Digital Substations

Enabling greater control and efficiency in operations

Digitalisation is a fast emerging trend in the power sector, driven by the need to introduce efficiency in grid operations and maintenance (O&M). In recent years, although automated systems have largely replaced conventional equipment in modern substations, there is still a significant amount of conventional equipment and copper wiring at the bay and process levels, and between primary and secondary equipment. Digital substations are simpler, more compact and safer than conventional substations. These substations have an optical fibre communication backbone in place of traditional copper connections. With benefits such as increased flexibility and availability, reduced cost, and lower risk and environmental impact, digital substations are among the key emerging trends in the power industry.

Architecture

Digital substations comprise smart primary devices and intelligent electronic devices (IEDs) to achieve information sharing and interoperability centred on the IEC 61850 protocol. An IED is a microprocessor-based protection and control device for power equipment, such as circuit breakers, transformers and capacitor banks.

The architecture of a digital substation has three levels – process, protection and control, and station. The implementation of the process bus is a crucial element of digital substation architecture. The process bus, based on IEC 61850, allows the deployment of optical fibre network in place of copper wiring between IEDs and various other devices. Therefore, the substation’s status and performance parameters can be shared in real time through digital signals without complicated wiring.

At the protection and control level, secondary equipment such as numerical relays interact with the field via process bus and with the digital control system via the station bus. At the station level, operations, engineering functions and reporting take place. The devices at this level include gateways, remote terminal units (RTUs) and engineering workstations.

The IEC 61850 optical network operates using Ethernet protocol. Within this framework, traditional digital signals are transmitted using a generic object-oriented substation event (GOOSE). GOOSE replaces conventional binary inputs and outputs with digital models and enables signals to be transmitted in a specific time period. This is essential to ensure the reliability and timely operation of interconnected IEDs.

Switchgear digitalisation

In order to achieve the maximum benefits from a digital substation, digitalisation of primary components like transformers as well as high and medium voltage switchgear is necessary. There are solutions that help to integrate control and protection IEDs with the switchgear in substations. More advanced switchgear has digital current and voltage sensors integrated into each panel, along with IEDs compatible with the IEC 61850 protocol. This aids in monitoring the function of the switchgear continuously, thereby giving advance warning when critical current flows and enabling predictive maintenance.

Benefits

Digital substations come with a range of benefits for utilities. These include higher efficiency, lesser space requirement, greater reliability of equipment and better safety. Since digital substations are equipped with features of remote monitoring and diagnostics, utilities can evaluate their performance continuously. Grid operators can, therefore, detect anomalies and plan maintenance in advance to prevent substation breakdowns. In contrast, conventional substations rely on traditional diagnostic methods wherein corrective action is taken after a failure. In addition, digital substations have enhanced features to ensure cybersecurity as its system data management software continuously looks for possible cyberthreats. Further, digital substations are equipped with a number of sensors that help mitigate transient stresses.

Also, digitalising can reduce the quantity of copper in air-insulated switchgear substations by 80 per cent through the use of fibre optics. In addition, it helps reduce the space requirement at the relay house by up to 60 per cent, the outage time by up to 50 per cent, the carbon footprint by up to 50 per cent, and the installation time by up to 40 per cent. This represents significant cost savings for utilities. Besides, digital substations are equipped with current and voltage sensors, which do not require regular maintenance or calibration. In contrast, traditional substations require large and bulky testing equipment that needs to be properly calibrated. Further, digitalised communications within a substation can increase control, facilitate the integration of intermittent renewables and improve safety.

In the coming years, the availability of advanced communication solutions, platforms to run analytics at high speed, cheaper sensors, and software to handle large amounts of data are expected to drive the growth of digital substations.

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