Methodology for protection of current transformers from open circuit burden

A protection system for a feeder comprising:

• a first current transformer at a first location on the feeder;
• a control unit that acts responsively to a predetermined DF to interrupt feeder current;
• wherein the first current transformer is connected to a first shunt resistor;
• wherein the control unit interrupts feeder current within a time period T after development of an open fault in a first current-transformer loop;
• wherein the time T is less than a time period in which a rate of power dissipation within the first shunt resistor reaches a power dissipation rate limit for the first shunt resistor;
• a second current transformer at a second location on the feeder;
• and
• a compensation network connected to the second current transformer to compensate for DF error resulting from presence of the first shunt resistor,
• wherein the compensation network includes a series resistor coupled with the second current transformer, and
• wherein the series resistor has a value that, when added to a resistance value of wiring between the second current transformer and a burden resistor associated with the second current transformer, produces a net resistance value equal to a wiring resistance between the first current transformer and a burden resistor associated with the first current transformer.

A method for operating an electrical power system comprising the steps of:

• passing electrical current on a feeder from a power source to electrical loads through a first current transformer to produce a first monitoring current in a first current-transformer loop;
• passing a portion of the monitoring current through a first shunt resistor connected across the first current transformer;
• interrupting power passage on the feeder in the event of an open circuit fault in the first current-transformer loop;
• passing electrical current on the feeder via a second current transformer to produce a second monitoring current in a second current-transformer loop;
• monitoring a differential between the first and the second monitoring currents;
• and
• passing a portion of the second monitoring current through a series resistor of a compensation network coupled with the second current transformer to reduce error-producing effects of the first shunt resistor,
• wherein the series resistor has a value that, when added to a resistance value of wiring between the second current transformer and a burden resistor associated with the second current transformer, produces a net resistance value approximately equal to a wiring resistance between the first current transformer and a burden resistor associated with the first current transformer,
• wherein interrupting power passage on the feeder is performed within a time T after development of an open fault in the first current-transformer loop;
• and
• wherein the time T is less that a time period in which a rate of within the first shunt resistor reaches a rated limit for power dissipation rate for the first shunt resistor.