CN105425178A - Ferromagnetic element's iron core loss measuring method based on random waveform low frequency power supply - Google Patents

Abstract

The invention relates to a ferromagnetic element's iron core loss measuring method based on a random waveform low frequency power supply. The ferromagnetic element's iron core loss measuring method comprises the steps: 1) establishing a T type equivalent circuit taking regard of hysteresis and eddy current loss, for a ferromagnetic element; 2) applying a random waveform low frequency power supply to calculate the eddy current loss equivalent resistance Re; 3) drawing a limitation magnetization loop line according to the voltage and current under the iron core saturation condition; 4) multiplying the time integral value of the flux linkage on the magnetization loop line (the area of the magnetization loop line) by the frequency to calculate the hysteresis loss; and 5) calculating the eddy current loss through the power frequency induction electromotive force and the eddy current equivalent resistance, and adding the hysteresis and eddy current loss, and then obtaining the ferromagnetic element's iron core loss. The ferromagnetic element's iron core loss measuring method can complete the test when the frequency is far lower than the power frequency and the power frequency voltage, and has lower requirement for the test power supply waveform, and can greatly reduce the test equipment capacity, and can reduce the mass, and the volume of the test equipment, and can effectively reduce the safety risk for the staff and the tested products during the testing process, and has accuracy being identical to the power frequency test.

Description

A kind of ferromagnetic element core loss measuring method based on random waveform low-frequency power

Technical field

The present invention relates to electric power ferromagnetic element core loss and measure test, the core loss being specially adapted to mutual inductor, reactor, transformer etc. is measured.

Background technology

Transformer is primary equipment important in electric system, carries out open circuit loss, load loss test in the standards such as GB50150 " Erection works of electrical installations Standard for handover test of electric equipment ", DL/T596 " power equipment preventive trial code " to transformer.But the method for testing of the ferromagnetic element core losss such as transformer conventional at present, normally open-circuit test and short-circuit test are carried out to transformer, a jumbo power transformer is carried out opening a way, short-circuit test often needs big current, high-tension power-supply device, experimental facilities is heavy, bulky, be not easy to carry transport.Therefore core loss test tool that is how convenient, that efficiently complete the ferromagnetic elements such as transformer is of great significance.Thus the present invention proposes a kind of random waveform low-frequency power that adopts to measure the method for ferromagnetic element core loss, can greatly reduce experiment power supply capacity, reduce testing equipment volume and weight.

Summary of the invention

For the deficiency of above-mentioned existing ferromagnetic element core loss measuring method, the present invention proposes a kind of measuring method adopting the ferromagnetic element core loss of random waveform low-frequency power.The method adopts low-frequency power can reduce the capacity of experimental power supply greatly, reduces experiment power supply volume and weight, to power supply wave shape not requirement can make square wave, triangular wave, sine wave.

In order to achieve the above object, the present invention adopts following technical scheme:

Based on a ferromagnetic element core loss measuring method for random waveform low-frequency power, it is characterized in that, measuring process is:

1) with one, the electromagnetic relationship of ferromagnetic element is considered that the T-shaped equivalent electrical circuit of magnetic hysteresis eddy current loss is expressed, this circuit is by magnetizing inductance L _m, eddy current loss resistance R _e, hysteresis loss resistance R _hthe parallel connection of three again with first and second winding D.C. resistance R _dc1, R _dc2with leakage inductance L _{1 σ}, L _{2 σ}be in series, u ₂t () puts on the terminal voltage (primary side open circuit) in Secondary Winding when being test, e (t) is Secondary Winding induced potential, i _et () is the equivalent current of eddy current loss, i _ht () is the equivalent current of magnetic hysteresis loss, i _mt () flows through R _hand L _mthe electric current of the parallel branch of composition, i _ext () is exciting current, P is active power, P _tit is core loss; Consider Transformer Winding leakage reactance, above-mentioned parameter meets formula (1), formula (2);

$u_2\left(t\right)=i_{ex}\left(t\right)\·R_{dc2}+L_{2\mathrm{\σ}}\frac{{\mathrm{di}}_{ex}\left(t\right)}{dt}+e\left(t\right)---\left(1\right)$

i _ex(t)＝i _m(t)+i _e(t)(2)

2) Secondary Winding direct current resistance R is first measured _dc2, then in Secondary Winding, apply voltage, measure a winding voltage u ₁(t), Secondary Winding active-power P, voltage u ₂(t), exciting current i _ex;

Due to primary side open circuit, therefore winding induced potential is:

e(t)＝u ₁(t)/n

Wherein, n is the no-load voltage ratio of primary side to secondary side.

3) core loss is made up of magnetic hysteresis loss and eddy current loss two parts, magnetic hysteresis loss P _hbe directly proportional to frequency, eddy current loss P _eto square being directly proportional of frequency, namely formula (3), (4), (5) are set up;

P _T＝P _H+P _E＝α·f+β·f ²(3)

4) power supply adopting random waveform to export, applies different frequency f to ferromagnetic element Secondary Winding ₁, f ₂f _mthe voltage of (low frequency is to reduce power supply capacity) (m≤2, but in order to parameter estimation accuracy higher, generally get m≤3, m is also unsuitable excessive, excessive test trouble), make core sataration, measurement active-power P ₁, P ₂p _mwith exciting current i _ex1(t), i _ex2(t) ... i _exmt (), calculates the core loss P under different frequency by formula (4) _t1, P _t2p _tm;

$\left\{\begin{array}{c}{P}_{T1}=P_1-{I^2}_{ex1}{R}_{dc2}\\ P_{T2}=P_2-{I^2}_{ex2}{R}_{dc2}\\ .\\ .\\ .\\ P_{Tm}=P_m-{I^2}_{exm}{R}_{dc2}\end{array}\right.---\left(4\right)$

I in above formula _exk(k=1,2 ... m) be exciting current i _exkthe root-mean-square valve of (t);

5) mode of formula (3) expression formula matrix at multiple frequencies expresses the relation of core loss and frequency such as formula shown in (5); To same ferromagnetic element, under same magnetic is close, α, β are constants, in order to make calculating more accurate, adopt least square method to ask the value of α, β by formula (7);

$\left[\begin{array}{ccc}{f}_1& & f_1^2\\ f_2& & f_2^2\\ & .& \\ & .& \\ & .& \\ f_m& & f_m^2\end{array}\right]\×\left[\begin{array}{c}\mathrm{\α}\\ \mathrm{\β}\end{array}\right]=\left[\begin{array}{c}{P}_{Tl1}\\ P_{T2}\\ .\\ .\\ .\\ P_{Tm}\end{array}\right]---\left(5\right)$

Abbreviation can obtain:

FX＝P(6)

Wherein: $F=\left[\begin{array}{ccc}{f}_1& & f_1^2\\ f_2& & f_2^2\\ & .& \\ & .& \\ & .& \\ f_m& & f_m^2\end{array}\right],X=\left[\begin{array}{c}\mathrm{\α}\\ \mathrm{\β}\end{array}\right],P=\left[\begin{array}{c}{P}_{Tl1}\\ P_{T2}\\ .\\ .\\ .\\ P_{Tm}\end{array}\right]$

α, β is tried to achieve by least square method:

X＝(F ^TF) ^-1×F ^TP(7)

6) the equivalent resistance R of the eddy current loss of iron core _ecan calculate by formula (8), wherein E ₁, E ₂e _mthe Secondary Winding induced potential root-mean-square valve under several frequency respectively;

$\left\{\begin{array}{c}{R}_{e1}=\frac{E_1^2}{\mathrm{\β}\·f_1^2}\\ R_{e2}=\frac{E_2^2}{\mathrm{\β}\·f_2^2}\\ .\\ .\\ .\\ R_{em}=\frac{E_m^2}{\mathrm{\β}\·f_m^2}\end{array}\right.,R_e=\frac{R_{e1}+R_{e2}+\mathrm{...}+R_{em}}{m}---\left(8\right)$

7) R is flow through _hand L _mthe total current i of the parallel branch of composition _mcalculate by formula (11);

$i_m\left(t\right)=i_{ex}\left(t\right)-i_e\left(t\right)=i_{ex}\left(t\right)-\frac{e\left(t\right)}{R_e}---\left(9\right)$

8) to ferromagnetic element demagnetization, iron core residual flux ψ is made ₀=0; By power supply, ferromagnetic element Secondary Winding is applied to the low-frequency voltage of the frequency-invariant of random waveform, make the ferromagnetic element iron core degree of depth saturated; In the process, use the instrument of high-speed sampling, measure and record the instantaneous voltage u of a winding ₁(t) and exciting current instantaneous value i _ex(t).To voltage e (t) integration on magnetizing inductance, calculate magnetic linkage ψ (t) of core section by formula (10), according to the cycle of power supply output frequency, find ψ (t) and i _mthe corresponding relation of (t), with ψ (t) for ordinate, i _mt () is horizontal ordinate graphing, be the magnetization loop of iron core, according to the difference of output voltage, can obtain the cluster magnetization loop that magnetic flux summit is different;

$\mathrm{\ψ}\left(t\right)={\∫}_0^t\[e\left(t\right)\]dt---\left(10\right)$

The line on the summit of all magnetization loop is exactly fundamental magnetization curve, and the magnetization loop that the saturated rear measurement of the iron core degree of depth obtains is exactly limit magnetization loop, and limit magnetization loop is divided into ascending branch and decline branch;

9) fundamental magnetization curve and the limit magnetization loop of iron core has been recorded according to above-mentioned steps, the mode of magnetization loop compression in the patent " mutual inductor volt-ampere characteristic test and calculating " adopting this seminar to propose early stage; Suppose induction electromotive force e (the t)=U in Secondary Winding _mcos (ω t), (ω=100 π, U _mincrease gradually, until current saturation) then the i.e. summit of magnetization loop, it correspond to the loop line (according to the compression of limit magnetization loop) on magnetization loop bunch, so just obtains a magnetization loop ψ-i under power frequency corresponding to line-frequency induction electromotive force e (t) _m; Can magnetic hysteresis loss be calculated according to magnetization loop:

Namely magnetic hysteresis loss equals ψ-i on magnetization loop _mthe area in besieged city is multiplied by frequency f again.According to magnetization loop compression, the magnetic hysteresis loss under free voltage so just can be obtained;

10) so just can in the hope of the core loss under power frequency according to formula (12), E is the induction electromotive force effective value in Secondary Winding under power frequency, and Re is eddy current loss equivalent resistance, ∮ ψ di _mfor the area that magnetization loop surrounds.

Step 1 of the present invention) described ferromagnetic element equivalent-circuit model is the T-shaped equivalent electrical circuit considering magnetic hysteresis and eddy current loss.

Step 4 of the present invention) described Secondary Winding induction electromotive force converts secondary side through no-load voltage ratio obtain by measuring a winding voltage.

Step 4 of the present invention) ~ 6) described ferromagnetic element eddy current loss equivalent resistance first adopts many group low-frequency power data, calculates eddy current loss factor β, at the eddy current equivalent resistance Re that averages according to several groups of data according to the principle of least square.

Step 9 of the present invention) to calculate the mode of magnetic hysteresis loss be the magnetization loop obtained by the compression of limit magnet ring loop line under corresponding power-frequency voltage, magnetic hysteresis loss corresponding under calculating relevant voltage according to magnetization loop area.

The present invention compares with existing technology, and the present invention possesses following advantage:

1. adopt low-frequency power to test, make core sataration, experiment power supply capacity is little, and testing equipment volume is little, lightweight, is easy to carry.

2. experiment power supply waveform is unrestricted, can be triangular wave, square wave, sinusoidal wave, comparatively speaking, produces low-frequency square-wave and is more prone to than generation low-frequency sine.

Accompanying drawing explanation

In order to make ferromagnetic element core loss measuring method of the present invention, principle more clear, below in conjunction with accompanying drawing, the present invention is further described in detail, wherein:

Fig. 1 is that ferromagnetic element core loss measures test equivalent electrical circuit;

Fig. 2 is iron core magnetization loop bunch; 1-limit magnetization loop decline branch in figure, 2-limit magnetization loop ascending branch, 3-limit magnetization loop bunch.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail:

(1) Fig. 1 sets up transformer volt-ampere characteristic test equivalent electrical circuit in accompanying drawing to specifications.This circuit is by magnetizing inductance L _m, eddy current loss resistance R _e, hysteresis loss resistance R _hthe parallel impedance of three and first and second winding D.C. resistance R _dc1, R _dc2with leakage inductance L _{1 σ}, L _{2 σ}be in series, u ₂t () puts on the terminal voltage (primary side open circuit) in Secondary Winding when being test, e (t) is Secondary Winding induced potential, i _et () is the equivalent current of eddy current loss, i _ht () is the equivalent current of magnetic hysteresis loss, i _mt () flows through R _hand L _mthe electric current of the parallel branch of composition, i _ext () is exciting current measurement Secondary Winding direct current resistance R _dc.

(2) Secondary Winding direct current resistance R is measured _dc2, find a secondary side no-load voltage ratio n according to nameplate.

(3) power supply adopting random waveform to export, applies different frequency f to ferromagnetic element Secondary Winding ₁, f ₂f _mvoltage (m≤2, but in order to parameter estimation accuracy higher, generally get m≤3, m is also unsuitable excessive, excessive test trouble), make core sataration, measurement active-power P ₁, P ₂p _mwith exciting current i _ex1(t), i _ex2(t) ... i _exmt (), calculates the core loss P under different frequency by formula (1) _t1, P _t2p _tm;

$\left\{\begin{array}{c}{P}_{T1}=P_1-{I^2}_{ex1}{R}_{dc2}\\ P_{T2}=P_2-{I^2}_{ex2}{R}_{dc2}\\ .\\ .\\ .\\ P_{Tm}=P_m-{I^2}_{exm}{R}_{dc2}\end{array}\right.---\left(1\right)$

(4) core loss and frequency meet the relation of formula (2); To same mutual inductor, under same magnetic is close, α, β are constants, ask the value of α, β by formula (3);

$\left[\begin{array}{ccc}{f}_1& & f_1^2\\ f_2& & f_2^2\\ & .& \\ & .& \\ & .& \\ f_m& & f_m^2\end{array}\right]\×\left[\begin{array}{c}\mathrm{\α}\\ \mathrm{\β}\end{array}\right]=\left[\begin{array}{c}{P}_{Tl1}\\ P_{T2}\\ .\\ .\\ .\\ P_{Tm}\end{array}\right]---\left(2\right)$

Abbreviation can obtain:

FX＝P(3)

Wherein: $F=\left[\begin{array}{ccc}{f}_1& & f_1^2\\ f_2& & f_2^2\\ & .& \\ & .& \\ & .& \\ f_m& & f_m^2\end{array}\right],X=\left[\begin{array}{c}\mathrm{\α}\\ \mathrm{\β}\end{array}\right],P=\left[\begin{array}{c}{P}_{Tl1}\\ P_{T2}\\ .\\ .\\ .\\ P_{Tm}\end{array}\right]$

α, β is tried to achieve by least square method:

X＝(F ^TF) ^-1×F ^TP(4)

(5) the equivalent resistance R of eddy current loss _ecan calculate by formula (5), E ₁, E ₂e _mthe Secondary Winding induced potential root-mean-square valve under several frequency respectively;

$\left\{\begin{array}{c}{R}_{e1}=\frac{E_1^2}{\mathrm{\β}\·f_1^2}\\ R_{e2}=\frac{E_2^2}{\mathrm{\β}\·f_2^2}\\ .\\ .\\ .\\ R_{em}=\frac{E_m^2}{\mathrm{\β}\·f_m^2}\end{array}\right.,R_e=\frac{R_{e1}+R_{e2}+\mathrm{...}+R_{em}}{m}---\left(5\right)$

(6) R is flow through _hand L _mthe current i of the parallel branch of composition _mcalculate by formula (6);

$i_m\left(t\right)=i_{ex}\left(t\right)-i_e\left(t\right)=i_{ex}\left(t\right)-\frac{e\left(t\right)}{R_e}---\left(6\right)$

(7) to ferromagnetic element demagnetization, iron core residual flux ψ is made ₀=0; By power supply, ferromagnetic element Secondary Winding is applied to the low-frequency voltage of the frequency-invariant of random waveform, make the ferromagnetic element iron core degree of depth saturated; In the process, use the instrument of high-speed sampling, measure and record the instantaneous voltage u of a winding ₁(t) and exciting current instantaneous value i _ex(t).To voltage e (t) integration on magnetizing inductance, calculate magnetic linkage ψ (t) of core section by formula (7), according to the cycle of power supply output frequency, find ψ (t) and i _mthe corresponding relation of (t), with ψ (t) for ordinate, i _mt () is horizontal ordinate graphing, be the magnetization loop of iron core, according to the difference of output voltage, can obtain the cluster magnetization loop that magnetic flux summit is as shown in Figure 2 different;

$\mathrm{\ψ}\left(t\right)={\∫}_0^t\[e\left(t\right)\]dt---\left(7\right)$

The line on the summit of all magnetization loop is exactly fundamental magnetization curve, and the magnetization loop that the saturated rear measurement of the iron core degree of depth obtains is exactly limit magnetization loop, and limit magnetization loop is divided into ascending branch and decline branch;

(8) fundamental magnetization curve and the limit magnetization loop of iron core has been recorded according to above-mentioned steps, the mode of magnetization loop compression in the patent " mutual inductor volt-ampere characteristic test and calculating " adopting this seminar to propose early stage; Suppose induction electromotive force e (the t)=U in Secondary Winding _mcos (ω t), (ω=100 π, U _mincrease gradually, until current saturation) then $\mathrm{\ψ}\left(t\right)={\∫}_0^{t}e\left(t\right)dt=\frac{1}{\mathrm{\ω}}{U}_{m}sin\left(\mathrm{\ω}t\right),{\mathrm{\ψ}}_{\max }=\frac{1}{\mathrm{\ω}}{U}_m,$ The i.e. summit of magnetization loop, it correspond to the loop line (according to the compression of limit magnetization loop) on magnetization loop bunch, so just obtains a magnetization loop ψ-i under power frequency corresponding to line-frequency induction electromotive force e (t) _m.Can magnetic hysteresis loss be calculated according to magnetization loop:

Namely magnetic hysteresis loss equals ψ-i on magnetization loop _mthe area in besieged city is multiplied by frequency f again.According to magnetization loop compression, the magnetic hysteresis loss under free voltage so just can be obtained.

(9) so just can in the hope of the core loss under power frequency according to formula (9), E is the induction electromotive force effective value in Secondary Winding under power frequency, and Re is eddy current loss equivalent resistance, ∮ ψ di _mfor the area that magnetization loop surrounds.

Claims (5)

1., based on a ferromagnetic element core loss measuring method for random waveform low-frequency power, it is characterized in that, measuring process is:

1) with one, the electromagnetic relationship of ferromagnetic element is considered that the T-shaped equivalent electrical circuit of magnetic hysteresis eddy current loss is expressed, this circuit is by main inductance L _m, eddy current loss resistance R _e, hysteresis loss resistance R _hthe parallel connection of three again with first and second winding D.C. resistance R _dc1, R _dc2with leakage inductance L _{1 σ}, L _{2 σ}be in series, u ₂t () puts on the terminal voltage (primary side open circuit) in Secondary Winding when being test, e (t) is Secondary Winding induced potential, i _et () is the equivalent current of eddy current loss, i _ht () is the equivalent current of magnetic hysteresis loss, i _mt () flows through R _hand L _mthe electric current of the parallel branch of composition, i _ext () is exciting current, P is active power, P _tit is core loss; Consider Transformer Winding leakage reactance, above-mentioned parameter meets formula (1), formula (2);

$u_2\left(t\right)=i_{ex}\left(t\right)\·R_{dc2}+L_{2\mathrm{\σ}}\frac{{\mathrm{di}}_{ex}\left(t\right)}{dt}+e\left(t\right)---\left(1\right)$

i _ex(t)＝i _m(t)+i _e(t)；(2)

2) Secondary Winding direct current resistance R is first measured _dc2, then in Secondary Winding, apply voltage, measure a winding voltage u ₁(t), Secondary Winding active-power P, voltage u ₂(t), exciting current i _ex;

Due to primary side open circuit, therefore winding induced potential is:

e(t)＝u ₁(t)/n

Wherein, n is the no-load voltage ratio of primary side to secondary side;

3) core loss is made up of magnetic hysteresis loss and eddy current loss two parts, magnetic hysteresis loss P _hbe directly proportional to frequency, eddy current loss P _eto square being directly proportional of frequency, namely formula (3), (4), (5) are set up;

P _T＝P _H+P _E＝α·f+β·f ²；(3)

4) power supply adopting random waveform to export, applies different frequency f to ferromagnetic element Secondary Winding ₁, f ₂f _mthe voltage of (low frequency is to reduce power supply capacity) (m≤2, but in order to parameter estimation accuracy higher, generally get m≤3, m is also unsuitable excessive, excessive test trouble), make core sataration, measurement active-power P ₁, P ₂p _mwith exciting current i _ex1(t), i _ex2(t) ... i _exmt (), calculates the core loss P under different frequency by formula (4) _t1, P _t2p _tm;

$\left\{\begin{array}{c}{P}_{T1}=P_1-{I^2}_{ex1}{R}_{dc2}\\ P_{T2}=P_2-{I^2}_{ex2}{R}_{dc2}\\ \·\\ \·\\ \·\\ P_{Tm}=P_m-{I^2}_{exm}{R}_{dc2}\end{array}\right.---\left(4\right)$

I in above formula _exk(k=1,2 ... m) be exciting current i _exkthe root-mean-square valve of (t);

5) mode of formula (3) expression formula matrix at multiple frequencies expresses the relation of core loss and frequency such as formula shown in (5); To same ferromagnetic element, under same magnetic is close, α, β are constants, in order to make calculating more accurate, adopt least square method to ask the value of α, β by formula (7);

$\left[\begin{array}{c}\begin{array}{cc}{f}_1& f_1^2\end{array}\\ \begin{array}{cc}{f}_2& f_2^2\end{array}\\ \·\\ \·\\ \·\\ \begin{array}{cc}{f}_m& f_m^2\end{array}\end{array}\right]\×\left[\begin{array}{c}\mathrm{\α}\\ \mathrm{\β}\end{array}\right]=\left[\begin{array}{c}{P}_{TI1}\\ P_{T2}\\ \·\\ \·\\ \·\\ P_{Tm}\end{array}\right]---\left(5\right)$

Abbreviation can obtain:

FX＝P(6)

Wherein: $F=\left[\begin{array}{c}\begin{array}{cc}{f}_1& f_1^2\end{array}\\ \begin{array}{cc}{f}_2& f_2^2\end{array}\\ \·\\ \·\\ \·\\ \begin{array}{cc}{f}_m& f_m^2\end{array}\end{array}\right],X=\left[\begin{array}{c}\mathrm{\α}\\ \mathrm{\β}\end{array}\right],P=\left[\begin{array}{c}{P}_{TI1}\\ P_{T2}\\ \·\\ \·\\ \·\\ P_{Tm}\end{array}\right]$

α, β is tried to achieve by least square method:

X＝(F ^TF) ^-1×F ^TP；(7)

6) the equivalent resistance R of the eddy current loss of iron core _ecan calculate by formula (8), wherein E ₁, E ₂e _mthe Secondary Winding induced potential root-mean-square valve under several frequency respectively;

$\left\{\begin{array}{c}{R}_{e1}=\frac{E_1^2}{\mathrm{\β}\·f_1^2}\\ R_{e2}=\frac{E_2^2}{\mathrm{\β}\·f_2^2}\\ \·\\ \·\\ \·\\ R_{em}=\frac{E_m^2}{\mathrm{\β}\·f_m^2}\end{array}\right.,R_e=\frac{R_{e1}+R_{e2}+...+R_{em}}{m}---\left(8\right)$

7) R is flow through _hand L _mthe total current i of the parallel branch of composition _mcalculate by formula (11);

$i_m\left(t\right)=i_{ex}\left(t\right)-i_e\left(t\right)=i_{ex}\left(t\right)-\frac{e\left(t\right)}{R_e}---\left(9\right);$

8) to ferromagnetic element demagnetization, iron core residual flux ψ is made ₀=0; By power supply, ferromagnetic element Secondary Winding is applied to the low-frequency voltage of the frequency-invariant of random waveform, make the ferromagnetic element iron core degree of depth saturated; In the process, use the instrument of high-speed sampling, measure and record the instantaneous voltage u of a winding ₁(t) and exciting current instantaneous value i _ex(t); To voltage e (t) integration on magnetizing inductance, calculate magnetic linkage ψ (t) of core section by formula (10), according to the cycle of power supply output frequency, find ψ (t) and i _mthe corresponding relation of (t), with ψ (t) for ordinate, i _mt () is horizontal ordinate graphing, be the magnetization loop of iron core, according to the difference of output voltage, can obtain the cluster magnetization loop that magnetic flux summit is different;

$\mathrm{\ψ}\left(t\right)={\∫}_0^t\[e\left(t\right)\]dt---\left(10\right)$

The line on the summit of all magnetization loop is exactly fundamental magnetization curve, and the magnetization loop that the saturated rear measurement of the iron core degree of depth obtains is exactly limit magnetization loop, and limit magnetization loop is divided into ascending branch and decline branch;

9) fundamental magnetization curve and the limit magnetization loop of iron core has been recorded according to above-mentioned steps, the mode of magnetization loop compression in the patent " mutual inductor volt-ampere characteristic test and calculating " adopting this seminar to propose early stage; Suppose induction electromotive force e (the t)=U in Secondary Winding _mcos (ω t), (ω=100 π, U _mincrease gradually, until current saturation) then $\mathrm{\ψ}\left(t\right)={\∫}_0^{t}e\left(t\right)dt=\frac{1}{\mathrm{\ω}}{U}_{m}sin\left(\mathrm{\ω}t\right),{\mathrm{\ψ}}_{max}=\frac{1}{\mathrm{\ω}}{U}_m,$ The i.e. summit of magnetization loop, it correspond to the loop line (according to the compression of limit magnetization loop) on magnetization loop bunch, so just obtains a magnetization loop ψ-i under power frequency corresponding to line-frequency induction electromotive force e (t) _m; Can magnetic hysteresis loss be calculated according to magnetization loop:

$P_H=fV\∫BdH=fV\∫\frac{\mathrm{\ψ}}{NS}d\left(\frac{{\mathrm{Ni}}_m}{l}\right)=f\∫{\mathrm{\ψdi}}_m---\left(11\right)$

Namely magnetic hysteresis loss equals ψ-i on magnetization loop _mthe area in besieged city is multiplied by frequency f again; According to magnetization loop compression, the magnetic hysteresis loss under free voltage so just can be obtained;

10) so just can in the hope of the core loss under power frequency according to formula (12), E is the induction electromotive force effective value in Secondary Winding under power frequency, and Re is eddy current loss equivalent resistance, ∫ ψ di _marea for magnetization loop surrounds:

$P_T=P_E+P_H=\frac{E^2}{R_e}+f\∫{\mathrm{\ψdi}}_m=\frac{{U_m}^2}{R_e}+f\∫{\mathrm{\ψdi}}_m---\left(12\right).$

2. a kind of ferromagnetic element core loss measuring method based on random waveform low-frequency power according to claims 1, is characterized in that, step 1) described ferromagnetic element equivalent-circuit model is the T-shaped equivalent electrical circuit considering magnetic hysteresis and eddy current loss.

3. based on a kind of ferromagnetic element core loss measuring method based on random waveform low-frequency power described in claims 1, it is characterized in that, step 4) described Secondary Winding induction electromotive force converts secondary side through no-load voltage ratio obtain by measuring a winding voltage.

4. based on a kind of ferromagnetic element core loss measuring method based on random waveform low-frequency power described in claims 1, it is characterized in that, step 4) ~ 6) described ferromagnetic element eddy current loss equivalent resistance first adopts many group low-frequency power data, eddy current loss factor β is calculated, at the eddy current equivalent resistance Re that averages according to several groups of data according to the principle of least square.

5. based on a kind of ferromagnetic element core loss measuring method based on random waveform low-frequency power described in claims 1, it is characterized in that, step 9) to calculate the mode of magnetic hysteresis loss be the magnetization loop obtained by the compression of limit magnet ring loop line under corresponding power-frequency voltage, magnetic hysteresis loss corresponding under calculating relevant voltage according to magnetization loop area.