Overcurrent protection device

An electrical overcurrent trip unit for an electrical interrupting device, said overcurrent trip unit comprising:

• means for sensing an electrical current in an electrical interrupting device, the electrical current having a magnitude and a time period;
• means responsive to said sensing means for providing a trip signal as a predetermined function of the magnitude and the time period of the electrical current flowing in said electrical interrupting device, said predetermined function including a long time delay portion having a long time delay adjustment range and also including a short time delay portion having a short time delay adjustment range for a short time delay pickup and a short time delay time period;
• means for adjusting said long time delay adjustment range and said short time delay adjustment range, said adjusting means allowing for an overlap of said long time delay adjustment range and said short time delay adjustment range;
• and
• means for preventing said electrical interrupting device from tripping as a function of said long time delay portion prior to said short time delay time period whenever the magnitude of the electrical current is less than said short time delay pickup.

An overcurrent trip unit for an electrical interrupting device including electrical phase currents having a magnitude, said overcurrent trip unit comprising:

• first means including a plurality of current transformers (CT's) each having a secondary winding for generating a secondary phase current in each of said secondary windings representative of the electrical phase currents in said electrical interrupting device;
• second means responsive to said first means for providing a signal representative of the secondary phase current having a largest peak magnitude;
• means for adjusting a magnitude of a first signal;
• third means responsive to said second means for continuously providing a second signal as a function of the magnitude of the first signal and the largest peak magnitude of said secondary phase currents in said electrical interrupting device, said third means including means for providing said second signal even during a condition when said CT's are saturated;
• and
• means responsive to said second means and said second signal for initiating a trip signal.

An overcurrent trip unit for an electrical interrupting device adapted for connection in an electrical system with a downstream electrical interrupting device having means generating a first interlock signal having a first value when electrical current through said downstream electrical interrupting device exceeds a preset value and having a second value otherwise, said overcurrent trip unit comprising:

• current sensing means for sensing an electrical current flowing through said electrical interrupting device;
• trip means responsive to said current sensing means for selectively generating a trip signal as a predetermined long delay function of a first magnitude and a first time period of said electrical current sensed by said current sensing means and a predetermined short delay function of a second magnitude greater than said first magnitude and a second time period shorter than said first time period;
• and
• zone interlock means generating a trip signal in response to said second value of said first interlock signal and a current sensed by said current sensing means which is at least as great as said first magnitude for a selected time interval which is shorter than said first time period.

An electrical system comprising a downstream electrical interrupting device, an upstream electrical interrupting device and an intermediate electrical interrupting device connected between said downstream electrical interrupting device and said upstream electrical interrupting device, each of said electrical interrupting devices including an overcurrent trip unit comprising current sensing means sensing current through the electrical interrupting device, and trip means selectively generating a trip signal in response to a predetermined long delay function of current through said electrical interrupting device of a first magnitude for a first time interval, and a short delay function of current through said electrical interrupting device of a second magnitude greater than said first magnitude and a second time interval shorter than said first time interval;

• and
• zone interlock means including means in said overcurrent trip unit of said downstream electrical interrupting device generating a zone-in interlock signal for said intermediate electrical interrupting device having a first value when current through said downstream electrical interrupting device is above said downstream magnitude for said first electrical interrupting device and a second value otherwise, means in said overcurrent trip unit of said intermediate electrical interrupting device generating a zone-out interlock signal having a first value when current through said intermediate electrical interrupting device exceeds the first magnitude for said intermediate electrical interrupting device and having a second value otherwise, and generating a trip signal for said intermediate electrical interrupting device when said zone-in signal has said second value and said current in said intermediate electrical interrupting device is at least as great as said first magnitude for said intermediate electrical interrupting device for a selected time interval shorter than said first time interval for said intermediate electrical interrupting device, and means in said overcurrent trip unit of said upstream electrical interrupting device generating a trip signal for said upstream electrical interrupting device when said zone-out interlock signal has said second value and said current in said upstream electrical interrupting device is at least as great as said first magnitude for said upstream electrical interrupting device for a selected time interval which is less than said first time interval for said upstream electrical interrupting device.

An overcurrent trip unit for an electrical interrupting device, said overcurrent trip unit comprising:

• current sensing means for sensing an electrical current flowing through said electrical interrupting device, the electrical current having a magnitude and a time period;
• trip means responsive to said current sensing means for generating a trip signal as a predetermined function of the magnitude and the time period of the electrical current flowing through said electrical interrupting device;
• status means indicating an open and a closed status of said electrical interrupting device;
• making current discriminator means responsive to said current sensing means for actuating said trip means to generate a trip signal in response to the electrical current flowing through said electrical interrupting device which exceeds a preset value only within a preset positive time interval after said status means indicates that said electrical interrupting device is closed.

An overcurrent trip unit for an electrical interrupting device, said overcurrent trip unit comprising:

• means for sensing an electrical current in an electrical interrupting device, the electrical current having a magnitude and a time period;
• means responsive to said sensing means for providing a trip signal in accordance with a selectable predetermined function of the magnitude and the time period of the electrical current flowing in said electrical interrupting device, said selectable predetermined function defines a long time delay portion and is selected from a plurality of programmed functions;
• and
• wherein said means responsive to said sensing means includes means for communicating with a remote communications device, said plurality of programmed selective functions being selected from said remote communications device.

An overcurrent trip unit for an electrical interrupting device, said overcurrent trip unit comprising:

• means for sensing an electrical current in an electrical interrupting device, the electrical current having a magnitude and a time period;
• means responsive to said sensing means for providing a trip signal in accordance with a selectable predetermined function of the magnitude and the time period of the electrical current flowing in said electrical interrupting device, said selectable predetermined function defines a long time delay portion an is selected from a plurality of programmed functions;
• and
• wherein said means responsive to said sensing means includes means storing setpoints and wherein said communicating means includes means for allowing said remote communications device to read said plurality of programmed functions and said setpoints.

An overcurrent trip unit for an electrical interrupting device including electrical phase currents having a magnitude, said overcurrent trip unit comprising:

• first means including a plurality of current transformers each having a secondary winding for generating a secondary phase current in each of said secondary windings representative of the electrical phase currents in said electrical interrupting device;
• second means responsive to said first means for providing a signal representative of the secondary phase current having a largest peak magnitude;
• third means responsive to said second means for providing a reference signal as a function of the largest peak magnitude of said secondary phase currents in said electrical interrupting device, said third means including means for providing said reference signal even during a condition when said current transformers are saturated;
• said third means also including means for providing a pulse width modulated signal which pulse width is variable as a function of a selected magnitude at which said trip signal is initiated;
• means for adjusting a magnitude related to said secondary phase currents in said electrical interrupting device at which said reference signal is initiated;
• and
• means responsive to said second means and said third means for initiating a trip signal.