CN109839537B - Method for judging harmonic measurement accuracy of transformer substation CVT - Google Patents
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Abstract
A method for judging harmonic measurement accuracy of a transformer substation CVT comprises the steps of measuring at a bus capacitor voltage transformer and a line current transformer in the transformer substation to obtain fundamental voltage, fundamental power, each harmonic voltage content and a harmonic current value; comprehensively judging the running state of the line based on the power characteristics of the line in no-load, and calculating the equivalent fundamental wave impedance of the no-load line through the fundamental wave reactive power and the fundamental wave voltage; determining the relation between the fundamental wave impedance and the harmonic frequency according to the equivalent fundamental wave impedance attribute, and further calculating each harmonic impedance of the no-load line; and finally, calculating each harmonic voltage value of the no-load circuit according to each harmonic current value and corresponding harmonic impedance based on ohm's law, then calculating each harmonic voltage content, comparing the voltage content with each measured harmonic voltage content, and judging the accuracy of CVT harmonic voltage measurement. The harmonic monitoring and treatment of the high-voltage system provides support so as to ensure the safe, stable and economic operation of the transformer substation.
Description
Technical Field
The invention relates to the technical field of electrical measurement, in particular to a method for judging the accuracy of transformer substation CVT harmonic measurement.
Background
With the rapid development of technologies such as power electronics and new energy, the harmonic voltage level of a power system is continuously increased, the harmonic problem of a high-voltage system needs to be solved urgently, and accurate measurement of the harmonic is a precondition for controlling the harmonic. In recent years, Capacitive Voltage Transformers (CVTs) have been greatly improved in terms of design and manufacturing level and product quality, and the operational reliability has been significantly improved. Meanwhile, with the continuous deepening of the ultrahigh voltage power grid construction and urban and rural power grid construction transformation aspects in China, the CVT has the advantages of good insulation reliability, high measurement precision, small operation and maintenance workload, excellent economy, no ferromagnetic resonance with the system, low manufacturing cost, capability of being used as a coupling capacitor for power line carrier communication and the like in a high-voltage system, and is widely applied to the high-voltage and ultrahigh voltage power systems in China. According to the regulations in national standard GB/T4703-2007 capacitor voltage transformers, CVTs adopted in a high-voltage power grid can completely meet the requirements of a system in the aspects of measurement accuracy of fundamental voltage, system protection and fundamental signal conversion of an automatic device, and for high-voltage and ultrahigh-voltage power systems needing harmonic voltage measurement, certain errors always exist in measurement results due to the influence of inherent transmission characteristics of the CVTs. Plain text regulations in national standards for utility grid harmonics: "capacitive voltage transformers cannot be used for harmonic measurement".
At present, CVT is widely used in high-voltage substations for harmonic voltage measurement, the accuracy of measurement results is difficult to judge, and a qualitative analysis and quantitative judgment method for whether CVT harmonic voltage measurement is accurate or not is lacked.
Disclosure of Invention
The invention mainly aims to overcome the defects in the prior art and provides a method for judging the harmonic measurement accuracy of a transformer substation CVT (continuously variable transmission), which can simply and quickly calculate the content of each harmonic voltage of the transformer substation through the fundamental voltage, the current and the power of a no-load line of a high-voltage transformer substation, judge the accuracy of the harmonic measurement of the transformer substation CVT on the basis of the measured value and the calculated value of the content of the harmonic voltage, and provide support for the harmonic monitoring and management of a high-voltage system so as to ensure the safe, stable and economic operation of the transformer substation.
The invention adopts the following technical scheme:
a method for judging the accuracy of transformer substation CVT harmonic measurement is characterized by comprising the following steps:
step 1, selecting a transformer substation with an unloaded line or a line in an unloaded state, and measuring at a capacitance voltage transformer and a line current transformer of a bus of the transformer substation to obtain fundamental voltage, fundamental power, voltage content of each harmonic and current value of each harmonic;
step 2, comprehensively judging the running state of the line based on the fundamental wave power characteristics of the line in no-load, and then calculating the equivalent fundamental wave impedance of the no-load line through the fundamental wave reactive power and the fundamental wave voltage;
step 3, determining the relation between the equivalent fundamental wave impedance and the harmonic frequency according to the equivalent fundamental wave impedance, and further calculating each harmonic impedance of the no-load line;
and 4, calculating each harmonic voltage value of the no-load circuit according to each harmonic current value of the no-load circuit and each obtained harmonic impedance based on ohm's law, then calculating each harmonic voltage content rate by combining each harmonic voltage content rate definition, comparing with each measured harmonic voltage content rate, and judging the accuracy of CVT harmonic voltage measurement.
In the step 1, the fundamental wave voltage U in the three-phase system is obtained by using the electric energy quality analyzer for synchronous measurement1Single-phase fundamental wave active power PS1Single-phase fundamental wave reactive power QS1And the voltage content of each subharmonic HRUhAnd the value of each harmonic current Ih；
In step 2, based on the single-phase fundamental wave active power P when the line is in no-loadS1Single-phase fundamental wave reactive power QS1And judging the running state of the line.
The equivalent fundamental wave impedance
The harmonic impedances
h is the harmonic order.
In the step 1, the method further comprises measuring the active power P of the three-phase total fundamental waveT1And three-phase total reactive power QT1(ii) a In step 2, three-phase total fundamental wave active power P based on no-load time of the lineT1And three-phase total reactive power QT1And judging the running state of the line.
The equivalent fundamental wave impedance
The harmonic impedances
h is the harmonic order.
And comprehensively judging the running state of the line based on the fundamental wave power characteristics when the line is in no-load, and if the fundamental wave power characteristics meet ideal state conditions, actual state conditions and change trend conditions, the line is in no-load state.
In step 3, the voltage value U of each subharmonic waveh *＝Ih×XCh。
In step 4, the calculated voltage content of each subharmonic
In step 4, comparing the voltage content of each subharmonic obtained by calculation and measurement:
according to khThe value size is used for judging the accuracy of CVT harmonic voltage measurement, and the specific judgment process is as follows:
when k ishWhen the voltage is more than 1, the h harmonic voltage measured by the CVT is amplified by the amplification factor kh；
When k ishWhen the voltage is 1, the h harmonic voltage measured by the CVT is accurate;
when k ishWhen the voltage is less than 1, the h harmonic voltage measured by the CVT is reduced by 1/kh。
As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following advantages:
according to the method, the content of each harmonic voltage of the transformer substation can be simply and quickly calculated through the fundamental voltage, the current and the power of the no-load line of the high-voltage transformer substation, the accuracy of transformer substation CVT harmonic measurement is judged based on the measured value and the calculated value of the content of the harmonic voltage, and support is provided for monitoring and governing the harmonic of a high-voltage system, so that the safe, stable and economic operation of the transformer substation is ensured.
Drawings
Fig. 1 is a schematic flow chart of a method for determining accuracy of harmonic measurement of a CVT of a substation according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of an empty-load line test point provided by an embodiment of the invention;
FIG. 3 is a power trend graph of an unloaded circuit according to an embodiment of the present invention;
the invention is described in further detail below with reference to the figures and specific examples.
Detailed Description
The invention is further described below by means of specific embodiments.
Fig. 1 is a schematic flow chart of a method for determining accuracy of harmonic measurement of a substation CVT provided in an embodiment of the present invention, where the method includes:
step 1, selecting a high-voltage substation with an unloaded line or a line in an unloaded state;
the judgment method provided by the invention is suitable for the transformer substation with the no-load line, and the application range of the method is limited necessarily in consideration of the fact that the number of the transformer substations meeting the condition is small. The method can also be applied if there is a line in an unloaded state in the substation, such as a power supply line of an electrified railway traction station.
Synchronously measuring the voltage and the current of a no-load line at a bus Capacitor Voltage Transformer (CVT) and a line Current Transformer (CT) in a transformer substation by using an electric energy quality analyzer so as to obtain fundamental voltage, fundamental power, and the content of each harmonic voltage and the value of each harmonic current;
as shown in fig. 2, which is a schematic view of a no-load line measuring point provided in the embodiment of the present invention, in a specific actual measurement process, a power quality analyzer is used for synchronous measurement to obtain a fundamental phase voltage U in a three-phase system1Single-phase fundamental wave active power PS1Single-phase fundamental wave reactive power QS1And single-phase each harmonic voltage content HRUhAnd harmonic current value Ih(ii) a If single phase cannot be measuredPower, can utilize three-phase total fundamental wave active power PT1And three-phase total fundamental wave reactive power QT1And (4) replacing.
Step 2, comprehensively judging the running state of the line based on the power characteristics of the line in no-load, and then calculating the fundamental wave impedance of the no-load line through the fundamental wave reactive power and the fundamental wave voltage;
the process of the step specifically comprises the following steps:
in an electric power system, a high-voltage power supply line is generally equivalent to a pi model, when the line is in no-load, the current in the line is ignored, the line can be equivalent to a parallel capacitor to the ground, and the measured line power is characterized as follows.
The method is characterized in that: under ideal conditions, the single-phase power of the unloaded line is PS10 and QS1Less than 0; for the same reason, the total power of three phases is PT10 and QT1＜0。
The second characteristic: and (3) a trend changing condition, namely, the active power and the reactive power of the fundamental wave are kept to be stable in a measuring period, namely, the trend changing condition is kept to be a horizontal state.
The characteristics are three: under actual state conditions, the influence of measurement errors is considered, and the active power of the fundamental wave approaches zero.
Therefore, when the measured fundamental wave power characteristics of the line meet the requirement of 3 points, the line can be judged to be in an idle state at the moment. On the basis, the equivalent fundamental wave impedance of the no-load line is calculated by using the fundamental wave reactive power and the fundamental wave voltage according to the following formula.
Step 3, determining the relation between the fundamental wave impedance and the harmonic frequency according to the equivalent fundamental wave impedance attribute of the no-load line, and further calculating each harmonic impedance of the no-load line;
the specific process of the step is as follows:
the unloaded line impedance characteristic is represented as a capacitance,according to the frequency response characteristic of the capacitor, the harmonic capacitive reactance and the harmonic frequency are in inverse proportion, and then each harmonic capacitive reactance X of the no-load circuit is calculatedChWhere h is the harmonic order.
And 4, calculating each harmonic voltage value of the no-load circuit according to each harmonic current value and corresponding harmonic impedance of the no-load circuit based on ohm's law, then calculating each harmonic voltage content according to the harmonic voltage content definition, comparing the harmonic voltage content with each measured harmonic voltage content, and judging the accuracy of CVT harmonic voltage measurement.
The process of the step specifically comprises the following steps:
based on ohm's law, according to the value of each harmonic current I of the no-load linehAnd corresponding harmonic capacitive reactance XChCalculating the voltage value U of each harmonic wave of the no-load lineh *：
Uh *＝Ih×XCh
Further, the HRU of each harmonic voltage content is calculated according to the definition of the harmonic voltage contenth *：
And finally, comparing the voltage content of each subharmonic obtained by calculation and measurement:
according to khThe accuracy of CVT harmonic measurement can be judged according to the value, and the specific judgment process is as follows:
when k ishWhen the voltage is more than 1, the h harmonic voltage measured by the CVT is amplified by the amplification factor kh；
When k ishWhen the voltage is 1, the h harmonic voltage measured by the CVT is accurate;
when k ishWhen the voltage is less than 1, the h harmonic voltage measured by the CVT is reduced by the reduction factor of
The following detailed description is given to the above process with reference to a specific example, the numerical values used in this example are only examples, and a user may make corresponding changes according to actual needs, in this example, a 220kV bus direct-connection electrified railway traction transformer of a 220kV substation measures bus voltage and no-load line current from a capacitive voltage transformer and a line current transformer by using an electric energy quality analyzer at the head end (substation side) of a power supply line of the traction transformer, and obtains a three-phase total fundamental wave power trend as shown in fig. 3, which satisfies the line no-load power characteristics.
Measured fundamental single-phase voltage U1130.4kV, the three-phase total fundamental capacitance average reactive power is QT12.39Mvar, 5 th harmonic voltage content HRU52.21%, 5 th harmonic current value I50.35A. The no-load line fundamental wave impedance is calculated according to the following method:
further, 5-order harmonic impedance of the no-load line is calculated according to an inverse proportional relation between line harmonic impedance and harmonic frequency:
then based on ohm's law, calculating 5 th harmonic voltage values of the no-load line according to the 5 th harmonic current value and the harmonic impedance of the no-load line as follows:
U5 *＝I5×XC5＝0.39A×4.26kΩ＝1.66kV
further, the harmonic voltage content ratio of 5 th order is calculated according to the definition of the harmonic voltage content ratio as follows:
finally, 5-order harmonic voltage measurement value HRU of capacitor voltage transformer5And the theoretical calculated value HRU5 *Comparing to obtain the ratio of:
it can be seen that the bus capacitor voltage transformer of the station amplifies the voltage content of the 5 th harmonic by about 1.74 times.
It is noted that those skilled in the art will recognize that embodiments of the present invention are not described in detail herein.
The above description is only an embodiment of the present invention, but the design concept of the present invention is not limited thereto, and any insubstantial modifications made by using the design concept should fall within the scope of infringing the present invention.
Claims (9)
1. A method for judging the accuracy of transformer substation CVT harmonic measurement is characterized by comprising the following steps:
step 1, selecting a transformer substation with an unloaded line or a line in an unloaded state, and measuring at a capacitance voltage transformer and a line current transformer of a bus of the transformer substation to obtain fundamental voltage, fundamental power, voltage content of each harmonic and current value of each harmonic;
step 2, comprehensively judging the running state of the line based on the fundamental wave power characteristics of the line in no-load, and calculating the equivalent fundamental wave impedance of the no-load line through the fundamental wave reactive power and the fundamental wave voltage when the line is judged to be in no-load;
step 3, determining the relation between the equivalent fundamental wave impedance and the harmonic frequency according to the equivalent fundamental wave impedance, and further calculating each harmonic impedance of the no-load line;
and 4, calculating each harmonic voltage value of the no-load circuit according to each harmonic current value of the no-load circuit and each obtained harmonic impedance based on ohm's law, then calculating each harmonic voltage content rate by combining each harmonic voltage content rate definition, comparing with each measured harmonic voltage content rate, and judging the accuracy of CVT harmonic voltage measurement.
2. The method for judging harmonic measurement accuracy of the substation CVT according to claim 1, characterized in that in the step 1, the fundamental voltage U in the three-phase system is obtained by synchronous measurement of the power quality analyzer1Single-phase fundamental wave active power PS1Single-phase fundamental wave reactive power QS1And the voltage content of each subharmonic HRUhAnd the value of each harmonic current Ih(ii) a In step 2, based on the single-phase fundamental wave active power P when the line is in no-loadS1Single-phase fundamental wave reactive power QS1And judging the running state of the line.
3. The method for judging harmonic measurement accuracy of the substation CVT according to claim 2, wherein the equivalent fundamental impedance is
The harmonic impedances
h is the harmonic order.
4. The method for determining the harmonic measurement accuracy of the substation CVT according to claim 1, wherein the step 1 further includes measuring three-phase total fundamental active power PT1And three-phase total reactive power QT1(ii) a In step 2, three-phase total fundamental wave active power P based on no-load time of the lineT1And three-phase total reactive power QT1And judging the running state of the line.
5. As claimed inSolving 4 the method for judging the accuracy of the harmonic measurement of the CVT of the transformer substation, which is characterized in that the equivalent fundamental wave impedance
The harmonic impedances
h is the harmonic order, U1Is the fundamental voltage.
6. The method for judging the harmonic measurement accuracy of the transformer substation CVT according to claim 2 or 4, characterized in that the operating state of the line is comprehensively judged based on the fundamental wave power characteristics of the line in no-load, and if the fundamental wave power characteristics meet ideal state conditions, actual state conditions and change trend conditions, the line is in no-load state;
under ideal condition, the active power of the fundamental wave of the unloaded line is PS10 and QS1<0; the active power of the three-phase total fundamental wave is PT10 and QT1<0；
The method comprises the following steps that (1) a variation trend condition is adopted, wherein fundamental wave active power and reactive power are required to keep certain stability in a measurement period, namely the variation trend is kept in a horizontal state;
under actual state conditions, the influence of measurement errors is considered, and the active power of the fundamental wave approaches zero.
7. The method for judging harmonic measurement accuracy of the substation CVT according to claim 3 or 5, characterized in that in step 3, the harmonic voltage value U is set toh *＝Ih×XCh，IhThe harmonic current values are each.
8. The method for determining the harmonic measurement accuracy of the transformer substation CVT according to claim 7, wherein in step 4, the calculated content rate of each harmonic voltage is
9. The method for judging the harmonic measurement accuracy of the substation CVT according to claim 8, characterized in that in step 4, the calculated and measured harmonic voltage content ratios of each order are compared:
according to khThe value size is used for judging the accuracy of CVT harmonic voltage measurement, and the specific judgment process is as follows:
when k ish>1, the h harmonic voltage measured by the CVT is amplified by a factor kh；
When k ishWhen the voltage is 1, the h harmonic voltage measured by the CVT is accurate;
when k ish<1, the h harmonic voltage measured by the CVT is reduced by a factor of 1/kh；
HRUhThe measured voltage content of each harmonic is shown.
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| CN103048637A (en) * | 2012-12-19 | 2013-04-17 | 华北电力大学 | Method for testing broadband characteristic of CVT (capacitor voltage transformer) by high voltage harmonic |
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| 陈宜皇 等.电容式电压互感器在谐波背景下测量误差的分析.《电测与仪表》.2015,第52卷(第24期), * |
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