Detection of high resistance earth faults in medium voltage networks using higher harmonics

The influence of the network asymmetry on the settings and sensitivity of an earth fault protection using higher harmonics

“…• From the attached characteristics, in the worst case scenario that can occur in the real network (I CS = 100 A, C 0p = 1%, C 01p = 2.5%) with extremely high content of the third harmonic k 3p = 5%, the asymmetry reactive power Q 031 does not exceed 25 mVAr. With such a threshold, the protection using the reactive power criterion Q 031 is able to detect earth faults with very high non-linear resistance R F , reaching up to several tens kΩ, as shown in publications [4,5].…”

“…The method based on the use of the reactive power criterion Q 0h of higher harmonics of zero sequence current and voltage generated by the non-linear resistance R F in a short-circuit is promising in terms of detection of high resistance faults. Preliminary tests have shown [4,5] that in symmetric networks can detect short circuits with resistance R F > 100 kΩ using this criterion.…”

“…To detect high-resistance earth faults, unconventional methods must be used. In works [4,5], it was shown that such short-circuits can be detected by the reactive power criterion for higher harmonics of zero sequence current and voltage. This criterion comes down to the main dependence:…”

“…suited. The asymmetry reactive power for third harmonics is the smallest, and, as shown in [4][5][6], the non-linear resistance of the earth fault, especially an arc resistance [13][14][15][16], generates mainly the third harmonics of the zero sequence current and voltage. The protection using criterion Q 031 will have the lowest setting and the highest sensitivity.…”