A ground fault current limiter, in which reactors are connected in series to a neutral point for compensating for capacitances to ground of a power switches capable of turning ON/OFF at a high speed are connected in parallel with respective reactors, occurrence of a ground fault is detected from a phase difference between a zero-phase sequence current and a zero-phase sequence voltage at time of sampling, an optimal compensation quantity of capacitances to ground is computed based on the zero-phase sequence current and the zero-phase sequence voltage at time of occurrence of a ground fault, and ON/OFF of the switches are controlled thereby to alter the reactor quantity so as to correspond to the compensation quantity

Ground fault current limiter and method of limiting ground fault current

The method of phase-shifting a voltage applied to a susceptance interconnecting a phase line of a first polyphase AC network with a corresponding phase line of a second polyphase AC network, both AC networks being synchronous, comprises the steps of: connecting a primary winding of a transformer in series with the susceptance; deriving from the AC networks, an excitation voltage having a phase angle with respect to a phase voltage provided by the phase line of the first AC network; and applying the excitation voltage to a secondary winding of the transformer, whereby the excitation voltage combines through the transformer with the phase voltage to cause phase-shifting of the voltage applied to the susceptance. This method is implemented with a phase-shifting interconnecting apparatus comprising series transformer arrangements having primary windings in series with capacitive and inductive susceptances, and secondary windings for receiving excitation voltages derived from the phase voltages of the first AC network. Angles ofphase-shifting produced by the series transformer arrangements can be changed either by changing portions of the primary windings connected in series with the susceptances, or by modulating amplitudes of the excitation voltages.

Method of phase-shifting voltages applied to susceptances interconnecting two synchronous polyphase AC networks and a phase-shifting interconnecting apparatus thereof

A triple core transformer including a coupler connected to a third core between two primary windings. Two sets of twisted pairs are wound around each primary core such that a strand of each pair communicates with primary each core. One strand of each pair is wound denser than the complementary strand of that pair. The denser strands are connected to a third winding around the third core. The third winding is wound in a series of segments. Each of the segments is connected to the preceding segment in a wire twist.

Triple core toroidal transformer

A system stabilizing controller for estimating and controlling stability of a power grid includes a collection unit collecting grid information including a power flow amount from the power grid and a calculation unit calculating a generator shedding amount at a fault observation point on the basis of the grid information and estimating a correlation line on the basis of the power flow amount and generator shedding amount. The calculation unit determines a generator phase angle curve that is the relationship between the internal generator phase angle of a generator connected to the power grid and the power flow amount, determines a stability limit power flow amount on the basis of the amounts of generator acceleration energy and deceleration energy in the generator phase angle curve, determines a stability limit generator shedding amount corresponding to the stability limit power flow amount, and estimates a correlation line including a stability limit point.

System stabilizing control device and method

Phase-shifting apparatus for interconnecting two synchronous polyphase ac networks

An interconnecting apparatus for electric power systems wherein two electric power systems are connected to each other with a series transformer and the secondary winding of the series transformer is energized with a compensating voltage whose value and polarity are such that it cancels the voltage drop developed across said transformer when said electric power systems are normally operating. The compensating voltage is derived from the secondary winding of an exciting transformer inserted between the central point of the series transformer and the earth. The secondary winding of the series transformer is connected in delta and the secondary winding of the exciting transformer is star-connected. If it is necessary, the exciting transformer may be provided with a tertiary winding to control the voltages of the respective power systems by the voltage of this tertiary winding.

Keizo Nakayam

Papers

Interconnecting apparatus with impedance insertion means for electric power systems