US 5,477,408 A · System for detecting certain erroneous fault-indicating data in a protective relay for power systems

Abstract

The system includes a blocking counter which is set to 255 quarter cycles and the output contacts of the protective relay are blocked for five quarter cycles if the first order difference between two successive quarter-cycle samples of current is above a selected threshold, referred to as the last previous and the first samples. The first order difference between the first and the next successive (second) samples is compared against a second threshold and the instantaneous value of the current sample is compared against the second threshold. If both comparisons are above the second threshold, then the output contacts are unblocked. If not, such that a constant DC A/D converter output or an A/D spike is indicated, then the outputs remain blocked for the full five quarter cycles, which is sufficient time to permit the A/D spike to disappear and to recognize a constant DC output from the A/D converter.

Claims12

Dependent claims

A system for preventing a fault response for certain data conditions occurring in a protective relay, comprising:

means determining the difference between the magnitude of a sample of a power signal on a power line and the magnitude of a previous sample;
means comparing said difference against a first threshold value;
means for blocking the relay from initiating a fault response for a preselected period of time if the first threshold value is exceeded by said difference;
means for testing a selected characteristic of successive samples of the power signal against a second threshold value during the preselected period of time, following determination that the first threshold value has been exceeded by said difference;
and
means for unblocking the relay prior to the termination of said preselected period of time if the selected characteristic is greater than the second threshold value.

3 more elements

Dependencies are inferred from the claim text.

System for detecting certain erroneous fault-indicating data in a protective relay for power systems

Life of this patent

System for detecting certain erroneous fault-indicating data in a protective relay for power systems

Life of this patent

Abstract

Claims12