Table 1. Previous Blackout Analysis
The modern and luxurious life styles with the increased automated machinery and devices have increased the demand for electrical energy. This has been one of the primary reasons to maintain prescribed standards in the field of electrical energy in terms of reliability, power quality, and stability of power system network. When such highly interconnected power system network experiences a disturbance like unbalances in load, frequencies, unnecessary tripping, or due to some external causes, it leads to unsynchronization with power grid effecting a massive damage to economy of the country. So it is important and necessary to have high secured power system. Even though Indian power system is well equipped, well designed with protection system, a massive power outage has been taken place in Mumbai in October 2020 leaving many areas affected. This paper describes a detailed study on Mumbai power outage 2020.
Modern electric power system is divided into three unitsgeneration, transmission, distribution. Thus electric power system became a most complex and massive network in protecting and safeguarding all the three components. Due to increasing demand of electric energy it grabbed a great importance in modern lives of automation. To operate such critical power system network, operating power system limits, stability constraints needed to be considered at every point of time. Even a small power interruption results in heavy losses in production, marketing field, interruptions in telecommunications and banking sector effecting in larger number of transactions, sudden stoppage of sensitive equipment like ventilators and other health operated devices in intensive care units may even ruin some lives. It is important to maintain perfect balance between generation and consumption because, when unbalance occurs in power system, there is a chance of blackout (Caplin, 2011; Hudedmani et al., 2019). A blackout leaves certain part of regions into dark affecting millions of people. Blackouts are majorly caused due to catastrophic failures, insulation failures, unbalances in load and frequencies, unnecessary tripping of lines and also caused by external causes like snow, ice, lightning and so on. This results in severe economic and technical loss to the country.
Therefore, a modern technology is developed with safe operation, fast automation systems, implementation of FACTS and HVDC concepts for improved power system, some advanced computer programs with intelligent and controlled algorithms were installed to avoid power outages and to ensure improved power system network.
Generally, blackouts is serious problem in power system irrespective of how long it is occurred and how intensified it is. As blackouts causes technical and economical aspects and the entire power system is highly interconnected there are some chances of getting larger consequences, increasing the number of switching actions in power system network to improve reliability of the system.
Previously, blackouts had been taken place in some countries due to different reasons and causes leaving much damage to the power system network and customers. However, studying and analyzing the past blackouts will help to minimize the future blackouts, decreases the probability of occurrence of blackouts and their results. Some of the severe and recent blackouts are mentioned and tabulated in the Table 1 along with causes.
Table 1. Previous Blackout Analysis
Two dangerous power outages in sequence affected the greater part of both northern and eastern India leaving 300 million people affected. The reason for blackout is such that circuit breakers on 400 kv Bina-Gwalior line which is feeding into Agra-Bareily transmission section tripped and cascaded power failures through the grid. And consequently all major power stations were shutted down in almost five affected states estimating shortage of 32 GW. And the system failed again due to problems in relay near Agra leading to shutdown of power stations across the affected parts of India.
Bheramara substation in Bangladesh cannot handle power capacity exceeding 400 MW. The loss of power at Bheramara reduced the frequency to 45 cycles per second and caused an electric surge that finally caused the blackout throughout the country.
One of the power transmission lines broken in an incident of rebel attack with tripping of 6000 MW of electricity.
The blackout in Turkey has taken place for duration of 8 hours. This is due to line maintenance on the main East-West corridor, connecting hydroelectric power rich Eastern Turkey. The remaining lines became overloaded after Osmanca-Kursunla line tripped because the system has been not in a (N-1) contingency.
Kenya blackout resulted in a loss of 180 MW of power and 44 million people got affected. This is due to the situation when a monkey fell on transformer at Gitaru Hydro electric power station and then tripped.
The blackout is due to electric current disruption - a disturbance on transmission side of Ungaran and Pemalang 500 kV line which resulted in energy transfer from east to west affecting 21.3 million people.
This blackout is due to vegetation fire occurred on the all three lines of 765 kV between Guridam, Hydro electric power plant and Malena substation leaving many people affected and every services got affected. Similarly, most of the other blackouts have taken place in different countries, however, only few of them are discussed in this paper (Haes Alhelou et al., 2019; Supriya et al., 2019).
It is important to learn about islanding schemes in order to understand how power outages impacts. Mumbai power islanding system has been developed in 1981 and Tata power supply executed the islanding system to save the city from blackouts in the events of grid failure and if so these blackouts will occur. It may lead to law and order problems too, as the city is densely populated and associated with serving as financial hub of the nation. The Mumbai islanding system is strong and unique with the guaranteed assurance of uninterruptable power supply to the whole city of Mumbai. It also saved Mumbai from nearly 27 blackouts and events in various different times with different technical problems associated with it. The system has been developed by TATA power supply with the following objectives: load generation balance, avoiding tripping of generators, load shedding with fast opening/ closing of designated feeders in order to match load generation balance and quick restoration of system with instantaneous isolation of all identified tie points.
In maintaining high and rich islanding system, frequency is serving as one of the critical parameters. If frequency of the system dropped, islanding system restores and sustains by having combination of under frequency control and power flow into the grid which will trigger the islanding scheme. Further it also provided islanding scheme coupling with reversal power flow. And similarly, if frequency of the system increases, auto restoration scheme helps to stabilize frequency of islanding system and maintains normal condition. If still, the islanding scheme fails to restore the system or isolate the system, backup islanding schemes, redundancy is provided for smooth power flow.
Suppose in case of grid failure, the Mumbai islanding system is highly capable enough to assure continuity of power supply to city. Even if there is a breakdown in the Western Regional Power Grid, Tata power supply system is isolated automatically from the rest of grid saving the power system network and minimizes the fault on network.
As electricity power grid is human made system, the errors and technical problems are quite natural but whatever it may be it is required to have proper protection system in order to safeguard electrical appliances and for hassle free human lives.
A massive power outage happened in the financial capital of India, Mumbai in October 2020 due to the failure in grid system. Basically, Indian power grid has five different regional based grids and these are of course synchronized to each other. This type of power outage has recorded as worst blackout over decades that too in a highly infrastructure state and most of the services got interrupted, customers got affected. Mainly, the sources of electric power in Mumbai were fulfilled by state-run Brihan mumbai electric supply and transport (BEST), Adani Electricity and TATA power supply into city with the customers of about 10.5 lakhs, 27 lakhs, 7 lakh customers respectively. It has been claimed that the power outage in Mumbai has been interrupted due to TATA's incoming supply failure, which has been one of the leading generation and distribution companies.
On the careful investigation, and according to the document issued by Tata power supply, it is evident that at around 10:00 am Maharashtra State Electricity Transmission Company Limited (MSETCL's) 400 KV transmission line got tripped at kalwa. This used to supply power to Mumbai and its surrounding areas such as Mumbai Central, Thane, Jogeshwari, Wadala, Chembur, Dadar, Kandavili and so on. And at the same time, according to Tata power supply, the Pune-Kalwa line has been under forced shut down since the previous day due to line to line fault (R-Y line fault in the system). Further, MSETCL called for emergency shutdown for second power line of capacity 400 kV Kalwa-Pagdhe and maintenance work started on Kalwa-Pagdhe line and estimated to clear the fault and planned to bring into original position after attending the fault but it has been failed. This led to tripping in third power line of Kalwa-Pagdhe which is carrying 634 MW. Consequently, Kalwa, Kharghar power plants also tripped along with heavy sparking leading to complete shutdown in Pune-Kharghar line. It is observed that Pune- Kharghar raised upto nearly 900 MW capacity and tripped by resulting in sudden load drop in Mumbai power system network. It is estimated that there is a total load loss of 2600 MW in Mumbai. The supply has been restored back by supplying power from three hydro units and Trombay gas and coal units. As soon as MSETCL transmission lines were connected and the entire power system network has been in stable condition.
Many years ago, when electric power came into existence, the power system network has been very limited and their operational and maintenance structure has not been much as complex as today's power system network (Parihar & Bhaskar, 2018). As the electric load demand has been in rise, deregulation of electric sector had taken place and eventually high secured protection for power system came into implementation.
However, in the past years, many blackouts had taken place, which were discussed in the earlier section. These blackout events led to sudden tripping of transmission lines, mal operation of various automatic switches, unnecessarily leading complexity in network and many more issues with huge loss of production to industries, interruption to domestic and commercial customers. The main root causes of every blackout have been studied carefully, various causes were investigated and proper protection schemes with advanced techniques are implemented. As a solution to cascaded events and cascaded tripping of transmission lines, modernization of power system with advanced schemes is preferred for reliable operation of power system.
It is necessary to keep focus on impacts of power blackouts because; the study on impacts derives technical and economic aspects of power systems. Due to multiple tripping and cascading events taken place on Kalwa- Padghe line, load has dropped down and suddenly there has been a major power cut in the city of Mumbai which took duration of nearly 8 to 10 hours for complete restoration of power supply. It has been estimated that around 50 Lakh domestic customers and commercial customers suffered power cuts.
As power outage is unplanned, uncertain and sudden, lot of services and customers got affected badly. Telecommunications and banking sector were completely halted, traffic lights and signals in some areas of the city stopped working. As the power breakdown happened in middle of peak hours, Mumbai Central, Suburban, Metropolitan trains came to standstill and remained for over four hours, forcing and advising the travelers, commuters to change their travel plan by at least one day. Eventually, hearings at Mumbai high court were postponed. Even Mumbai water supply to the households, and commercial customers who are located at far away from the region has been also impacted. The most severe impact was faced by Hospital Management System and hospitals. As Covid-19 pandemic is on rolls, many patients who are on ventilator and Intensive Care Units were affected. Health officials and Government instructed hospitals to arrange a suitable amount of fuel to provide power for the sake of patients for at least 8 to 10 hours of duration. Some patients were shifted to the other places where proper backup was provided. Mumbai disaster control team operated with the mobile diesel generators as standby for emergency purposes. Conduct of examinations in some areas of city got postponed. However, fortunately, Mumbai airport and Mumbai stock exchange remained unaffected from the power outage as they are protected by their own backup systems.
It is important and necessary to protect the Indian power grid and Indian power system as the most of the essential work rely on electricity. In order to ensure smooth and reliable operations the following system must be ensured: the islanding system with high sophisticated schemes, techniques to reduce isolation times in case of breakdowns, fast fault detection systems, regular maintenance with time to time monitoring, implementation of new updated technologies, adopting new concepts like incorporating FACTS controllers into transmission lines for smooth power flow, HVDC, smart grid technologies, advancements in safety and effective development in distributed energy sources, exploration of new technologies and its effects (Adibi & Martins, 2015; Jadhav et al., 2019). The interruptions rate should be minimized as much as possible to maximum extent. The redundancy technique, contingency analysis of transmission network will also help to assure reliability in the system.