Method for detecting open phase of startup/standby transformer based on optical CT

Patent metadata

Field	Value
Publication number	US-11422204-B2
Application number	US-201816962692-A
Country	US
Kind code	B2
Filing date	May 2, 2018
Priority date	Feb 11, 2018
Publication date	Aug 23, 2022
Grant date	Aug 23, 2022

Abstract

The present invention discloses a method for detecting open phase of a startup/standby transformer based on optical CT. A startup/standby transformer in a power plant is in a no-load condition for a long time as a standby power supply. Once a single-phase open phase fault occurs, there is no significant change in the voltage phasor and voltage sequence component of each side. If not found in time, the defect may pose a great threat to the safe operation of the power plant. In the present invention, the optical CT is used to detect a three-phase current of the high-voltage side of the startup/standby transformer. If the current satisfies an open phase criterion, it is determined that an open phase fault occurs, and then, an alarm signal is given after a delay and an operator is informed to handle the fault in time. Therefore, the operation reliability of the startup/standby transformer system in the power plant is enhanced.

First claim

The invention claimed is:

1. A method for detecting open phase of a startup/standby transformer based on optical coherence tomography (CT), comprising the following steps:
step 1: using optical CT to measure a three-phase current on a high-voltage side of the startup/standby transformer;
step 2: receiving, by an open phase detection device, a current signal output by the optical CT, calculating the three-phase current on the high-voltage side of the startup/standby transformer in real time, and determining whether an open phase fault occurs according to the current; and
step 3: if it is determined that an open phase fault occurs, issuing an alarm signal after a set delay or acting to trip;
wherein the specific method for determining whether an open phase fault occurs in step 2 is: when the current of a certain phase is lower than a set threshold value, determining that the open phase fault occurs in the phase; and the identification formula is as follows:
I p <k 1× I p.0   (1)

in formula (1), I p is the real-time calculated fundamental amplitude of the current of a certain phase on the high-voltage side of the startup/standby transformer, I p.0 is the fundamental amplitude of the current of the phase on the high-voltage side of the startup/standby transformer under a no-load condition, and k1 is a reliability coefficient ranging from 0.5 to 0.8.

2. A method for detecting open phase of a startup/standby transformer based on optical coherence tomography (CT), comprising the following steps:
step 1: using optical CT to measure a three-phase current on a high-voltage side of the startup/standby transformer;
step 2: receiving, by an open phase detection device, a current signal output by the optical CT, calculating the three-phase current on the high-voltage side of the startup/standby transformer in real time, and determining whether an open phase fault occurs according to the current; and
step 3: if it is determined that an open phase fault occurs, issuing an alarm signal after a set delay or acting to trip;
wherein the specific method for determining whether an open phase fault occurs in step 2 is: when the current of a certain phase on the high-voltage side of the startup/standby transformer does not satisfy the symmetry, determining that the open phase fault occurs in the phase; and the identification formulas are as follows:
(| I A |<k 2×| İ B −İ C |)  (2)

(| I B |<k 2×| İ C −İ A |)  (3)

(| I C |<k 2×| İ A −İ B |)  (4)

formulas (2), (3), and (4) respectively correspond to phase-A, -B, and -C disconnections, wherein İ A , İ B , and İ C are the real-time calculated fundamental phasors of the three-phase current on the high-voltage side of the startup/standby transformer, and k2 is a reliability coefficient ranging from 0.25 to 0.4.

Assignees

• Nr Electric Co Ltd
• Nr Engineering Co Ltd

Inventors

• Chen Jiasheng
• Wang Guang
• Wang Kai
• Wang Yao
• Chen Jun
• Zhang Qixue
• Guo Zigang
• Li Huazhong

Classifications

• G01R31/62 Primary

  Testing of transformers · CPC title

• G08B21/02

  Alarms for ensuring the safety of persons · CPC title

• G01R31/54

  Testing for continuity · CPC title

• G01R31/308

  using non-ionising electromagnetic radiation, e.g. optical radiation {(investigating or analysing materials by the use of optical means G01N21/00; image analysis G06T7/00)} · CPC title

• 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