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In this paper, investigations are carried out to explore the impact of generator distance phase backup protection (Relay (21)) on the generator overexcitation thermal capability. These investigations have included the performance of Relay (21) when it is set to provide thermal backup for the generator during two common system disturbances, namely a system fault and a sudden application of a large system load while the overexcitation limiter (OEL) is in service. The results of these investigations have shown that the current setting of Relay (21) for generator thermal backup protection restricts the overexcitation thermal capability of the generator. Such a restriction does not allow the generator to supply its maximum reactive power during such events. The paper highlights the need for conducting in-depth dynamic stability studies to evaluate the existing setting of the generator distance phase backup protection relay in order to allow the generator to fulfill the system requirements during major disturbances to ensure adequate level of voltage stability.