Digital protective relay

Patent metadata

Field	Value
Publication number	US-9755656-B2
Application number	US-201615003728-A
Country	US
Kind code	B2
Filing date	Jan 21, 2016
Priority date	Feb 6, 2015
Publication date	Sep 5, 2017
Grant date	Sep 5, 2017

Abstract

The present disclosure relates to provide an active erroneous sample elimination device or erroneous sample elimination method for a relay capable of correctly implementing erroneous sample elimination processing even during a plurality of electrical disturbances mixed with an electrical quantity detection signal, and a digital protective relay according to the present disclosure may include a converter that samples an analog signal and converts the sampled signal to a digital signal; and a processor that searches an inflection point at which an electrical variation quantity varies from an increase to a decrease or from a decrease to an increase based on the digital signal, and compares an electrical variation quantity prior to and subsequent to the inflection point with a preset electrical quantity.

First claim

What is claimed is:

1. A digital protective relay, comprising:
a converter configured to sample an analog signal and convert the sampled analog signal to a digital signal; and
a processor configured to:
search an inflection point at which an electrical variation quantity varies from an increase to a decrease or from a decrease to an increase based on the digital signal, wherein the electrical variation quantity comprises at least one of current variation amount or voltage variation amount;
compare the electrical variation quantity prior to and subsequent to the inflection point with a preset electrical quantity; and
substitute electrical quantity data at the inflection point with electrical quantity data prior to a predetermined period when the digital signal is determined as an electrical disturbance.

2. The digital protective relay of claim 1 , wherein the processor is further configured to:
perform a Discrete Time Fourier Transform on the digital signal for a predetermined period of time;
compare a first convergence value at which a transformed value is increased and then converged with a predetermined normal convergence value;
determine the digital signal as a harmonic wave when a difference between the first convergence value and the predetermined normal convergence value exceeds a predetermined difference; and
determine the digital signal as the electrical disturbance when the electrical variation quantity is larger or equal to a reference electrical variation quantity.

3. The digital protective relay of claim 2 , wherein the processor is further configured to perform a root mean square processing on the digital signal when the digital signal is determined as the harmonic wave.

4. A noise elimination method for a digital relay, the method comprising:
sampling an analog signal of an electrical quantity detection signal and converting the sampled analog signal to a digital signal;
searching an inflection point at which an electrical variation quantity varies from an increase to a decrease or from a decrease to an increase based on the digital signal by a processor, wherein the electrical variation quantity comprises at least one of current variation amount or voltage variation amount;
comparing the electrical variation quantity prior to and subsequent to the inflection point with a predetermined normal reference electrical variation quantity by the processor; and
substituting an electrical quantity data at the inflection point with an electrical quantity data prior to a predetermined period by the processor when the digital signal is determined as an electrical disturbance where an electrical variation quantity prior to and subsequent to the inflection point is not less than a predetermined normal reference electrical variation quantity.

5. The method of claim 4 , further comprising:
performing a Discrete Time Fourier Transform on the digital signal for a predetermined period of time;
comparing a first convergence value at which a transformed value is increased and then converged with a predetermined normal convergence value;
determining that a harmonic wave is mixed with an electrical quantity detection signal to perform root mean square processing on the digital signal when a difference between the first convergence value and the normal convergence value exceeds a predetermined difference.

Assignees

• Lsis Co Ltd

Inventors

• Kim Jiung

Classifications

• G01R31/50

  Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections (testing of sparking plugs H01T13/58) · CPC title

• G01R19/2509

  Details concerning sampling, digitizing or waveform capturing · CPC title

• G01R19/252

  using analogue/digital converters of the type with conversion of voltage or current into frequency and measuring of this frequency · CPC title

• H02H1/04

  Arrangements for preventing response to transient abnormal conditions, e.g. to lightning {or to short duration over voltage or oscillations; Damping the influence of DC component by short circuits in AC networks} · CPC title

• H02H7/262 Primary

  involving transmissions of switching or blocking orders · CPC title