PROTECTION SYSTEM OF POWER LINE WITH NEUTRAL GROUND RESISTOR AND DESIGN METHOD THEREOF

摘要

The present invention provides a system for protecting a power system by using a neutral ground resistor. The present invention includes: a main incoming line receiving power from a power company; a main transformer connected to the main incoming line to lower a voltage of the main incoming line and transmit the power to a Δ connection; a bus receiving the voltage lowered by the main transformer transmitted thereto; a main line switch installed between the main transformer and the bus to be able to disconnect the bus so that the bus is separated from the main transformer; a ground transformer connected to the bus and configured of a Y connection; a ground line switch installed between the ground transformer and the bus to be able to separate the ground transformer from a main bus; a neutral ground resistor installed between a neutral point of the Y connection of the ground transformer and a ground; a ground current transformer measuring current flowing through the neutral ground resistance; and a ground protection relay controlling the main line switch by using the current of the ground current transformer. Accordingly, the main purposes of the present invention are to i) determine a method for calculating a required capacity of the ground transformer, ii) determine a method for calculating the size of the neutral ground resistor and the magnitude of an effective current that can flow through the resistor, iii) determine a method for calculating a limit of resistance that safely protects insulation of electrical equipment by preventing a voltage phase of a sound phase from exceeding two times a normal voltage when one line is grounded, iv) determine a method for setting the ground resistor as a standard to improve efficiency of parts management and a method for calculating the capacity of a shunt reactor inevitably installed on a line to offset capacitive current when earth charting current is excessive, and v) determine a method for rationalization of the protection system and reduction of the number of electric facilities when receiving electricity from a long line like a railroad.