Current limiting device for an electric power system

Polyphase current limiting apparatus comprising:

• (a) two current limiting devices, each comprising:
• (1) two normally-closed circuit interrupters, each interrupter comprising a set of separable contact structures,
• (2) means for electrically connecting said interrupters in series comprising an electrical conductor connected between said two interrupters, with one interrupter at the source side and one at the load side of said conductor,
• (3) a normally-open switch,
• (4) means comprising said switch and effective when said switch is closed for electrically connecting said conductor to ground via a low-impedance conductive path located electrically between said interrupters,
• (5) switch-operating means responsive to a fault on the circuit extending through the series-combination of said two interrupters for rapidly closing said switch, thereby connecting said conductor to ground through said switch,
• (6) said switch-operating means operating at such high speed that effective closing of said switch occurs within 1/4 cycle of power frequency current after inception of said fault, thereby effecting current-limiting action with respect to current through said series-combination of interrupters on the load side of said conductive path to ground, said conductive path having a sufficiently low impedance upon closing of said switch to divert through said conductive path despite the presence of said fault sufficient current to effectively produce said current-limiting action,
• (7) means comprising a mechanical coupling between said switch-operating means and one of the contact structures of said source-side interrupter for opening said interrupters in response to said fault sufficiently rapidly that said source-side interrupter interrupts the current therethrough at one of the first three natural current zeros following fault-inception and said load-side interrupter interrupts the current therethrough shortly thereafter, and
• (8) an impedance connected in parallel with said series combination of interrupters, and with no effective connection between said impedance and said conductor except through said interrupters, for conducting current, limited in magnitude by said impedance, around said interrupters when said interrupters have interrupted the respective currents therethrough following their aforesaid opening,
• (b) means for connecting the interrupters of one current limiting device in one phase of a polyphase circuit and means for connecting the interrupters of the other current limiting device in a second phase of said polyphase circuit, and
• (c) means for causing the interrupters of both of said phases to be promptly opened in response to a fault on one of said phases.

Polyphase current limiting apparatus comprising:

• (a) two current limiting devices, each comprising:
• (1) two normally-closed circuit interrupters, each interrupter comprising a set of separable contact structures,
• (2) means for electrically connecting said interrupters in series comprising an electrical conductor connected between said two interrupters, with one interrupter at the source side and one at the load side of said conductor,
• (3) a normally-open switch,
• (4) means comprising said switch and effective when said switch is closed for electrically connecting said conductor to ground via a low-impedance conductive path located electrically between said interrupters,
• (5) switch-operating means responsive to a fault on the circuit extending through the series-combination of said two interrupters for rapidly closing said switch, thereby connecting said conductor to ground through said switch,
• (6) said switch-operating means operating at such high speed that effective closing of said switch occurs within 1/4 cycle of power frequency current after inception of said fault, thereby effecting current-limiting action with respect to current through said series-combination of interrupters on the load side of said conductive path to ground, said conductive path having a sufficiently low impedance upon closing of said switch to divert through said conductive path despite the presence of said fault sufficient current to effectively produce said current-limiting action,
• (7) means comprising a mechanical coupling between said switch-operating means and one of the contact structures of said source-side interrupter for opening said interrupters in response to said fault sufficiently rapidly that said source-side interrupter interrupts the current therethrough at one of the first three natural current zeros following fault-inception and said load-side interrupter interrupts the current therethrough shortly thereafter, and
• (8) an impedance connected in parallel with said series combination of interrupters, and with no effective connection between said impedance and said conductor except through said interrupters, for conducting current, limited in magnitude by said impedance, around said interrupters when said interrupters have interrupted the respective currents therethrough following their aforesaid opening,
• (b) means for connecting the interrupters of one current limiting device in one phase of a polyphase circuit and means for connecting the interrupters of the other current limiting device in a second phase of said polyphase circuit, and
• (c) means responsive to a fault on either phase for operating the current limiting device in the associated phase independently of the current limiting device in the other phase.

A current limiting device comprising:

• (a) a normally-closed circuit interrupter adapted to be connected in series with a power circuit and having a source terminal and a load terminal at opposite electrical sides respectively of said circuit interrupter,
• (b) a normally-open switch,
• (c) means comprising said switch and effective when said switch is closed for electrically connecting said load terminal to ground via a low-impedance conductive path located electrically at the load terminal side of said circuit interrupter,
• (d) switch-operating means responsive to a fault on said power circuit at the load terminal side of said circuit interrupter for rapidly closing said switch, thereby connecting said load terminal to ground through said switch,
• (e) said switch-operating means operating at such high speed that effective closing of said switch occurs within 1/4 cycle of power frequency current after inception of said fault, thereby effecting current-limiting action with respect to current passing in series through said interrupter and said load terminal into the portion of said power circuit at the load side of said conductive path to ground, said conductive path having a sufficiently low impedance upon closing of said switch to divert through said conductive path despite the presence of said fault sufficient current to effectively produce said current-limiting action,
• (f) means mechanically interconnecting said interrupter and said switch-operating means for opening said interrupter in response to said fault sufficiently rapidly that said interrupter interrupts current through the interrupter at one of the first three natural current zeros following fault-inception,
• (g) an impedance connected in parallel with said interrupter for conducting current, limited in magnitude by said impedance, around said interrupter when said interrupter has interrupted the current therethrough,
• (h) and means for reopening said low-impedance conductive path immediately after said interrupter has interrupted and while said interrupter is still open for interrupting current then flowing through said low-impedance conductive path.

A current limiting device comprising:

• (a) a normally-closed circuit interrupter adapted to be connected in series with a power circuit and having a source terminal and a load terminal at opposite electrical sides respectively of said circuit interrupter, said interrupter comprising separable contact structures,
• (b) a normally-open switch,
• (c) means comprising said switch and effective when said switch is closed for electrically connecting said load terminal to ground via a low-impedance conductive path located electrically at the load terminal side of said circuit interrupter,
• (d) switch-operating means responsive to a fault on said power circuit at the load terminal side of said circuit interrupter for rapidly closing said switch, thereby connecting said load terminal to ground through said switch,
• (e) said switch-operating means operating at such high speed that effective closing of said switch occurs within 1/4 cycle of power frequency current after inception of said fault, thereby effecting current-limiting action with respect to current passing in series through said interrupter and said load terminal into the portion of said power circuit at the load side of said conductive path to ground, said conductive path having a sufficiently low impedance upon closing of said switch to divert through said conductive path despite the presence of said fault sufficient current to effectively produce said current-limiting action,
• (f) means comprising a mechanical coupling between said switch-operating means and one of the contact structures of said interrupter for opening said interrupter in response to said fault sufficiently rapidly that said interrupter interrupts current through the interrupter at one of the first three natural current zeros following fault inception,
• (g) an impedance connected in parallel with said interrupter for conducting current, limited in magnitude by said impedance, around said interrupter when said interrupter has interrupted the current therethrough, and
• (h) means effective while said interrupter is open for blocking the flow of current through the series combination of said impedance and said low-impedance conductive path to ground without blocking the flow of current through the series combination of said impedance and a load connected to said power circuit at the load side of said device.

Polyphase current limiting apparatus comprising:

• (a) two current limiting devices, each comprising:
• (1) a normally-closed circuit interrupter adapted to be connected in series with a power circuit and having a source terminal and a load terminal at opposite electrical sides respectively of said circuit interrupter,
• (2) a normally-open switch,
• (3) means comprising said switch and effective when said switch is closed for electrically connecting said load terminal to ground via a low-impedance conductive path located electrically at the load terminal side of said circuit interrupter,
• (4) switch-operating means responsive to a fault on said power circuit at the load terminal side of said circuit interrupter for rapidly closing said switch, thereby connecting said load terminal to ground through said switch,
• (5) said switch-operating means operating at such high speed that effective closing of said switch occurs within 1/4 cycle of power frequency current after inception of said fault, thereby effecting current-limiting action with respect to current passing in series through said interrupter and said load terminal into the portion of said power circuit at the load side of said conductive path to ground, said conductive path having a sufficiently low impedance upon closing of said switch to divert through said conductive path despite the presence of said fault sufficient current to effectively produce said current-limiting action,
• (6) means mechanically interconnecting said interrupter and said switch-operating means for opening said interrupter in response to said fault sufficiently rapidly that said interrupter interrupts current through the interrupter at one of the first three natural current zeros following fault-inception,
• (7) an impedance connected in parallel with said interrupter for conducting current, limited in magnitude by said impedance, around said interrupter when said interrupter has interrupted the current therethrough,
• (8) and means for reopening said low-impedance conductive path immediately after said interrupter has interrupted and while said interrupter is still open for interrupting current then flowing through said low-impedance conductive path,
• (b) means for connecting the interruptors of one of said current limiting devices in one phase of a polyphase circuit and means for connecting the interrupters of the other of said current limiting devices in another phase of said polyphase circuit, and
• (c) means for causing the interrupters of both said phases to be promptly opened in response to a fault on one of said phases.

A current limiting device having a source terminal and a load terminal at opposite electrical sides thereof comprising:

• (a) a normally-closed first circuit interrupter adapted to be connected in series with a power circuit in a location between said terminals, said interrupter comprising separable contact structures,
• (b) a normally-open switch,
• (c) means comprising said switch and effective when said switch is closed for electrically connecting the load terminal side of said first interrupter to ground via a low-impedance conductive path located electrically at said load terminal side,
• (d) switch-operating means responsive to a fault on said power circuit at the load terminal side of said first circuit interrupter for rapidly closing said switch, thereby connecting said load terminal to ground through said switch,
• (e) said switch-operating means operating at such high speed that effective closing of said switch occurs with 1/4 cycle of power frequency current after inception of said fault, thereby effecting current-limiting action with respect to current passing in series through said interrupter and said load terminal into the portion of said power circuit at the load side of said conductive path to ground, said conductive path having a sufficiently low impedance upon closing of said switch to divert through said conductive path despite the presence of said fault sufficient current to effectively produce said current-limiting action,
• (f) means comprising a mechanical coupling between said switch-operating means and one of the contact structures of said interrupter for opening said interrupter in response to said fault sufficiently rapidly that said interrupter interrupts current through the interrupter at one of the first three natural current zeros following fault inception,
• (g) an impedance connected in parallel with said interrupter for conducting current, limited in magnitude by said impedance, around said interrupter when said interrupter has interrupted the current therethrough, and
• (h) means effective while said interrupter is open for blocking the flow of current through the series combination of said impedance and said low-impedance conductive path to ground without blocking the flow of current through the series combination of said impedance and a load connected to said power circuit at the load side of said device, and in which:
• (i) said blocking means of (h) comprises an additional interrupter located between said terminals and connected in series with said first interrupter and in parallel with said impedance, considered with respect to the normal load current path through the current limiting device,
• (j) said low-impedance conductive path is connected between ground and a junction point between said two interrupters, and
• (k) no effective connection is present between said impedance and said junction point except through said interrupters.

A current limiting device comprising:

• (a) a normally-closed circuit interrupter adapted to be connected in series with a power circuit and having a source terminal and a load terminal at opposite electrical sides respectively of said circuit interrupter, said interrupter comprising separable contact structures,
• (b) a normally-open switch,
• (c) means comprising said switch and effective when said switch is closed for electrically connecting said load terminal to ground via a low-impedance conductive path located electrically at the load terminal side of said circuit interrupter, said conductive path having a sufficiently low impedance upon closing of said switch to divert through said conductive path despite the presence of said fault sufficient current to effectively produce said current-limiting action,
• (d) switch-operating means responsive to a fault on said power circuit at the load terminal side of said circuit interrupter for rapidly closing said switch, thereby connecting said load terminal to ground through said switch,
• (e) said switch-operating means operating at such high speed that effective closing of said switch occurs witin 1/4 cycle of power frequency current after inception of said fault, thereby effecting current-limiting action with respect to current passing in series through said interrupter and said load terminal into the portion of said power circuit at the load side of said conductive path to ground,
• (f) means for opening said interrupter in response to said fault sufficiently rapidly that said interrupter interrupts current through the interrupter at the first natural current zero following fault-inception,
• (g) an impedance connected in parallel with said interrupter for conducting current, limited in magnitude by said impedance, around said interrupter when said interrupter has interrupted the current therethrough, and
• (h) means effective while said interrupter is open for blocking the flow of current through the series combination of said impedance and said low-impedance conductive path to ground without blocking the flow of current through the series combination of said impedance and a load connected to said power circuit at the load side of said device.

A current limiting device having a source terminal and a load terminal at opposite electrical sides thereof comprising:

• (a) a normally-closed first circuit interrupter adapted to be connected in series with a power circuit in a location between said terminals, said interrupter comprising separable contact structures,
• (b) a normally-open switch,
• (c) means comprising said switch and effective when said switch is closed for electrically connecting said load terminal to ground via a low-impedance conductive path located electrically at the load terminal side of said circuit interrupter, said conductive path having a sufficiently low impedance upon closing of said switch to divert through said conductive path despite the presence of said fault sufficient current to effectively produce said current-limiting action,
• (d) switch-operating means responsive to a fault on said power circuit at the load terminal side of said circuit interrupter for rapidly closing said switch, thereby connecting said load terminal to ground through said switch,
• (e) said switch-operating means operating at such high speed that effective closing of said switch occurs within 1/4 cycle of power frequency current after inception of said fault, thereby effecting current-limiting action with respect to current passing in series through said interrupter and said load terminal into the portion of said power circuit at the load side of said conductive path to ground,
• (f) means for opening said interrupter in response to said fault sufficiently rapidly that said interrupter interrupts current through the interrupter at the first natural current zero following fault-inception,
• (g) an impedance connected in parallel with said interrupter for conducting current, limited in magnitude by said impedance, around said interrupter when said interrupter has interrupted the current therethrough, and
• (h) means effective while said interrupter is open for blocking the flow of current through the series combination of said impedance and said low-impedance conductive path to ground without blocking the flow of current through the series combination of said impedance and a load connected to said power circuit at the load side of said device, and in which:
• (i) said blocking means of (h) comprises an additional interrupter located between said terminals and connected in series with said first interrupter and in parallel with said impedance, considered with respect to the normal load current path through the current limiting device, and
• (j) said low-impedance conductive path is connected between ground and a junction point between said two interrupters.