Every new power system project whether a 500 MW solar farm, a 200 MW BESS project, or a new 345 kV transmission line requires a suite of power system studies before a single piece of equipment is purchased or a permit application is filed. These studies are not bureaucratic formalities; they are the engineering analyses that prove your design is safe, reliable, and capable of meeting regulatory requirements under the full range of operating conditions the system will experience.
At American Power Engineers, power system studies are a foundational service that underpins every project we support, from initial feasibility through NERC compliance and commissioning. This comprehensive guide explains the major study types, their technical foundations, required deliverables, and the engineering software used to perform them.
What Are Power System Studies and Why Are They Required?
Power system studies are computational analyses of electrical power systems that use mathematical models to predict system behavior under defined operating conditions. The fundamental purpose of these studies is to answer engineering questions that cannot be answered by inspection alone:
- Is this transmission line thermally adequate for expected loads under contingency conditions?
- Will this generator’s protection settings respond correctly to faults at remote system locations?
- Does this substation’s grounding grid limit touch and step voltages to safe levels?
- Will this new solar farm cause power quality problems for adjacent industrial customers?
The answers to these questions determine equipment ratings, protection settings, design configurations, and increasingly — regulatory compliance. NERC reliability standards, interconnection technical requirements, and utility planning criteria all specify required studies and define the criteria that study results must satisfy.
Load Flow (Power Flow) Studies
The load flow study sometimes called a power flow study is the foundation of virtually all other power system analyses. It computes the steady-state voltages, angles, and power flows throughout a network for defined operating conditions.
Applications of Load Flow Studies
Thermal Rating Verification: Load flow results identify transmission lines, transformers, and cables operating above their rated capacity (thermal overload) under normal (N-0) and contingency (N-1, N-2) conditions. Overloaded elements require reinforcement, modification, or operating restrictions.
Voltage Profile Analysis: Load flow studies verify that bus voltages throughout the study area remain within acceptable limits (typically ±5% for transmission, ±10% for distribution) under all study conditions. Voltage violations require reactive compensation, transformer tap changes, or system reinforcement.
Generation Dispatch Assessment: For generation interconnection studies, load flow analysis verifies that adding the proposed resource to the system does not create thermal overloads or voltage violations that would require network upgrades, or quantifies the upgrade costs if they do.
Contingency Analysis: N-1 contingency analysis simulating the outage of each single transmission element is a fundamental NERC TPL reliability requirement. Load flow tools automate this process across hundreds of contingencies.
Load Flow Software Platforms
Industry-standard platforms for load flow studies include:
PSS/E (Siemens PTI): The dominant platform for bulk transmission system studies in North America. PSS/E is used by virtually all major ISOs/RTOs and most large utilities as their standard power flow tool. Our engineers are proficient in PSS/E for both steady-state and dynamic simulation.
PowerWorld Simulator: A highly capable platform with an intuitive graphical interface, widely used for educational studies, regional planning analyses, and visualization-heavy applications.
ETAP: Primarily used for industrial power systems and distribution substations, with strong integration between load flow, motor starting, arc flash, and protective device coordination analyses.
OpenDSS: An open-source platform developed by EPRI for distribution system analysis, increasingly used for DER interconnection and hosting capacity studies.
Short Circuit (Fault Current) Studies
Short circuit studies calculate the fault currents that flow through the power system during various types of fault conditions: three-phase (3Φ), single-line-to-ground (SLG), line-to-line (LL), and double-line-to-ground (DLG). These results are used to:
Select Interrupting Equipment: Circuit breakers, fuses, and other interrupting devices must be rated to safely interrupt fault currents. Short circuit studies confirm that existing equipment ratings are adequate and specify minimum required interrupting ratings for new equipment.
Size Protective Equipment: Current transformers, protection relays, and bus differential zones must be designed for the expected fault current magnitude and X/R ratio.
Evaluate Ground Grid Performance: Fault current magnitude and distribution through the earth determine ground potential rise (GPR) and influence the design of substation grounding systems.
Assess Momentary and Interrupting Duty: Per ANSI C37 standards, circuit breakers have both a momentary duty rating (peak current in the first half-cycle) and an interrupting duty rating (symmetrical RMS current at the time of contact part). Short circuit studies must compute both.
Stability Studies: Transient and Voltage Stability
Transient Stability Analysis
Transient stability studies assess whether generators remain in synchronism (stay “in step”) with the rest of the power system following large disturbances such as:
- Three-phase fault followed by line clearing
- Loss of a large generating unit
- Sudden load loss following transmission switching
The critical stability metric is the Critical Clearing Time (CCT) the maximum fault duration that the power system can tolerate without losing synchronism. For transmission-connected generation, protection relay clearing times must be faster than the CCT.
Transient stability simulation uses dynamic generator models that include:
- Generator electrical characteristics (subtransient, transient, and synchronous reactances)
- Excitation system dynamics
- Governor and turbine dynamics
- Power system stabilizer (PSS) models
- IBR control system models
Our power system studies team uses PSS/E dynamic simulation for transient stability analysis, employing WECC-certified and user-defined dynamic models for all major generator technologies.
Voltage Stability Analysis
Voltage instability — the collapse of bus voltages due to inadequate reactive power support is a distinct phenomenon from transient angle instability. Voltage stability analysis uses:
P-V Curves: Show the relationship between active power loading and bus voltage, identifying the nose point (maximum power transfer before voltage collapse).
Q-V Curves: Assess reactive power margin the additional reactive power that would be needed to maintain voltage stability at a given loading condition.
Modal Analysis: Identifies the system buses and branches most responsible for voltage stability risk, guiding targeted reactive compensation investments.
Electromagnetic Transient (EMT) Studies
EMT studies represent the most detailed and computationally intensive level of power system simulation. Unlike positive-sequence phasor simulation tools (PSS/E, PowerWorld), EMT tools model the instantaneous time-domain behavior of electrical systems at sub-millisecond resolution.
EMT analysis is required when:
- Assessing IBR control system interactions with the transmission system (sub-synchronous oscillations, control instabilities)
- Evaluating harmonic performance of power electronics-based equipment
- Simulating transformer inrush and ferroresonance during switching events
- Validating EMT models against field disturbance recordings
- Studying HVDC system behavior during AC system disturbances
- Meeting NERC and ISO EMT model submission requirements
The industry-standard EMT simulation platform for IBR compliance studies is PSCAD/EMTDC, developed by the Manitoba Hydro International (MHI). American Power Engineers maintains PSCAD simulation capability across all current versions, with expertise in developing and validating IBR models for all major inverter OEMs.
Harmonic Studies
Harmonic studies evaluate the power quality impact of non-linear loads and power electronics-based equipment (including IBRs) on the power system. The governing standard for harmonic limits is IEEE 519-2022, which specifies maximum voltage and current harmonic distortion limits at the Point of Common Coupling (PCC).
Harmonic studies are required for:
- Utility-scale solar farms and wind farms (IBR harmonic injection)
- Large motor drives and variable frequency drives (VFD)
- Arc furnaces and other high-power non-linear loads
- BESS with bidirectional power conversion systems
- Capacitor bank installations (resonance assessment)
Harmonic resonance is a particularly dangerous condition where capacitive elements in the power system resonate with inductive elements at a frequency near a significant harmonic of the fundamental. Resonance can amplify harmonic voltages to levels that damage equipment and cause interference with communication systems and protective relays.
Arc Flash Studies
Arc flash analysis performed in accordance with IEEE 1584-2018 and required by NFPA 70E and OSHA computes the thermal energy release during an arcing fault at each switchgear and equipment location. Results determine:
- Incident Energy (IE): The thermal energy per unit area at the working distance, measured in cal/cm²
- Arc Flash Boundary (AFB): The distance at which incident energy equals 1.2 cal/cm² the threshold for second-degree burns to unprotected skin
- Required PPE Level: The arc-rated personal protective equipment required for each location
Arc flash study results are documented in equipment labels and used to develop electrical safety work procedures and PPE selection guidelines in accordance with NFPA 70E.
Grounding Studies
IEEE 80-based grounding studies design and verify substation grounding grids to ensure safe touch and step voltages during ground fault conditions. Modern grounding analysis uses SES CDEGS software for complex grounding systems with non-uniform soil models, buried infrastructure, and multiple grounding points.
Key outputs of a grounding study include:
- Ground potential rise (GPR) during maximum fault current conditions
- Touch voltage contours throughout the substation yard
- Step voltage contours beyond the substation fence
- Transferred potential assessment for connected structures and pipelines
PSSE vs. PSCAD: Choosing the Right Simulation Platform
A question we frequently receive from clients: when should I use PSS/E and when should I use PSCAD?
The answer depends on the phenomena being studied:
| Study Type | Preferred Tool |
| Load flow / power flow | PSS/E, PowerWorld, ETAP |
| Transient stability (positive sequence) | PSS/E |
| Small-signal stability | PSS/E with eigenvalue analysis |
| IBR control interactions (sub-synchronous) | PSCAD |
| Harmonic analysis | PSCAD, ETAP |
| EMT model validation | PSCAD |
| Protection relay coordination | ETAP, SKM DAPPER |
| Arc flash | ETAP, SKM DAPPER |
| Grounding | SES CDEGS |
Our team maintains expertise across all of these platforms, allowing us to apply the right tool for each specific analysis need. See our power system studies services page for a complete list of study capabilities.
Interconnection Study Process: From Scoping to Final Report
The interconnection study process for new generation resources typically follows a defined sequence mandated by the applicable ISO/RTO or utility interconnection tariff:
Feasibility Study (Scoping Study): A preliminary analysis that identifies potential upgrade requirements and provides a rough-order-of-magnitude cost estimate. Results inform the developer’s go/no-go decision.
System Impact Study (SIS): A more detailed analysis of the network impacts of the proposed interconnection, including identification of required network upgrades and their costs allocated to the applicant.
Facilities Study: Detailed engineering to specify the exact scope, specifications, and cost of required interconnection facilities.
Generator Interconnection Agreement (GIA): The binding contractual agreement between the Generator Owner and the Transmission Owner that specifies required facilities, milestones, and performance requirements.
Our POI interconnection engineering services support generator owners through every stage of this process, from initial scoping through GIA negotiation and final commissioning.
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