Protection Coordination in Electrical Substations Chile 2026

Protection coordination in electrical substations is the technical process of setting and verifying the joint operation of relays, instrument transformers, and circuit breakers so that, when a fault occurs, only the device closest to the faulted point operates while the rest of the system stays in service. In Chile, this study is governed by the Technical Standard for Service Security and Quality (NTSyCS), issued by the National Energy Commission and overseen by the National Electrical Coordinator. It is a mandatory requirement for the commissioning of any installation connecting to the National Electrical System, whether as part of the National Transmission System (STN) or the Dedicated Transmission System (STD).

If your project requires a protection coordination study for electrical substations and you need to validate that it meets the requirements of the National Electrical Coordinator, this guide covers the full process: from the principles of selectivity to the setting methodology and the most common errors in Chilean projects.

What is protection coordination in electrical substations?

Protection coordination in electrical substations consists of defining and verifying the settings of each protection function (relays, fuses, breakers, and auxiliary devices) so that operation during faults is selective, fast, sensitive, and reliable. Selectivity—also called relay coordination—requires that the relay closest to the fault point act first, and that backup relays operate only if the primary relay fails to respond within the expected time (Chinchilla Contreras, 2021).

Without proper protection coordination in electrical substations, a fault in one bay can take an entire substation, a transmission line, or—in extreme cases—the stability of the National Electrical System out of service. In large mining, renewable generation, and transmission projects in Chile, the study is not a regulatory formality: it defines the operability and safety of the system from the moment of commissioning. Its correct development is articulated with the overall design of the installation, described in our guide on what the installation of an electrical substation in Chile looks like.

Chilean regulatory framework: NTSyCS, RPTD, and National Electrical Coordinator requirements

In Chile, the requirements for protection coordination in electrical substations are regulated primarily by three regulatory bodies:

• Technical Standard for Service Security and Quality (NTSyCS), issued by the National Energy Commission (CNE) and overseen by the National Electrical Coordinator (CEN). The version in force, dated January 2025, defines the minimum requirements for the protection of busbars, lines, transformers, storage systems, and HVDC links (CNE, 2025).
• Technical Regulatory Standards RPTD No. 05, No. 07, and No. 11 from the Superintendency of Electricity and Fuels (SEC), which establish insulation criteria, electrical clearances, and general design for high-voltage substations.
• Technical guide for protection systems from the National Electrical Coordinator, which details the minimum functions required by installation type, redundancy criteria, and monitoring requirements.

To connect a new project to the STN or the STD, the CEN requires a validated protection coordination study for electrical substations, submitted within the connection management process. Without this deliverable, there is no commissioning (Universidad de Chile Repository, 2023). In Dedicated Transmission System projects, classification does not depend on the voltage level but on the use of the installation. Details on voltage levels are analyzed in the article on electrical voltage levels in Chile.

At ESINEL Ingenieros, the design team produces the protection coordination study for electrical substations integrated with short-circuit, power flow, and stability studies, on platforms such as ETAP and DIgSILENT PowerFactory.

Fundamental principles of selectivity: five design criteria

A well-executed protection coordination system in electrical substations is measured by five critical attributes:

• Selectivity. Only the relay closest to the fault should trip. Backup relays operate with an intentional delay (typical coordination step: 200–400 ms) to allow the primary protection to act first.
• Speed. Fault clearing within the system’s critical times—usually between 80 and 100 ms for faults on high-voltage busbars—to avoid thermal damage and loss of angular stability.
• Sensitivity. The operating threshold must detect all foreseeable faults, including high-impedance faults, without acting under normal load conditions or permissible transients.
• Reliability. The probability of correct operation when required. It involves primary protection, local breaker backup, and remote backup properly coordinated with one another.
• Security. The probability of not operating incorrectly. Reliability and security are inversely proportional: increasing one tends to reduce the other, which requires finding a balance based on risk analysis (Chinchilla Contreras, 2021).

These five criteria translate into concrete, verifiable parameters: pickup current, time dial, characteristic curve, maximum torque angle, blocking settings, logic interlocks, and coordination margins. The protection coordination study for electrical substations materializes these attributes into auditable settings for each relay in the project.

Most common protection functions and ANSI codes in substations

International practice uses the ANSI/IEEE C37.2 codes to identify protection functions. In Chilean transmission substations, the most used are the following:

ANSI Code	Function	Typical application in Chilean substations
21	Distance	220 kV and 500 kV transmission lines
50	Instantaneous overcurrent	Feeders, transformers, short lines
51	Time overcurrent	Backup on lines and transformers
51N	Neutral overcurrent	Ground fault detection
67	Directional overcurrent	Lines in meshed networks
67N	Directional neutral overcurrent	Ground faults in meshed networks
87	Differential	Busbars, transformers ≥12 MVA, lines
86	Trip and lock-out	Blocking on critical internal faults
49	Thermal image	Transformer overload
63	Buchholz / pressure / level	Mechanical protection of transformers
50BF	Breaker failure	Local backup required by NTSyCS
79	Automatic reclosing	Overhead lines with transient faults

Differential protection (ANSI 87) is the basis for busbars, transformers with ratings equal to or greater than 12 MVA, and lines with the characteristics defined in the NTSyCS. For correct protection coordination in electrical substations, the design team must model the system, calculate fault levels at each busbar, define the curves of downstream and upstream relays, and verify the selectivity margin in each case. This work is complemented by our content on types of electrical substations in Chile and their uses.

Types of relays and their role in protection coordination

The relays that make up the protection system are grouped according to their operating principle. This classification determines how they are integrated into protection coordination in electrical substations within the substation and with the protections of the upstream and downstream network.

Overcurrent relays (ANSI 50/51)

They operate upon detecting a current above the programmed threshold. They can be instantaneous (50) or time-delayed with an inverse, very inverse, or extremely inverse curve (51). In coordination, the curves are plotted on a log-log current vs. time plane, and the time dials are adjusted so that the downstream curve always remains below the upstream curve with the appropriate coordination margin.

Differential relays (ANSI 87)

They compare the current entering and leaving the protected zone. Their selectivity is absolute: they operate only on internal faults. They are used in transformers (87T), busbars (87B), and lines (87L). They are the primary protection where speed is critical, since they act without time delay.

Distance relays (ANSI 21)

They calculate the impedance from the relay to the fault point. They operate in stepped zones (Z1, Z2, Z3) with increasing times. They are the standard for 220 kV and 500 kV transmission lines in Chile, where their speed in zone 1 and their coordination with remote zones make it possible to clear critical faults within a few cycles.

Directional relays (ANSI 67/67N)

They discriminate the direction of current flow. They are used in meshed networks where a fault can be fed from several ends. They are fundamental in protection coordination in electrical substations for projects with distributed generation or multiple links (Universidad de Chile Repository, 2019).

Breaker failure relays (ANSI 50BF)

They detect that a breaker did not open after a trip command and trip the adjacent breakers. They are part of the local backup required by the NTSyCS and are mandatory in substations of 154 kV and above.

The evolution toward multifunction numerical relays has significantly modified protection coordination in electrical substations: a single IED (Intelligent Electronic Device) can integrate 50/51/67/87/79/25/27/59 and communicate via IEC 61850 with the rest of the substation (Revista Electricidad, 2018). This requires updated design criteria that take advantage of the flexibility without losing traceability of the settings or introducing conflicts between functions.

Methodology of a protection coordination study for electrical substations

A professional protection coordination study for electrical substations follows a technical sequence that ESINEL has consolidated in transmission and mining projects in the North and Central regions of Chile. The eight critical steps are the following:

• Collection of baseline information. Current single-line diagram, electrical parameters of equipment (transformers, lines, generators), data of installed relays, instrument transformer ratios (CT and VT), Protection Audit, and the status of connection management before the CEN.
• System modeling. Construction of the electrical model in specialized software (ETAP, DIgSILENT PowerFactory, CYME). Cross-validation with the official models of the National Electrical Coordinator.
• Preliminary studies. Power flow, three-phase and single-phase short circuit, and stability analysis where applicable. The results feed directly into the calculation of settings.
• Definition of protection philosophy. Selection of primary and backup functions for each element, aligned with the NTSyCS and with the operational practice of the owner or concessionaire.
• Calculation of settings. For each relay: pickup current, time dial, characteristic curve, ground sensitivity, distance zones, reach, blocking settings, interlocks, and trip logic.
• Selectivity verification. Graphical coordination on log-log plots, verification of coordination steps, and fault simulation at each busbar to confirm the expected operation in all dispatch scenarios.
• Documentation. Calculation report, setting tables per relay, coordination drawings, and configuration file (CFG, RIO, or equivalent) ready to download to the IED in the field.
• Injection testing. During commissioning, the settings are verified with secondary—and, where applicable, primary—injection equipment. Any discrepancy between the documented setting and the relay’s actual setting is an operational risk that must be corrected before energizing (SMC Internacional, 2025).

This workflow is repeatable, auditable, and traceable. At ESINEL, deliverables are generated in a format compatible with the client’s engineering platform and are integrated into the BIM model when the project requires it. The connection between protection coordination in electrical substations and BIM coordination is described in more detail in our article on BIM in electrical substations.

Common errors in protection coordination in electrical substations

Experience in construction inspection (ITO) and in the review of external studies reveals error patterns that recur frequently. Identifying them in time is part of the value provided by well-executed protection coordination in electrical substations:

• Poorly defined CT ratios. An error in the transformation ratio of the current transformers invalidates all calculated settings. It is the most frequent error and the most expensive to correct after energization.
• Incompatible curves between levels. Mixing IEC normal inverse curves downstream with IEEE moderately inverse curves upstream creates non-coordination points at certain current ranges.
• Lack of coordination with the upstream network. Forgetting the existing settings of the Coordinator’s network or of the dedicated segment operator leads to untimely operations and non-selective disconnections.
• Failing to account for distributed generation. NCRE (non-conventional renewable energy) plants connected at the distribution level modify short-circuit flows depending on the dispatch scenario. Without directional protections, selectivity is lost.
• Documentation misaligned with the relay’s actual setting. Software models that do not match the firmware or the active setting group in the field. This is only detected with functional on-site testing (SMC Internacional, 2025).
• Omission of breaker failure backup (50BF). Required by the NTSyCS for substations of 154 kV and above; its absence or poor configuration is a recurring finding in technical inspection processes.

The role of the Construction Inspector (ITO) is to detect these findings before energization. A protection coordination study for electrical substations that is well executed by the design engineer, combined with rigorous technical inspection of electrical works, prevents these failures from reaching operation.

Current trends: IEC 61850, numerical relays, and WAMPAC

The protection of electrical substations has changed more in the last fifteen years than in the previous fifty. Three trends dominate the current landscape in Chilean projects and shape protection coordination practices in electrical substations:

IEC 61850

An international standard for communication within the substation. It replaces copper wiring with Ethernet buses using GOOSE messaging for fast signals (tripping, blocking) and SV (Sampled Values) for digital samples of voltage and current from the Merging Units (MU). It reduces physical wiring, speeds up commissioning, allows logic to be tested in the lab before installation, and facilitates interoperability between manufacturers.

Multifunction numerical relays

A single IED can run differential, distance, overcurrent, and reclosing functions, with oscillography records, self-diagnostics, and SCADA communication. It increases the flexibility of protection coordination in electrical substations but requires clear criteria to avoid conflicts between functions, configuration errors, and loss of traceability over the active settings (Leiry Chinchilla, 2025).

WAMPAC (Wide Area Monitoring, Protection and Control)

Wide-area protection schemes that use synchronized measurements via PMU (Phasor Measurement Units) to detect and act on systemic disturbances: loss of generation, low-frequency oscillations, angular separation. In Chile, the CEN is progressively advancing these functions for the STN, especially in critical interconnections and HVDC links (Revista Electricidad, 2018).

These trends do not replace the fundamentals. Protection coordination in electrical substations still demands the same rigor in the calculation of settings, in the verification of selectivity, and in documentation. What changes is the tool and the scope of the system, not the underlying technical logic.

The role of the design engineer in protection coordination

ESINEL Ingenieros carries out the protection coordination study for electrical substations as part of the detailed electrical engineering package, integrated with several disciplines:

The substation design: single-line diagram, layout, electrical clearances, and equipment arrangement.

The design of associated transmission lines, where length and impedance condition the setting of distance protections.

The preliminary electrical studies: short circuit, power flow, stability, and dynamic analysis.

The ITO in large-mining substations, where the study is validated against the relay’s actual setting on site during testing and energization. The team has more than two decades of experience modeling, calculating, and delivering protection coordination studies for electrical substations for STN and STD projects and for free clients in large mining, renewable generation, and dedicated transmission. The function is strictly one of design, specification, modeling, and technical supervision: ESINEL specifies, models, coordinates, supervises, and verifies; it does not physically execute the works or supply equipment. The sector’s comparative experience is addressed in our analysis of electrical substation design companies in Chile.

Frequently asked questions about protection coordination in electrical substations

Conclusion

Protection coordination in electrical substations is not a regulatory formality: it is the nervous system of the substation. A well-executed study defines the difference between safe operation for decades and an event that affects end customers, the stability of the National Electrical System, or the integrity of critical equipment.

In Chile, the requirements of the National Electrical Coordinator and the growing complexity of the system—with more variable renewable generation, more HVDC links, more storage systems, and an increasingly meshed network—raise the technical standard every year. Rigorous methodology, documentary traceability, and integration with the other electrical studies are the three levers that make it possible to meet that standard without overdesigning or leaving blind spots. If your project requires a protection coordination study for connection to the STN, the STD, or for a high-voltage industrial installation, the team at ESINEL Ingenieros can support you from initial modeling through validation at commissioning. Let’s set up a technical conversation at contact ESINEL Ingenieros or review the full portfolio in our engineering projects section.

References

Chinchilla Contreras, L. (2021). Criterios de diseño de un sistema de protecciones eléctricas. LinkedIn Pulse. View source

Comisión Nacional de Energía. (2025). Norma Técnica de Seguridad y Calidad de Servicio. January 2025. Santiago, Chile. View source

Leiry Chinchilla. (2025). Funciones de protección en las subestaciones de transmisión. View source

Universidad de Chile Repository. (2023). Desarrollo de un programa de cálculo y análisis de protecciones diferenciales de barra, línea y transformador. View source

Universidad de Chile Repository. (2019). Coordinación de protecciones de sistemas eléctricos de potencia mediante formulación de problema de optimización. View source

Revista Electricidad. (2018). Coordinador Eléctrico Nacional define prácticas para la operación de sistemas de protecciones. View source

SMC Internacional. (2025). Inyección primaria vs inyección secundaria: cómo probar relés de sobrecorriente ANSI 50/51 en subestaciones. View source