and duration of interruptions and with minimum spikes. This article evolves the need for an integrated approach for substation automation and finally proposes an integrated substation control system (ISCS) as the final objective of substation automation; the intention is not to devise strategies for an unmanned operation of substations, but to supplement the operator with more knowledge, data and facilities and to help him to be more effective in his operations. The article also discusses the approach for substation automation in Indian context. The requirement for suitable substation design and staff training is also discussed. The problems of financing and return on investment are also briefly discussed.
There are many aspects to the management of an electrical network. The primary function of the transmission network is the interconnection of all the generating stations to the load centres across a large geographical area. Control of active and reactive power flows, reliable and fast fault isolation, and stability of the network under transient conditions (resulting from fault and switching operations) are the major issues of concern. The distribution network on the other hand distributes the power at a load centre to the various load points at acceptable levels of voltage, frequency and reliability. Total circuit lengths of a distribution network is at least twice as much as a transmission network with probably 20 times more nodal points. The substations in the network link the transmission network to the distribution networks. These substations require constant monitoring locally, and also from the transmission and distribution control centres to ensure overall effectiveness of the electrical network control and management.
As in many advanced countries, the importance of transmission network control was realised as the network grew in size with increased operational problems. Many Indian utilities went in for centralised load despatch centre. Gradually, a few of these utilities commissioned Supervisory Control and Data Acquisition (SCADA) systems with remote terminal units at major substations and a computerised Master Station at the Central Load Despatch Centre. Power Grid Corporation of India spearheaded further progress in this area by proposing and commissioning large SCADA/EMS centres at the national and regional levels. In the area of Distribution Networks, Rural Electric Corporation of India have put in their best efforts in standardising the Rural Load Management System requirements. Several utilities are well on their way to implement these systems to monitor and control the low voltage distribution networks in the rural and agricultural areas. A comprehensive Distribution Management System with its associated Geographic Information Systems, Automated Mapping and Facilities Management systems (GIS/AM/FM) is also being planned by a few utilities.
Remote control requirements
In a power system, requirements of remote control facility arise from different considerations. Some of them are:
- to keep a safe distance from the power equipment
- to have a reliable data logging device
- to have a centralised control of different equipment
- to obtain unmanned operation at some sites
- to have a centralised control of a network.
In India, both in industrial and utility areas of electrical power generation and distribution, unmanned operation is never a major issue. However, collection of reliable data for operation and planning was always a problem. The problem is more severe when data is affected during electrical faults associated with fast transients.
Requirements of substation control
As mentioned earlier, overall network management systems will have to be complimented by an equally efficient monitoring and control of the substations. The requirements of the substations on their own have also prompted development of many sophisticated devices in interlocking, protection, monitoring, recording and metering areas. Initial remote control and automation schemes for substations were hard-wired systems. With advent of microprocessors, logic circuits became easily programmable and simplified. Programmable Logic Controllers (PLCs) and Distributed Controlled Systems (DCS) were sone of the developments which took place in many process industries including power plants. Many of the above features were getting concentrated on a single integrated device, which is now known to the industry as Intelligent Electronic Device or IED. The advancement in substation control devices started in the area of protection. The electromagnetic relays went through an evolutionary process. Relays were provided with manual reset, master reset, self reset, and remote reset facilities. Multifunction relays and self-diagnostic relays were the next steps leading to solid state and numerical protection schemes. Programmability was also achieved to set the relay accurately on site. As protection schemes got advanced to facilitate early detection of electrical faults and fast clearance of the same, the number of protective devices increased. For example, a fault in a transformer was to be detected by one or more of the following protective devices:
- Transformer differential protection
- Restricted earth fault protection
- Overflux protection
- Earth fault protection
Every one of these schemes is required to measure the current and/or voltage on the protected circuit. One idea was to collect all voltages and currents at once with high resolution and accuracy and supply these values as required to all the other devices including the metering devices. Next step was to integrate all the protection in one IED. Many times it was required for devices to inter-operate with each other like in the case of an inter-tripping scheme. This led to the facility of communication port for these devices. With communication ports available in most of these protection and metering devices, the next step was to link them through a local area network to a desktop PC, with man-machine and graphics user interfaces. This is one way of evolution of integrated Substation Control System. Some suppliers of such systems have even provided interfaces to communicate with a remote master at Load Despatch Centres with their IEDs behaving more like remote terminal units (RTUs). One major disadvantage with these IED-based systems was that they were all proprietory systems. They had very little interoperability with systems of other manufacturers, and sometimes even with the latter versions of the same manufacture.
With the provision of several relays for different protective functions, monitoring of these relay indications was facilitated by installing annunciation panels to centralise all the alarms and indications. These indications and alarms needed to be sequentially time-tagged to properly analyse the fault and to check for the correct operation of the protection scheme. This led to the requirement of sequence events loggers. Some selected events and measurements were required to be tracked through the fault incidence, with a very high resolution and with some pre-fault history also. This requirement was met by the provision of Disturbance Recorders for tracking selected events and measurements during the pre/post periods of the triggering events.