Summary of the invention
In view of this, the invention provides a kind of threephase potential transformer and three-phase based on D_dot principle and affect voltage compensating method, wherein threephase potential transformer have that volume is little, simple in structure, the feature such as good insulation preformance and measurement safety, when wherein three-phase affects voltage compensating method to measurement, influencing each other between three-phase line made analysis, with this, obtains the measured value that approaches truth.
The invention provides a kind of threephase potential transformer based on D_dot principle, comprise: ring electrode I, ring electrode II, insulating support, direct earth capacitance, described insulating support comprises: semicircle bracket I, semicircle bracket I I and sway brace, described sway brace is arranged on described semicircle bracket I, on the sidewall of semicircle bracket I I, and described semicircle bracket I, semicircle bracket I I with one heart setting is formed for the through hole passing for measured conductor, described ring electrode I, ring electrode II arranges with one heart, and be embedded in respectively in described semicircle bracket I and semicircle bracket I I, described ring electrode I, ring electrode II by wire and described direct earth capacitance and connect, described oscillograph and described direct earth capacitance are in parallel.
Further, described ring electrode I, ring electrode II are the metallic aluminium ring that shape is identical.
Further, the internal diameter of described ring electrode I, ring electrode II is between 60 to 70mm, and external diameter is between 70 to 80mm.
Further, also comprise: be arranged on described sway brace for regulating the adjusting knob of described semicircle bracket I I, the tightness of trip bolt is adjustable, and in the time of screw pine, semicircle bracket I I can move up and down, and when reaching correct position, screw is screwed.
Further, the adjustable range scope between described semicircle bracket I, II is between 0 to 50mm.
The present invention also provides a kind of three-phase based on D_dot principle to affect voltage compensating method, comprises the steps:
By a wherein phase voltage V of three-phase voltage
1access the threephase potential transformer based on D_dot principle as above;
The voltage V at the direct earth capacitance two ends of threephase potential transformer described in employing oscilloscope measurement
out;
Adopt formula:
Calculate V
1;
Wherein,
with
be respectively capacitor C
14and C
15,
for C
25with C
35value in parallel,
for C
24with C
34shunt capacitance, the resistance on the concentric conductor that r is connecting electrode,
for C
m, C
p, R
0, R
p, C
0the comprehensive parameters forming, wherein C
ijthe electric capacity that represents i electric wire and j electrode, C
mfor direct earth capacitance, R
pand C
presistance, electric capacity that the measuring sonde of introducing while being respectively access oscillograph is introduced, R
oand C
0be respectively resistance, electric capacity that access oscillograph is introduced.
Beneficial effect of the present invention:
Threephase potential transformer based on D_dot principle of the present invention mainly consists of a few parts such as ring electrode, insulating support and direct earth capacitancies, it has the characteristics such as volume is little, simple in structure, especially the electrode of annular can reduce maximum electric field intensity to reach the object that improves dielectric level, there is good dynamic range and transient state feature, guarantee to measure security simultaneously.
Meanwhile, the present invention's influencing each other between three-phase line when measuring performs an analysis, and proposes thus a kind of compensation method, and oscilloscope measurement result is revised, and obtains the measured value that approaches truth, can reflect comparatively exactly voltage waveform situation of change on cable.
Embodiment:
As shown in Figure 1, be the principle schematic of D_dot sensor, it is enclosed the
metallic conductor 1 with high conductivity in
insulator 2 and forms the simplest D_dot sensor, wherein
for the electric field intensity of measured point, on metallic conductor surface, do a closed
Gauss surface 4, and use Gauss theorem to obtain to it:
Q is in closed Gauss surface 4 to be the induced charge on metallic conductor 1 in formula (1), A
eqfor the equivalent area of sensor, it is relevant with the shape and structure of metallic conductor in sensor 1 and the angle of Gauss surface and electric field vector direction.
After
metallic conductor 1 is connected with ground connection build-out resistor R by
cable 3, in
metallic conductor 1, electric charge moves formation electric current
and on ground connection build-out resistor R, produce pressure drop:
(formula 2).
Therefore, D_dot sensor output V
0electric field intensity with measured point
derivative to the time is linear, so this D_dot sensor can be for electric field measurement.
Because the measurement of D_dot sensor is to be coupled and to be detected tested voltage by electric charge, itself and CVT (the Capacitor Voltage Transformer measuring by energy transmission realization, capacitance type potential transformer) difference, it can realize noncontacting measurement, therefore while being applied in the transformer station of voltage levels, can so that secondary side almost without any electric current, export, when realizing secondary side safety detection, assurance does not impact primary side, and because whole sensor does not exist inductive device, avoided the threat of the ferroresonance of sensor generation.
As shown in Figures 2 and 3, the threephase potential transformer based on D_dot principle provided by the invention comprises: ring electrode I1, ring electrode II2, insulating support and direct earth capacitance 4.
Wherein, insulating support comprises: semicircle bracket I 31, semicircle bracket I I32 and sway brace 33, sway brace 33 is arranged on the sidewall of semicircle bracket I 31 and semicircle bracket I I32, and semicircle bracket I 31, semicircle bracket I I32 with one heart setting are formed for the through hole passing for measured conductor 6, and the size of this through hole is between 12 to 16mm.
Wherein, on sway brace 33, be provided with for regulating the adjusting knob of semicircle bracket I I position, and the adjustable range scope between semicircle bracket I, II is between 0 to 50mm.Concrete, adjusting knob can be trip bolt, and its tightness is adjustable, and in the time of screw pine, semicircle bracket I I can move up and down, and when reaching correct position, screw is screwed.
Wherein, ring electrode I1, ring electrode II2 arrange with one heart, and are embedded in respectively in semicircle bracket I 31 and semicircle bracket I I32, ring electrode I1, ring electrode II2 by wire (for example: concentric conductor) with direct earth capacitance 4 with connect.
Wherein, ring electrode I1, ring electrode II2 are the metallic aluminium ring that shape is identical.
Wherein, the internal diameter of ring electrode I1, ring electrode II2 is between 60 to 70mm, and external diameter is between 70 to 80mm.
The dead ring of making for insulating material between ring electrode I1, II2 and conductor 6 in Fig. 3, for for example clamping tight and fixed conductor 6(: copper rod), the A in Fig. 3 in addition
eqfor voltage on electric wire.
In addition, during measurement, as shown in Figure 3, oscillograph 5 is in parallel with direct earth capacitance 4, can survey the voltage of threephase potential transformer output.
The present embodiment, mainly by a few parts such as ring electrode, insulating support and direct earth capacitancies, formed, it has the characteristics such as volume is little, simple in structure, especially the electrode of annular can reduce maximum electric field intensity to reach the object that improves dielectric level, there is good dynamic range and transient state feature, guarantee to measure security simultaneously.
By the voltage access oscillograph of the 4 two ends outputs of direct earth capacitance in Fig. 3, Observable output voltage waveforms.As shown in Figure 3, the output voltage of voltage transformer (VT) top electrode can be expressed as simultaneously:
(formula 3)
C wherein
1for the electric capacity between upper and lower two electrodes shown in Fig. 3 (being electrode I, electrode II), C
2for output capacitor shown in Fig. 3 (being direct earth capacitance).
The present invention's influencing each other between three-phase line when measuring performs an analysis, and proposes thus a kind of compensation method, and oscilloscope measurement result is revised, and obtains the measured value that approaches truth, reflects comparatively exactly voltage waveform situation of change on cable.
Idiographic flow is as follows:
If the impact of the measurement mechanism such as resistance, oscillograph, can obtain output voltage U on consideration concentric conductor
o(s):
That is:
(formula 4)
As Fig. 4, C wherein
1, C
2for the electric capacity of upper lower half circle becket and wire, R
1, R
2for connecting the resistance on the concentric conductor of upper lower half circle becket, C
mfor the electric capacity between voltage transformer (VT) and ground, be also for measuring the measurement electric capacity of output voltage, Z simultaneously
scfor measuring, use oscillographic equiva lent impedance, it and C
min parallel for measuring.
If consider again the impact of other two relative voltage transformer (VT) on three-phase line, can obtain metering circuit Fig. 5.
It is 1,2,3 that A, B, C cable are numbered, and each layer of electrode is numbered respectively 4,5,6,7,8,9, the V in circuit
1, V
2, V
3be respectively the virtual voltage on each phase cable, C
ijthe electric capacity that represents i cable and j electrode, for example: C
14the electric capacity that represents No. 1 cable and No. 4 electrodes, C
mfor the capacity cell on output voltage in sensor measurement, R
pand C
pbe respectively resistance, electric capacity that 10 times of probes (having connected the measuring sonde that expands 10 times of waveforms during access oscillograph) are introduced, R
oand C
0be respectively resistance, electric capacity that access oscillograph is introduced, consider thus the mutual capacitance between the electrode of adjacent phase circuit and this phase upper sensor, and this is performed an analysis, by revising oscilloscope measurement result, can compensate, acquisition approaches the voltage waveform of truth.
In foregoing circuit, the mutual capacitance of each electrode and conductor is intrinsic parameter, can solve and obtain by electric field being carried out to finite element analysis, and measurement mechanism oscillograph parameter is known, therefore finally can revise the measurement result of voltage transformer (VT), and make result approach truth by compensation measurement.
In experiment, we utilize electromagnetic software to build model, solve the mutual capacitance between each electrode and conductor, and its equivalent electrical circuit as shown in Figure 5.
If (corresponding voltage is V to get A phase circuit
1) analyze (making B, C two-phase input voltage source is 0), its equivalent electrical circuit, as accompanying drawing 6, will have following relation:
(formula 5)
(formula 6)
That is:
(formula 7)
In formula
with
be respectively the capacitor C in Fig. 5
14and C
15,
for C
25with C
35value in parallel,
for C
24with C
34shunt capacitance,
for C
m, C
p, R
0, R
p, C
0the comprehensive parameters forming.
Can find out V thus
outwith V
1there is fixing relation, can be expressed as the form of transport function, this transport function with
r is relevant, if known these parameters, known V
1with V
outrelation.
For formula is simplified, if three-phase line position is symmetrical, even in figure
so
(formula 8)
By above analysis, the invention provides a kind of three-phase based on D_dot principle affects voltage compensating method, and it comprises the steps:
Step 1, by a wherein phase voltage V of three-phase voltage
1access the threephase potential transformer based on D_dot principle as above.
The voltage V at the direct earth capacitance two ends of threephase potential transformer described in step 2, employing oscilloscope measurement
out.
Step 3, employing formula (7) or (8) calculate V
1, i.e. the voltage of the phase of surveying.
Lift an example below, this process described:
As shown in Figure 7 in test unit, by being arranged on three voltage sensors on three-phase wire and the lightning protection of ground and pole line, form.Wherein the electric wire of three horizontal positioned has 10 meters far away apart from ground, the about 5.78KV of voltage magnitude on cable conductor, and frequency 50Hz, every phase is respectively A, B, C from left to right.
In l-G simulation test, we use X1000 high-voltage probe to measure magnitude of voltage and the phase place on three-phase line, measurement result V
1as shown in table 1.
Table one:
By Multi simulation running and test, we obtain on electric wire and between electrode, (comprise the comprehensive parameters of electrode I, electrode II and three wire capacitance, can try to achieve by Thevenin's theorem) capacitor C forming
10the capacitor C obtaining with sensor manufacturer withstand voltage test
1Mwhen (being direct earth capacitance) meets following the relation:
C
1M=0.17C
10(formula 8)
Now, threephase potential transformer output voltage shows below on oscillograph:
Table two:
By the V of formula 7
1with V
outrelation, calculate the voltage V on electrode
1' magnitude of voltage and phase pushing figure, as follows:
Table three:
Contrast table one is known with the data that table three obtains, as stated above, and calculating sensor output V
outcorresponding V
1', with actual value V
1compare, magnitude of voltage and phase pushing figure differ very little, have improved the measuring accuracy of sensor.Can reflect comparatively exactly the situation of change of voltage waveform on cable thus.
The present invention, by improving D_dot sensor construction and considering to analyze adjacent phase electric field and the impact of measurement mechanism on metering circuit on three-phase line, a kind of compensation method is proposed thus, oscilloscope measurement result is revised, obtain thus approaching the numerical value of truth, be conducive to floating voltage variation and fault diagnosis and on-line monitoring and the over-voltage waveform that captures high frequency in relay protection system, to line voltage, measurement is significant.
Finally explanation is, above embodiment is only unrestricted in order to technical scheme of the present invention to be described, although the present invention is had been described in detail with reference to preferred embodiment, those of ordinary skill in the art is to be understood that, can modify or be equal to replacement technical scheme of the present invention, and not departing from aim and the scope of technical solution of the present invention, it all should be encompassed in the middle of claim scope of the present invention.