Abstract
Utility encounters situations like when one out of two power transformers in the substation requires maintenance and only one transformer remains in operation. To meet the load requirements of a maximum number of customers,if not all,the only transformer needs to be overloaded. Due to various load types within the service territory,utilities need to understand the customers' maximum dynamic loading amount to overload a transformer in an emergency. We propose the iteration process with real-world substation data,which considers the concept of a coordinated substation for optimal power flow. We found to what extent the only 138 kV//13.8 kV,30/40/50 MVA transformer can be safely overloaded beyond its nameplate's maximum rating for a minimum time. Within that time,the utility personnel can work on the substation yard and switchgear room safely and comfortably to bring back the other transformer in operation. We found from the perspective of power flow that with increased dynamic loading,transformer secondary current increases. Therefore,under the maximum dynamic loading condition,we should calculate the asymmetric fault current on the 13.2 kV switchgear bus to select the suitable CTs and develop a protection scheme accordingly.
Highlights
Utility encounters situations like when one out of two power transformers in the substation requires maintenance and only one transformer remains in operation
As utility personnel works in the substation and switchgear room to energize the second transformer within the minimum time, their safety needs to be ensured
The loss of one transformer and overloading of the remaining only transformer in the substation requires an in-depth understanding of the customer's loading types, maximum rated capacity of the bus of the only switchgear, asymmetric fault currents on the 13.2 kV bus, arc flash incident energy, and arc flash boundary to ensure the workforce's safety and comfortability
Summary
THE utility provides power to residential, commercial, and industrial customers. each type of customer needs a different type of load over time. Due to the different transmission line parameters, each of these two sections may not have the proper combination of source and load This issue is more critical when a substation has two transformers, and one of them is out of service for maintenance, and only one remains energized to supply power to the customers reliably. Arc flash boundary needs to be considered in the medium-voltage switchgear cubicles to know the hazard risk category (HRC) requirements and minimum personal protective equipment (PPE) required to ensure the safety of personnel [16]. This is the first paper that brought the issues of high voltage 138 kV by 13.8 kV ring configured substation design and switchgear's asymmetric fault current and arc flash incident energy together.
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