Ground monitoring system

In a ground wire sensor circuit for use with an electrical power cable that includes power conductors, at least one ground wire and at least one other wire that is not a power conductor, wire, wherein said ground wire and other wire are joined together at one end of the power cable by a resistance means of given value, and wherein a sensing signal is coupled between the other ends of the ground wire and pilot wires to form a ground monitoring loop, said sensing signal being at a sensing frequency that is substantially different from that of the electrical power to be carried on the power conductors, the combination comprising

• means presenting a high impedance to said sensing signal coupled to the ground wire adjacent said resistance means to substantially confine the sensing signal to said loop,
• means for sampling the sensing signal voltage on said ground monitoring loop and for producing a sampled voltage signal in response thereto,
• means for sampling the sensing signal current in said ground monitoring loop and for producing a sampled current signal in response thereto,
• means for comparing said sampled voltage signal with said sampled current signal and for producing a comparison output signal when a predetermined relationship exists between the compared signals,
• circuit control means having at least first and second operating conditions, and
• means responsive to said comparison output signal for changing the operating condition of the circuit control means from its first to its second operating condition upon occurrence of said comparison output condition.

In a ground wire sensor circuit for use with an electrical power cable that includes power conductors, at least one ground wire and a ground check, or pilot, wire, wherein said ground wire and pilot wire are joined together at one end of the power cable by a resistance means of given value, and wherein a sensing signal is coupled between the other ends of the ground and pilot wires to form a ground wire monitoring loop, said sensing signal being at a sensing frequency that is substantially different from that of the electrical power to be carried on the power conductors, the combination comprising

• means presenting a high impedance to said sensing signal coupled to the ground wire adjacent said resistance means to substantially confine the sensing signal to said loop,
• means for sampling the sensing signal voltage on said ground monitoring loop and for producing a sampled voltage signal in response thereto,
• means for sampling the sensing signal current in said ground monitoring loop and for producing a sampled current signal in response thereto,
• means for comparing said sampled voltage signal with said sampled current signal and for changing a first comparison output signal from a first to a second value when an increase in the sampled voltage signal and a decrease in the sampled current signal meets a predetermined relationship, thereby to provide an open circuit signal,
• means for comparing said sampled voltage signal against another signal to produce a second comparison output when a decrease in the magnitude of the sampled voltage signal relative to said another signal meets a given relationship, thereby to provide a short circuit signal,
• control means having at least first and second conditions for controlling the application of power to said cable,
• means responsive to at least one of said open or short circuit signals for changing the condition of said control means for interrupting the application of power to the power conductors of said cable upon occurrence of said open or short circuit signals.

In a ground wire sensor circuit for use with an electrical power cable that includes power conductors, at least one ground wire and at least one other wire that is not a power conductor, wherein said ground wire and other wire are joined together at one end of the power cable by a resistance means of given value, and wherein a sensing signal is coupled between the other ends of the ground and other wires to form a ground wire monitoring loop, said sensing signal being at a sensing frequency that is substantially different from that of the electrical power to be carried on the power conductors, and wherein the power conductors of the cable are connected to a source of power through circuit interrupting means,

• the method of testing the electrical condition of said loop, comprising the steps
• substantially blocking the sensing signal from leaving the loop at a region on the ground wire that is adjacent said resistance means,
• sampling the sensing signal voltage on said loop and producing a sampled voltage signal in response thereto,
• sampling the sensing signal current in said loop and producing a sampled current signal in response thereto,
• determining when either one or both of the sampled voltage and current signals deviates from a predetermined condition and producing a corresponding comparison signal in response thereto,
• changing the condition of a circuit control means in response to the production of a comparison output signal, said circuit control means being adapted to control said circuit interrupting means that connects the power conductors to a source of power.

In a ground wire sensor circuit for use with an electrical power cable that includes power conductors, at least one ground wire and at least one other wire that is not a power conductor, wherein said ground wire and other wire are joined together at one end of the power cable by a resistance means of given value, and wherein a sensing signal is coupled between the other ends of the ground and other wires to form a ground wire monitoring loop, said sensing signal being at a sensing frequency that is substantially different from that of the electrical power to be carried on the power conductors, and wherein the power conductors of the cable are connected to a source of power through circuit interrupting means and power utilization means is coupled to said one end of the cable,

• the method of testing the electrical condition of said loop, comprising the steps
• substantially blocking the sensing signal from flowing to earth ground from the end of said loop adjacent the resistance means,
• sampling the sensing signal voltage on said loop and producing a sampled voltage signal in response thereto,
• sampling the sensing signal current in said loop and producing a sampled current signal in response thereto,
• comparing the sampled voltage and current signals and producing a comparison output signal when a predetermined relationship exists between the compared signals, and
• changing the condition of a circuit control means in response to the production of a comparison output signal, said circuit control means being adapted to control said circuit interrupting means that connects the power conductors to a source of power.