CN111983327A - Method for measuring grounding impedance of large grounding grid - Google Patents
Method for measuring grounding impedance of large grounding grid Download PDFInfo
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- CN111983327A CN111983327A CN202010679854.2A CN202010679854A CN111983327A CN 111983327 A CN111983327 A CN 111983327A CN 202010679854 A CN202010679854 A CN 202010679854A CN 111983327 A CN111983327 A CN 111983327A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/20—Measuring earth resistance; Measuring contact resistance, e.g. of earth connections, e.g. plates
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Abstract
The invention relates to a method for measuring the grounding impedance of a large grounding grid, which comprises the following steps: measuring the grounding impedance by adopting frequency conversion equipment to reduce the error of the grounding impedance; and the grounding resistance is measured in a capacitance compensation mode through the series capacitor so as to reduce the capacity of the test transformer. Compared with the conventional test method for measuring the grounding impedance, the method is more accurate, higher in economical efficiency, more accurate in measurement result and higher in economical efficiency, and has higher reliability and authenticity than the grounding impedance obtained by a simulation experiment.
Description
Technical Field
The invention belongs to the technical field of electrical tests, and particularly relates to a method for measuring grounding impedance of a large grounding grid.
Background
In order to ensure that the human body is not injured, the grounding impedance test is carried out on a power plant and a transformer substation, the grounding impedance is compared with a design value, the accuracy of the grounding impedance test is critical, and if the grounding impedance is larger than the design value, a ground network is required to be modified, so that casualties and economic losses caused by accidents are avoided. The existing grounding impedance test method has large measurement error, large capacity of a test transformer and high test cost.
Disclosure of Invention
The present invention aims to provide a method for measuring the grounding impedance of a large grounding grid, so as to solve the technical problems.
The invention provides a method for measuring the grounding impedance of a large grounding grid, which comprises the following steps:
measuring the grounding impedance by adopting frequency conversion equipment to reduce the error of the grounding impedance;
and the grounding resistance is measured in a capacitance compensation mode through the series capacitor so as to reduce the capacity of the test transformer.
Further, the measuring the ground impedance by the device adopting frequency conversion to reduce the error of the ground impedance comprises:
the test power supply is rectified into a direct current power supply through a frequency conversion cabinet, the direct current power supply is inverted into an alternating current power supply, and the alternating current power supply passes through an isolation transformer and then is subjected to grounding impedance measurement.
Further, the measuring the ground resistance by capacitance compensation through the series capacitor to reduce the capacity of the test transformer includes:
before the test, the length of current line is calculated, the value of inductance per kilometer is calculated to obtain corresponding inductance, the different frequency voltage of 60 Hz-45 Hz is used, and the capacitance to be supplemented is determined by frequency to make XL≈XCObtaining the capacitance needing to be connected in parallel; wherein XLIs a current level reactance; xCTo compensate for the compensation capacitance of the current stage.
Furthermore, the length of the current line is 4-5 times of the diagonal line of the grounding grid of the power plant and the transformer substation, the length of the voltage line is 0.618 times of the current line, the current line is an inductive load, and compensation is performed through a capacitor.
By means of the scheme, the method for measuring the grounding impedance of the large grounding grid is more accurate than a conventional method for measuring the grounding impedance, higher in economical efficiency and more accurate in measuring result, higher in economical efficiency, and more reliable and truer than the grounding impedance obtained through a simulation experiment.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical solutions of the present invention more clearly understood and to implement them in accordance with the contents of the description, the following detailed description is given with reference to the preferred embodiments of the present invention and the accompanying drawings.
Drawings
Fig. 1 shows an embodiment of a method for measuring the ground impedance of a large ground grid according to the present invention.
In the figure: w-power meter, A1-frequency-selecting ammeter, A2-frequency-selecting ammeter and V2-frequency-selecting voltmeter.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
Referring to fig. 1, the present embodiment provides a method for measuring ground impedance of a large ground grid, including:
1) the equipment adopting frequency conversion measures the grounding impedance so as to reduce the error of the grounding impedance:
the test power supply is rectified into a direct current power supply through a frequency conversion cabinet, the direct current power supply is inverted into an alternating current power supply, and the alternating current power supply passes through an isolation transformer and then is subjected to grounding impedance measurement.
2) The grounding resistance is measured in a capacitance compensation mode through the series capacitor so as to reduce the capacity of the test transformer:
before the test, the length of current line is calculated, the value of inductance per kilometer is calculated to obtain corresponding inductance, the different frequency voltage of 60 Hz-45 Hz is used, and the capacitance to be supplemented is determined by frequency to make XL≈XCObtaining the capacitance needing to be connected in parallel; wherein XLIs a current level reactance; xCTo compensate for the compensation capacitance of the current stage.
The length of the current line is 4-5 times of the diagonal line of the grounding grid of the power plant and the transformer substation, the voltage line is 0.618 times of the current line, the current line is inductive load, and compensation is carried out through a capacitor.
When the grounding impedance test is carried out on a large hydropower station, zero sequence current flows through a transformer substation of a power plant, errors are generated on the grounding impedance test, the error of the grounding impedance measurement can be reduced by adopting a variable frequency power supply, the ground grids of the large transformer substation and the hydropower station are large, so that the test current line is long, the inductance in the test current line cannot be ignored, and the test current line can be generated in the test process in the actual processThe success rate factor decreases and the capacity of the transformer increases, which is based on the principle that when the compensation capacitor is not provided, the required transformer capacity is S ═ I2 2×(RL+XL+Z1)＝I2 2×(RL+WL+Z1) Wherein R isLIs a current level resistor; xLIs a current level reactance; z1Is a ground impedance; l is a current level inductance value; w is the angular velocity, the required transformer capacity when adding the compensation capacitor is
Wherein R isLIs a current level resistor; l is a current level inductance value; c is compensation capacitance; z1Is a ground impedance; w is the angular velocity. When compensating, make the best of
Wherein, XCA compensation capacitor of the current stage; xLA current-level reactance, the capacitance to be compensated when a current voltage of 60Hz is added is
Wherein, L is the inductance of the current level, C is the capacitance of the actual compensation, and the grounding resistance R is obtainedg11，
Wherein L is1For the inductance of the grounding resistor, when the current voltage of 45Hz is added, the capacitance to be compensated is
Wherein, L is the inductance of current level, C is the capacitance of actual compensation, and the grounding resistance R is obtainedg12，
The average value of the resistances is
The compensation capacitor can also be adjusted through the power factor table to make the power factor approach to 1,
wherein Z is the final grounding impedance value, Rg is the grounding resistance, L1The inductance value of the grounding reactance measured under the condition that the current level is 60 Hz; l is2The inductance value of the grounding reactance measured at 45Hz is the current level.
In a large-scale grounding grid, in the process of measuring grounding impedance, all zero-sequence currents of a power plant and power transformation flow through, mutual inductance of other lines can also change voltage, and therefore errors can be generated on the grounding impedanceL≈XCThe capacity of the test transformer is reduced in a compensation mode, so that the impedance of the grounding grid can be effectively measured, the test cost is reduced, and the economic benefit is created.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, it should be noted that, for those skilled in the art, many modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.
Claims (4)
1. A method for measuring the grounding impedance of a large grounding grid is characterized by comprising the following steps:
measuring the grounding impedance by adopting frequency conversion equipment to reduce the error of the grounding impedance;
and the grounding resistance is measured in a capacitance compensation mode through the series capacitor so as to reduce the capacity of the test transformer.
2. The method of claim 1, wherein the step of measuring the ground impedance by using a frequency conversion device to reduce the error of the ground impedance comprises:
the test power supply is rectified into a direct current power supply through a frequency conversion cabinet, the direct current power supply is inverted into an alternating current power supply, and the alternating current power supply passes through an isolation transformer and then is subjected to grounding impedance measurement.
3. The method for measuring the grounding impedance of the large grounding grid according to claim 1, wherein the step of measuring the grounding resistance by means of capacitance compensation through a series capacitor to reduce the capacity of the test transformer comprises the following steps:
before the test, the length of current line is calculated, the value of inductance per kilometer is calculated to obtain corresponding inductance, different frequency voltages of 60Hz and 45Hz are used, and the capacitance to be supplemented is determined by frequency to make XL≈XCObtaining the capacitance needing to be connected in series; wherein XLIs a current level reactance; xCTo compensate for the compensation capacitance of the current stage.
4. A method of measuring large earthed network earthing impedance according to claim 3, characterized in that the length of the current line is 4-5 times the diagonal of the power plant and substation earthed network, the voltage line is 0.618 times the current line, the current line is inductive load, compensated by capacitance.
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Citations (8)
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| CN205067604U (en) * | 2015-06-10 | 2016-03-02 | 苏州工业职业技术学院 | Experimental equipment of integrating of single -phase short -circuit impedance of transformer |
| CN107192885A (en) * | 2017-05-18 | 2017-09-22 | 四川中鼎科技有限公司 | Using alien frequencies, the method for high-current test large hydropower station Grounding impedance |
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