Driving the Evolution of PAC Systems – your questions answered!

Angela P P, Lead Asset Lifecycle Engineer – HVDC, National Grid, UK: Most TSOs use a mix of simulation environments that support both RMS level and electromagnetic transient modelling, because different studies require different levels of detail. Suppliers typically provide models that include the full converter control structure so that steady state and dynamic behaviour can be assessed consistently.

Validation is usually done in stages: first by checking the control block behaviour against the design intent, then ensuring consistency across the different modelling environments, and finally comparing the model response with factory or commissioning data. 

Claus Leth Bak, Professor, Head of Section of Power Systems and Microgrids, Aalborg University (AAU), Denmark: EMT tools like PSCAD or similar. Validation with measurements from real life.

Angela P P: When it comes to economic viability, it’s very case dependent. CSC can be more cost efficient for long distance bulk transfer on strong grids, while VSC often becomes more viable where controllability, weak-grid operation, renewables integration, or multi terminal capability are required. So the ‘better’ option really depends on the specific network needs and project context.

Alexander Tsylin, Senior Lead Specialist for Plant Control and Protection Systems, Ørsted, Denmark: For today’s HVDC technology, VSC-based HVDC has higher losses, while economic viability depends on the application: classic CSC/LCC is still cheaper for a few very large point‑to‑point links, but VSC is generally more attractive for future, flexible grids as it can connect weak grids and enable multi-terminal and meshed HVDC systems.

John Wright, Europe and Africa Technical Application Engineering Leader & Product Growth Leader, GE Grid Solutions, UK: As we transition to digitisation all information is good - the key is that we share it. From a protection point of view, the teams in Denmark have valuable experience and are already sharing. 

Alexander Tsylin: Denmark’s success in integrating high shares of wind power is driven by strong transmission planning, close TSO–DSO coordination, effective use of interconnectors, and advanced system operation supported by accurate forecasting and flexible markets. A key lesson for the UK is that high wind penetration can be achieved reliably through early grid reinforcement, operational flexibility, and system-wide coordination, not just by adding more renewable generation.

Alexander Tsylin: From my perspective, adding many SMRs and/or fusion plants would not justify returning to a “simpler, top-down grid”, but rather rebalance the system. The future grid will likely be more hybrid and distributed, even with significant SMR/fusion capacity as such plants are designed for localized deployment at the transmission level, not fully centralized mega-plants.

Alexander Tsylin:70/80-year-old substations and power plants remain widespread, with high proportion of primary assets (transformers, breakers, turbines) still operational after 40-80 years, capable of 10–20 more years through condition-based maintenance and refurbishment.

Secondary systems (protection, SCADA) are the limiting factor, typically lasting only 15–30 years before obsolescence forces replacement due to technological change, cybersecurity requirements, and support limitations, making them the main drivers for refurbishment even when primary assets remain mechanically sound.

As a result, modern asset management increasingly focuses on selective life extension of primary plant combined with periodic renewal and digitalisation of secondary systems to maintain reliability, compliance, and operability.

Angela P P: When the assets are in good condition, lightly stressed, operated within design limits and regularly maintained, they perform reliably for several decades. However, lifespan is highly case specific and longevity depends on several varying factors such as mechanical wear (in electromechanical devices), component ageing (capacitors, coils, contacts), environmental exposure (humidity, temperature), maintenance history etc. So while many P&C relays can physically last far beyond their nominal design life, their true remaining life varies by asset and condition and not by age alone.

John Wright:  For many years a mixed skill set will be required as we have a mixed generation of PAC. However, as we move towards digitisation knowledge of communications and standards will be critical in addition to basic power system and protection knowledge. You will also see a change in the way we test systems - the tools are more computer based and require a different skill set.

We will start to see more specialists, such as network engineers with deep knowledge of the communications network. Critical for designing, testing and debugging systems. These Engineers may not have the detailed protection knowledge. Also, we are all moving towards a common goal if interoperability to IEC61850 - this standard describes the Engineering process, so skills will develop in line to meet the standard.

Alexander Tsylin: Please take a look at CIGRE TB "977 - Education, qualification and continuing professional development of engineers in protection, automation and control" for more insights.

John Wright: Many in the UK are already on  this journey - it is the scale that is varying - Station Bus is common practice - Process Bus is somewhere between pilot sites and bays integrated into a conventional substation. For others Process Bus will be the standard going forward. It’s important to understand that we have the capability to deliver DSS - its sometimes a matter of economics and capabilities of Engineers.

John Wright:  For many years a mixed skill set will be required as we have a mixed generation of PAC. However, as we move towards digitisation knowledge of communications and standards will be critical in addition to basic power system and protection knowledge. You will also see a change in the way we test systems - the tools are more computer based and require a different skill set.

we will start to see more specialists, such as network engineers with deep knowledge of the communications network. Critical for designing, testing and debugging systems. These Engineers may not have the detailed protection knowledge. Also, we are all moving towards a common goal if interoperability to IEC61850 - this standard describes the Engineering process, so skills will develop in line to meet the standard.

Alexander Tsylin: Please take a look at CIGRE TB "977 - Education, qualification and continuing professional development of engineers in protection, automation and control" for more insights.

Alexander Tsylin: Yes, there are certain developments in both areas:

1. Progress exists through UCA IUG interoperability tests and Edition 2 conformance certification, but full "plug-and-play" interchangeability remains limited. GOOSE/SV exchange works reliably between certified IEDs from different vendors, though manual SCD file edits are often needed for complex schemes. CIGRE B5.69 TB 949 documents multi-vendor process bus pilots with 80-90% success rates.

2. Legacy IEDs typically support IRIG-B and SNTP, have hardware limitations and often lack PTP support. Integrating the legacy systems requires use of protocol converters/gateways.

John Wright: The art of protection is distinguishing between a healthy and fault condition. Many relays look at the fault signature during a certain operating window - often determined by the filtering techniques used i.e. fourier etc. If the signature is dynamic during the operating window then an in correct decision can be made or if the wrong filtering techniques are used then the decision comes too late and the plant is already damaged.

In addition to this as discussed in the webinar certain types of protection use techniques to ensure that they operate correctly in certain conditions - i.e. polarising techniques. One example is the use of negative phase sequence - depending on the type of REN or the country the control system that provides negative phase sequence support may vary - this can result in an unpredictable result. Therefore we study the signatures to make sure the algorithms work correctly. They can be tested in many ways - off line modelling  to hardware in the loop.

Alexander Tsylin: While fully integrated secondary-injection hardware inside switchgear is not widespread, the industry is moving toward semi-automated and remote protection testing. Modern IEDs already include extensive self-diagnostics and built-in test functions, and digital substations using IEC 61850 (process bus, test modes) make automated functional testing increasingly practical.

The main barriers to full adoption are safety assurance, legacy equipment, and utility confidence that automated tests are equivalent to traditional secondary injection. As a result, the near-term trend is toward IED-driven, software-based and remotely controlled testing.

John Wright: Virtualisation is gaining traction as it can save Engineering time, reduce time on site and reduce down time during any reconfiguration. It gives a level of comfort that the system is working correctly without having large amounts of equipment. So in theory the more of the system that is virtualised the more efficient this process is.

Alexander Tsylin: Virtual RTUs might come into play close to 2030s.

John Wright: Virtualisation is gaining traction as it can save Engineering time, reduce time on site and reduce down time during any reconfiguration. It gives a level of comfort that the system is working correctly without having large amounts of equipment. So in theory the more of the system that is virtualised the more efficient this process is.

Alexander Tsylin: New PAC technologies driven by high IBR penetration, WAMPAC, and centralized or virtualized architectures are opening major research areas for academia, including protection and control co-design for low-inertia systems, model- and data-driven protection methods, wide-area and system-level protection concepts, AI-assisted and explainable PAC functions, cyber-physical security of protection systems, and PAC-enabled asset management and digital twins.

Overall, the field is shifting toward system-aware, software-defined, and data-informed PAC, requiring closer integration of power systems, control, communications, and software engineering research.

Angela P P: Over the next decade we expect to focus on building confidence in the next generation of PAC architectures, particularly around process bus and virtualised or centralised PAC systems. The industry has already laid the digital foundations with numerical IEDs, and the next step is progressing through process bus pilots and open loop virtualised substation trials to understand performance, operational impacts, and long term benefits. These technologies support greater standardisation across architectures, interfaces, and data models, making future upgrades and lifecycle management more manageable.

At the same time, a heavier reliance on digital systems increases the importance of cybersecurity, so secure architectures, segregation, access controls, and continuous monitoring will be central considerations.

Overall, adoption will remain incremental and risk based, reflecting the long lifecycles, interoperability requirements, and operational practicality that shape decision making.

Alexander Tsylin: Denmark operates with annual average % of non-sync. generation of 55-65%; quite frequently (during some hours) it can reach 80-100%; observed maximum is >100%.

Success in integrating high shares of non-sync. generation and system's operational stability are driven by strong transmission planning, close TSO–DSO coordination, effective use of interconnectors, and advanced system operation supported by accurate forecasting and flexible markets.