The transmission segment in India has witnessed significant growth over the past few years, both in terms of size and technology uptake. So far, the supervisory control and data acquisition (SCADA) system has been the key technology used by transmission utilities to monitor the energy flow in the grid. The complexities in grid operations have increased owing to greater renewable integration, growing number of distributed energy sources (mostly connected at the distribution level), and growth in power demand and limited transmission network capacity. Therefore, there is a need for new monitoring methods and technologies. Recent advancements in communications and analytics technologies have led to the deployment of new solutions, resulting in improved grid management. These include the wide area monitoring system (WAMS) and phasor management units (PMUs). The Smart Grid Vision and Roadmap for India document prepared by the Ministry of Power in 2013 stated that WAMS and PMUs should be implemented for the entire transmission system. The roadmap also focused on the indigenisation of WAMS and PMU technology.
To this end, the Unified Real Time Dynamic State Measurement (URTDSM) project is being undertaken by Power Grid Corporation of India Limited (Powergrid). It is one of the biggest projects of its kind across the globe. Over 1,600 PMUs are planned to be installed across the country under the project. While the progress has been slow so far, the project is expected to significantly enhance grid management once it is completed.
WAMS and PMU
WAMS is based on phasor measurement technology for data acquisition. It consists of four key elements – PMUs, phasor data concentrators (PDCs), communication networks and analytical software. PMUs are devices that measure electricity flow, voltage and current magnitude, frequency levels, and rate of change of frequency and phase angle through the grid using a common time source for synchronised data collection. In a typical WAMS network, PMUs are strategically placed throughout the electricity grid, covering the diverse network. The PDCs, which are centrally located in the system, collect information from PMUs through a communication network. The PDCs send this synchrophasor data to state load despatch centres, which in turn send it to regional load despatch centres and subsequently to the National Load Despatch Centre. They also raise an alarm during emergency situations and facilitate smooth grid operations. The alarm helps prevent network-related disturbances to spread to larger areas. WAMS also allows real-time monitoring of the transmission system over wide areas, which helps detect and counteract any grid instability that comes up. It not only addresses reliability concerns, but also resolves operational issues by power transfer capacity and blocking/deblocking of distance relay zones during power swings on a real-time basis. The PMUs usually report data at the rate of 25 to 30 samples per second while the traditional SCADA system collects data only once in 10 seconds. Therefore, PMUs are able to capture and provide data related to frequency differences that last for even a fraction of a second. The SCADA system has the capability to provide only a steady-state view of the power system, while PMUs facilitate real-time measurements and dynamic visualisation of the power system.
A WAMS pilot project was undertaken in the northern grid from April 2010 to May 2011, under which PMUs were installed across eight substations. Subsequently, similar projects were initiated in other regions and a total of 64 PMUs were installed. Following the successful implementation of pilot projects, the URTDSM project was rolled out in 2012 to improve system operation through the implementation of WAMS. Under the project, 1,669 PMUs along with 32 PDCs are planned to be installed as a part of the control centres across the five regional grids. Of these, 929 PMUs will be installed at the interstate transmission system and 740 PMUs at the state transmission utility network. Further, 57 PDCs and 16 remote consoles are planned to be installed under the project.
In addition, the project involves setting up a communication network. The communication infrastructure forms the backbone of the project. The PMUs are connected to the control centres over the communication network and any disturbance in the communication network will lead to failure of the complete system. The communication network under this project is proposed to be built on optic fibre technology, which offers low latency due to its high bandwidth.
Two packages have been awarded for implementing the project – Package I for the northern, eastern and north-eastern regions and Package II for the western and southern regions. The packages have been awarded to Alstom SAS (France), Alstom Grid (UK) and GE T&D India Limited (earlier known as Alstom T&D India).
The project is planned to be implemented in two phases based on the availability of the existing and upcoming fibre optic communication links. Around 1,186 PMUs are planned to be installed under Phase I of the project and the remaining 483 under Phase II. The total cost for setting up the WAMS under the project is estimated at Rs 2.39 billion. Of this, about Rs 1.7 billion is for Phase I and the remaining for Phase II. The cost of the communication system (optic fibre and communication terminals) is estimated at Rs 1.16 billion.
The project was awarded in January 2014 and was scheduled to be completed within 24 months. However, it has faced several delays due to slow implementation. Phase I, which was scheduled to be completed in 2014-15, is still under implementation. So far, surveys for identifying PMU and PDC locations (except a few locations) have been undertaken and about 450 PMUs have been installed. Over 1,000 PMUs are reportedly under various stages of implementation. Meanwhile, analytics software planned under the project has been developed.
One of the challenges faced during the implementation has been the reluctance of power producers to install PMUs at their sites. Further, the number of PMUs to be installed is being continuously revised with new substations coming online. This has led to a lot of rework in the contract with Alstom and thus delays in the execution of the project.
Meanwhile, Powergrid had submitted a petition to the Central Electricity Regulatory Commission (CERC) to obtain regulatory approval for the implementation of Phase II of the URTDSM. The commission denied approval for Phase II in September 2016 in view of the delay in the execution of Phase I. The CERC had directed Powergrid to expedite the works under Phase I and seek approval for Phase II only after substantial progress had been made under Phase I.
While the project roll-out has no doubt been slow, once commissioned, it promises to improve grid management. The PMUs being deployed under the URTDSM project will provide real-time measurements and reduce the dependence on estimates for managing energy flow in the grid. This will ease the congestion in the corridors, improve transmission asset utilisation and lower the energy costs for consumers. With the implementation of WAMS and the increase in the cleared volume of electricity, revenues are estimated to increase by Rs 7.3 billion over a minimum period of 20 years. WAMS will also help in the large-scale integration of renewable energy sources. Moreover, these solutions will set a benchmark for smart grid technologies in the transmission segment.