Abstract
Due to load growth and various load types within the service territory, utilities need to enhance the utilization of substations. In any case, towards the coordinated substation design, the utilization of the transformers' most total capacity cannot be reduced just because there is a lack of proper coordination between transmission and distribution systems. The transmission and distribution systems' stability and safe operability must be investigated in a coordinated substation. The critical issues are the asymmetric fault currents on the high voltage and arc-related safety issues on the distribution switchgear at different dynamic loading scenarios. We found that when one 138 kV transmission line and two transformers are energized, with increased dynamic loading, from 40% and above, the substation, as a whole, gets gradually more stressed. Because of the highest amount of fault currents on the 138 kV bus, to avoid CT saturation, we need to consider that three transmission lines are connected, and all three transformers are running at 100% dynamic loading. At this value of dynamic loading, in the 13.2 kV switchgear, the incident energy is 2 cal/cm2, and the arc flash boundary is four feet, which ensures that all workers need to wear the proper arc-rated clothes to work on any de-energized cubicle of the switchgear.
Highlights
The utility provides power to the different types of customers- residential, commercial, and industrial
We found that the asymmetrical fault current increases with more energized 138 kV transmission lines connected to the substation
To consider the highest amount of asymmetric fault current and select an appropriate CT that will not saturate, we considered that three transmission lines are connected, and all three energized transformers are running at 100% dynamic loading
Summary
The utility provides power to the different types of customers- residential, commercial, and industrial. This paper brought the issues of high voltage 138 kV by 13.8 kV substation design and 13.2 kV switchgear's highest possible fault current and arc-related incident energy together. In the application-based substation design, different loading scenarios considering asymmetrical fault current and arc flash-related issues together make this paper unique. Asymmetric fault current, coordination of 138 kV transmission and 13.8 kV distribution systems, and arc flash incident energy must be conceptualized in an integrated approach at the project's onset. Towards optimal power flow through the substation, the effects of dynamic loading on the fault current (FC) on the HV and MV buses, and arc-related issues together These approaches were applied to one of our projects to construct a 138 kV by 13.8 kV substation
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