Safe and efficient operation of power grids requires IT to provide real-time information on the state of the grid and communication technology for reliable and fast delivery of this critical information.

Today, utilities have undertaken large-scale deployment of supervisory control and data acquisition (SCADA) systems for real-time data transfer. As the deployment of SCADA systems leads to the issue of data latency, these installations need to be supported by an effective data communication system. A reliable communication network is required in transmission markets such as India, where availability-based tariffs (ABTs) and open access are being implemented for effective operations. Smart grids are another driver for the increasing adoption of communication technology.

Utilities are implementing projects based on wide area measurement system (WAMS) technology, involving phasor measurement units (PMUs), to understand the dynamics of the SCADA system. Communication systems are also needed for remote meter readings for distant renewable-energy-based power generating stations, line protection, geographic information system mapping and remote substation operations (unmanned substations). For internal activities such as using the management information system and enterprise resource planning, utilities use VoIP and intranet networks.

Evolution of communication

Initially, power demand was met through local generation. Subsequently, to increase the reliability of power supply, power plants were connected with transmission lines and voice communication networks (using public switched telecom network [PSTN] and power line carrier communication [PLCC]). This communication system was adequate for managing interconnected generators and preventing outages. As more elements were added to the transmission network, PLCC was used for meeting teleprinting, telemetering and teleprotection requirements.

Later, to communicate with isolated substations, telephone technologies such as very high frequency (VHF) and high frequency (HF) radio, satellite phones and microwaves were used. Subsequently, data acquisition systems were in-stalled using PSTN copper wires and GSM technology for automated pooling of energy data from various substations. To manage the increasing complexity of the transmission grid, utilities are now installing optic fibre for acquiring real-time data along with voice communication systems.

Available technologies

The communication technology for power systems has evolved over the years with PLCC being the oldest medium. PLCC is a dedicated, safe and economical system, and is part of utilities’ own transmission networks, thereby reducing dependence on service providers. Over the years, analog PLCC has given way to digital solutions. However, due to bandwidth limitations, the technology can transfer only a low-to-medium quantum of data. Utilities with large networks are also witnessing frequency congestion while using PLCC.

VHF wireless sets operate in open mode and, therefore, do not experience network congestion. Also, VHF can be used for contacting several users simultaneously. Utilities deploy this technology for load management in the distribution system. On the other hand, HF radio technology is used for communicating over long distances. However, both VHF and HF require licences for adoption. Another long distance communication tool is satellite phones. But these are expensive and require a licence for usage.

A relatively low-cost communication option is microwave. Though microwave has a high bandwidth, it requires a licence and line of sight for operations. It is also a weather-dependent technology. Leased copper lines have high bandwidth and are more reliable, but make utilities dependent on the service provider.

Optic fibre is one of the latest and most efficient communication technologies being deployed by power utilities globally. The use of optical ground wire (OPGW), a proven technology, ensures minimum additional load on transmission towers as it replaces the existing ground wire. Fittings/ Accessories for OPGW have already been standardised. The installation of OPGW is relatively faster as compared to other technologies, even in live line conditions. Further, it can be installed offline through a normal stringing method.

Unlike wireless, the internet, general packet radio service (GPRS) and leased lines, which do not provide adequate security of the system, optic fibre-based communication networks comprise dedicated links and are thus secured from public interference. Further, direct access to the cable can be easily detected through security surveillance, while remote access of the signal in the cable is impossible due to its dielectric nature.

The Indian experience

Most of the Indian transmission utilities, both at the central and state levels, have prepared plans to deploy modern communication technology for managing their grids efficiently.

At present, the central transmission utility (CTU), Power Grid Corporation of India Limited (Powergrid), operates a 25,000 km OPGW network. Over the next two-three years, it plans to replace its existing microwave hops with 20,000 km of OPGW and add another 20,000 km of OPGW for connecting its substations. For data acquisition through SCADA systems, the utility plans to deploy PLCC links between 132 kV and 66 kV substations and area/state control centres, VSAT links to connect important remote stations and control centres, an OPGW network on its 220 kV and above transmission network, and route data through redundant paths.

Powergrid plans to deploy high speed telecom transmission networks for developing a fibre optic transmission system along with a strong network management system; and use state-of-the-art plesiochronous digital hierarchy equipment for creating a wideband access telecom network.

The CTU plans to set up national transmission asset monitoring centres  to enable centralised monitoring, operation and management of all substations, and remote operation and management of transmission assets. It would provide 100 Mbps bandwidth between various control centres and the backbone network and 10 Mbps between substations and the backbone network, along with redundancy in the system. Powergrid’s telecom arm, POWERTEL, will provide MPLS technology and internet protocol/Ethernet-based virtual private networks for the project. The CTU will utilise its fibre network, which was developed under the Unified Load Despatch Centre scheme, as well as leased lines from telecom service providers wherever needed.

Powergrid is also implementing the Unified Real Time Dynamic Measurement System project, under which WAMS comprising PMUs will be installed. The scheme will help monitor events missed by the SCADA system, measure the stress on the grid and identify issues which may arise while increasing renewable energy injection into the grid. The system will have a latency requirement of 100 milliseconds from PMUs to the phasor data centre and around 1 TB of data per month will be transferred from 120 PMUs. In the second phase of this scheme, 10,000 km of OPGW will be installed.

Under the Smart City/Smart Grid project, the first pilot will be implemented in Puducherry, where Powergrid will set up systems for smart public services. The communication needs for such a project are optic/copper wire and wireless technology.

State-owned transmission utility Gujarat Energy Transmission Corporation Limited (GETCO) plans to phase out first- and second-generation technologies such as PLCC and microwave with third-generation technologies like OPGW. GETCO is installing OPGW on all new 400 kV lines for communication, protection, control and SCADA as well as on its strategic transmission network. It also plans to establish a communication network for WAMS. For remote ABT meter reading, the state transco will utilise GPRS connectivity.

Challenges

India is yet to develop a clear road map/regulation for using telecom in the power sector. It also needs to develop its own standards for communications infrastructure, which will form the basis for interoperability, cyber security, etc. Indian transmission utilities need to identify their communication needs in parallel instead of an “add-on” to transmission planning as retrofitting communication infrastructure is usually costlier than incorporating it right at the transmission planning stage.

Based on presentations by

P.K. Agarwal, Deputy General Manager, National Regional Load Despatch Centre, Power System Operation Corporation;

H.S. Kaushal, Chief Manager, Load Despatch and Control, Powergrid; and

R.P. Satani, Deputy Engineer, Engineering, GETCO, at a Power Line conference on Telecom Needs for the Power Sector