CN1124846A - Dynamic measuring method and apparatus for D.C. resistance of power transformer - Google Patents

Abstract

The method and device for dynamically measuring the DC resistance of electric power transformer with different capacities and models features that by regulating the electric potential and resistance of external circuit, the steady-state value and time constant of charge current-time curve for the object to be tested are respectively regulated to their pre-defined constant values. Its advantages include high measuring speed, and wide adaptability.

Description

The dynamic measurement method of power transformer direct current resistance and measurement mechanism

The present invention relates to a kind of measuring method and measurement mechanism of power transformer direct current resistance.

At present, the direct current resistance measuring method of Winding in Power Transformer all is the static measurement method basically both at home and abroad, promptly adopt the mode that adds constant pressure source or constant voltage, constant current source switching at the winding two ends that winding is charged, when reaching, charging current stablizes when constant, adopt bridge method to measure the resistance of winding, or adopt other method to measure the voltage at winding two ends, electric current, calculate direct current resistance.Because the time constant of high-power transformer is very big, also will be for a long time even will reach relative charging stable state, although adopted some to shorten the method and apparatus in duration of charging at present, Measuring Time is still longer, the versatility of device is poor.

The purpose of this invention is to provide a kind of quick, accurate, suitable new method and surveying instrument of measuring all kinds of DC Resistance of Transformer.

Adopt the direct current resistance of this method measuring transformer can divide for three steps carried out, at first with a circuit that contains regulated power supply and adjustable resistance, we are called same electrochemical potential E ', sameization resistance R ' circuit be connected on the two ends of tested winding, rule of thumb or the instructions of transformer E ' and R ' are adjusted an initial value.Energized then, in the dynamic process of charging, detect and calculate same electrochemical potential E ' and sameization resistance R by pick-up unit ' desired value, after this cut off the electricity supply, with E ', R ' by the desired value adjustment of measuring, its purpose of adjusting E ', R ' is: make the steady-state value and the time constant of electric current one time curve in the charging process reach predetermined steady state value respectively, charging current one time curve during the straight resistance of promptly measuring various windings is all basic identical.In the 3rd step, energized again in the charging dynamic process, is measured the instantaneous value of different current/voltages constantly by pick-up unit, calculates the resistance value of tested winding by the differential equation of separating circuit.

The principle of this method invention is with the linear equation of separating after the differential equation in the dynamic process replaces separating stable state, therefore reaches with kinetic measurement to replace steady state measurement.Utilize the equivalent circuit diagram-6 transformer charging current curve map-7 of transformer charging to further specify as follows below:

If: t ₁, t ₂Be two moment in the charging process.Can obtain: $u\left(t_1\right)=\mathrm{Ri}\left(t_1\right)+L\frac{\mathrm{di}}{\mathrm{dt}}{|}_{t1}-----\left(1\right)$ $u\left(t_2\right)=\mathrm{Ri}\left(t_2\right)+L\frac{\mathrm{di}}{\mathrm{dt}}{|}_{t2}-----\left(2\right)$ Get in the following formula $\frac{\mathrm{di}}{\mathrm{dt}}{|}_{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="A9411752800071.png"\; state="\{\{state\}\}">t</figure-callout>}1}=\frac{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="i"\; filenames="A9411752800071.png"\; state="\{\{state\}\}">i</figure-callout>}}_1}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="A9411752800071.png"\; state="\{\{state\}\}">t</figure-callout>}}_1}={\mathrm{<figure-callout\; id="1"\; label="D"\; filenames="A9411752800071.png"\; state="\{\{state\}\}">D</figure-callout>}}_1$ $\frac{\mathrm{di}}{\mathrm{dt}}{|}_{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="A9411752800071.png"\; state="\{\{state\}\}">t</figure-callout>}2}=\frac{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="i"\; filenames="A9411752800071.png"\; state="\{\{state\}\}">i</figure-callout>}}_2}{\mathrm{\&Delta;}{\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="A9411752800071.png"\; state="\{\{state\}\}">t</figure-callout>}}_2}={\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="A9411752800071.png"\; state="\{\{state\}\}">D</figure-callout>}}_2$

By separating the differential equation (1), (2), the value that can draw R following (R is the direct current resistance of Transformer Winding) $R=\frac{u\left(t_1\right)\&bull;D_2-u\left(t_2\right)\&bull;D_1}{i\left(t_1\right)\&bull;D_2-i\left(t_2\right)\&bull;D_1}-----\left(3\right)$

Because the shape of charging current one time curve of different Transformer Winding has a great difference, therefore, the difference that measures the Δ i, the Δ t that obtain for different winding surveying instruments is very big, cause the error of the DC Resistance of Transformer R that calculates very big, so must carry out particular processing to charging current one time curve.The present invention carries out sameization processing, and the R ' of sameization processing, the value of E ' need provide by a test,

Transfer E '=A volt R=B Europe earlier

Then $i\&ap;\frac{E\&prime;}{R\&prime;}(1-e^{\frac{-R\&prime;}{L}t})=\frac{A}{B}(1-e^{-\frac{B}{L}t})-----\left(4\right)$ When t=c substitution during second (4) formula $i\left(c\right)=\frac{A}{B}(1-e^{-\frac{B}{L}C})-----\left(5\right)$ Solve L by (5) formula $L=\frac{B\&bull;C}{\ln \frac{A}{A-B\&bull;i\left(c\right)}}-----\left(6\right)$

If stipulating that time constant after the sameization processing is unified is D second, the stable state DC current is unified for the F peace, then can obtain sameization parameters R ' and the value of E '. $R\&prime;=\frac{L}{D}=\frac{B\&bull;C}{D\&bull;\ln \frac{A}{A-B\&bull;i\left(c\right)}}-----\left(7\right)$

E’＝F·R’ (8)

Behind (7), (8) formula adjustment external circuit, measured range transformer, its charging current one time curve is basic identical, and device can be measured the direct current resistance of winding exactly.

After utilizing this method to measure a winding, when surveying the resistance of this tapping again, only need to change the external connection of measuring, no longer carry out together-change the adjustment of desired value E ', R '.

Implementing the measurement mechanism that the inventive method is made, mainly be made of three parts, see Fig. 1, is respectively regulated power supply (1), sameization resistance (2), microcomputer measurement instrument (3).(4) be tested transformer.The structure of regulated power supply (1) is seen figure-2, figure-3, and wherein (5) are the ac rectifying power source parts, and its input is an alternating current 220V, through bridge rectifier and L, C filtering, again after voltage stabilizing as a direct supply of instrument.Another direct supply is storage battery dedicated (6), and (5) send into output voltage regulator (8) through switch (7) separately respectively with (6).(8) circuit structure is provided by figure-3, and the direct supply of (8) input is after inverter (9), high-frequency transformer (10), (11) three links of secondary rectifying and wave-filtering, again as the direct supply output after regulating; Comparator circuit (12) amplifying circuit (13), control circuit of duty ratio (14) are the voltage stabilizing FEEDBACK CONTROL parts of power supply.(15) be reference power source, regulate the output voltage values of (8) by regulating (15).

The structure of sameization resistance (2)-4 is provided by figure, and (2) connect resistance-switch that several electricity (17) and switch (18) be in parallel to forming again by an adjustable resistance (16).

Microcomputer measurement instrument part at first by analog input channel with DC voltage and current signal respectively through V/V transducer (19), I/V transducer (20) is converted to the signal that the A/D change-over circuit can be discerned, each is after sampling keeps chip (21), by multi-channel switch (22) control timesharing and follow-up amplifier (23) and A/D circuit (24) connection, digital signal after the A/D conversion is sent into data bus, deposit RAM chip (27) in by MCS51 single-chip microcomputer (25) control, after data acquisition finishes, microcomputer (25) fetches data from (27), draw the resistance value of measurand as calculated, operating key (28), show (29), printer (30) provides operating personnel control and information output function to instrument through parallel port (31) and microcomputer (25) contact.(32) be amplifier gain control circuit, (33) are internal power supply.(26) be the procedure stores chip.

The structured flowchart of figure-1 device

Figure-2 power supply architecture figure

Figure-3 electric power output voltage controller structure figure

Figure-4 sameization resistance junction compositions

Figure-5 microcomputer measurement instrument theory diagrams

Figure-6 transformers charging equivalent circuit diagram

Figure-7 transformer charging current curve maps

Claims (5)

1, a kind of measuring method that detects the Winding in Power Transformer direct current resistance, employing applies the adjunct circuit that contains power supply and resistance on tested winding, by detecting and calculating charge characteristic salt line acquisition direct current resistance numerical value, it is characterized in that: measure and divided for three steps carried out, at first with a circuit that contains regulated power supply and adjustable resistance, claim same electrochemical potential E ', sameization resistance R again ' circuit be connected on the two ends of tested winding, and E ', R ' are adjusted an initial value; Energized then, in the dynamic process of charging, detect and calculate the desired value of E ', R ', deenergization by pick-up unit, with E ', R ' data adjustment according to target, reach predetermined steady state value respectively to the steady-state value and the time constant of the charging current-time curve that makes tested winding; In the 3rd step, energized detects the different instantaneous values of electric current, voltage constantly in the dynamic process of charging again, calculates the resistance value of tested winding by the differential equation of separating circuit.

2, according to claim 1 described detection method, it is characterized in that: after measuring the resistance of a winding, when surveying the resistance value of this tapping again, only need to change external connection, no longer carry out the adjustment of sameization desired value E ', R '.

3, the pick-up unit of making according to the described method of claim 1 is characterized in that: device is made of regulated power supply (1), sameization resistance (2), Microcomputer Detecting instrument (3) three parts.

4, pick-up unit according to claim 3 is characterized in that: sameization resistance (2) is by an adjustable resistance (16), and resistance one switch that connect several resistance (17) and switch (18) are in parallel again is to forming.

5, pick-up unit according to claim 3 is characterized in that: the structure of regulated power supply (1) is; Ac rectifying power source (5), direct-flow storage battery (6) connect output voltage regulator (8) after by switch (7) parallel connection.

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