Modified algorithm for directional earth-fault protection without voltage inputs

Wide range algorithm for directional earth‐fault protection without voltage inputs

“…The idea and algorithm were published in [20]. Improved algorithm [21] uses only one phase current instead of three phase currents. This way, the absolute phase and amplitude symmetry of the reference value is achieved.…”

“…Also, the required number of measurements is reduced from 4 to 2 per feeder. However, both algorithms [20,21] have the same limitation: a load of the feeders must be known in a range of 60°. In case of exceeding the predefined range, the relay will make mistakes.…”

“…Described methodology was improved using only one phase current [21]. Indicator of the direction of the other two phases is calculated using the same current, previously shifted for 2π/3 rad (m/3 samples) and 4π/3 rad (2m/3 samples).…”

“…id c = 4m The advantage of the algorithm [21] is the absolute phase and amplitude symmetry of the reference value, which was kept by artificial shifting of the measured phase current. In the case of using the original phase currents [20], this symmetry would be impaired due to the impact of fault currents.…”

“…Also, in isolated neutral networks two-phase overcurrent protection is often used instead of three-phase overcurrent protection because of economic reasons and better selectivity in case of double earth-fault. In such cases, the improved algorithm [21] solves the problem of missing phase current measurement. Tripping conditions of both algorithms are the same and are given in Table 1, column 2.…”