Abstract
The coordination between protective devices is the process of determining the most appropriate timing of power interruption during abnormal conditions in the power system. The aim of this work is to coordinate the protection of the 33/11 kV power distribution substation in Iraq using the CYME 7.1 software package. In this paper overcurrent and earth fault relays are simulated in two cases, with time delay setting and instantaneous setting, to obtain the Time Current Characteristics (TCC) curves for each Circuit Breaker (CB) relay of Al-Karama substation (2×31.5 MVA, 33/11 kV) in Babil distribution network. The short circuit current at each CB is calculated and accordingly, the protection coordination for Al-Karama substation has been simulated. The TCC curves have been obtained in two cases for overcurrent and earth fault relays; in a case with time delay setting and in the case with the instantaneous setting. The setting takes into consideration the short circuit current at the furthest point of the longest outgoing feeder and the shortest outgoing feeder.
Highlights
Appropriate protection schemes with proper protection coordination are necessary to maintain the power system reliability and avoid damage to very costly equipment such as power transformers
The phase-to-earth fault current is used for setting the earth fault relays, while the three-phase short circuit current is used for setting the phase relays [1, 2, 3]
The short circuit current on busbar 132 kV for Hilla north substation is 15989.5 A according to the Ministry of Electricity (MoE)
Summary
Appropriate protection schemes with proper protection coordination are necessary to maintain the power system reliability and avoid damage to very costly equipment such as power transformers. The correct operation of protective relays and Auto-Reclosers during transient faults will minimize permanent tripping in the distribution network. Substation and downstream Auto-Reclosers are very much essential to maintain the high reliability in Medium Voltage distribution network. There is a requirement of revising the existing protection settings of Medium Voltage level with the rapid development of distribution networks in Iraq. The objective of the study is to determine the best protection co-ordination of the Medium Voltage system of AL-Krama substation 33/11 kV in the Babil power distribution network. Protection settings of relays at grid substation and downstream Auto-Reclosers of the selected grid substation will be analyzed according to IEC standards to determine the coordination in Medium Voltage level
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