Power System Studies: The Complete Engineering Reference for Generation and Transmission

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

The 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 engineering 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.

Final Thoughts

Power system studies aren’t a compliance checkbox, they’re the engineering work that determines whether your equipment is rated correctly, your protection scheme actually protects, and your workers know what they’re walking up to before they open a panel. Load flow, short circuit, arc flash, relay coordination, and harmonic analysis each answer a different question, but they build on the same system model and the same accurate data, which is why they’re rarely one-off exercises.

Whether you’re planning a new interconnection, upgrading an aging substation, or closing out a NERC compliance gap, the right time to scope these studies is before the design is locked in — not after a utility comment letter or an audit finding forces the issue.

FAQs

What’s the difference between a load flow study and a short circuit study?

A load flow study models the system under normal, steady-state operating conditions voltages, power flows, and loading across buses, transformers, and lines. A short circuit study models the system under abnormal fault conditions to determine available fault current for equipment ratings and protection settings. Most engineering scopes include both, since short circuit results depend on the same system model the load flow study establishes.

Do I need all five studies, or can I scope just one?

It depends on the trigger. A new interconnection request usually needs load flow and short circuit at minimum. Anywhere workers interact with energized equipment, OSHA and NFPA 70E expect an arc flash study. Relay coordination is typically bundled with short circuit results, since coordination can’t be verified without fault current data. Harmonic analysis is only required when the system has significant non-linear or power-electronic loads (VFDs, inverters, rectifiers) or when a utility interconnection agreement specifically calls for it. If you’re unsure what your project needs, that’s a scoping conversation worth having before work starts, not after.

How often do these studies need to be updated?

There’s no single universal interval it depends on the standard and the change. Arc flash studies are commonly refreshed every 5 years per NFPA 70E guidance, or sooner if equipment, settings, or system configuration change. NERC-registered entities have their own refresh triggers under standards like PRC-005 and PRC-019, some of which reset in as little as 90 calendar days after a qualifying change. As a general rule: if a breaker, relay setting, transformer, or major load/generation addition changes, the studies built on the old configuration are no longer valid.

What software is used to perform power system studies?

ETAP, SKM PowerTools/DAPPER, PSS/E, and PowerWorld are the industry-standard platforms, depending on the utility scale, voltage class, and study type. The output is only as reliable as the input data accurate one-line diagrams, equipment nameplate data, and verified impedance values matter more than which software runs the calculation.

Can I run these studies myself with an online calculator?

Quick calculators are useful for early-stage planning rough fault current estimates, voltage drop checks, or transformer loading but they’re not a substitute for a full study. A professional study incorporates the complete system model, verified field data, contingency (N-1) scenarios, and a licensed engineer’s review, none of which a standalone calculator can replicate.

Do power system studies need to be stamped by a licensed Professional Engineer?

For most utility submittals, NERC compliance documentation, and any deliverable used for equipment specification or safety programs (arc flash labels included), yes — a PE stamp is expected or required. Confirm this with your utility or AHJ early in scoping, since it affects both timeline and who can perform the work.

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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