CN102707147B - Method for testing impedance characteristic of large electrical equipment based on frequency-sweep method - Google Patents

Abstract

The invention relates to a method for testing the impedance characteristic of large electrical equipment based on a frequency-sweep method, which belongs to the field of measurement technique of electrical equipment. The method is suitable for testing the impedance characteristic of the large electrical equipment, through testing the internal resistance of a signal source and the voltage division ratio of the tested equipment, the impedance characteristic of an external circuit is obtained, and the method has the characteristics of wider frequency band, higher precision, small interference and the like. The measurement process of the method comprises four steps of equipment connection, cable parameter calibration, impedance measurement and post-processing calculation; the internal resistance of an instrument and the impedance of a cable are taken into consideration for the measurement, and through the wave process theory, the characteristic impedance of the tested equipment is reversely deduced from the measured impedance; and a measurement system comprises an impedance analyzer, a measurement kit, a coaxial cable and the like. By the method, the testing interference and the generated error are reduced, and the measurement precision of the impedance is improved.

Description

A kind of method of testing of the large scale electrical power unit impedance operator based on frequency sweep method

Technical field

The method of testing that the present invention relates to a kind of large scale electrical power unit impedance operator based on frequency sweep method, belongs to power equipment field of measuring technique.

Background technology

In electric system, except generator, the inactive components such as power transformer, high voltage reactor, high-voltage capacitor, all the resistance value of available devices port is equivalently represented.Impedance operator is not only the important intrinsic parameter of power equipment itself, is also the basis of apparatus for establishing model in Power System Analysis.The Measurement accuracy of power equipment impedance operator has great importance for the work such as the simulation analysis of electric system, the calculating of electro-magnetic transient transient state, fault reproduction, design evaluation and research.

For the measurement of mini-plant impedance operator, the method for existing comparative maturity, can directly be connected and be measured by impedometer at present.And to the large scale electrical power unit in super, extra-high voltage system, as the impedance operator of transformer, reactor etc., due to the singularity of its structure, lack at present fixing testing apparatus and practical measuring method.First, large scale electrical power unit bulky (length reaches tens meters of magnitudes), high-pressure side to be measured and low pressure end are distant, and device port cannot directly be connected with the test lead of impedometer; Secondly, in measuring process, have stray parameter due under high frequency, the variation of the introducing of connecting line and self parameter all can affect to measurement result.

Summary of the invention

The object of the invention is to propose a kind of method of testing of the large scale electrical power unit impedance based on frequency sweep method, to overcome the above-mentioned defect in prior art, with connecting tested device port and impedometer with the concentric cable of screen layer, by the intrinsic standoff ratio of the internal resistance of measuring-signal source and equipment under test, to obtain the impedance operator of large scale electrical power unit.

The method of testing of the large scale electrical power unit impedance based on frequency sweep method that the present invention proposes, comprises following steps:

(1) tested large scale electrical power unit, stube cable, measurement annex, impedometer and computing machine are put successively according to measuring position;

(2) make the terminal of stube cable distinguish short circuit and open circuit, measure respectively short-circuit impedance Zcs and the open-circuit admittance Yco of stube cable with impedometer at the head end of stube cable, according to short-circuit impedance Zcs and open-circuit admittance Yco, calculate cable attenuation constant γ and cable nature impedance Z c:

(3) high-pressure side of tested large scale electrical power unit is connected with low pressure end by described stube cable with described measurement annex, and makes connecting interface place fill fixing by metal adhesive tape and metal wool; Making to measure annex is connected with described impedometer by stube cable; Impedometer is connected by signal wire with described computing machine;

(4) computing machine is according to the current reading Z of impedometer _rwith tested large scale electrical power unit impedance Z _tthe following relation existing, calculates the impedance Z t of tested power equipment:

$Z_R=Z_c\left(\frac{1+{\mathrm{\ρ}}_2{e}^{-2\mathrm{\γL}}}{1-{\mathrm{\ρ}}_1{e}^{-2\mathrm{\γL}}}\right)$

${\mathrm{\ρ}}_1=\frac{Z_{\mathrm{in}}-Z_c}{Z_{\mathrm{in}}+Z_c},$ ${\mathrm{\ρ}}_2=\frac{Z_t-Z_c}{Z_t+Z_c},$

Wherein, Z _infor the internal impedance of impedometer, L is cable length cable resistance.

The method of testing of the large scale electrical power unit impedance based on frequency sweep method that the present invention proposes, its advantage is the testing impedance that this measuring method is applicable to large scale electrical power unit, has frequency band wider, precision is higher, the features such as little that are disturbed.Measure based on frequency sweep method, make full use of the feature that large scale electrical power unit DC impedance is low, improve survey frequency scope and signal intensity, in the higher frequency range of frequency, output response that can be larger with less sine wave generator, to obtain desirable measuring accuracy.Secondly, this method, by the high frequency stray parameter of connecting line, is paid attention to by measurement and the demarcation of the stube cable parameter to fixation measuring position; Meanwhile, this method has been considered equipment internal resistance, stube cable impedance and the direct relation of equipment under test impedance, calculates by data, makes measurement result more accurate.

Accompanying drawing explanation

Fig. 1 is the schematic diagram of the inventive method.Wherein A is electric impedance analyzer, and B is stube cable.Vs, Zin are equivalent source and the internal resistance of measuring equipment, the natural impedance that Zc is cable, Z _rfor measuring impedance, the impedance that Zt is tested power equipment.

Fig. 2 is the device connection diagram that uses the inventive method.

In Fig. 2,1 is stube cable, and 2 is tested large scale electrical power unit, and 3 is stube cable, and 4 for measuring annex, and 5 is impedometer, and 6 is computing machine.

Embodiment

The method of testing of the large scale electrical power unit impedance based on frequency sweep method that the present invention proposes, its schematic diagram as shown in Figure 1, comprises following steps:

(1) tested large scale electrical power unit 2, stube cable 1 and 3, measurement annex 4, impedometer 5 and computing machine 6 are put successively according to measuring position;

(2) make the terminal of stube cable 1 distinguish short circuit and open circuit, measure respectively short-circuit impedance Zcs and the open-circuit admittance Yco of stube cable 1 with impedometer 5 at the head end of stube cable 1, according to short-circuit impedance Zcs and open-circuit admittance Yco, calculate cable attenuation constant γ and cable nature impedance Z c:

(3) high-pressure side of tested large scale electrical power unit 2 is connected with described stube cable 1 and 3 with low pressure end, and it is fixing that connecting interface place is filled by metal adhesive tape and metal wool, the cable other end is connected with described measurement annex 4 simultaneously; Making to measure annex 4 is connected with impedometer 5 by stube cable 1; Impedometer 5 is connected by signal wire with described computing machine 6, and as shown in Figure 2, measurement annex and electric impedance analyzer wherein complement one another;

(4) computing machine 6 is according to the current reading Z of impedometer _rwith tested large scale electrical power unit impedance Z _tthe following relation existing, calculates the impedance Z t of tested power equipment:

$Z_R=Z_c\left(\frac{1+{\mathrm{\ρ}}_2{e}^{-2\mathrm{\γL}}}{1-{\mathrm{\ρ}}_1{e}^{-2\mathrm{\γL}}}\right)$

${\mathrm{\ρ}}_1=\frac{Z_{\mathrm{in}}-Z_c}{Z_{\mathrm{in}}+Z_c},$ ${\mathrm{\ρ}}_2=\frac{Z_t-Z_c}{Z_t+Z_c},$

Wherein, Z _infor the internal impedance of impedometer, L is cable length cable resistance.

Below introduce in detail the inventive method principle of work:

Whole measuring method is divided into following four steps:

The 1st step: stube cable parameter calibration

Because the survey of this measuring method considers that by the impedance of cable, in measuring system, the resistance value recording comprises cable resistance and tested design impedance, therefore cable data has considerable influence to test result; Stray parameter under high frequency can change again the impedance operator of stube cable itself simultaneously, and these factors all can affect measurement result, before and after measuring, cable resistance is measured to demarcation, can effectively reduce introducing error.

The parameter that need need demarcate stube cable comprises: short-circuit impedance Zcs, open-circuit admittance Yco, and cable length L.First cable is fixed according to measuring the position requiring, while guaranteeing it to outside stray parameter and the 2nd, 3 pacing amount, remain unchanged, respectively the terminal of cable is carried out to short circuit and open circuit, in impedometer measuring appliance impedance operator for head end, the result recording is its short-circuit impedance Zcs and open-circuit admittance Yco.Measurement result the processing in step 3 is provided provide parameter foundation.

The 2nd step: measuring equipment connects

Cable one end is connected on tested equipment high-pressure side, and ground wire is connected with device housings simultaneously, and test signal is finally connected to terminal by measurement annex, impedometer; Connecting interface place fills fixing by metal adhesive tape and metal wool.Whole tested equipment and measuring system connection layout are as shown in Figure 2.

The 3rd step: design impedance characteristic test

Utilize impedometer, the resultant impedance that records stube cable and tested equipment is measured Z _r, record data are for aftertreatment.

The 4th step: Data Post

Measure equivalent electrical circuit and principle as shown in Figure 1, impedance measurements is Z _r, available following formula calculates the relation between it and tested impedance, cable resistance and equipment internal impedance:

$Z_R=Z_c\left(\frac{1+{\mathrm{\ρ}}_2{e}^{-2\mathrm{\γL}}}{1-{\mathrm{\ρ}}_1{e}^{-2\mathrm{\γL}}}\right)---\left(1\right)$

${\mathrm{\ρ}}_1=\frac{Z_{\mathrm{in}}-Z_c}{Z_{\mathrm{in}}+Z_c},$ ${\mathrm{\ρ}}_2=\frac{Z_t-Z_c}{Z_t+Z_c}---\left(2\right)$

$\mathrm{\γ}=\sqrt{Z_{\mathrm{cs}}\·Y_{\mathrm{co}}},$ $Z_c=\sqrt{Z_{\mathrm{cs}}/Y_{\mathrm{co}}}---\left(3\right)$

Wherein, Zcs, Yco are respectively cable short-circuit impedance cable and the open-circuit admittance that in step 2, demarcation obtains, for calculating accordingly the natural impedance Z c of cable, and cable attenuation constant γ, L is cable length.

By with formula (1)-(3), measurement result is proofreaied and correct, can obtain the impedance Z t of tested power equipment.

In an embodiment of this method, surveying instrument and the major parameter of employing are as shown in table 1.

Table one surveying instrument parameter

Claims (1)

1. a method of testing for the large scale electrical power unit impedance based on frequency sweep method, is characterized in that the method comprises following steps:

(1) tested large scale electrical power unit, stube cable, measurement annex, impedometer and computing machine are put successively according to measuring position;

(2) make the terminal of stube cable distinguish short circuit and open circuit, measure respectively short-circuit impedance Zcs and the open-circuit admittance Yco of stube cable with impedometer at the head end of stube cable, according to short-circuit impedance Zcs and open-circuit admittance Yco, calculate cable attenuation constant γ and cable nature impedance Z c: $\mathrm{\γ}=\sqrt{Z_{\mathrm{cs}}\·Y_{\mathrm{co}}},$ $Z_c=\sqrt{Z_{\mathrm{cs}}/Y_{\mathrm{co}}};$

(3) high-pressure side of tested large scale electrical power unit is connected with described measurement annex by described stube cable with low pressure end; Making to measure annex is connected with described impedometer by stube cable; Impedometer is connected by signal wire with described computing machine;

(4) computing machine is according to the current reading Z of impedometer _rwith tested large scale electrical power unit impedance Z _tthe following relation existing, calculates the impedance Z of tested power equipment _t:

$Z_R=Z_c\left(\frac{1+{\mathrm{\ρ}}_2{e}^{-2\mathrm{\γL}}}{1-{\mathrm{\ρ}}_1{e}^{-2\mathrm{\γL}}}\right)$

${\mathrm{\ρ}}_1=\frac{Z_{\mathrm{in}}-Z_c}{Z_{\mathrm{in}}+Z_c},{\mathrm{\ρ}}_2=\frac{Z_t-Z_c}{Z_t+Z_c},$

Wherein, Z _infor the internal impedance of impedometer, L is cable length.

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