Design and Analysis of a Four-Step Distance Protection Scheme for the Port Harcourt 132kV Sub-Transmission Network.
Abstract
In electrical power systems, transmission lines are needed for the conveyance of large amounts of power across great distances; but their length makes identification of flaws difficult. This article uses the Port Harcourt 132 kV sub-transmission network as a case study to concentrate on the use of distance protection concepts for medium and long transmission lines. We performed a load flow study using ETAP tools and the Newton-Raphson approach to evaluate the system's current operating status. The study found that 17 of the 21 buses were critically undervoltage, with total active and reactive power losses of 40,030 kW and 115,534 kVAr, respectively. This shows how important it is to control voltage and lower power loss. On the high-voltage winding, seven power transformers were tapped. Shunt capacitor banks and on-load tap changers were used to control the voltage and lower the power loss, giving a total of 145,000 kVAr. A load flow analysis showed that things got better: all buses ran within safe voltage ranges; total active and reactive power losses went down from 40,030 kW to 24,095.6 kW and from 115,534 kVAr to 61,446.5 kVAr, respectively. To determine the maximum and minimum fault current magnitudes at several system buses, a short-circuit study was carried out in line with the IEC 60909 standard. The lowest is 18.993 kA; the overall maximum fault current is indicated by the results as 186.681 kA. With zone 1 configured for instantaneous operation covering 80% of the line, zone 2 programmed to activate within 0.2 seconds for 100% of the line, zone 3 set to operate at 0.6 seconds for 120% of the line, and zone 4 designated to operate within 1 second for faults occurring in the reverse direction, we developed a four-step distance protection scheme. A three-phase fault was put on different parts of the line, and the relay sent out trip signals in the right places. This proved that the distance relay designs worked as planned.
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