CN101034119B - Measuring method for power distribution network ground capacity - Google Patents

Abstract

This invention relates to a earth capacity measuring method of distribution network. The invention includes following step steps: cascading one controlled reactor at opening trigonometry side of distribution network voltage transformer, infusing one constant size frequency-changing electric current signal from opening trigonometry side of voltage transformer by controlled reactor, measuring return voltage; change signal frequency, search one resonant frequency of system; Then change size of reactor, use same method to find out another resonant frequency of system, then figure out earth capacity value of distribution network. This method completely avoid impact of electrical leakage of switching station transformer, greatly advance measuring accuracy, possess security, immediacy and such on merit.

Description

The measuring method of power distribution network ground capacitance

Technical field

The present invention relates to a kind of measuring method of power distribution network ground capacitance.

Background technology

At present domesticly existingly mainly contain two kinds to the method that electrical network injects test frequency signal measurement power distribution network ground capacitance by voltage transformer (VT):

A kind of is the signal that injects a fixed frequency by substation bus bar voltage transformer (VT) triangle side, by the equiva lent impedance at measuring-signal decanting point place, converts directly according to no-load voltage ratio then and calculates;

Another kind is to utilize the frequency variation signal source, and an inductance in parallel in tester calculates system's ground capacitance by seeking resonance frequency.

The shortcoming of these two kinds of methods is the influences that reckon without the short-circuit impedance of bus-bar potential transformer, measuring accuracy is reduced greatly, in fact because substation bus bar voltage transformer (VT) short-circuit impedance is bigger, therefore under most applicable cases, may not obtain correct test result according to the method described above, time error be arranged even be several times of actual value.

Summary of the invention

For solving the existing low technical matters of the existing measuring accuracy of power distribution network ground capacitance measuring method, the invention provides a kind of measuring method of accurate power distribution network ground capacitance, the short-circuit impedance that has solved bus-bar potential transformer influences the problem of measuring accuracy, has improved the accuracy that the power distribution network ground capacitance is measured.

The technical scheme that the present invention solves the problems of the technologies described above may further comprise the steps:

1) at REgulatable reactor l of substation bus bar voltage transformer (VT) open delta side series connection ₁

2) through reactor l ₁Inject the frequency conversion current signal of a constant magnitude from voltage transformer (VT) open delta side;

3) measure the voltage signal that injection signal two ends are returned, change and inject signal frequency, measure corresponding return voltage signal

With the injection current signal

Phase angle Value is found out

The angular frequency of the minimum value correspondence that value goes to zero is a resonance angular frequency ω of system ₁

4) change reactor l ₁Make its size be l ₂, through reactor l ₂From the frequency conversion current signal of a constant magnitude of voltage transformer (VT) open delta side injection, measure and inject the voltage signal that the signal two ends are returned, change and inject signal frequency, the return voltage signal that measurement is corresponding

With the injection current signal

Phase angle

Value is found out

The angular frequency of the minimum value correspondence that value goes to zero is another resonance angular frequency ω of system ₂

5) utilize following formula to calculate power distribution network three-phase ground capacitance value:

$3C=9\·\frac{{\mathrm{\ω}}_1^2-{\mathrm{\ω}}_2^2}{{\mathrm{\ω}}_1^2{\mathrm{\ω}}_2^2{k}^2(l_2-l_1)}$

K is a transformer voltage ratio in the following formula.

Above-mentioned steps 1) size of REgulatable reactor is 1mH～100mH in.

Technique effect of the present invention is: the present invention is at REgulatable reactor of substation bus bar voltage transformer (VT) open delta side series connection, inject the frequency conversion current signal through REgulatable reactor to tested network system again, find at least two system resonance frequencies by changing the reactor size that connects, calculate the power distribution network ground capacitance thus.Complete irrelevant with the mutual inductor leakage inductance of the calculating of power distribution network ground capacitance in the inventive method, so avoided of the influence of transformer station's mutual inductor leakage inductance fully to test result, improved measuring accuracy greatly.And have safe, quick, widely applicable advantage, thoroughly solved the technical barrier that transformer station mutual inductor leakage inductance influences power distribution network ground capacitance measuring accuracy.

The present invention is further illustrated below in conjunction with accompanying drawing.

Description of drawings

Fig. 1 is a wiring diagram of the present invention.

Fig. 2 is measuring principle figure of the present invention.

Fig. 3 is a measurement equivalent schematic diagram of the present invention.

Embodiment

Referring to Fig. 1, Fig. 1 implements wiring diagram of the present invention for utilizing electrical network bus-bar potential transformer and power distribution network ground capacitance measuring instrument 3.The electrical network bus-bar potential transformer has former limit winding 1 and secondary winding 2.Two windings are three phase windings, and former limit winding 1 adopts the star-star connection mode, i.e. get access to grid A, B, C line of its head end, ground connection again after the tail end Y-connection.Secondary winding 2 is the open-delta mode of connection, promptly the initial and end of three phase windings is connected, fall out two connector lugs, wherein a connector lug seals in REgulatable reactor 6 backs and sends terminal 5 with the current signal that another connector lug connects power distribution network ground capacitance measuring instrument 3, and the voltage signal input terminal 4 of power distribution network ground capacitance measuring instrument 3 is directly parallel in current signal and sends on the terminal 5.

Power distribution network ground capacitance measuring instrument 3 is sent terminal 5 injects constant size to voltage transformer (VT) through REgulatable reactor frequency conversion current signal by current signal

Measure the return voltage signal by voltage signal input terminal 4

The voltage measured of comparative voltage signal input terminal 4 again

Send the injection current of terminal 5 with current signal

Phase angle difference

Adopt and seek The minimum value method that value goes to zero is determined the resonance frequency of system.

Measuring principle of the present invention as shown in Figure 2.Controllable impedance l of voltage transformer (VT) open delta side series connection ₁, by the frequency conversion current signal of measure and control device to a constant magnitude of open delta side injection

Change the frequency of injecting signal, measure the return voltage signal of a series of angular frequency correspondence With the injection current signal

Phase angle Value is found out

The angular frequency of the minimum value correspondence that value goes to zero ₁, be the system resonance angular frequency.Change controllable impedance, make its size be l ₂, use the same method again and find out another system resonance angular frequency ₂

Measurement equivalent schematic diagram of the present invention can get according to resonance principle as shown in Figure 3 thus:

${\mathrm{\&omega;}}_1({\mathrm{<figure-callout\; id="1"\; label="L"\; filenames="H2007100344589E00013.png"\; state="\{\{state\}\}">L</figure-callout>}}_1+L^{\&prime;})=\frac{3}{{\mathrm{\&omega;}}_{1}C}$

${\mathrm{\&omega;}}_2(L_2+L^{\&prime;})=\frac{3}{{\mathrm{\&omega;}}_{2}C}$

L wherein ₁, L ₂Be respectively controllable impedance l ₁, l ₂Convert the value behind the voltage transformer (VT) primary side.L ' is the total leakage inductance of voltage transformer (VT) reduction to the voltage transformer (VT) primary side.

Above-mentioned two formulas of simultaneous get:

$3C=9\&CenterDot;\frac{{\mathrm{\&omega;}}_1^2-{\mathrm{\&omega;}}_2^2}{{\mathrm{\&omega;}}_1^2{\mathrm{\&omega;}}_2^2(L_2-L_1)}$

If transformer voltage ratio is k, then the controllable impedance reduction has L behind primary side ₁=k ²l ₁, L ₂=k ²l ₂Then the value of power distribution network ground capacitance is:

$3C=9\&CenterDot;\frac{{\mathrm{\&omega;}}_1^2-{\mathrm{\&omega;}}_2^2}{{\mathrm{\&omega;}}_1^2{\mathrm{\&omega;}}_2^2{k}^2(l_2-l_1)}.$

From following formula as can be seen, electric capacity in the method for testing of the present invention calculates with total leakage inductance L ' of voltage transformer (VT) irrelevant, therefore this method of testing has been eliminated the influence of mutual inductor leakage inductance to test result fully, has improved the measuring accuracy of power distribution network ground capacitance greatly.

Table 1 has been listed result and actual measured capacitance values, the wherein f of experiment measuring capacitance ₁, f ₂Corresponding voltage mutual inductor open delta side seals in controllable impedance l respectively ₁, l ₂The time system resonance frequency; C is the single-phase ground capacitance that is connected to the voltage transformer (VT) primary side; C _CalculateThe single-phase ground capacitance value of coming out for data computation by experiment.

Table 1

As can be seen from Table 1, this measuring method has been eliminated the influence of voltage transformer (VT) leakage reactance to measurement result, and the measuring error maximum is no more than 2.74%, the measuring accuracy height.

Claims (2)

1. the measuring method of a power distribution network ground capacitance comprises the steps:

1) at REgulatable reactor l of substation bus bar voltage transformer (VT) open delta side series connection ₁

2) through reactor l ₁Inject the frequency conversion current signal of a constant magnitude from voltage transformer (VT) open delta side;

3) measure the voltage signal that injection signal two ends are returned, change and inject signal frequency, measure corresponding return voltage signal With the injection current signal

Phase angle

Value is found out

The angular frequency of the minimum value correspondence that value goes to zero is a resonance angular frequency ω of system ₁

4) change reactor l ₁Make its size be l ₂, through reactor l ₂From the frequency conversion current signal of a constant magnitude of voltage transformer (VT) open delta side injection, measure and inject the voltage signal that the signal two ends are returned, change and inject signal frequency, the return voltage signal that measurement is corresponding

With the injection current signal Phase angle

Value is found out

The angular frequency of the minimum value correspondence that value goes to zero is another resonance angular frequency ω of system ₂

5) utilize following formula to calculate power distribution network three-phase ground capacitance value:

$3C=9\&CenterDot;\frac{{\mathrm{\&omega;}}_1^2-{\mathrm{\&omega;}}_2^2}{{\mathrm{\&omega;}}_1^2{\mathrm{\&omega;}}_2^2{k}^2(l_2-l_1)}$

K is a transformer voltage ratio in the following formula.

2. the measuring method of power distribution network ground capacitance according to claim 1 is characterized in that: the size of REgulatable reactor is 1mH～100mH in the described step 1).

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