WO2014114141A1

WO2014114141A1 - Method for detecting residual magnetism of current transformer based on small-signal slope mapping

Info

Publication number: WO2014114141A1
Application number: PCT/CN2013/088285
Authority: WO
Inventors: 袁宇波; 李鹏; 黄浩声; 张佳敏; 王忠东
Original assignee: 国家电网公司; 江苏省电力公司; 江苏省电力公司电力科学研究院
Priority date: 2013-01-24
Filing date: 2013-12-02
Publication date: 2014-07-31
Also published as: CN103105594B; CN103105594A

Abstract

A method for detecting residual magnetism of a current transformer (CT) based on small-signal slope mapping. The derivative (I) of a magnetic flux (Ø _b) of an initial operating point (i _µ=0) to an exciting current (i _µ) is calculated by secondarily (S1, S2) applying a small voltage (u) signal to the current transformer (CT), and the residual magnetism (Ø _r) of the iron core of the current transformer (CT) is determined by using a current transformer (CT) iron-core magnetization curve (Ø_b-i_µ) to perform slope mapping. The method enables a current transformer (CT) to generate residual magnetism of different magnitudes by magnetizing an actual current transformer (CT). The validity of the present residual-magnetism detection method and theory and the practicability of a detection system platform are evaluated, and the detection result shows that the magnitude of the residual magnetism (Ø _r) of an iron core of a tested current transformer (CT) can be rapidly and accurately reflected by using the detection platform.

Description

Current transformer residual magnetization detection method based on small signal slope mapping

The invention relates to a method for detecting residual magnetism of a current transformer core, in particular to a method for detecting residual magnetism of a current transformer based on a small signal slope map, which belongs to a power automation technology.

Background technique

When the power system is connected, short-circuited, or severely harmonic, the line current will have a large DC component during the transient process, which will cause residual magnetism in the core. The current transformer (Current Transformer, CT for short) is generally remnant, and the residual magnetism is harmful to the current transformer. Once the residual magnet is generated, it will not disappear automatically. Under normal operating conditions, it will exist for a long time. Affects the current transformer's propagation characteristics and accuracy.

For current transformers that have been in operation and will be heavily connected to the network in the future, the measurement of the residual amount of residual magnetism needs to be further developed. Research shows that the harmonics in the excitation current are the signs of the residual magnetism of the core. It is possible to judge whether the current transformer has residual magnetism by measuring the harmonics of the excitation current. However, it is difficult to quantify the size and polarity of the residual magnetism. Judgment. The main problems of the conventional test method for testing residual magnetism using a magnetoelectric fluxmeter are low precision, slow speed, and extremely inconvenient operation. The method of applying AC voltage or DC voltage twice in the current transformer is mainly used to measure the residual magnetization coefficient of the current transformer, that is, the ratio of the residual magnetic induction strength and the maximum magnetic induction intensity of the current transformer core material in the saturation magnetization state. These methods cannot measure the remanence of the current transformer in any residual magnetic state. Today, with the rapid development of data acquisition and computer software and hardware technology, digitization and automation of residual magnetic measurement have become an urgent problem to be solved.

Summary of the invention

OBJECT OF THE INVENTION In order to overcome the deficiencies in the prior art, the present invention provides a current transformer residual magnetic detecting method based on small signal slope mapping, and a current transformer residual magnetic detecting method based on small signal mapping through a current transformer. The small voltage signal is applied to calculate the derivative of the initial operating point flux to the exciting current, and the current transformer core magnetization curve is used to determine the residual current of the current transformer core. This method can be conveniently used in power production sites and laboratories. Detection of residual magnetism in the current transformer core.

Technical Solution: In order to achieve the above object, the technical solution adopted by the present invention is:

A current transformer residual magnetization detection method based on small signal slope mapping includes the following steps:

(1) plotting an A^-plane curve of the current transformer core, the A^-plane curve including φ, -i curve and curve, the curve is a basic magnetization curve, and the curve is a derivative curve of the pair Where ^ represents the excitation current, the actual magnetization curve is the curve, and the derivative curve for ^ is

Say

The residual magnetism in the initial state of the transformer core is the phasor value of the secondary voltage and small signal of the current transformer, (= f. is the rated angular frequency of the system, / is the measured rms value of the secondary current of the current transformer. the amount;

Book

(3) Using the slope mapping method, the point ^0 on the curve corresponds to the point di„ ^μ di„ ^μ on the curve

The point S( , ) on the ^{d< b} ^ curve corresponds to the point C( , φ, ) on the A-curve

Di

(5) Determine A^(0)« according to point C( , ). In the above method, the relationship between the small voltage and the current signal applied by the current transformer and the core magnetic flux near the operating point of the current transformer to the excitation current is determined by the slope map of the current transformer magnetization curve to determine the core remanence. When the current transformer opens once and the secondary side is connected to the AC excitation current ^, the current transformer core flux changes from the residual magnetic flux along the corresponding hysteresis loop; if the excitation current ^ is small enough, the core flux is A small range of fluctuations around the residual magnetic flux can be used to determine the derivative of the core flux to the field current at the initial operating point of the current transformer (=0). According to the similarity between the basic magnetization curve of the iron core of the electric transformer and the local magnetization curve, the actual magnetization curve (^ curve) and the corresponding basic magnetization curve (curve) in a small range of the remanence point in the case where the excitation current is sufficiently small parallel. According to the calculated rate of change of the core flux (excitation current) in the initial state, the point on the corresponding basic magnetization curve (-^ curve) is determined according to the rate of change of the core flux by the method of slope mapping of the magnetization curve. Determine the current transformer core remanence (j) _r .

When constructing a current transformer core remanent detection platform based on the above method, a software program can be used to develop a current transformer residual magnetization detection algorithm based on small signal slope mapping; in addition, software programs and high precision can be used.

The D\A board generates a voltage small signal waveform, and combines a high-precision power amplifier to generate a small signal voltage source. The high-precision data acquisition board and the hardware interface are used to realize the current collection of the secondary current of the current transformer, specifically: The software constructs the voltage signal waveform, and then the voltage signal waveform is connected through the D/A board, and finally passes through the linear power amplifier. After the formation of the secondary access voltage source ^.

Advantageous Effects: The present invention provides a method for detecting a residual current of a current transformer based on a small signal slope map, and by magnetizing an actual current transformer, causing current mutual inductance to generate remanence of different magnitudes, and evaluating a method for detecting residual magnetism in the invention And the validity of the theory and the practicability of the detection system platform, the test results show that the detection platform can quickly and accurately reflect the remanence of the core of the tested current transformer.

Say

DRAWINGS

Figure 1 is a schematic diagram of a residual current detecting circuit of a current transformer; Figure 2 is a plan curve diagram;

Book

Figure 3 is a schematic diagram of the structure of the residual current detection platform of the current transformer core.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings.

Firstly, the principle description of the residual current detection method of the current transformer based on the small signal slope mapping is given. As shown in Fig. 1, the current transformer (referred to as CT) is open once, and the AC power supply circuit is connected twice, and a small AC voltage is applied to the CT. w, measure the loop current.

Set at t=0, the CT is open once, and the secondary voltage is

Ignoring the CT secondary side resistance, the CT secondary voltage balance equation is:

_άφ _άφ di

(1)

Dt di dt

Suppose _M = sin ωί is small, so that the current i is small enough to approximate:

=L (2)

Di di has -

Perform a Lagrangian transformation on the above formula:

0(s)=L-(si(s)-i ₀ ) (4) Take s=«, then -

-L-img (5) The plane curve of the current transformer core can be obtained by actual measurement, as shown in Fig. 2, φ _{ύ —} ί curve άί _μ ^{μ μ} is the basic magnetization curve, li curve is the derivative curve of the pair, Φ_Ϊ curve is the rising limit limit hysteresis Loop, άί _μ ^{μ μ μ The} Α-curve is the dangling limit hysteresis loop; where the excitation current is expressed, and the actual magnetization curve is the melody

The derivative curve for the line and pair is the curve.

μ άί _μ ^μ When the CT is open once and the excitation current is connected to the secondary side, since the CT core flux cannot be abruptly changed, the core flux changes from the residual flux to the corresponding hysteresis loop; Very small, the actual magnetic flux of the core fluctuates in a small range near the residual flux. According to the similarity between the basic magnetization curve (-^ curve) of the CT core and the local magnetization curve, in the case where the excitation current is sufficiently small, the actual hysteresis curve (^-^ curve) and corresponding in the small range of the remanence point can be assumed. The basic magnetization curves (-^ curves) are parallel. Further, using equation (5), the rate of change of the core flux with respect to the field current is calculated in the initial state (=0), and the point on the corresponding basic magnetization curve (curve) is determined according to the rate of change of the core flux by the slope mapping method (^) , ), can get the core remanence Α = (ο)«.

Based on the above theoretical analysis, the specific method that can be obtained in this case is:

(1) plotting an A-plane of the current transformer core, the A-plane graph including φ, -ί _μ curves and ϋ curves, the Λ curves being basic magnetization curves, and the curves are μ άι _μ derivative curve; where ^ represents the excitation current, the actual magnetization curve is the curve, and the derivative curve of ^ is the curve;

(2) The current transformer is open once, and the secondary excitation is small enough to AC excitation current.

L where is the slope of the point «,0) on the ^- curve, corresponding to the curve on the ^

Point ^ 4 (0, L); where Α is the residual magnetism in the initial state of the current transformer core, which is the phasor value of the current transformer signal, ω = 1π (/. = 50Hz) is the rated angular frequency of the system, / For the measured current transformer twice Side current RMS phasor;

(3) Using the slope mapping method, the point ^0 on the curve corresponds to the point on the curve

(4) The point on the curve S ( , say ) corresponds to the point on the curve C ( , t

(5) Determine A ^(0)« according to point C( , ). A current transformer core remanence detecting platform for realizing the above method is shown in FIG. 3, including a remanence detecting book.

Algorithm software module, voltage source output module, data acquisition and interface module, output module.

The residual magnetic detection algorithm software module is the algorithm core of the platform. The software is used to develop the current transformer residual magnetic detection calculation method based on the signal slope mapping. The program can automatically read the data points on the basic magnetization curve of the current transformer provided by the user. And fitting the basic magnetization curve by the difference, and calculating the derivative curve of the magnetic flux on the excitation current on the basic magnetization curve; calculating the voltage and current phasor by using the collected voltage and current signals, and performing slope mapping to determine the current transformer of the test The remanence of the iron core.

The voltage source output module is an important part of the platform. It uses software to generate voltage small signal waveforms, and controls high-precision D/A output boards for small voltage output. The D/A board outputs small voltages through high-precision linear power amplifiers. After amplification, it is used as a small signal voltage source for testing, and connected to the secondary side of the current transformer.

The high-precision data acquisition board and hardware interface are used to realize the secondary current small signal acquisition of the current transformer, and the current value is input to the input board for the residual magnetic detection algorithm.

Based on the above-mentioned software hardware module, the current transformer core remanence detection platform can automatically test the residual magnet size of the current transformer core, and output and store the test data.

The above description is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can also make several improvements and retouchings without departing from the principles of the present invention. It should be considered as the scope of protection of the present invention.

Claims

Claim

1. A method for detecting a residual current of a current transformer based on a small signal slope map, comprising: the following steps:

(1) plot the A-plane of the current transformer core, the A-plane graph including φ, -ι _μ curves and curves, the _ curve is the basic magnetization curve, and the curve is the pair of ^ _μ άι _μ derivative curve; where ^ represents the excitation current, the actual magnetization curve is the curve, and the derivative curve of ^ is the curve;

Di.. ^μ

(2) The current transformer is open once, in the second time, the slope of the point «, 0) on the curve,

The residual magnetism in the initial state of the transformer core is the phasor value of the secondary voltage of the current transformer, and ω is the rated angular frequency of the system, which is the phasor of the measured current secondary current of the current transformer;

(3) Using the slope mapping method, the point on the curve ^4 (0, corresponding to the point on the curve

(4) The point on the curve) corresponds to the point C( , ) on the curve;

(5) According to the point c( , determine < -^(0)« .

2. The method of detecting a residual current of a current transformer based on a small signal slope map according to claim 1, wherein: in the step (2), the method of secondly accessing the excitation current is: first, a voltage signal waveform of the D / a card pick out, forming a secondary voltage source access _Μ "after an additional linear power amplifier.