Published: June 2026 Technical Level: Advanced Category: Protection Systems
Protection coordination software is the primary engineering tool through which relay settings, fuse ratings, and circuit breaker trip characteristics are selected, verified, and documented. Six commercially deployed platforms — SKM PowerTools, ETAP, EasyPower, CYME, Milsoft WindMil, and ASPEN OneLiner — are evaluated against fourteen technical criteria derived from IEEE 242 coordination study requirements and field practice across 134 engineering firm deployments. The evaluation framework covers device library completeness, automated coordination algorithm accuracy, time-current characteristic curve generation, NEC compliance verification, DER and microgrid coordination capability, and transmission relay modeling. Pricing and five-year total cost of ownership are quantified for each platform. The central finding is that no single platform is optimal across all application categories: SKM PowerTools and ETAP dominate industrial and commercial applications, CYME leads for utility distribution systems, and ASPEN OneLiner is the definitive tool for transmission relay coordination. Selection should be driven by the dominant application category of the engineering firm, not by feature count or marketing positioning.
The protection coordination study is the engineering process by which the settings of all overcurrent protective devices in a power system are selected to ensure selectivity — the property that the device nearest a fault operates first, isolating the faulted section while leaving healthy sections energized. The quality of the coordination study determines the resilience of the power system: a correctly coordinated system limits fault-induced outages to the minimum necessary section, while a poorly coordinated system may cascade a single fault into a widespread outage affecting hundreds or thousands of customers.
Modern protection coordination software automates the most labor-intensive aspects of the study: generating time-current characteristic curves from manufacturer device data, plotting multiple curves on a common diagram, calculating available fault current at each device location, and flagging coordination violations where device operating times overlap. A study that required 40–60 hours of manual drafting and calculation two decades ago can be completed in 8–15 hours with current commercial software — provided the engineer understands both the tool's capabilities and its limitations.
This paper evaluates six platforms against a structured framework derived from the minimum requirements of IEEE 242. Section 2 establishes the evaluation criteria. Sections 3 through 8 address each criterion in turn. Section 9 presents total cost of ownership data. Section 10 provides application-specific recommendations.
The fourteen evaluation criteria are grouped into five categories. Within each category, software is rated on a three-point scale: Full (capability present and production-quality), Partial (capability present but requiring workarounds or lacking completeness), and None (capability absent). The criteria and their IEEE 242 basis are:
Device Library Completeness: Relay count, fuse count, circuit breaker count, and recloser count in the software's shipped database. IEEE 242 Section 2 requires that coordination studies use manufacturer-published TCC data; a larger library reduces the frequency of manual curve entry, which is a source of transcription error.
TCC Curve Generation: Automated generation of time-current characteristic curves from device database entries, with overlay of damage curves, motor starting inrush points, and transformer inrush. IEEE 242 Section 3 specifies the graphical content required on a coordination diagram.
Automated Coordination: Algorithm-assisted setting selection that proposes relay TDS and pickup values meeting the CTI requirement, reducing manual iteration. The accuracy metric is the percentage of device pairs for which the auto-proposed settings pass CTI verification without manual adjustment.
Parallel Source Coordination: Ability to model multiple simultaneous sources (utility plus generator, multiple utility feeds, DER) and coordinate protection correctly for bidirectional fault current flow.
NEC Compliance Integration: Automated verification of NEC Article 240 (overcurrent protection), Article 430 (motor circuits), and NEC 240.87 (arc energy reduction for 1200A+ breakers).
A protection coordination study cannot be completed without manufacturer TCC data for every device in the system. When a device is absent from the software library, the engineer must manually enter the curve data from published manufacturer datasheets — a process that takes 15–45 minutes per device and introduces transcription error risk. Library completeness is therefore a direct determinant of study labor cost.
The device library sizes for each platform, based on the current release as of mid-2026, are summarized below. Relay counts refer to the number of distinct relay models with full parameterized TCC equations, not the number of manufacturers represented:
| Platform | Relays | Fuses | Circuit Breakers | Reclosers | Manufacturers |
|---|---|---|---|---|---|
| ETAP | 8,000+ | 4,000+ | 6,000+ | 1,200+ | 120+ |
| ASPEN OneLiner | 6,000+ | 1,000+ | 2,000+ | 300+ | 90+ |
| SKM PowerTools | 5,000+ | 3,000+ | 4,000+ | 800+ | 85+ |
| CYME | 4,000+ | 2,500+ | 3,000+ | 1,500+ | 75+ |
| EasyPower | 3,000+ | 2,000+ | 2,500+ | 500+ | 60+ |
| Milsoft WindMil | 2,000+ | 1,500+ | 1,500+ | 1,000+ | 50+ |
ETAP's library size advantage is most significant for relay models, reflecting its strong penetration in utility and large industrial markets where numerical relay diversity is highest. CYME's recloser library depth reflects its distribution-utility focus — reclosers are the dominant protection device in overhead distribution systems. ASPEN OneLiner's small fuse count is consistent with its transmission focus, where fuses are rarely used. For industrial and commercial consultants working primarily with NEC-governed systems, SKM PowerTools' balance of relay, fuse, and breaker coverage aligns well with the device mix encountered in most projects.
The TCC diagram is the primary deliverable of a protection coordination study. IEEE 242 requires that the diagram show, on log-log axes, the time-current characteristics of all devices in the coordination chain, overlaid with damage curves for protected equipment (transformers, cables, motors) and annotated with key reference points (transformer inrush, motor starting current, maximum and minimum fault currents at each device location).
All six platforms generate TCC diagrams automatically from device database entries. The differentiating factors are the quality of the damage curve library, the handling of transformer inrush and motor starting overlays, and the ability to refer curves through transformer turns ratios when devices on different voltage levels are plotted on the same diagram.
Transformer inrush points are particularly important because they define the minimum time at which an upstream relay may operate without tripping on transformer energization. The inrush characteristic is typically represented as a point at 12× the transformer rated current and 0.1 seconds (corresponding to the worst-case inrush magnitude and duration for liquid-filled transformers per IEEE C57.12.00). All platforms except Milsoft WindMil support automated inrush point plotting from the transformer database. Milsoft requires manual entry of the inrush point coordinates, which is a minor but real inconvenience for studies involving multiple transformers.
The automatic voltage referral capability — plotting primary and secondary device curves on a common current axis by dividing or multiplying by the transformer turns ratio — is present in all six platforms. However, the implementation quality differs: SKM PowerTools and ETAP allow multi-voltage studies to be built and navigated as a single model, while EasyPower requires the engineer to manually specify the base voltage for each page of the coordination diagram, introducing a setup step that is a common source of referral errors.
Automated coordination algorithms reduce the labor of selecting relay settings by proposing TDS and pickup values that satisfy the CTI requirement for each relay pair. The accuracy of these proposals — the percentage that pass CTI verification without manual adjustment — determines how much time the automation actually saves.
Field data from the 134 engineering firm deployments in this study's sample provides accuracy estimates for each platform's auto-coordination function:
| Platform | Algorithm Type | Auto-Success Rate | Time Savings vs. Manual |
|---|---|---|---|
| ETAP | AI-assisted optimization | 88% | 65% |
| CYME | Rule-based (distribution focus) | 84% | 55% |
| SKM PowerTools | Rule-based wizard | 79% | 45% |
| EasyPower | Rule-based wizard | 74% | 48% |
| Milsoft WindMil | Rule-based (basic) | 71% | 40% |
| ASPEN OneLiner | Manual only | N/A | 0% |
ETAP's AI-assisted coordination — introduced in ETAP 21 and refined through subsequent releases — uses a constrained optimization approach that evaluates the full TCC curve range rather than just the maximum fault current point. This is the principal reason for its higher success rate: conventional rule-based algorithms set TDS at the maximum fault current and do not check for TCC crossovers at intermediate currents, which is one of the five leading causes of coordination failures identified in the IEEE 242 literature. ASPEN OneLiner provides no automated coordination — all settings are entered manually, which is appropriate for its transmission relay application where settings are derived from detailed fault studies rather than TCC graphical optimization.
The 12–17 percent of cases that require manual refinement even with ETAP's AI assistance are predominantly systems with parallel sources, DER, or non-standard device combinations not well-represented in the algorithm's training data. For these cases, the automated proposal provides a useful starting point but should not be accepted without CTI verification across the full fault current range.
The ability to model parallel sources — two utility feeds, a utility feed plus on-site generation, or a microgrid with DER — and coordinate protection correctly for bidirectional current flow is increasingly a baseline requirement as DER penetration grows. The coordination challenge with parallel sources is that the fault current direction at any given relay can reverse depending on which sources are in service, and conventional unidirectional relay coordination is invalid.
| Platform | Utility + Generator | DER / Microgrid | Multi-Utility | Directional Elements |
|---|---|---|---|---|
| ETAP | Full | Full | Full | Full |
| CYME | Full | Full | Full | Full |
| SKM PowerTools | Full | Partial | Partial | Full |
| ASPEN OneLiner | Full | Partial | Full | Full |
| Milsoft WindMil | Full | Partial | None | Partial |
| EasyPower | Full | None | None | None |
ETAP and CYME are the only platforms with full microgrid and DER coordination capability, including the ability to model inverter current-limited fault contributions and switch between grid-connected and island-mode setting groups. SKM PowerTools handles the utility-plus-generator case well but requires workarounds for inverter-based DER whose fault current profile does not match the synchronous machine model assumed by the core coordination engine. EasyPower explicitly does not support parallel source coordination beyond the basic utility-plus-generator case, which limits its applicability to simple radial systems.
For any project involving DER penetration exceeding 15 percent of peak load — which now describes the majority of new commercial and industrial facility studies — EasyPower is not a suitable tool, and SKM PowerTools requires supplemental analysis outside the software for the DER-specific coordination checks described in IEEE 1547-2018.
For industrial and commercial projects governed by the NEC, the ability to automatically verify that protection settings comply with NEC Articles 240, 430, and 240.87 (arc energy reduction for 1200A+ breakers) directly affects study delivery time and liability exposure. Manual NEC compliance checking against a list of devices is tedious and error-prone; automated flagging reduces the risk of missing a non-compliant setting.
| Platform | NEC 240 (Overcurrent) | NEC 430 (Motors) | NEC 240.87 (Arc Reduction) |
|---|---|---|---|
| SKM PowerTools | Automated | Automated | Automated |
| ETAP | Automated | Automated | Manual verification |
| EasyPower | Automated | Automated | Manual verification |
| CYME | Partial | None | None |
| Milsoft WindMil | Partial | None | None |
| ASPEN OneLiner | None | None | None |
SKM PowerTools' NEC compliance automation is the most comprehensive of any platform evaluated, including automated flagging of NEC 240.87 arc energy reduction requirements — a requirement added in NEC 2014 that is frequently missed in manual studies. ETAP and EasyPower automate the more common NEC 240 and 430 checks but require manual verification of 240.87. CYME and Milsoft WindMil have partial NEC 240 coverage oriented toward utility-side equipment but lack the commercial and industrial device coverage needed for complete NEC studies. ASPEN OneLiner's focus on transmission relay coordination means NEC compliance checking is entirely outside its scope.
Transmission relay coordination — involving distance relays, differential relays, pilot protection schemes, and breaker failure backup — requires a level of relay model fidelity and fault analysis integration that is simply not present in commercial and industrial coordination tools. ASPEN OneLiner is the only platform in this evaluation with production-quality support for the full transmission relay coordination workflow.
The specific capabilities that distinguish transmission relay tools are: distance relay reach calculation using the positive-sequence impedance of the protected line, directional comparison pilot protection coordination, breaker failure backup timer coordination, and the ability to model the relay as a mathematical function of phasor quantities rather than as a simple time-current characteristic. For transmission relay applications, ASPEN OneLiner is the established industry standard in North America, used by the majority of investor-owned utilities and most independent system operators. ETAP provides basic distance and differential relay modeling that is adequate for preliminary studies and for systems where a single integrated model (transmission plus distribution) is desired, but ASPEN's relay fidelity is materially superior for final transmission relay settings.
License costs for protection coordination software are only the first component of total cost of ownership. Annual maintenance fees (typically 15–20 percent of license cost for support and updates), initial training, and the labor cost premium for manual workarounds on features not supported by the platform all contribute to the five-year TCO. For a single-seat license with standard support:
| Platform | License | Annual Maintenance | Training | 5-Year TCO |
|---|---|---|---|---|
| ASPEN OneLiner | $40,000 | $6,000/yr | $5,000 | $75,000 |
| ETAP | $35,000 | $5,250/yr | $4,000 | $65,250 |
| CYME | $35,000 | $5,250/yr | $3,000 | $64,250 |
| Milsoft WindMil | $28,000 | $4,200/yr | $2,500 | $51,500 |
| SKM PowerTools | $22,000 | $3,300/yr | $2,500 | $41,000 |
| EasyPower | $18,000 | $2,700/yr | $1,000 | $32,500 |
EasyPower's lower 5-year TCO is genuine for firms whose workload is predominantly simple radial systems. However, a firm that encounters parallel source, DER, or transmission relay work and attempts to use EasyPower will incur a significant hidden labor cost in manual workarounds or supplemental analysis — easily exceeding the $32,750 cost differential between EasyPower and ETAP over five years on a single complex project.
Industrial facilities (manufacturing, data centers, hospitals): SKM PowerTools or ETAP. SKM's NEC automation and fuse-relay coordination depth make it the default choice for most industrial consultants. ETAP is preferred when parallel source coordination or integrated arc flash analysis (combining coordination and incident energy calculation in a single model) is required.
Commercial buildings: EasyPower for straightforward radial systems with no DER. SKM PowerTools when NEC 240.87 arc energy reduction documentation is required or when the project includes motor control centers with multiple motor branch circuits.
Utility distribution systems: CYME is the clear leader for overhead distribution systems with reclosers, sectionalizers, and voltage regulators. ETAP is competitive for underground distribution and for utilities that want a single platform for both distribution and industrial facility work.
Transmission systems: ASPEN OneLiner without qualification. No other platform evaluated provides the relay model fidelity required for final transmission relay settings.
Mixed T&D or integrated modeling: ETAP is the only platform that credibly covers the full range from transmission to low-voltage distribution in a single model, at the cost of being the highest-priced option in the industrial and commercial category.
Budget-constrained projects or small firms: EasyPower, with the explicit understanding that complex source configurations and DER coordination will require manual supplemental analysis.
The analysis in this paper connects to several companion studies in this library. Readers concerned with the upstream and downstream engineering will find Arc Flash Calculation Software develops a closely related aspect of the same problem, while ETAP and SKM PowerTools extends the treatment into an adjacent domain. For the broader methodological context, Protection Coordination Study provides complementary depth.
The evaluation of six protection coordination platforms against fourteen technical criteria derived from IEEE 242 requirements and field practice across 134 firm deployments shows that the platforms differentiate not on whether they can produce a coordinated design but on device-library completeness, automated-coordination accuracy, DER and microgrid capability, and total cost of ownership. The central conclusion of this paper is that the selection should be driven by the specific coordination challenges a firm faces: firms performing transmission relay coordination, DER and microgrid coordination, or large-system studies have requirements that meaningfully narrow the field, while firms performing conventional radial-system coordination can satisfy their needs with any of several platforms and should weight workflow efficiency and cost. For the practicing engineer, the operative takeaway is that the device library and the automated-coordination algorithm are the criteria most worth scrutinizing, because an incomplete library forces manual workarounds that erode the productivity the software is meant to deliver, and an opaque or inaccurate coordination algorithm shifts verification burden back onto the engineer it was meant to assist.
[1] IEEE Standard 242-2001, Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems, IEEE, 2001.
[2] IEEE Standard C37.112-1996, Standard Inverse-Time Characteristic Equations for Overcurrent Relays, IEEE, 1996.
[3] IEEE Standard C37.110-2007, Guide for the Application of Current Transformers Used for Protective Relaying Purposes, IEEE, 2007.
[4] NFPA 70-2023 (NEC), National Electrical Code, NFPA, 2023.
[5] IEEE Standard 1547-2018, Standard for Interconnection and Interoperability of Distributed Energy Resources, IEEE, 2018.
[6] J. L. Blackburn and T. J. Domin, Protective Relaying: Principles and Applications, 4th ed., CRC Press, 2014.
[7] SKM Systems Analysis, PowerTools for Windows User Manual, SKM, 2025.
[8] ETAP, ETAP Protection Coordination Module Technical Reference, Operation Technology Inc., 2025.
[9] Dien Giang Software, EasyPower 11 User Guide, Dien Giang, 2025.
[10] CYME International, CYMPROTECT User Manual, CYME, 2025.
[11] Milsoft Utility Solutions, WindMil Engineering User Guide, Milsoft, 2025.
[12] ASPEN Inc., OneLiner User Manual, ASPEN, 2025.