Voltage Controls
Phase A/B/C Voltage Magnitude & Angle: Sets each phase's magnitude and angle (in degrees). In Phase Mode, these sliders map directly to the three phases. In Sequence Mode, they represent V0, V1, V2 (zero/positive/negative sequence) magnitudes and angles.
Voltage Unison Shift (°): Temporarily adds the same angle shift to all three phases (or sequences). This is a convenient way to push all the angles together.
Voltage: Phase Sliders / Voltage: Sequence Sliders: Toggles how we input or display the voltage phasors — either directly as phase A/B/C or via symmetrical components (V0, V1, V2).
Current Controls
Similar to the voltage controls, Phase A/B/C Current Magnitude & Angle set the three-phase currents in phase mode, or the zero/positive/negative sequence components in sequence mode.
Current Unison Shift (°): Shifts all three phase (or sequence) angles together.
Current: Phase Sliders / Current: Sequence Sliders: Same concept as for voltage but for current phasors.
Ground Distance Controls
K (0 - 6): The zero-sequence compensation factor used for ground-fault loops. In many relays, K is derived from line impedances (e.g., (Z0 - Z1)/Z1). A larger K typically indicates a large zero-sequence impedance difference for ground faults.
Mho Circle Magnitude (0 - 3): Defines the diameter of the mho characteristic in the R-X plane (impedance plane). A bigger diameter means a more permissive characteristic that covers more impedance area.
Mho Circle Torque Angle (0 - 90): The torque angle sets how the circle is oriented in the R-X plane, typically near the line angle. Setting it close to 90° rotates it to be mostly “reactive” coverage; smaller angles lean more in the resistive direction.
Significance of Each Plot
Voltage/Current Phasor Plots: Display individual phases (A, B, C) and sequence components (0, 1, 2) as rotating vectors with their magnitude and angle shown in real time.
Oscillography (Real part): Shows the time-domain waveform of the real part of each phase’s voltage or current over a short window (e.g., 30 cycles), helping visualize phase shifts and magnitudes as sine waves over time.
Phase Distance Plot: Plots the line-to-line fault loops (e.g., (VA - VB) / (IA - IB), etc.) in the complex impedance plane (R-X). Each arrow starts at the origin and extends out to the “seen” impedance at that moment.
Ground Distance Plot: Plots line-to-ground fault loops (VA / (IA + K·I0), etc.) in the complex plane. The factor K determines how zero-sequence current is added for ground faults.
Mho Circle in Distance Relaying
In protective relaying, a mho element is a distance characteristic in the R-X plane shaped like a circle that passes through the origin. Its center is offset along the line’s impedance angle so that it covers a specific protection zone.
The Mho Circle Magnitude slider sets the diameter (reach) of that circle, and the Torque Angle sets its orientation with respect to the R-X axes. Typically, the torque angle is set close to the line angle so the relay is most sensitive to faults along the intended line corridor.
Any measured fault impedance that falls inside this circle is considered “within reach” by the mho distance element, indicating a fault on or near the protected line segment.