Differential protection method in an electrical power supply system and protective apparatus for carrying out a differential protection method

A differential protection method for generating a fault signal and for protecting a component of an electrical system, the method comprising:

• measuring respective current measurement values at two or more different measurement locations of the component with current transformers at the measurement locations of the component;
• forming differential current values and stabilization values from the current measurement values;
• estimating, from successive differential current values and associated stabilization values, estimated differential current values and associated estimated stabilization values, and estimating therefrom at least one value of an expected future profile of the differential current values and the associated stabilization values;
• forming a respective estimated differential current value in each case from a present differential current value and a differential current value directly preceding the present differential current value, and forming a respective estimated stabilization value in each case from a present stabilization value and the stabilization value directly preceding the present stabilization value;
• conducting a tripping range test by evaluating a position of a measurement value pair formed from an estimated differential current value and a respectively associated estimated stabilization value;
• and
• if the tripping range test indicates that a measurement value pair formed from one of the estimated differential current values and the respectively associated estimated stabilization value lies in a predefined tripping range, generating the fault signal to cause switching devices for limiting the component to open and to disconnect the component from the electrical system;
• and
• comparing the estimated differential current values with a differential current threshold value and also generating the fault signal if a predefined number of successive estimated differential current values exceed the differential current threshold value to cause the switching devices for limiting the component to open and to disconnect the component from the electrical system.

An electrical protective apparatus for forming a fault signal and for protecting an electrical component, the apparatus comprising:

• connections for direct or indirect connection of at least two current transformers disposed at mutually different measurement locations of the electrical component;
• an evaluation device connected to receive current signals from said current transformers through said connections, said evaluation device configured to convert said current signals into current measurement values;
• said evaluation device being configured to form differential current values and stabilization values from the current measurement values, and said evaluation device being configured to:
• estimate, from successive differential current values and associated stabilization values, estimated differential current values and associated estimated stabilization values, and to estimate therefrom at least one value of an expected future profile of the differential current values and the associated stabilization values;
• form a respective estimated differential current value in each case from a present differential current value and a differential current value directly preceding the present differential current value, and to form in each case a respective estimated stabilization value from the present stabilization value and the stabilization value directly preceding the present stabilization value;
• conduct a tripping range test by evaluating a position of a measurement value pair formed from an estimated differential current value and a respectively associated estimated stabilization value;
• and
• if the tripping range test indicates that a measurement value pair formed from one of the estimated differential current values and the respectively associated estimated stabilization value lies in a predefined tripping range, to generate the fault signal to cause switching devices for limiting the electrical component to open and to disconnect the electrical component.

A differential protection method for generating a fault signal and for protecting an electrical component in an electrical system, the method comprising:

• measuring respective current measurement values at two or more different measurement locations of the component with current transformers at the measurement locations of the component;
• forming differential current values and stabilization values from the current measurement values;
• estimating, from successive differential current values and associated stabilization values, estimated differential current values and associated estimated stabilization values, and estimating therefrom at least one value of an expected future profile of the differential current values and the associated stabilization values;
• forming a respective estimated differential current value in each case from a present differential current value and a differential current value directly preceding the present differential current value, and forming a respective estimated stabilization value in each case from a present stabilization value and a stabilization value directly preceding the present stabilization value;
• conducting a tripping range test by evaluating a position of a measurement value pair formed from an estimated differential current value and a respectively associated estimated stabilization value;
• if the tripping range test indicates that a measurement value pair formed from one of the estimated differential current values and the respectively associated estimated stabilization value lies in a predefined tripping range, generating the fault signal to cause switching devices for limiting the component to open and to disconnect the component from the electrical system;
• and
• if a predefined number of successive measurement value pairs lie in a predefined stabilization range, blocking an output of the fault signal.