Ground fault protective device

Claim 2

A protective system for a polyphase alternating-current system comprising a current transformer adapted to be connected to means for obtaining an output current which varies with the ground current in said system for providing an alternatingcurrent output which varies with the ground current in said system, rectifying means having input terminals connected to said current transformer and output terminals for providing a unidirectional output current which varies with the ground current in said system, a resistor and an energy-storing capacitor connected in series circuit relationship with one another, the series circuit being connected across the output terminals of said rectifying means to provide a signal across said resistor which varies with the ground current in said system, and a level-detecting circuit connected to said resistor for producing an output substantially instantaneously when the signal across said resistor exceeds substantially a predetermined value.

Claim 3

The system as claimed in claim 1 wherein a semiconductive means is connected in parallel with said energy-storing capacitor for limiting the maximum voltage across said capacitor to substantially a predetermined value.

Claim 4

The system as claimed in claim 2 wherein the semiconductive means comprises at least one Zener diode.

Claim 5

The system as claimed in claim 1 wherein an additional means is connected in circuit relation with said energy-storing capacitor and said level-detecting circuit to be responsive to the output of said level-detecting circuit for producing a second output after a predetermined time delay which is initiated upon the occurrence of the output of said level-detecting circuit.

Claim 6

The system as claimed in claim 2 wherein an additional means is connected in circuit relation with said energy-storing capacitor and said level-detecting circuit to be responsive to the output of said level-detecting circuit for producing a second output after a predetermined time delay which is initiated upon the occurrence of the output of said level-detecting circuit.

Claim 7

A protective relay device comprising a pair of terminals adapted to be connected to means for obtaining an output current which varies with the ground current in a polyphase alternating-current system, a current transformer connected to said terminals for deriving from current supplied to said terminals an alternating output current which varies with the current flowing between said terminals, rectifying means connected to said current transformer for deriving a unidirectional output current which varies with the current flowing between said terminals, a resistor and an energy-storing capacitor connected in series circuit relationship with one another, said series circuit being connected to said rectifying means to provide a unidirectional current signal across said resistor which varies with the current flow between said terminals, a level-detecting circuit connected to said resistor for producing an output when the signal across said resistor exceeds substantially a predetermined value, and control means connected in circuit relatIon with said level-detecting circuit and said capacitor for discharging said capacitor after a predetermined time delay which starts when the output of said level-detecting circuit occurs.

Claim 8

A protective relay device comprising a pair of terminals adapted to be connected to means for obtaining an output current which varies with the ground current in a polyphase alternating-current system, a current transformer connected to said terminals for deriving from current supplied to said terminals an alternating output current which varies with the current flowing between said terminals, rectifying means connected to said current transformer for deriving a unidirectional output current which varies with the current flowing between said terminals, a resistor and an energy-storing capacitor connected in series circuit relationship with one another, said series circuit being connected to said rectifying means to provide a unidirectional current signal across said resistor which varies with the current flow between said terminals, a level-detecting circuit connected to said resistor for producing an output when the signal across said resistor exceeds substantially a predetermined value, and control means connected in circuit relatIon with said level-detecting circuit and said capacitor for discharging said capacitor after a predetermined time delay which starts when the output of said level-detecting circuit occurs.

Claim 9

The protective relay device as claimed in claim 6 wherein a semiconductive means is connected in parallel with said energy-storing capacitor for limiting the maximum voltage across said capacitor to substantially a predetermined value.

Claim 10

The protective relay device as claimed in claim 7 wherein the semiconductive means comprises at least one Zener diode.

Claim 11

A circuit breaker for a three-phase alternating-current system comprising a plurality of separable contacts adapted to be connected to said system, operating means for opening said contacts, means for obtaining an output current which varies with the ground current in said system, and a protective device operatively connected to said operating means and responsive to the ground current in said system for producing an output to actuate said operating means to open said contacts, said protective device comprising a current transformer connected to the above-mentioned means for providing an alternating-current output which varies with the ground current in said system, rectifying means having input terminals connected to said current transformer and output terminals for providing a unidirectional output current which varies with the ground current in said system, a resistor and an energy-storing capacitor connected in series circuit relation with one another across the output terminals of said rectifying means to provide a signal across said resistor which varies with the ground current in said system, a level-detecting circuit connected to said resistor for producing an output substantially instantaneously when the signal across said resistor exceeds substantially a predetermined value, and means operatively connected between said level-detecting circuit and said operating means for producing an additional output in response to the output of said level-detecting circuit to actuate said operating means to open said contacts.

Claim 12

A circuit breaker for a three-phase alternating-current system comprising a plurality of separable contacts adapted to be connected to said system, operating means for opening said contacts, means for obtaining an output current which varies with the ground current in said system, and a protective device operatively connected to said operating means and responsive to the ground current in said system for producing an output to actuate said operating means to open said contacts, said protective device comprising a current transformer connected to the above-mentioned means for providing an alternating-current output which varies with the ground current in said system, rectifying means having input terminals connected to said current transformer and output terminals for providing a unidirectional output current which varies with the ground current in said system, a resistor and an energy-storing capacitor connected in series circuit relation with one another across the output terminals of said rectifying means to provide a signal across said resistor which varies with the ground current in said system, a level-detecting circuit connected to said resistor for producing an output substantially instantaneously when the signal across said resistor exceeds substantially a predetermined value, and means operatively connected between said level-detecting circuit and said operating means for producing an additional output in response to the output of said level-detecting circuit to actuate said operating means to open said contacts.

Claim 13

The circuit breaker as claimed in claim 9 wherein a semiconductive means is connected in parallel with said energy-storing capacitor for limiting the maximum voltage across said capacitor to substantially a predetermined value.

Claim 14

The circuit breaker as claimed in claim 9 wherein an additional means is connected in circuit relation with said energy-storing capacitor and said level-detecting circuit to be responsive to the output of said level-detecting circuit for producing a second output after a predetermined time delay which is initiated upon the occurrence of said output of said level-detecting circuit.

Claim 15

The circuit breaker as claimed in claim 10 wherein the semiconductive means comprises a Zener diode.

Claim 16

The circuit breaker as claimed in claim 12 wherein an additional means is connected in circuit relation with said energy-storing capacitor and said level-detecting circuit to be responsive to the output of said level-detecting circuit for producing a second output after a predetermined time delay which is initiated upon the occurrence of said output of said level-detecting circuit.

Claim 17

A circuit breaker for a three-phase alternating current system comprising a plurality of separable contacts adapted to be connected to said system, operating means for opening said contacts, means for obtaining an output current which varies with the ground current in said system, and a protective relay device operatively connected to said system and responsive to the ground current in said system for producing an output to actuate said operating means to open said contacts, said protective relay device comprising a pair of terminals connected to said means for obtaining said output current, a current transformer connected to said terminals for deriving from the current supplied to said terminals an alternating output current which varies with the ground current in said system, rectifying Means connected to said current transformer for providing a unidirectional output current which varies with the ground current in said system, a resistor and an energy-storing capacitor connected in series circuit relationship with one another to said rectifying means to provide a unidirectional current signal across said resistor which varies with the ground current in said system, a level-detecting circuit connected to said resistor for producing an output when the signal across said resistor exceeds substantially a predetermined value, and control means operatively connected to said level-detecting circuit, to said capacitor and to said operating means for discharging said capacitor to actuate said operating means to open said contacts after a predetermined time delay which starts when the output of said level-detecting circuit occurs.

Claim 18

A circuit breaker for a three-phase alternating current system comprising a plurality of separable contacts adapted to be connected to said system, operating means for opening said contacts, means for obtaining an output current which varies with the ground current in said system, and a protective relay device operatively connected to said system and responsive to the ground current in said system for producing an output to actuate said operating means to open said contacts, said protective relay device comprising a pair of terminals connected to said means for obtaining said output current, a current transformer connected to said terminals for deriving from the current supplied to said terminals an alternating output current which varies with the ground current in said system, rectifying Means connected to said current transformer for providing a unidirectional output current which varies with the ground current in said system, a resistor and an energy-storing capacitor connected in series circuit relationship with one another to said rectifying means to provide a unidirectional current signal across said resistor which varies with the ground current in said system, a level-detecting circuit connected to said resistor for producing an output when the signal across said resistor exceeds substantially a predetermined value, and control means operatively connected to said level-detecting circuit, to said capacitor and to said operating means for discharging said capacitor to actuate said operating means to open said contacts after a predetermined time delay which starts when the output of said level-detecting circuit occurs.

Claim 19

The circuit breaker as claimed in claim 14 wherein a semiconductive means is connected in parallel with said energy-storing capacitor for limiting the maximum voltage across said capacitor to substantially a predetermined value.

Claim 20

The circuit breaker as claimed in claim 15 wherein the semiconductive means comprises at least one Zener diode.