Overvoltage protection circuit

Claim 2

An overvoltage protection circuit, comprising: a plurality of series connected thyristor means having an overvoltage protection function; a plurality of impedance means, each being connected in parallel with one of said thyristor means, respectively; and said plurality of impedance means including at least a first impedance means and at least a second impedance means, wherein said first impedance means comprising a first impedance circuit having a first impedance value and said second impedance means comprising a second impedance circuit.

Claim 3

The overvoltage protection circuit according to claim 1, wherein: each of said plurality of impedance means includes a series circuit of a snubber capacitor and a snubber resistor and a voltage grading resistor connected in parallel with said series circuit.

Claim 4

The overvoltage protection circuit according to claim 1, wherein: said plurality of impedance means includes at least one impedance means comprising a variable impedance circuit.

Claim 5

The overvoltage protection circuit according to claim 1, wherein: each of said plurality of thyristor means includes a VBO-free thyristor.

Claim 6

The overvoltage protection circuit according to claim 1, wherein: each of said plurality of thyristor means includes an anti-parallel circuit of two VBO-free thyristors having a second impedance value, said first impedance value being different from said second impedance value; wherein the turn-on voltage of said overvoltage protection circuit is finely adjusted based upon the values of said plurality of impedance means.

Claim 7

An overvoltage protection equipment for protecting an electric equipment from overvoltage, comprising; three overvoltage protection circuits connected between respective two phases of said electric equipment; each of said three overvoltage protection circuit, including a plurality of series connected thyristor means having an overvoltage protection function, and a plurality of impedance means, each being connected in parallel with one of said thyristor means, respectively, and said plurality of impedance means comprising at least a first impedance means and at least a second impedance means, wherein said first impedance means comprising a first impedance circuit having a first impedance value and said second impedance means comprising a second impedance circuit having a second impedance value, said first impedance value being different from said second impedance value; wherein the turn-on voltage of said overvoltage protection circuit is finely adjusted based upon the values of said plurality of impedance means.

Claim 8

An overvoltage protection equipment for protecting an electric equipment from overvoltage, comprising; three overvoltage protection circuits connected between respective two phases of said electric equipment; each of said three overvoltage protection circuit, including a plurality of series connected thyristor means having an overvoltage protection function, and a plurality of impedance means, each being connected in parallel with one of said thyristor means, respectively, and said plurality of impedance means comprising at least a first impedance means and at least a second impedance means, wherein said first impedance means comprising a first impedance circuit having a first impedance value and said second impedance means comprising a second impedance circuit having a second impedance value, said first impedance value being different from said second impedance value; wherein the turn-on voltage of said overvoltage protection circuit is finely adjusted based upon the values of said plurality of impedance means.

Claim 9

The overvoltage protection equipment according to claim 6, wherein: each of said plurality of thyristor means includes an anti-parallel circuit of two VBO-free thyristors.

Claim 10

An overvoltage protection equipment for protecting a synchronous motor and a rectifier for supplying DC power to a field circuit of said synchronous motor from overvoltage, comprising: an overvoltage protection circuit connected between said synchronous motor and said rectifier; said overvoltage protection circuit including a plurality of series connected thyristor means having an overvoltage protection function, and a plurality of impedance means, each being connected in parallel with one of said thyristor means, respectively, and said plurality of impedance means comprising at least a first impedance means and at least a second impedance means, wherein said first impedance means comprising a first impedance circuit having a first impedance value and said second impedance means comprising a second impedance circuit having a second impedance value, said first impedance value being different from said second impedance value; wherein the turn-on voltage of said overvoltage protection circuit is finely adjusted based upon the values of said plurality of impedance means.

Claim 11

An overvoltage protection equipment for protecting a synchronous motor and a rectifier for supplying DC power to a field circuit of said synchronous motor from overvoltage, comprising: an overvoltage protection circuit connected between said synchronous motor and said rectifier; said overvoltage protection circuit including a plurality of series connected thyristor means having an overvoltage protection function, and a plurality of impedance means, each being connected in parallel with one of said thyristor means, respectively, and said plurality of impedance means comprising at least a first impedance means and at least a second impedance means, wherein said first impedance means comprising a first impedance circuit having a first impedance value and said second impedance means comprising a second impedance circuit having a second impedance value, said first impedance value being different from said second impedance value; wherein the turn-on voltage of said overvoltage protection circuit is finely adjusted based upon the values of said plurality of impedance means.

Claim 12

The overvoltage protection equipment according to claim 8, wherein: each of said plurality of thyristor means includes an antiparallel circuit of two VBO-free thyristors.

Claim 13

A power converter, comprising: a plurality of bridge connected arm circuits; each of said arm circuits including a series circuit of a reactor and an overvoltage protection circuit; said overvoltage protection circuit including a plurality of series connected thyristor means having an overvoltage protection function, and a plurality of impedance means, each being connected in parallel with one of said thyristor means, respectively, and said plurality of impedance means comprising at least a first impedance means and at least a second impedance means, wherein said first impedance means comprising a first impedance circuit having a first impedance value and said second impedance means comprising a second impedance circuit having a second impedance value, said first impedance value being different from said second impedance value; wherein the turn-on voltage of said overvoltage protection circuit is finely adjusted based upon the values of said plurality of impedance means.

Claim 14

A power converter, comprising: a plurality of bridge connected arm circuits; each of said arm circuits including a series circuit of a reactor and an overvoltage protection circuit; said overvoltage protection circuit including a plurality of series connected thyristor means having an overvoltage protection function, and a plurality of impedance means, each being connected in parallel with one of said thyristor means, respectively, and said plurality of impedance means comprising at least a first impedance means and at least a second impedance means, wherein said first impedance means comprising a first impedance circuit having a first impedance value and said second impedance means comprising a second impedance circuit having a second impedance value, said first impedance value being different from said second impedance value; wherein the turn-on voltage of said overvoltage protection circuit is finely adjusted based upon the values of said plurality of impedance means.

Claim 15

The power converter according to claim 10, wherein: each of said plurality of thyristor means includes an anti-parallel circuit of two VBO-free thyristors.

Claim 16

A static var compensator, comprising: delta connected three arm circuits connected between respective two phases of a power system; each of said arm circuits including a series circuit of a reactor and an overvoltage protection circuit; said overvoltage protection circuit including a plurality of series connected thyristor means having an overvoltage protection function, and a plurality of impedance means, each being connected in parallel with one of said thyristor means, respectively, and said plurality of impedance means comprising at least a first impedance means and at least a second impedance means, wherein said first impedance means comprising a first impedance circuit having a first impedance value and said second impedance means comprising a second impedance circuit having a second impedance value, said first impedance value being different from said second impedance value; wherein the turn-on voltage of said overvoltage protection circuit is finely adjusted based upon the values of said plurality of impedance means.

Claim 17

A static var compensator, comprising: delta connected three arm circuits connected between respective two phases of a power system; each of said arm circuits including a series circuit of a reactor and an overvoltage protection circuit; said overvoltage protection circuit including a plurality of series connected thyristor means having an overvoltage protection function, and a plurality of impedance means, each being connected in parallel with one of said thyristor means, respectively, and said plurality of impedance means comprising at least a first impedance means and at least a second impedance means, wherein said first impedance means comprising a first impedance circuit having a first impedance value and said second impedance means comprising a second impedance circuit having a second impedance value, said first impedance value being different from said second impedance value; wherein the turn-on voltage of said overvoltage protection circuit is finely adjusted based upon the values of said plurality of impedance means.

Claim 18

The static var compensator according to claim 12, wherein: each of said plurality of thyristor means includes an anti-parallel circuit of two VBO-free thyristors.