Medium-Voltage Fault Location: Methods, Systems and Best Practices

Medium-voltage fault location is the key tool for grid operators, maintenance teams and service providers to efficiently narrow down faults in cable networks and secondary substations. Fast restoration of supply to healthy grid sections depends largely on precise section identification. Modern A. Eberle systems such as the EOR-1DS and EOR-3DS combine proven fault-location methods with digital substation integration to support switching operations and sustainably improve grid transparency.

Key Takeaways

• Structured narrowing down: Effective fault location starts with the precise identification of the affected grid segment in order to minimize field search times.
• Method diversity: Short circuits and earth faults require differentiated diagnostic approaches tailored to the respective grid topology and grounding type (compensated, isolated, earthed).
• System solutions: While the EOR-1DS provides robust, cost-efficient fault indication, the EOR-3DS serves as a multifunctional digitalization unit for modern secondary substations.
• Supplementary monitoring: Systems such as PQI-DA smart and the WebPQ® software support root-cause analysis and the documentation of transient events.

Why Fault Location in Medium-Voltage Grids Matters

Faults in medium-voltage grids must be narrowed down quickly and reliably so that outage times remain short and operational decisions can be made safely under time pressure. For grid operation, it is not enough merely to detect the presence of a fault. Selectivity is what matters:
Which feeder is affected?
In which direction did the fault current flow?

Fault location is therefore not an isolated device function, but an operational process. It includes event detection, section narrowing, selection of the appropriate method, support for switching operations, and traceable documentation. This strong practical focus is exactly what A. Eberle highlights in connection with the EOR-1DS.

In practice, three points are especially relevant:

• clear indications from the substation
• reliable section identification
• a fault-location method that matches the actual grid situation

Typical Faults in Medium-Voltage Grids

Short Circuits and Earth Faults

Short circuits generally lead to a fast and clear response in the grid. In practice, the key question is whether the affected section can already be reliably narrowed down using the available indications and substation information. Good fault location shortens the time needed for safe switching operations and for restoring supply to unaffected grid sections.

Earth faults are among the most relevant fault types in medium-voltage grids. Their assessment depends heavily on the grid topology, grounding type and measurement concept. For that reason, a simple fault alarm is often not enough. What is needed instead is a clear classification of the affected feeder so that the fault direction can be assessed correctly and the right grid segment can be handled.

Intermittent Faults and Cable Faults

Intermittent and restriking faults are especially challenging in medium-voltage grids because they do not appear as stable permanent faults. Depending on operating conditions, load or timing, the fault situation may present itself differently, which makes clear assignment more difficult. In cable grids, ageing, moisture, thermal stress or poor connections are also typical causes.

For cable fault location, A. Eberle highlights that fast section identification and precise localization of earth faults and short circuits reduce outage times and search effort. It is also emphasized that transients can reveal the fault direction and the fault inception. This is a major advantage for further assessment, especially in the case of recurring or difficult-to-capture events.

Fault Location in Practice: From the Event to Service Restoration

1. Capture the Fault and Build a Situational Picture

The process starts with the trip event, protection alarm, substation signal and the affected supply area. This information must be consolidated quickly into a reliable situational picture. At this early stage, it already becomes clear whether the subsequent fault-clearing process will be systematic or more reactive.

2. Narrow Down the Affected Section

Section identification is the operational core of fault location. It answers the question of which line section or feeder must be investigated and switched first. A. Eberle describes exactly this use case for the EOR-1DS as a typical application after a trip event, in the case of an unclear line section, to support switching operations, and to clarify recurring earth faults and intermittent short circuits.

3. Select the Appropriate Fault-Location Method

Which method makes sense depends on the grid structure, grounding type, voltage and current measurement, as well as the equipment installed in the substation. For the EOR-3DS, A. Eberle emphasizes that the advantages of many different fault-location methods can be combined through prioritization and weighting. This makes the system particularly suitable for applications in which fault location needs to be flexibly adapted to different grid situations.

4. Safeguard Switching Operations

Fault location does not end with an indication on the device. The real operational benefit only arises when the affected section can be safely isolated and healthy parts of the grid can be restored in a controlled way. For that reason, fault location, substation information and grid operation must be closely integrated.

5. Document Events and Evaluate Them Later

Fault records, logbooks and traceable event data are especially important when faults recur or cannot be clearly assessed immediately. For both the EOR-1DS and the EOR-3DS, A. Eberle lists fault records and logbook functions as part of the device concept. This improves not only the clarification of individual faults, but also the later assessment of recurring anomalies

Integrating Future-Proof Secondary Substations into the Distribution Grid

The following webinar recording directly builds on the requirements for event documentation, fault location and substation integration described above. In this video, Gerald Jacob, Product Manager EORSys, presents solution approaches showing how distribution system operators can use future-proof secondary substations to address the challenges of the energy transition in medium- and low-voltage grids. The focus is on the digitalization and automation of secondary substations and on how the EOR-1DS and EOR-3DS can be meaningfully integrated into modern distribution grid concepts.

Fault-Location Methods That Have Proven Effective in Medium Voltage

Fault location in medium-voltage grids is especially effective when the method used matches the actual grid situation. On the comparison page for the EOR-1DS and EOR-3DS, A. Eberle lists, among others, the qu2 wiper method, earth-fault wiper method, directional short-circuit and earth-fault detection, pulse location methods, wattmetric methods and reactive current methods. For the EOR-3DS, additional qui methods for restriking faults and harmonic methods are available.

Pulse Location Methods

Pulse location methods are particularly helpful when faults need to be narrowed down in a targeted way and directional information must be evaluated clearly. A. Eberle mentions this method both in the device comparison and explicitly for the EOR-1DS.

Wiper Methods

Wiper methods use the time progression of the event for fault evaluation. They play an important role especially in earth-fault events when a simple indication is not sufficient for selective classification. In the A. Eberle environment, the qu2 wiper method and earth-fault wiper method are among the core methods mentioned.

Wattmetric and Reactive Current Methods

These methods are particularly relevant in compensated or isolated grids. They help assess the fault direction more reliably and improve the narrowing down of the affected feeder. These methods are also listed on A. Eberle pages as available or relevant approaches.

Methods for Complex Fault Scenarios

In the case of restriking or intermittent faults, standard methods reach their limits more quickly. This is where the EOR-3DS stands out, because additional qui methods and harmonic methods are available and the advantages of different methods can be combined in a weighted manner. This creates greater flexibility in more demanding fault scenarios.

Integrating Fault Indicators and Digital Secondary Substations Effectively

Fault location becomes much more efficient when fault indicators are not viewed in isolation, but as part of a consistent substation concept. For cost-sensitive applications involving combined short-circuit and earth-fault indication, the EOR-1DS is positioned as a fault indicator for the secondary substation. The EOR-3DS, by contrast, is explicitly described as a fault indicator for the digital secondary substation and additionally as a digitalization unit.

EOR-1DS

The EOR-1DS is a compact combined short-circuit and earth-fault indicator that, according to A. Eberle, offers all essential fault-location methods. The device can be used as a non-directional short-circuit and earth-fault indicator with pulse location or as a directional short-circuit and earth-fault indicator with pulse location and qu2 wiper method. Additional strengths highlighted by A. Eberle include simple parameter setting even without software, a large memory for fault records and logbook data, and practical support for operations, engineering and service with clear guidance for fault narrowing, switching operations and service restoration.

EOR-3DS

The EOR-3DS combines short-circuit and earth-fault location in one compact device and, according to A. Eberle, can be used both as a classic fault indicator and as a digitalization unit for secondary substations. The device supports multiple methods, can be freely parameterized with AEToolbox and offers extensive communication options. These include MQTT, IEC 60870-5-101/104, IEC 60870-5-103 including fault records, DNP 3.0, IEC 61850 GOOSE, and Modbus RTU/TCP. In addition, up to six devices can be connected via the Modbus master function.

Digital Secondary Substations

Digital secondary substations combine fault location, measured values, communication and grid operation within a common concept. In the webinar and in A. Eberle’s knowledge article, it is highlighted that standardized digitalization improves grid transparency and can make grid operation more efficient. This is especially relevant for distribution system operators when substations are expected not only to provide local indications, but also to be integrated into a modern remotely monitored operating concept.

Direct Comparison in Practical Use

Criterion	EOR-1DS	EOR-3DS
Basic role	Cost-efficient fault indicator for the secondary substation	Fault indicator for the digital secondary substation
Methods	Essential methods, including pulse location and qu2 wiper	Multiple methods with prioritization and weighting
Parameter setting	Simple, possible even without software	Freely parameterizable with AEToolbox
Communication	Modbus RTU Remote	Including MQTT, IEC 60870-5-101/104, IEC 60870-5-103, DNP 3.0, IEC 61850 GOOSE, Modbus RTU/TCP

When Supplementary Monitoring Makes Sense

Fault location and permanent monitoring do not serve the same purpose, but they complement each other in many applications. Fault indicators help narrow down faults quickly after a trip event and identify affected sections. Permanently installed monitoring systems provide additional transparency when recurring events, fault records, long-term data or structured analysis are required.

For this supplementary layer, A. Eberle describes PQI-LV, PQI-DA smart and PQI-DE as key components of a system for measurement tasks in low-, medium- and high-voltage grids. The analyzers can be used as disturbance recorders with a sampling rate of up to 41 kHz, as power quality measuring devices and as grid analyzers. WebPQ® is positioned as the central analysis software for permanently installed disturbance recorders and power quality monitoring devices.

This distinction is helpful in practice:

• Fault indicators support fast narrowing down directly after the event.
• Monitoring systems provide additional measurement and trend data.
• WebPQ® enables centralized, structured analysis across multiple devices.