Frontiers of Technology in Transmission and Distribution Automation

Introduction

Modern electricity grid is being powered by growing number of DERs (Distributed Energy Resources). DERs supply energy from the edge of the grid, close to load centers, to the local distribution grid and also to the transmission grid, in a bidirectional electricity flow. Integration of DERs into the grid necessitates a compatible design with high level automation of the T&D systems that facilitates bidirectional flow, new measurements, controls and protection. Advancements in T&D substation automation, protection, and control systems are pivotal in decarbonizing the electricity grid while maintaining its stability and security.

Significant advancements have been observed in recent years in T&D systems to enhance grid stability in the wake of integration of DERs, BESS (Battery Energy Storage Systems), and Electric Vehicles (EV). Innovative technologies driven by research and development are leading the way in modernizing the grid, building efficiency, improving reliability and accelerating energy transition, as explained in this paper.

Digital Substations

Digital substations replace conventional analog communication with digital communications which enhances efficiency and reliability. They use advanced sensors, automation, and communication technologies to monitor and control electrical equipment in real-time to optimize substation asset performance, reduce outages, and improve reliability.

They support the integration of RE sources and provide flexibility and responsiveness in managing variable power inputs, control systems and grid protection. They support real-time data integration, analytics and faster decision-making, which helps in reducing maintenance costs, increasing asset safety and reliability. IEC 61850 international standard ensures multi-vendor interoperability between Intelligent Electronic Devices (IEDs) within the digital substation. The key benefits of digital substations are enhanced safety and protection, improved monitoring with real-time data, asset optimization, reduced downtime and lesser maintenance costs.

Volt/VAR optimization (VVO) 

For an efficient distribution grid operation, it is critical to manage both voltage levels and reactive power using VVO. This helps in reducing system losses and controlling peak demand. In VVO, voltage control devices at the substation are used to reduce the voltage drop from the substation to the load end and maintain the service voltage to customers within defined limits. VVO reduces peak demand, optimizes energy consumption and increases power throughput from reactive power management. The efficiency gains are realized from a reduction in the system voltage and power losses.

Phasor Measurement Units (PMUs)

PMUs are used for transmission system monitoring, control and protection. They measure time-stamped voltage and current phasors using synchronized GPS clock. The time-synchronized PMUs provide real-time observability and state estimation of the transmission system, enabling operators to assess the state of the network and respond quickly to grid disturbances.  These values help smart grid adaptive VVO solutions to be more accurate. PMUs transmits time-synchronized data from geographically diverse network locations to the Wide Area Monitoring, Protection and Control System (WAMPACS) or WAMS.   

Wide-Area Monitoring System (WAMS)

Transmission SCADA (Supervisory Control and Data Acquisition) system is used for high-level monitoring and control of the grid. However, due to structural changes in the grid to cope with demand volatility and growing integration of renewable energy systems, SCADA alone is not sufficient and WAMS is used to monitor fast system transients in modern power systems. 

WAMS receives dynamic phasor data (voltage, current and frequency) from PMUs which are used to monitor the grid in real-time, detect fluctuations and identify vulnerabilities. With this data, WAMS keeps track of network situational awareness and maintains grid stability at all times, and particularly during unpredictable generation and volatile demands.

Supervisory Control and Data Acquisition (SCADA)

The primary function of SCADA is data acquisition, processing, visualization and control of T&D parameters from across the network, to enable safe and reliable T&D operations. The Arithme­tic Logic Unit (ALU) in SCADA is used for Automatic Demand Response (ADR) management, condition-based load shedding, voltage, load and frequency monitoring. The Control Unit (CU) in SCADA is used for grid protection, circuit switching and fault restoration. SCADA application can manage grid contingencies, protect the grid against voltage or load overshoots, prevent cascade trippings, and balance electricity demand.  Advanced SCADA includes automated tools e.g. Advanced Distribution Management System (ADMS) and Energy Management System (EMS), for energy accounting, dispatch scheduling, feeder management, demand response, voltage and frequency control, and grid balancing.  

Innovations in Grid Modernization

Most leading innovations in grid modernization are aimed to make it more resilient (self-healing), adaptive (flexible), secure and reliable, with the help of the following technologies: 

• Solid-State Transformers (SSTs): SSTs have emerged as a better alternative to traditional transformers. They use solid-state electronics, enabling better control of voltage and current, bidirectional power flow, integration of RE sources and grid decarbonization. 

• Battery Energy Storage System (BESS): Digital Substations, equipped with battery energy storage systems, provide the ability to manage peak loads, stabilize voltage, regulate frequency, provide backup during power outages and improve reliability.

• Automatic Power Factor Correction (APFC): Inductive loads require active power (KW) to perform actual work, and reactive power (KVAR) to maintain the magnetic field. Though reactive power is necessary for inductive loads, it imposes an undesirable burden on supply by causing the current to be out of phase with the voltage. APFC calculates the reactive power consumed by inductive load and compensates the lagging power factor using capacitor bank. Low PF can be due to significant phase difference between voltage and current at load terminals or harmonic distortions, which can be improved by APFC or harmonic filters.

• Advanced Charging Infrastructure: Modern substations are being upgraded to support the increasing demand from EV (Electric Vehicle) charging stations. The transition to electric mobility is one of the strategies to decarbonize the transport sector, and the grid has to adapt and be flexible enough to support the load of EVs while charging, without affecting grid stability.   

• Internet of Things (IoT) in Grid Management: IoT facilitates real-time monitoring of the grid with the help of sensors deployed across T&D network to capture real-time voltage, current, and other parameters. IoT data is transmitted in real-time to monitor grid health, detect abnormalities, proactively address network issues and conduct predictive maintenance. IoT sensors help in implementing demand response programs for efficient grid management, monitor grid disturbances and reduce peak loads. IoT can be leveraged to integrate DERs, BESS and EVs seamlessly into the grid.

Conclusion

The technologies discussed in this whitepaper are critical for creating future smart and stable T&D grid infrastructure, which are safe and reliable, and adaptive to variable DER connections without compromising grid stability and quality of supply. Enabled by innovative research and development, the future grid ecosystem aims to achieve the key result areas (KPIs), namely:

• Enhanced Grid Reliability: Reduction in outages and improved response times to disturbances, with real-time monitoring, control and protection

• Increased Grid Flexibility: Capacity to add DERs on demand with increased flexibility, and quickly adapt to unpredictable changes during volatile demand and unpredictable DER connections

• Operational Efficiency: Optimized asset utilization, operational cost savings, better network observability and safe, full-automated controls