An Energy Transition Energy Transition Roadmap for Electrical Utilities Dimension 2: Technology

In our previous blog post discussing the Energy Transition Roadmap for Electrical Utilities, we looked at challenges and solutions for achieving Energy Transition objectives for the fundamental aspects of power systems – namely power generation, transmission and distribution, and customer demand. Today, we shift our focus to the technology needed to monitor and control electrical resources on the grid, and how they need to evolve in the Energy Transition journey.

There are many aspects of this Technology dimension:

Power Production is monitored by an Energy Management System (EMS)
Transmission Grid is monitored by a Transmission Management System (TMS)
Distribution Grid is monitored by a Distribution Management System (DMS), and more extensively these days by an Advanced Distribution Management System (ADMS).
Distributed Energy Resources (DERs) may be monitored by Distributed Energy Resource Management Systems (DERMS).

Providing Context - Stability through Inertia

For many decades the stability of the power system depended on the inertia of the large generators. Using reverse frequency droop settings on the governors of the generating units allowed for countering the results of faults on the system. If there was a loss of a large generator, it meant that there was more load than generation. This would cause the frequency to start reducing. The reduction in frequency would automatically cause the online generating units to produce more power to counteract the drop in frequency. This nearly immediate automatic response was then backed up by other system responses such as commanding the setpoints of other generators to increase to counteract the drop in generation. This resulted in the system remaining at a stable frequency and becoming rebalanced. On the other hand, if a large load was lost, the frequency would rise, the amount of generation would be automatically reduced, and the system would respond by lowering other generating unit setpoints.

An underlying principle of this methodology was the substantial inertia of the numerous large generating unit rotors that tended to keep spinning as required. This worked for many decades until entities began adding renewable generation, such as wind farms and solar farms - power resources that did not come with large inertia. The renewable generation resources may have had frequency control in the invertors connecting them to the grid, but in the early days of renewable generation operation, it was standard operating procedure to command them to disconnect from the system during faults. However, the loss of the renewable generation could worsen the frequency problem or make it better, depending on the fault type. If the fault was a loss of generation, then dumping more generation would make the problem worse. If the fault was a loss of load, dumping the renewable generation would make the system better.

Defining the Problem

The Renewable Energy Challenge - As the penetration of renewable generation is growing, power system engineers are modifying their approach to operating these resources. There is ongoing research and testing, and Grid Forming Inverters are being proposed as a solution. Grid forming inverters enable renewable generation resources to partly act as inertia-based resources. This means that a particular renewable generation resource can reduce generation in the event of a loss of load. However, in order for renewable generation to increase the output in response to loss of generation elsewhere, it must have some kind of energy storage that is rapidly available, such as a Battery Energy Storage Systems (BESS). A renewable resource with BESS that has enough energy stored can provide a reverse frequency droop characteristic in response to a fault on the system. Research is still needed on how the rapid frequency change is handled by the power electronics of the solar inverters or the wind farm convertors.

The key takeaway from this discussion is that as the system shifts to a large mix of renewable energy resources, it must also be built with tools that allow the power system to remain stable in response to faults.

Fault Current Detection - The other side of the question of inertia is related to faults on the system that can result in short circuit currents. Traditional rotor-based generators provide high short circuit currents into a fault because of their inherent large inertia. Renewable Energy Resources do not provide high short circuit currents in the same way, because they are connected to the grid through electronic based inverters. The lack of high short circuit currents in the event of a fault has detrimental effects on fault coordination, which is based on protection relays reading the high short circuit currents. While research is still ongoing in solving this challenge through novel protection schemes and relays, BESS could once again be a potential solution. For example, if a large solar farm also has BESS, this could enable it to shift the load and provide additional current into a fault to enable the protection systems to work.

Voltage Support - The other aspect of power systems is voltage support. The system needs reactive power to ensure that the voltage profiles of the system are within acceptable limits and that the power will flow from the resources to the loads. This means that large renewable resources have to be planned with reactive resources as required. Many Wind Farms and some Solar Farms have been built with additional Reactive and Capacitive resources. The amount needed will be dependent on the existing voltage situation in the Grid. Voltage support may require the addition of reactive resources on site at the Wind/Solar resources.

Planning & Load Balancing - The historical procedure for day-to-day planning is to perform load forecasts based on weather and factor in any planned outages. This ensures there is power available to supply the load as it varies during the day according to normally expected load curves, and when affected by weather and unusual events. A given self-contained area will ensure that it balances its load and generation throughout the day as well as its purchase/sales of power with other entities. The area interties are planned with neighbours, and these planned flows are compared with actual flows on the interties to adjust internal generation. The difference between planned interchange and actual interchange is called the Area Control Error (ACE). The North American Electric Reliability Corporation (NERC) rules require each area to keep ACE near zero and take action to return it to zero when it diverges.

To summarize, the work of monitoring, analyzing and controlling a power system network involves the following main issues:

Generation load balancing for frequency stability
ACE management for additional generation-load balancing
Reactive power placement and availability for voltage stability
Use of Generation inertia and relay protection to respond to system faults
Ensuring that sufficient generation is available for rapid deployment for response to contingencies but also scheduled and available to follow load profiles
Scheduling and directing generation changes to follow the load curve
Analyzing and preparing to react to new contingencies when the system experiences a contingency and may be in an unusual state

The Bulk Electrical System and Energy Transition

Renewable generation is intermittent and, while it can be predicted somewhat accurately, a bulk electrical system with high penetration of renewable generation must always have backup generation ready to replace large amounts that may be lost. It will be necessary to have bulk-level BESS or similar storage available to mitigate the effects of rapid loss or change in output levels of renewable generation. The loss of renewable generation may also mean that the replacement generation is located in different areas, changing the pattern of flow within the power system.

System Response and Contingencies

The main issue with the transmission grid is that multiple contingencies from strong storms can make system response very complex or result in a large reduction in the BESS energy available. Hydrogen is being proposed as the Energy Transition replacement for natural gas-fired generation. This requires an excess of renewable generation to manufacture enough hydrogen for use during minimal availability of renewables and limited storage.

Monitoring, Analysis, and Control on the Generation Level

It will be important to have extensive weather monitoring along with AI pattern analysis. Utilities can rely on weather forecasters to plan from 7 days to 1 or 2 days ahead, but they will need large arrays of measurement points utilized by all utilities to understand upcoming conditions for more immediate planning.

Weather Monitoring and AI Integration

Large solar/wind monitoring arrays within a utility’s footprint will allow the utility to understand local wind and cloud cover and how it is moving, enabling more accurate predictions of renewable outputs and localized temperature changes. AI will be trained to provide predictions that can be compared with actual measurements for continuous improvement. Utilities can optimize their other generation alongside more accurate forecasting of intermittent generation to better use their storage, allowing for smoother generation changes and more efficient hydrogen generation planning.

Data Collection and Simulation

Data collected from monitoring can be tested in simulations to refine a utility’s understanding of operations concerning the sun, clouds, wind, and storage, improving efficiency over time. Utilities will also be able to use simulations of faults in different places to learn how to respond effectively to different combinations of generation, storage, and load, aiding in arranging reactive power resources to support voltage as power flow patterns change.

Existing and Needed Tools

Currently, utilities use numerous tools for monitoring, analyzing, and simulating to effectively plan, operate, and respond to contingencies. These include power flow, state estimation, contingency analysis, reliability assessment, simulations, and transient stability analysis. Utilities use tools to optimize the use of generation based on cost and fuel availability, and other factors and tools for optimizing reactive resources to maintain voltage profiles.

Flexible AC Transmission System (FACTS)

FACTS devices assist with controlling reactive flow. Utilities will continue to need these tools and substation monitoring while using additional monitoring of transmission lines to enable real-time thermal ratings.

Additional Requirements

Utilities will need to add large arrays of weather monitoring for wind and cloud cover. AI tools with large capacities are required to handle the vast amount of real-time information about actual wind/solar conditions and predictions. This will enable utilities to forecast intermittent resource production and optimize storage use more precisely.

Simulation Tools for Optimization

Since weather patterns vary, utilities may also need to simulate how wind and sun resources vary based on historical data to improve storage and hydrogen production optimization. Continued use of simulation tools will help understand different faults and system responses, with research on Grid Forming Inverters to ensure they respond effectively to contingencies.

Inverter Based Resources (IBRs)

Research indicates that IBRs may respond to system issues differently depending on the problem. System monitoring (e.g. use of field Phasor Measurement Units (PMUs) with very fast communications and central processing) must rapidly understand and inform IBRs of the exact problem (e.g., a single-phase fault on Phase A) to enable precise responses (e.g., injecting extra current on Phase A to interrupt the fault). This must occur within milliseconds, utilizing the smart software of IBRs for effective system support.

Distribution System and Energy Transition

The Energy Transition will significantly impact the distribution system. The presence of substantial renewable/intermittent resources on the distribution network may result in two-way power flows. Currently, power flows from generation through the transmission system and into the distribution system on a one-way trip to customers. Adding solar/wind to the distribution system along with BESS and other storage types will radically change power flows, potentially opening an energy market at the distribution level and introducing Distribution System Operators (DSOs).

Fault Response on the Distribution System

Currently, renewable power generation disconnects from the distribution feeder during faults, typically in response to zero voltage. This means renewable power is lost unless local BESS charges up. Traditional distribution utility responses to faults involve opening breakers feeding the fault. Many utilities now use feeder reconfiguration with automated/controllable switches, identifying fault locations, opening switches to isolate the faulted section, and re-energizing unaffected segments.

Advanced Distribution Management Systems (ADMS)

Utilities use networked meter reading for hourly meter readings and last gasp detection to identify power loss or faults. Smart meters providing additional interval data within the hour would help utilities analyze and understand customer loads, facilitated by AI tools marketed by various companies.

Outage Management Systems (OMS)

Most utilities have an OMS that utilizes data from controllable switches and meters to reconfigure systems automatically or recommend switching orders to return to normal configurations. The OMS often works in conjunction with an ADMS, which uses SCADA systems for extensive data management, incorporating data from Distributed Energy Resources (DERs) and providing it to Distributed Energy Resource Management (DERMS) tools.

Virtual Power Plants (VPP)

Many entities have created VPPs, conglomerates of numerous customers creating virtual resources. These include customers allowing load control during peak times, grouping small solar or wind resources with BESS for extra utility. Combined with renewable resources, BESS, and controllable load, VPPs form versatile resources, requiring extensive communication points and data management for effective monitoring and control.

Future of the Distribution System

The distribution system of the future may exhibit varying load curves daily due to sun, wind, temperature, and market conditions. Feeder protection systems must adapt to manage resources larger than loads, with power flowing back to substations. Utilities might find it beneficial to have large BESS at transmission substations to act as buffers, smoothing out load shifts and easing transmission system management.

Comprehensive Monitoring Needs

While the transmission systems will continue to monitor substations, capacitor banks, and FACTS devices, adding BESS and advanced monitoring to handle unpredictable load curves, distribution systems must monitor, understand, and analyze a larger number of status and analog points from numerous sites, controlling more devices and issuing requests to numerous devices.

Market and Communication Integration

A market will mediate the costs of resources and loads participating in it, while working with regular loads not engaged in the market. Effective operation will require extensive communication points, high-speed data processing, and secure, corruption-free data exchange.

The Grid Edge

Monitoring transmission and distribution facilities with intelligent measuring devices (e.g., detailed transformer monitoring, advanced line monitoring, real-time monitoring of important load/gen/BESS customers).
Physical control: switchable line devices (breakers, smart grid switches), controllable load/gen/BESS sites.
Utility requests: asking customers to adjust their load/gen/BESS, general requests for emergency assistance, potentially communicating directly with customers' smart controllers.
Price Signals: sending customers distribution-level load/gen/BESS price signals.
Transmission level: continued generation/substation/transmission monitoring with additional monitoring (e.g., using PMUs for power angle monitoring) to enable accurate instructions to Grid Forming inverters.

Control Centers:

Increased communication connectivity to the system.
Interaction with power markets and their price signals to predict power flow trends and load centers with more complex load profiles, learning from weather impacts on them.
Intelligent power forecasts for wind/solar to manage changes in storage use and hydrogen generation.
Monitoring IBR-based resources to determine fault current adequacy settings.
Using existing power system monitoring tools like state estimation, Volt/Var system balancing, and contingency tools that account for Grid Forming inverters' responses to different system issues, and synchronous condensers.
Rapidly responding to system contingencies with instructions to resources and loads within milliseconds.

Communications:

Utilizing various telecom technologies for rapid data interchange, ensuring real-time data availability to all entities.
Exchanging historical data like load, use, weather, and solar/wind patterns.

Overall, achieving effective Energy Transition goals requires a coordinated effort across all facets of the transmission and distribution systems, supported by advanced monitoring, AI integration, and robust communication infrastructure.

Acumen has a team of professionals dedicated to helping utilities create a path to enable the Energy Transition. Book a call today with experts from our Operations Technology team to better deal with the technological challenges of this once in a generation energy transition!