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Determine fault direction — forward or reverse — using windowed averaging over the fault period.
The Directional tab determines whether a fault is forward (in the protected zone, away from the bus) or reverse (behind the relay, toward the source). This discrimination is essential for coordinated protection on meshed networks, parallel feeders, and ring bus configurations where overcurrent magnitude alone cannot distinguish fault location.
The tab has two sub-tabs: Phase Fault and Earth Fault. Phase fault analysis uses the 90-degree quadrature connection to determine per-phase direction using cross-phase voltages. Earth fault analysis uses zero-sequence quantities ( and , or a dedicated from a core-balance CT) to determine ground fault direction.
Rather than relying on a single measurement at one cursor position, all directional results are averaged over an automatically detected fault window using a majority vote across every cycle in the faulted period. This produces a far more robust directional decision. Detego also automatically detects the network earthing type and sets the appropriate relay characteristic angle (RCA) as a default.
The Phase Fault sub-tab analyzes per-phase direction using cross-phase polarizing voltages. Each phase element (A, B, C) uses the voltage 90 degrees away from its own phase as the reference, which maintains reliable polarization even when voltage collapses on the faulted phase. This is the standard approach for phase-to-phase and multi-phase fault direction.
The Earth Fault sub-tab analyzes zero-sequence direction using the residual voltage () and residual current (). When the recording contains a dedicated residual current channel (CBCT), Detego uses it in preference to the calculated phase sum. This sub-tab also shows the auto-detected earthing type and recommended RCA.
The default sub-tab is automatically selected based on fault detection results. If zero-sequence current activity is detected (indicating earth fault involvement), the Earth Fault sub-tab is shown first. Otherwise, the Phase Fault sub-tab is the default.
Detego automatically detects fault inception and clearance from or phase current transients and defines a fault window spanning that period. The window boundaries appear as draggable slider handles on a timeline bar, and can also be adjusted by entering start/end values directly in milliseconds.
The directional decision is computed independently for every power-frequency cycle within the fault window, then combined using a majority vote. The verdict banner reports the cycle counts explicitly — for example, “17 forward, 3 reverse, 0 low confidence” — so you can see exactly how consistent the directional indication is across the entire fault.
This windowed approach is significantly more robust than a single-point measurement taken at one cursor position. It naturally rejects transient effects at fault inception and clearance, and exposes any instability in the directional indication during the fault period.
The hero element at the top of the results area is the verdict banner. It presents the majority-vote direction as a large, color-coded label with the percentage of agreeing cycles:
On the Earth Fault sub-tab, the verdict banner also shows the auto-detected earthing type with a confidence badge and a “Change” button that opens the RCA override selector.
On the Earth Fault sub-tab, Detego automatically classifies the network earthing type from the zero-sequence measurements observed during the fault window. The detected type sets the default RCA preset, saving you from having to guess or look up the correct angle. You can always override the selection using the “Change” button on the verdict banner.
The classification recognises the following earthing types, each with its characteristic RCA:
| Earthing Type | Default RCA | Notes |
|---|---|---|
| Petersen coil (compensated) | 0° | Automatically enables the wattmetric method |
| Resistance earthed | 0° | Common on medium-voltage distribution networks |
| Solidly earthed — distribution | -45° | Typical for MV/HV distribution |
| Solidly earthed — transmission | -60° | Typical for EHV transmission |
| Insulated | +90° | Zero-sequence current is capacitive |
Each classification includes a confidence badge — HIGH, MODERATE, or LOW — reflecting how clearly the zero-sequence measurements match the expected signature. When confidence is low, verify the result against your network knowledge before relying on the default RCA.
When the COMTRADE recording contains a dedicated residual current channel — typically named Io1, IE, or In — Detego detects it automatically and uses it as the source for earth fault analysis. This is indicated in the auto-detect banner (for example, “I₀ = Io1 (CBCT)”).
A dedicated core-balance CT (CBCT) measurement is preferred over the calculated sum of phase currents () because it is measured directly and avoids the CT errors that accumulate when summing three separate transducers. This is especially important on compensated (Petersen coil) networks, where the phase CT sum often produces a noisy residual signal that can degrade the directional measurement.
The main display shows current vectors on a polar diagram with operate and restrain zones. The operate zone (upper half, shaded green) represents the forward direction; the restrain zone (lower half, shaded red) represents the reverse direction. The zero-torque line and maximum torque angle (MTA) are drawn for reference.
On the Phase Fault sub-tab, all three phase current vectors are plotted simultaneously, color-coded: A (red), B (blue), C (green). On the Earth Fault sub-tab, the residual current vector is shown against the zero-sequence polarizing reference.
The summary bar below the chart shows per-phase direction badges with margin percentages. Each badge is colored to indicate the result:
The margin percentage indicates how deep into the operate or restrain zone the operating point sits: 100% at the maximum torque angle (maximum sensitivity), 0% at the ±90° boundary. Higher margins mean more confident directional decisions.
Use the phase tabs (All, A, B, C) to switch between the combined 3-phase view and detailed single-phase views. The single-phase view shows the classic polar characteristic diagram with detailed numerical results: directional angle, RCA, margin, , polarizing voltage, and operating current.
Each phase element reports a directional power value , displayed in W or kW units. This is the real component of the torque product — the quantity that a relay uses to discriminate direction:
On the Earth Fault sub-tab with Petersen coil earthing, the wattmetric method is used and represents the zero-sequence active power — the only reliable directional discriminant on compensated networks.
The residual voltage () and residual current () are displayed for earth fault analysis. Under balanced conditions these are near zero; during ground faults they become non-zero, providing the operating and polarizing quantities for earth fault directional elements.
Under the Advanced collapsible section, enabling Neg-Seq Polarisation adds a separate card showing the and phasors, the angle between and , signal strength, and direction. Low signal strength warnings indicate the fault is nearly balanced and negative-sequence polarization may be unreliable.
| Setting | Default | Description |
|---|---|---|
| Phase Fault RCA Preset | 90°-30° (30°) | Selects RCA for phase fault directional elements. Presets: 30° (plain feeders), 45° (transformer feeders), or custom angle. |
| Earth Fault RCA Preset | Auto-detected | Auto-set by the earthing classifier based on zero-sequence measurements. Manual override options: resistance earthed (0°), solidly earthed distribution (-45°), solidly earthed transmission (-60°), insulated (+90°), Petersen coil (0°), or custom angle. |
| Fault Window | Auto-detected | Start and end of the fault period used for windowed averaging. Auto-detected from or phase current fault events. Adjustable via the slider handles or by entering start/end times in milliseconds. |
Additional settings — including Neg-Seq Polarisation toggle and Channel Override — are available under the Advanced collapsible section at the bottom of the panel.
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