Transformer differential relay

In a transformer differential relay of the type employing at least one operate signal and at least one restraint signal to generate a trip signal when the magnitude of the sum of said at least one operate signal exceeds the magnitude of the sum of said at least one restraint signal by a predetermined amount, means for enhancing reliability of operation of said relay in the presence of current transformer saturation, said means comprising:

• (a) means for generating a vector sum operate signal representative of the vector sum of currents flowing in at least two windings of a transformer;
• (b) means for generating a signal representative of the absolute value of said vector sum operate signal;
• and
• (c) means for generating an additional operate signal when the magnitude of the absolute value of said vector sum operate signal exceeds a first predetermined magnitude.

In a transformer differential relay of the type employing operate energy and restraint energy to generate a trip signal when the operate energy exceeds the restraint energy by a predetermined amount, means for enhancing reliability of operation in the presence of current transformer saturation, said means comprising:

• (a) means for generating a vector sum operate signal representative of the vector sum of currents flowing in at least two windings of a transformer;
• (b) means for generating a signal representative of the absolute value of said vector sum operate signal;
• and
• (c) means for generating additional operate energy when the magnitude of the absolute value of said vector sum operate signal exceeds a first predetermined magnitude.

In a transformer differential relay of the type employing at least one operate signal and at least one restraint signal to generate a trip signal when the magnitude of the sum of said at least one operate signal exceeds the magnitude of the sum of said at least one restraint signal by a predetermined amount, a method for enhancing reliability of operation of said relay in the presence of current transformer saturation, said method comprising the steps of:

• (a) generating a vector sum operate signal representative of the vector sum of currents flowing in at least two windings of a transformer;
• (b) generating a signal representative of the absolute value of said vector sum operate signal;
• and
• (c) generating an additional operate signal when the magnitude of the absolute value of said vector sum operate signal exceeds a first predetermined magnitude.

In a transformer differential relay of the type employing operate energy and restraint energy to generate a trip signal when the operate energy exceeds the restraint energy by a predetermined amount, a method for enhancing reliability of operation in the presence of current transformer saturation, said method comprising the steps of:

• (a) generating a vector sum operate signal representative of the vector sum of the currents flowing in at least two windings of a transformer;
• (b) generating a signal representative of the absolute value of said vector sum operate signal;
• and
• (c) means for generating additional operate energy when the magnitude of the absolute value of said vector sum operate signal exceeds a first predetermined magnitude.

A method for enhancing reliability of operation of a transformer differential relay comprising the steps of:

• (a) generating a first signal representative of currents flowing in at least two windings of a transformer;
• (b) generating a second signal representative of a positive portion of said first signal and a third signal representative of a negative portion of said first signal;
• (c) generating a harmonic restraint signal;
• (d) generating a first output signal when the algebraic sum of the magnitude of said harmonic restraint signal and said second signal exceeds a first predetermined value, and a second output signal when the algebraic sum of the magnitude of said harmonic restraint signal and said third signal exceeds a second predetermined value;
• and
• (e) providing a trip signal upon coincidence of said first and second output signals.

A transformer differential relay comprising:

• (a) means for generating a first signal representative of currents flowing in at least two windings of a transformer;
• (b) means for generating a second signal representative of a positive portion of said first signal and a third signal representative of a negative portion of said first signal;
• (c) first summing and integrating means and first level detection means for generating a first output signal when the magnitude of said second signal exceeds a first predetermined value;
• (d) second summing and integrating means and second level detection means for generating a second output signal when the magnitude of said third signal exceeds a second predetermined value;
• and
• (e) means for providing a trip signal upon coincidence of said first and second output signals.

A method for enhancing reliability of operation of a transformer differential relay comprising the steps of:

• (a) generating a first signal representative of currents flowing at least two windings of a transformer;
• (b) generating a second signal representative of a positive portion of said first signal and a third signal representative of a negative portion of said first signal;
• (c) generating, from first summing and integrating means and first level detection means, a first output signal when the magnitude of said second signal exceeds a first predetermined value;
• (d) generating, from second summing and integrating means and first level detection means, a second output signal when the magnitude of said third signal exceeds a second predetermined value;
• and
• (e) providing a trip signal upon coincidence of said first and second output signals.