Distance protection uses both current and voltage to detect errors. From these two sizes, the impedance (continuous) is continuously calculated.
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| Distance Protection Relay Installation on Transmission Lines |
In the event of a short circuit, the voltage suddenly collapses and a high current flows. This causes a small impedance according to the formula Z = U / I.
(The ideal short circuit takes place at U = 0)
A trigger time (eg 0 - 2 Ω → 0.2 s | 2 - 4 Ω → 2.5 s) is assigned for any impedance zone. A distance protection relay thus offers multiple triggering times. (Since the impedance value is determined by the line or cable part on which the current flows along the distance up to the fault point).Again, while the direction of the fault is detectable, a fault in the forward direction of 0.10 ohms, for example, can be separated from the mains within 0.05 seconds while this can be determined as 1.5 seconds for a fault in the reverse direction with the same impedance
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