28 March 2018

Tavrida Electric accomplished TEFCS pilot project in South Africa

Tavrida Electric has supplied a recloser for the biggest African power company Eskom, that generates approximately 95% of the electricity used in South Africa and approximately 45% of the electricity used in Africa. The project took place near Cape Town, in Badsberg trial site.

Customer’s power consumers were suffering because of frequent interruptions from earth faults, so Eskom started to look for a new solution to improve the situation. Company was searching for a single pole recloser with very specific controls (not found on a standard recloser) to be used as a TEFCS (Transient Earth Fault Clearing Scheme). Amongst other settings, the user must be able to set the TEFCS recloser not to lock out. Tavrida Electric’s Rec35 has those special programming capabilities.

Rec35 with custom programmed control is used as a neutral switching device. One pole of the recloser is connected in series with the NEC (neutral earth compensator) neutral and the substation earth mat.
The method is based on the following principle. Upon the detection of the earth fault (EF) current, Rec35 trips and recloses with a defined dead time, temporary converting the solid or low resistance earthed network into an isolated neutral network. Isolated neutral network with a single phase-to-earth fault has no fault current flow, except for a small capacitive current due to an unbalance in line capacitances to earth. During such an EF the whole system remains operational and the fault either self-extinguishes or develops into permanent fault, resulting in main protection operation after recloser recloses. The success rate of the TEFCS depends mainly on the type of EF, the speed with which the protection and switching device operate to minimize the amount of ionized air, and on how quickly the object causing the fault is moving away from the live equipment to establish safe clearance.

Test results and operating performance statistics over nearly a year period from trial site demonstrated impressive results. Nearly 87% of EF detected by Rec35 did not cause the interruption of feeder power supply.

TEFCS (transient earth fault clearing scheme) allows to reduce the number of momentary interruptions (improves system MAIFI). It benefits the customers of the utility (farmers, manufacturers, etc.) reducing their operational costs, material losses and/or equipment damage.