CN110632396B - Cable dielectric loss measuring method - Google Patents
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- CN110632396B CN110632396B CN201911071295.0A CN201911071295A CN110632396B CN 110632396 B CN110632396 B CN 110632396B CN 201911071295 A CN201911071295 A CN 201911071295A CN 110632396 B CN110632396 B CN 110632396B
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- 238000000034 method Methods 0.000 title claims abstract description 33
- 238000012360 testing method Methods 0.000 claims abstract description 24
- 238000005259 measurement Methods 0.000 claims abstract description 5
- 230000010355 oscillation Effects 0.000 claims description 32
- 230000003534 oscillatory effect Effects 0.000 claims description 13
- 239000003990 capacitor Substances 0.000 claims description 9
- 238000007599 discharging Methods 0.000 claims description 6
- 238000009413 insulation Methods 0.000 abstract description 7
- 238000001514 detection method Methods 0.000 abstract description 6
- 238000013016 damping Methods 0.000 abstract description 4
- 230000032683 aging Effects 0.000 abstract description 3
- 238000003745 diagnosis Methods 0.000 abstract description 2
- 230000009466 transformation Effects 0.000 abstract description 2
- 230000000737 periodic effect Effects 0.000 description 10
- 230000008859 change Effects 0.000 description 6
- 230000008569 process Effects 0.000 description 6
- 229920003020 cross-linked polyethylene Polymers 0.000 description 4
- 239000004703 cross-linked polyethylene Substances 0.000 description 4
- 238000004364 calculation method Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000004973 liquid crystal related substance Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
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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
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
- G01R27/2688—Measuring quality factor or dielectric loss, e.g. loss angle, or power factor
- G01R27/2694—Measuring dielectric loss, e.g. loss angle, loss factor or power factor
Abstract
A cable dielectric loss measuring method belongs to the field of power transformation and the field of measurement and test. The problem of among the prior art can't make the diagnosis to the insulating state of cable, can't evaluate the insulating ageing level of cable, lead to the detection efficiency low to the cable is solved. The invention constructs the relation between the attenuation coefficient beta and the dielectric loss tan delta, utilizes the attenuation coefficient beta to represent the dielectric loss tan delta, derives the dielectric loss tan delta from the attenuation characteristic of the damping sinusoidal voltage wave, eliminates the influence of offset voltage, and avoids the influence of inaccuracy caused by voltage offset on the dielectric loss tan delta. The method is mainly used for diagnosing the insulation performance of the cable.
Description
Technical Field
The invention belongs to the field of power transformation and the field of measurement and test.
Background
Crosslinked polyethylene (XLPE) cables are becoming the mainstream product in power cables due to their good electrical and mechanical physical properties. The XLPE cable has potential insulation defects for a variety of reasons, and if the defects cannot be found and eliminated in time, the XLPE cable poses a serious threat to the safe and stable operation of the power system. Compared with the existing mature cable insulation detection means, the problems of large equipment size, inconvenience in carrying and the like exist in the discovery process, and the detection technology is single, so that the comprehensive diagnosis of the insulation state of the cable cannot be made, and the detection efficiency is seriously influenced.
Disclosure of Invention
The invention provides a cable dielectric loss measuring method, which aims to solve the problem that the detection efficiency of a cable is low because the insulation state of the cable cannot be diagnosed and the insulation aging level of the cable cannot be evaluated in the prior art.
A method for measuring dielectric loss of cable is realized by adopting a cable oscillatory wave test system, wherein the test system comprises a direct current power supply U0Switch K1, system inductance L and system internal resistance R1；
DC power supply U0The high-voltage output end of the transformer is simultaneously connected with one end of a system inductor L and one end of a switch K1, and the other end of the system inductor L is connected with the system internal resistance R1Is connected to the system internal resistance R1The other end of the test system is used as a measuring end of the test system;
DC power supply U0The grounding end of the switch K1 is connected with the other end of the switch K1 and then is connected with a power ground, and the other end of the switch K1 is used as the other measuring end of the test system;
the measuring method comprises the following steps:
step one, equivalent the tested cable into a capacitor CcAnd a resistance R2After being connected in parallel, the two are connected in series between two measuring ends of the test system;
step two, the switch K1 is in an off state and passes through the direct current power supply U0Capacitor CcCharging, after charging, closing the switch K1, forming an oscillation loop by the tested cable and the test system, and at the moment, forming a capacitor CcDischarging;
step three, according to the capacitance CcObtaining an equivalent voltage oscillation waveform of the oscillation circuit under the condition of discharging, and obtaining values of an attenuation coefficient beta and an angular frequency omega according to the equivalent voltage oscillation waveform;
step four, because in the oscillating circuit, there is the following relation:
and generating a formula into a formula II to obtain the following relational expression:
wherein tan delta represents the dielectric loss of the tested cable;
delta represents the dielectric loss angle of the tested cable;
step five, because R1And L are known, and the values of the attenuation coefficient beta and the angular frequency omega obtained in the step three are substituted into a formula three, so that the value of the dielectric loss tan delta of the tested cable is obtained, and the measurement of the dielectric loss of the cable is completed.
Preferably, the functional relation of the equivalent voltage oscillation waveform of the oscillation circuit is:
u (t) denotes the capacitance C as a function of time tcThe voltage across;
e represents a natural logarithm;
alpha represents a proportionality coefficient, and
preferably, in step three, the obtaining of the value of the damping coefficient β according to the equivalent voltage oscillation waveform is implemented by:
and carrying out curve fitting on the equivalent voltage oscillation waveform by an exponential fitting method so as to obtain the attenuation coefficient beta.
Preferably, in step three, the obtaining of the value of the angular frequency ω according to the equivalent voltage oscillation waveform is implemented by:
and obtaining the frequency f of the equivalent voltage oscillation waveform according to the propagation period of the equivalent voltage oscillation waveform, and obtaining the value of the angular frequency omega according to the frequency f.
It is preferable that the first and second liquid crystal layers are formed of,
the method has the advantages that the relation between the attenuation coefficient beta and the dielectric loss tan delta is constructed, the dielectric loss tan delta is represented by the attenuation coefficient beta, the dielectric loss tan delta is derived from the attenuation characteristic of the damping sinusoidal voltage wave, a high-precision detection result is obtained, the obtaining process of the attenuation coefficient beta is obtained through a waveform fitting method, the influence of offset voltage is eliminated, and the influence of inaccuracy caused by voltage offset on the dielectric loss tan delta is further avoided.
The invention measures the dielectric loss of the cable by taking the oscillating wave as a voltage source so as to evaluate the insulation aging level of the cable.
The invention calculates the dielectric loss of the cable by analyzing the waveform attenuation condition of the oscillating wave.
Drawings
FIG. 1 is a schematic diagram of a cable oscillatory wave testing system according to the present invention;
FIG. 2 is a voltage oscillation waveform diagram; 11 below the oscillation wave, showing the trough of the first periodic wave; 12 above the oscillatory wave, representing the peak of the first periodic wave; 21 below the oscillatory wave, which represents the trough of the second periodic wave; 22 above the oscillatory wave, representing the peak of the second periodic wave; 31 below the oscillatory wave, which represents the trough of the third periodic wave; 32 above the oscillatory wave, representing the peak of the third periodic wave; 41 below the oscillatory wave, representing the trough of the fourth periodic wave; 42 above the oscillatory wave, representing the peak of the fourth periodic wave; the bottom 51 of the oscillatory wave, which represents the trough of the fifth periodic wave; 52 above the oscillatory wave, representing the peak of the fifth periodic wave;
fig. 3 is a comparison graph of β values of 10kV cables obtained by 3 different algorithms under different voltage biases, wherein a symbol a indicates a curve of β with change of bias voltage obtained by calculation using the first two positive peaks in fig. 2, a symbol B indicates a curve of β with change of bias voltage obtained by calculation using the last two negative peaks in fig. 2, and a symbol C indicates a curve of β with change of bias voltage obtained by the waveform fitting method of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The invention is further described with reference to the following drawings and specific examples, which are not intended to be limiting.
Referring to fig. 1, the embodiment is described, and the method for measuring the dielectric loss of the cable according to the embodiment is implemented by using a cable oscillatory wave test system, wherein the test system comprises a direct current power supply U0Switch K1, system inductance L and system internal resistance R1；
DC power supply U0The high-voltage output end of the transformer is simultaneously connected with one end of a system inductor L and one end of a switch K1, and the other end of the system inductor L is connected with the system internal resistance R1Is connected to the system internal resistance R1The other end of the test system is used as a measuring end of the test system;
DC power supply U0The grounding end of the switch K1 is connected with the other end of the switch K1 and then is connected with a power ground, and the other end of the switch K1 is used as the other measuring end of the test system;
the measuring method comprises the following steps:
step one, equivalent the tested cable into a capacitor CcAnd a resistance R2After being connected in parallel, the two are connected in series between two measuring ends of the test system;
step two, the switch K1 is in an off state and passes through the direct current power supply U0Capacitor CcCharging, after charging, closing the switch K1, forming an oscillation loop by the tested cable and the test system, and at the moment, forming a capacitor CcDischarging;
step three, according to the capacitance CcObtaining an equivalent voltage oscillation waveform of the oscillation circuit under the condition of discharging, and obtaining values of an attenuation coefficient beta and an angular frequency omega according to the equivalent voltage oscillation waveform;
step four, because in the oscillating circuit, there is the following relation:
and generating a formula into a formula II to obtain the following relational expression:
wherein tan delta represents the dielectric loss of the tested cable;
delta represents the dielectric loss angle of the tested cable;
step five, because R1And L are known, and the values of the attenuation coefficient beta and the angular frequency omega obtained in the step three are substituted into a formula three, so that the value of the dielectric loss tan delta of the tested cable is obtained, and the measurement of the dielectric loss of the cable is completed.
The method constructs the relation between the attenuation coefficient beta and the dielectric loss tan delta, represents the dielectric loss tan delta by using the attenuation coefficient beta, derives the dielectric loss tan delta from the attenuation characteristic of the damping sinusoidal voltage wave, eliminates the influence of offset voltage, and avoids the influence of inaccuracy caused by voltage offset on the dielectric loss tan delta.
Further, the functional relation of the equivalent voltage oscillation waveform of the oscillation circuit is as follows:
u (t) denotes the capacitance C as a function of time tcThe voltage across;
e represents a natural logarithm;
alpha represents a proportionality coefficient, and
further, in the third step, the implementation manner of obtaining the value of the attenuation coefficient β according to the equivalent voltage oscillation waveform is as follows:
and carrying out curve fitting on the equivalent voltage oscillation waveform by an exponential fitting method so as to obtain the attenuation coefficient beta.
In the embodiment, the obtaining process of the attenuation coefficient β is obtained by a waveform fitting method, so that the influence of offset voltage is eliminated, and the influence of inaccuracy caused by voltage offset and the dielectric loss tan δ is avoided.
Further, in the third step, the implementation manner of obtaining the value of the angular frequency ω according to the equivalent voltage oscillation waveform is as follows:
and obtaining the frequency f of the equivalent voltage oscillation waveform according to the propagation period of the equivalent voltage oscillation waveform, and obtaining the value of the angular frequency omega according to the frequency f.
Further, in the above-mentioned case,
a typical voltage oscillation waveform is shown in fig. 2, and the voltage decay with time can be seen, and the voltage waveform gradually decays with the same decay period.
In the prior art, any two peak values U are taken for calculating the attenuation coefficient beta1、U2Corresponding time t1，t2According to the formula seven, β is obtained:
fig. 3 shows a comparison graph of β values of 10kV cables obtained by 3 different algorithms under different voltage biases, where the 3 different algorithms are respectively: calculating beta by using the first two positive peaks (peaks) in the graph 2, calculating beta by using the first two negative peaks (valleys) in the graph 2 and obtaining beta by using a curve fitting method of the invention; in FIG. 3, except for the process of the present invention, β is obtained using equation seven.
Analyzing fig. 3, in fig. 3, theoretically, two voltage peaks can be arbitrarily selected, and β can be obtained by using formula seven. However, in practice, external influences such as noise and zero offset may make the value of β dependent on the peak selection. Taking the first two positive or negative peaks gives a relatively good signal-to-noise ratio, since these are the largest peaks. However, zero bias will have a greater effect on β. As can be seen in fig. 3.
In the process of obtaining the beta, the oscillating waveform is fitted by using a waveform fitting method, and the fitted beta value can remove the influence of zero offset and can provide the most stable result. In fig. 3 is shown the beta values of 30kV, 0.5 μ FXLPE cable samples, which if calculated using two maximum peaks or two minimum peaks, change with the change in bias voltage, while the beta value remains 7.57s regardless of the bias voltage change by the waveform fitting method-1And is substantially constant. The applied voltage was 30 kV.
The value of the dielectric loss tan delta of the present invention can be derived from the attenuation characteristics of the damped sinusoidal voltage wave. In order to avoid inaccuracy caused by voltage offset, the attenuation coefficient beta acquisition process is obtained by a waveform fitting method, and the influence of offset voltage is eliminated.
Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that features described in different dependent claims and herein may be combined in ways different from those described in the original claims. It is also to be understood that features described in connection with individual embodiments may be used in other described embodiments.
Claims (5)
1. The method for measuring the dielectric loss of the cable is characterized in that the method is realized by adopting a cable oscillatory wave test system, and the test system comprises a direct-current power supply U0Switch K1, system inductance L and system internal resistance R1；
DC power supply U0Between the high-voltage output terminal and the system inductor LOne end of the system inductor L is connected with one end of the switch K1 at the same time, and the other end of the system inductor L is connected with the system internal resistance R1Is connected to the system internal resistance R1The other end of the test system is used as a measuring end of the test system;
DC power supply U0The grounding end of the switch K1 is connected with the other end of the switch K1 and then is connected with a power ground, and the other end of the switch K1 is used as the other measuring end of the test system;
the measuring method comprises the following steps:
step one, equivalent the tested cable into a capacitor CcAnd a resistance R2After being connected in parallel, the two are connected in series between two measuring ends of the test system;
step two, the switch K1 is in an off state and passes through the direct current power supply U0Capacitor CcCharging, after charging, closing the switch K1, forming an oscillation loop by the tested cable and the test system, and at the moment, forming a capacitor CcDischarging;
step three, according to the capacitance CcObtaining an equivalent voltage oscillation waveform of the oscillation circuit under the condition of discharging, and obtaining values of an attenuation coefficient beta and an angular frequency omega according to the equivalent voltage oscillation waveform;
step four, because in the oscillating circuit, there is the following relation:
and generating a formula into a formula II to obtain the following relational expression:
wherein tan delta represents the dielectric loss of the tested cable;
delta represents the dielectric loss angle of the tested cable;
step five, because R1And L are known, and the values of the attenuation coefficient beta and the angular frequency omega obtained in the step three are substituted into a formula three, so that the value of the dielectric loss tan delta of the tested cable is obtained, and the measurement of the dielectric loss of the cable is completed.
2. The method as claimed in claim 1, wherein the equivalent voltage oscillating waveform of the oscillating circuit has a functional relationship of:
u (t) denotes the capacitance C as a function of time tcThe voltage across;
e represents a natural logarithm;
alpha represents a proportionality coefficient, and
3. the method for measuring the dielectric loss of the cable according to claim 1, wherein in the third step, the obtaining of the value of the attenuation coefficient β according to the equivalent voltage oscillating waveform is implemented by:
and carrying out curve fitting on the equivalent voltage oscillation waveform by an exponential fitting method so as to obtain the attenuation coefficient beta.
4. The method for measuring the dielectric loss of the cable according to claim 1, wherein in the third step, the value of the angular frequency ω obtained from the equivalent voltage oscillating waveform is obtained by:
and obtaining the frequency f of the equivalent voltage oscillation waveform according to the propagation period of the equivalent voltage oscillation waveform, and obtaining the value of the angular frequency omega according to the frequency f.
5. A method for measuring the dielectric loss of a cable according to claim 2,
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