Impedance Trajectory & Distance Protection
Upload a COMTRADE recording and instantly plot the impedance trajectory on an R-X diagram with configurable mho zones. Verify distance relay operation and zone coverage — free, in your browser.
Everything you need for distance protection analysis
R-X Diagram with Zone Overlays
See the measured impedance plotted on a clean R-X diagram with up to 8 configurable mho zone circles. Zones are color-coded and labeled for instant visual identification of which zone tripped.
Animated Impedance Trajectory
Scrub through the recording and watch the impedance point move in real time on the R-X diagram. Observe exactly when the impedance enters a zone and how quickly it traverses the characteristic.
Multi-Loop Analysis (AG/BG/CG/AB/BC/CA)
All six measurement loops are computed simultaneously — three phase-to-earth loops and three phase-to-phase loops. Switch between loops to identify the faulted phases and compare loop impedances.
Configurable Zone Settings
Set reach (ohms secondary), impedance angle, and time delay independently for each zone. Import relay settings directly from XRIO files to replicate the exact protection configuration.
Auto Faulted Loop Detection
Detego automatically identifies the faulted measurement loop using sequence component analysis and flags it on the diagram. No manual loop selection needed for most recordings.
Load Encroachment Overlay
Visualize the load impedance region on the R-X diagram to verify that protection zones do not encroach on normal load conditions — a critical check for long-line distance protection.
Why impedance trajectory matters
Distance relays operate by measuring the apparent impedance seen at the relay location. When a fault occurs, the impedance collapses toward the origin of the R-X diagram — the closer the fault, the smaller the impedance magnitude. A distance relay trips when this measured impedance falls inside a protection zone characteristic, typically a mho circle. Understanding this trajectory is essential for verifying correct relay operation, diagnosing mis-operations, and setting zone reaches that balance sensitivity against load encroachment.
Impedance trajectory analysis reveals information that waveforms alone cannot provide. A slow trajectory indicates evolving fault conditions or high fault resistance. An impedance that grazes a zone boundary may explain a delayed trip or an incorrect reach. Comparing the faulted loop trajectory against zone settings confirms whether the relay would have operated correctly — and at what speed. This makes trajectory visualization a standard step in any post-fault review or relay commissioning exercise.
Detego computes the apparent impedance for all six measurement loops — AG, BG, CG, AB, BC, and CA — using DFT-based phasor estimation applied to each sample interval. The result is a continuous impedance trajectory that can be overlaid on configurable mho zone circles. For more detail on the underlying calculation methods, see the distance protection theory page or the distance protection guide.
Frequently asked questions
Validate your distance protection
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