Zero Sequence Compensation Factor Effect on Distance Protection Ground Reach (Practical study)

摘要

Zero sequence compensation factor (Ko) is used for the correction of the distance protection reach in the case of ground faults. Ko is essential for the accurate determination of the ground fault location by distance protection on a transmission line. This is much more critical in the case of underground cables rather than the case of overhead lines because of small lengths of cables besides their low impedance per unit length. Ko should be set to reflect the actual grounding conditions of the protected cable or the distance protection will suffer from over or under reach [1]. A practical study based on actual measurements of Ko for different 52 cables within the Egyptian electricity network shows that distance protection ground reach is sensitive for the value of Ko.The soil nature and the grounding conditions normally affect the value of Ko of the over head lines as well as cables. However, this effect for the underground cables is greater.The paper shows the results of measuring Ko and its effect on the distance relay reach. It also shows that the setting of the factor Ko is a characterizing parameter for each cable feeder even if the feeders are in the same route. Normally an average value of Ko is taken for the three phases as all of the distance protection relays, up till now, deal only with a single valued Ko factor for the three phases.