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This paper presents the proper design of protective relay settings for tie-line tripping and load shedding of a cogeneration system in a high-tech science-based industrial park in Taiwan, ROC. To improve the power service quality for the industrial customers, two 161/161-kV transformers with tap changers have been designed to be in series with the tie line. According to the transient stability analysis, the voltage levels at the customer buses can be significantly improved during the time interval of utility fault. The reduction of the voltage drop at the cogeneration bus can also benefit the critical clearing time to restore the stable operation of the cogeneration units after system disturbance. To comply with the fault interruption capacity of the circuit breakers of other industrial customers served by the same utility substation, the series transformers can effectively reduce the fault current magnitude supplied by the cogeneration units. It is found that the application of the series transformers and the cogeneration system with proper protective relay settings can enhance the power service quality of high-tech industrial customers by providing better voltage control and transient stability.