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In high-voltage power systems, overload or short-circuit accidents occur frequently owing to the failure of the user equipment, leading to the occurrence of power accidents. Therefore, protective relays must be installed before and after each feeder to isolate the occurrence of faults and thus reduce damage to the power system. However, when the working power supply of the protective relay loses power, it will not be possible to isolate the accident feeder, and the failure of the power system will expand, severely affecting the reliability of the system power supply. Therefore, it is expressly stated by the Taiwan Power Company that a capacitor trip device (CTD) must be installed to ensure a power supply to the protective relay for highvoltage users. However, CTDs currently on the market often fail to ensure the proper operation of the protective relay owing to an insufficient capacitance or a low output operating voltage. Therefore, we propose a high-capacity CTD capable of performing self-tests and instant notification for network monitoring. Compared with the conventional CTD, our CTD can prevent instantaneous large current transfer to the powered device, ensuring that the power supply of the powered device is uninterrupted. It can accomplish the real-time monitoring of the power status, provide a stable power supply, prevent overcurrent, and protect equipment. It is a very important contribution to the protection of the relay system. [ABSTRACT FROM AUTHOR]

This paper presents the protective relay settings of tie line tripping and design of load-shedding scheme for an integrated steelmaking industrial power system to ensure system stability after a severe fault contingency on an external utility power network. The transient stability analysis of the industrial power system with the equivalent external Taipower system has been executed for an actual fault contingency in 2005. The mathematical models of 13 cogeneration units in the plant and several large generators of a nearby Taipower thermal plant are included in the computer simulation to solve the system transient response for the fault contingency to verify the accuracy of the models used. To prevent tripping of critical loads due to an external fault contingency, the undervoltage and under/overfrequency relays with proper settings are applied for the tripping of external and internal tie lines. To restore system stability of the industrial power system for the islanding operation after tie line tripping, load shedding is designed to disconnect a proper amount of noncritical loads by considering the governor response and protective constraints of cogeneration units. According to the transient stability analysis of the industrial power system with the proposed protective relay settings and load-shedding scheme, it is found that the voltage sag and oscillation problem caused by fault contingency in the external Taipower system can be mitigated if the tie line tripping is executed in time to prevent the shutdown of critical loads and tripping of cogeneration units. [ABSTRACT FROM AUTHOR]