Across the UK, a seismic shift is underway as companies, driven by renewable energy sources such as wind, solar photovoltaics (PV), and energy storage, seek to connect their generation systems to the National Grid and Distribution Network Operators (DNOs).
Electromagnetic transient (EMT) and root mean square (RMS) simulations are critical tools in the analysis and design of electrical power systems. Both methodologies have distinct applications and advantages, making them suitable for different studies.
This article aims to provide a brief overview of EMT and RMS simulations, their respective applications, the software used for these simulations, and the capabilities of Engineering Power Solutions (EPS) in performing these studies.
Key Takeaways:
- What are electromagnetic transients?
- EMT vs. RMS Studies
- Key Characteristics of EMT Simulations
- Key Characteristics of RMS Studies
- Common applications of EMT & RMS Simulations
- Software for EMT & RMS Simulations
What Are Electromagnetic Transients?
Electromagnetic transients are important phenomena in power systems that can occur in response to disturbances or sudden changes in the system, such as switching operations, lightning strikes, or faults. These transients can cause voltage spikes, current surges, and oscillations in the system, potentially leading to insulation breakdown, equipment damage, and a decrease in a power system’s overall stability and reliability.
National Grid and DNO requirements now mandate that new renewable energy projects submit comprehensive EMT models using tools like PSCAD. These models must intricately detail the electromagnetic behaviours of generators, inverters, harmonic filters, control systems, and other critical electrical components. This requirement arises due to the limitations of root mean square models in accurately representing power systems characterised by high penetration of inverter-based resources (IBRs).
EMT vs. RMS Studies
EMT Simulations
Electromagnetic Transient (EMT) simulations involve solving differential equations that describe the electrical behaviour of the system in the time domain. These simulations capture the instantaneous values of voltages and currents, making them ideal for analysing fast transient phenomena such as switching operations, fault conditions, and lightning strikes.
RMS Simulations
Root Mean Square (RMS) simulations use phasor representations of voltages and currents to solve the power system equations in the frequency domain. This approach assumes a quasi-steady-state operation and effectively studies the system’s behaviour over longer periods and under steady-state conditions.
Key Characteristics of EMT Simulations:
One of the key characteristics of electromagnetic transient simulations is time domain analysis, which addresses the power system’s differential equations over time. This allows for a precise and dynamic examination of a system’s behaviour. Also, these studies can model and analyse high-frequency oscillations. EMT simulations offer detailed and accurate representations of power electronic devices and control systems, ensuring a holistic understanding of the intricate interactions within the system.
Common Applications:
- Insulation Coordination Studies: Evaluate the dielectric strength of equipment.
- Ferro-resonance: Study the resonance of a capacitor and a nonlinear saturable inductance
- Switching Overvoltage Studies: Analyses transient overvoltages due to switching actions.
- Lightning Overvoltage Studies: Assesses the impact of lightning strikes on power systems.
- Sub-Synchronous Resonance (SSR) Studies: Studies interactions between mechanical and electrical systems in turbines.
- Very Short-Term Transient Stability Studies: Provides the stability of system generators against severe faults and contingencies.
Key Characteristics of RMS Simulations:
The key characteristics of RMS simulations include frequency domain analysis, using phasor calculations for voltages and currents, and offering a simplified yet effective method for analysing electrical systems. These simulations are conducted under the assumption that the power system is free from rapid transients and operating in a steady state. The simplification of complex calculations makes it easier to conduct RMS Simulations for large-scale power system networks.
Common Applications:
- Load Flow Studies: Determining the voltage, current, and power flow within the network.
- Short-Term Transient Stability Analysis: Assessing the system’s ability to remain stable after a disturbance.
- Fault Analysis: Studying the system’s response to short-circuit faults.
- Dynamic Stability Analysis: Evaluating the system’s response to small perturbations over time.
Software for EMT and RMS Simulations
Several software tools are available for performing EMT and RMS simulations, each with its own strengths and specific use cases.
EMT Simulation Software:
- PSCAD/EMTDC:
PSCAD is the industry standard for EMT simulations. Widely used for detailed time-domain analysis of power systems in the UK, PSCAD offers extensive capabilities for modelling power systems. - EMTP:
Electromagnetic Transients Program (EMTP®) is the reference for the simulation and analysis of power systems. With its unique capabilities and accuracy, EMTP® is the industry’s fastest, most accurate, and most stable software. - RTDS:
Real-Time Digital Simulator is another powerful tool for EMT simulations, enabling real-time testing and validation of power system models.
RMS Simulation Software:
- DIgSILENT Power Factory:
Known for its robust RMS simulation capabilities, DIgSILENT is used for load flow analysis, transient stability studies, and fault analysis. - PSS®E (Power System Simulator for Engineering):
Widely used for RMS studies, PSS®E provides comprehensive tools for steady-state and dynamic analysis of power systems.
EPS Capabilities in EMT and RMS Studies
At Engineering Power Solutions, we’re specialists in performing EMT and RMS simulations. We provide a wide range of tailored solutions that optimise the safety and performance of electrical power distribution systems.
Our team of power system consultants are adept at leveraging PSCAD to analyse fast transients, insulation coordination, SSR, and much more. We have a strong track record of tackling complex transient phenomena and delivering many different studies which involve:
- HVDC
- SVC
- FACTS
- Wind Farm Integration
Additionally, we have extensive experience utilising DIgSILENT Power Factory, and our electrical engineers excel in performing load flow, transient stability, and fault analysis. As an extension to your existing engineering teams, we ensure accurate and reliable results for steady-state and dynamic performance assessments.
Notable Projects:
Wind Farm Integration Studies:
EPS has conducted detailed Electromagnetic Transient studies to facilitate the seamless integration of onshore wind farms into the electrical grid. These studies were focused on addressing key issues such as fault ride-through, power quality, and control interactions to ensure smooth and stable operation.
Harmonic Resonance Analysis:
We have also conducted several harmonic studies for large-scale solar power plants across the UK. Our focus has been identifying and mitigating the potential resonance issues from inverter controls.
Conclusion
Understanding the differences between EMT and RMS simulations is crucial for selecting the appropriate methodology for power system studies. Notably, when considering the increased demand for grid connections from renewable sources like wind and solar PV. EMT simulations provide detailed time-domain analysis for fast transient phenomena. RMS simulations offer efficient frequency-domain analysis for steady-state and dynamic stability assessments.
EPS is a leading provider of both EMT and RMS simulation services, leveraging tools like PSCAD and DIgSILENT Power Factory to deliver comprehensive and accurate power system analyses. With a proven track record and expertise in a wide range of studies, EPS is well-positioned to guide organisations across the UK to safer, more compliant, and dependable power systems.
For more information on how EPS can assist with your power system studies, please contact our experts today.
References:
- A brief introduction to (real-time) simulations, Real-Time Digital Simulation Laboratory at UNSW Sydney, https://rtsunsw.home.blog/2019/10/17/real-time-simulations/
- Grid Code Modification Proposal Form, National Grid ESO, https://www.nationalgrideso.com/document/304536/download
