09-03-2010, 03:30 PM
10-03-2010, 09:47 PM
System for power transformer differential protection
In this invention, Current transformer (CT) secondary currents for the windings of a power transformer are used to produce a differential current and An operating current value is obtained from the differential current value. A restraining current value is obtained from processed winding current values.
TECHNICAL FIELD:
It pertains to the transformer internal fault protection for electric power transformers
BACKGROUND
In the occurrence of internal faults in a power transformer, rapid disconnection of the faulty transformer from the power system is necessary to avoid possible extensive damage to the transformer and also to preserve power system stability and power quality. phase overcurrent protection, differential protection using differential currents, and gas accumulator/rate of pressure rise protective techniques etc were used earlier for this purpose. Differential protection is currently widely used as protection against relay internal faults
DISCLOSURE OF THE INVENTION
This apparatus contains:
-A means for developing a differential current value from processed current values,which being the representative of transformer (CT) secondary current values obtained from the windings of a power transformer.
-a method for developing an operating current value from said differential current value;
-means for obtaining even harmonic values of said differential current value
-and a method for comparing the sum of the restraining current values and the even harmonic values with the operating current value and for producing an output signal which in turn is useful in producing a trip signal when the operating current value is larger than said sum.
Current transformer (CT) secondary currents for the windings of a power transformer are used to produce a differential current. An operating current value is obtained from the differential current value. And A restraining current value is obtained from processed winding current values. The Second and fourth harmonic values of the differential current are obtained and they are summed with a restraining current quantity which is a result of the restraining current multiplied by a slope characteristic factor.an output signal is produced which may be used as a trip signal If the operating current value is greater than the sum of the restraining current quantity and the second and fourth harmonic values. This tripping action can be blocked by selected blocking signals generated by another portion of the system.
For more visit:
http://patentstorm.us/patents/6356421/fulltext.html
In this invention, Current transformer (CT) secondary currents for the windings of a power transformer are used to produce a differential current and An operating current value is obtained from the differential current value. A restraining current value is obtained from processed winding current values.
TECHNICAL FIELD:
It pertains to the transformer internal fault protection for electric power transformers
BACKGROUND
In the occurrence of internal faults in a power transformer, rapid disconnection of the faulty transformer from the power system is necessary to avoid possible extensive damage to the transformer and also to preserve power system stability and power quality. phase overcurrent protection, differential protection using differential currents, and gas accumulator/rate of pressure rise protective techniques etc were used earlier for this purpose. Differential protection is currently widely used as protection against relay internal faults
DISCLOSURE OF THE INVENTION
This apparatus contains:
-A means for developing a differential current value from processed current values,which being the representative of transformer (CT) secondary current values obtained from the windings of a power transformer.
-a method for developing an operating current value from said differential current value;
-means for obtaining even harmonic values of said differential current value
-and a method for comparing the sum of the restraining current values and the even harmonic values with the operating current value and for producing an output signal which in turn is useful in producing a trip signal when the operating current value is larger than said sum.
Current transformer (CT) secondary currents for the windings of a power transformer are used to produce a differential current. An operating current value is obtained from the differential current value. And A restraining current value is obtained from processed winding current values. The Second and fourth harmonic values of the differential current are obtained and they are summed with a restraining current quantity which is a result of the restraining current multiplied by a slope characteristic factor.an output signal is produced which may be used as a trip signal If the operating current value is greater than the sum of the restraining current quantity and the second and fourth harmonic values. This tripping action can be blocked by selected blocking signals generated by another portion of the system.
For more visit:
http://patentstorm.us/patents/6356421/fulltext.html