WHITEPAPER: DEFERRING REPLACEMENT OF A 600 MVA, 345GRD Y/138GRD Y/ 13.8 kV SHELL TYPE WESTINGHOUSE AUTOTRANSFORMERPower transformers are essential components of transmission systems and often the most valuable asset in a substation. This 600 MVA autotransformer is the second oldest autotransformer in CPS Energy fleet. It is connected in parallel with a higher impedance autotransformer; therefore, it sees more load than its counterpart and has a combustible gas generation history. These conditions made this autotransformer the most logical candidate for replacement, but the high capital cost for a new unit requires further analysis to justify its replacement.
A condition assessment was performed and indicated that the autotransformer could continue in service for more years. So, the concern then became the autotransformer's reliability. An approach to address this reliability concern is to provide a method for early detection of incipient faults. On-line monitoring provides visibility of issues earlier, reducing the risk of unexpected failures and unscheduled outages, thus raising the reliability to an acceptable level. This paper presents the results of the comprehensive condition assessment carried out, the financial benefits and consequence of deferring this autotransformer replacement, and an evaluation of the economic contribution that could be expected from on-line monitoring.