CN209961868U - Circuit shunting structure for reverse short-distance measurement of grounding grid - Google Patents
Circuit shunting structure for reverse short-distance measurement of grounding grid Download PDFInfo
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- CN209961868U CN209961868U CN201822177678.3U CN201822177678U CN209961868U CN 209961868 U CN209961868 U CN 209961868U CN 201822177678 U CN201822177678 U CN 201822177678U CN 209961868 U CN209961868 U CN 209961868U
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Abstract
The utility model discloses a reverse short distance measurement circuit reposition of redundant personnel structure of ground net, including ground net, cable conductor and base tower, ground net surface has a plurality of base tower through cable conductor connection, and the central point of ground net is located same straight line with the base tower, and the distance between two adjacent base tower is 200m, and the base tower that is closest to ground net is 100m from the distance between the ground net, and this utility model discloses rational in infrastructure, equivalent circuit when only considering a base tower can be used and the reposition of redundant personnel coefficient is calculated, and the error can not be very big, can reduce the calculation degree of difficulty, improves the computational efficiency.
Description
Technical Field
The utility model relates to a reverse short distance measurement circuit of ground net shunts technical field, specifically is a reverse short distance measurement circuit of ground net reposition of redundant personnel structure.
Background
Substation grounding grids are generally not independent and often are electrically connected to other grounding grids or metal conductors. When the characteristic parameters of the grounding grid are measured, a power frequency or pilot frequency current is injected into the tested grounding grid, part of the current is distributed to the ground through the tested grounding grid, and the other part of the current is shunted through a lightning conductor, a cable shielding layer and the like.
The diversion path typically has the following parts:
(1) overhead ground wire shunt
Corresponding to a transformer substation grounding grid of 110kV or more, the overhead ground wire is generally connected with the transformer substation grounding grid through a portal frame, namely the grounding grid of a tower is connected with the transformer substation grounding grid, and test current injected into the grounding grid is shunted inevitably.
The high-voltage cable external shielding shunt can be regarded as generalized ground wire shunt, the cable terminal external shielding can be regarded as an overhead ground wire with certain resistance and connected with a grounding grid of an opposite side transformer substation or a tower, the topological structure of the grounding grid is changed, and test current can be shunted when the grounding grid is tested.
(2) The neutral point of the transformer being grounded. For a transformer with a grounding operation neutral point, the neutral point is equivalent to a grounding grid with the neutral point directly connected, part of test current may enter the neutral point of the transformer and flow into a system, but considering that the impedance of the transformer is relatively large compared with the grounding impedance of a transformer substation grounding grid, the shunt value of the neutral point of the transformer is very small, and the field actual measurement shows that the value is very small, only a few milliamperes can be ignored.
(3) Other metal conductors. A small part of grounding grid can be connected with an external grounding body on metal, such as a metal water pipe and the like, and the influence of the part is also considered on site.
SUMMERY OF THE UTILITY MODEL
An object of the utility model is to provide a reverse short distance measurement circuit reposition of redundant personnel structure of ground net, it is great mainly to current ground net test lightning conductor, cable shield line etc. to the measuring result influence, the condition of considering lightning conductor reposition of redundant personnel impedance when measuring ground net resistance has carried out analog analysis to carry out the calculation of reposition of redundant personnel coefficient through corresponding software, obtain the reposition of redundant personnel electric current of lightning conductor, just so calculate accurate ground resistance value, with the problem of proposing in solving above-mentioned background art.
In order to achieve the above object, the utility model provides a following technical scheme: the utility model provides a reverse short distance of ground net measures circuit reposition of redundant personnel structure, includes ground net, cable conductor and base tower, ground net surface has a plurality of base tower through cable conductor connection, the central point of ground net is located same straight line with the base tower, adjacent two distance between the base tower is 200m, is closest to the ground net the base tower is 100m from the distance between the ground net.
Preferably, the grounding grid adopts a disc electrode equivalent model, and the diameter of the grounding grid is 100 m.
Preferably, the base tower is equivalent to a corresponding disc electrode model with the radius of 2m, and the grounding resistance value of the base tower is 8-10 omega.
Preferably, the cable line is a steel strand GJ-80 lightning conductor.
Compared with the prior art, the beneficial effects of the utility model are that:
the equivalent circuit when only one base tower is considered can be used for calculating the shunt coefficient, the error is not large, the calculation difficulty can be reduced, and the calculation efficiency is improved.
Drawings
Fig. 1 is a schematic structural diagram of the present invention.
Fig. 2 is a simulation effect diagram.
Fig. 3 is a potential distribution diagram.
FIG. 4 is a schematic diagram of the current stage position.
FIG. 5 is a schematic diagram of the voltage pole position determined by the 0.618 method and the correct voltage pole position.
Fig. 6 is an equivalent circuit diagram in consideration of the distribution of the ground current to the ground potential.
Fig. 7 is a simulation diagram of Multisim when calculating the equivalent impedance value of the lightning rod tower system.
FIG. 8 is a COMSOL Multiphysics simulation ground potential distribution diagram.
Fig. 9 is a simulation circuit diagram when Multisim simulation considers only one base tower.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.
When the resistance of the grounding grid of the transformer substation is measured, part of the measured current flows away from the lightning conductor due to the connection between the lightning conductor and the grounding device, and then returns to the return electrode from the tower. This can introduce errors into the ground resistance measurement. In different regulations, regulations on the influence of the shunt of the lightning conductor are not uniform, but the influence of the lightning conductor is required to be considered. DL/T475-. DL/T621-2006 mentions that a tower grounding electrode can be used as a return electrode, but attention is paid to the effect of the lightning conductor shunting. When in-situ measurement, the influence of the shunt coefficient is to be eliminated, and the lightning wires of all incoming and outgoing lines of a transformer substation are untied for measurement. However, in practice, the lightning conductor and the grounding grid of the transmission line of some transformer substations are welded to be dead and cannot be untied, so that the influence of the shunting of the lightning conductor on the short distance measurement needs to be analyzed.
Referring to fig. 1, the present invention provides a technical solution: the utility model provides a reverse short distance measurement circuit reposition of redundant personnel structure of ground net, includes ground net 1, cable conductor 2 and base rod tower 3, and ground net 1 surface is connected with a plurality of base rod tower 3 through cable conductor 2, and the central point of ground net 1 and base rod tower 3 are located same straight line, and the distance between two adjacent base rod towers 3 is 200m, and the base rod tower 3 that is closest to ground net 1 is 100m from the distance between the ground net 1.
(1) Finite element modeling simulation of grounding grid with power transmission line
The finite element method is adopted to simulate the grounding measurement condition under the influence of one power transmission line. The grounding grid adopts a disc electrode equivalent model and has the diameter of 100 m. The span of the transmission line is 200m, the base numbers of the towers are increased according to a simulation result, and the influence of the remote towers on the shunting is gradually reduced, so that 10 base towers close to each other are considered in the model. The tower is equivalent by adopting a corresponding disc electrode model, and the grounding impedance is 8-10 omega.
And setting each parameter in the COMSOL Multiphysics finite element simulation model. Selecting a steel strand GJ-80 lightning conductor, wherein the span of the first base tower is 100m, and the span of the tower is 200m from the second base. The resistivity of the soil is 100 omega m, the grounding resistance of the tower is 8.23 omega, and the equivalent is a disc with the radius of 2 m. The impedance value of the first span wire is, starting from the second span wire, the wire impedance value of each span is:
Zd2=Zd3=...=Zdn=(0.6+j0.37)Ω (3.1)
as shown in fig. 2 and the following table:
the low current distribution can be seen from the table. The substantially gradual decrease trend eventually decreases to near zero. The ground current of the first base tower and the ground current of the second base tower are approximately equal. This is because the towers are also under the influence of the potential distribution of the grounding grid, the first base tower is closer to the grounding grid, and the voltage difference between the first base tower and the grounding grid is smaller, so that the current distribution is significantly higher than that of the second base tower. As can be seen from the simulation of the presence of one transmission line, the shunt can account for around 15% of the measured current.
Due to the influence of the shunt of the lightning conductor, the ground current condition of the grounding measurement in the transformer substation area is greatly changed. The ground point location is influenced by not only the grounding grid and the return electrode, but also the ground current of the tower can influence the ground potential distribution. As shown in fig. 3, the variation of the ground potential can be seen from the simulation result. It is therefore necessary to analyze the impact of the lightning conductor shunts on the short-range measurements of the earth resistance.
(2) Influence of current pole position on lightning conductor shunt during ground impedance measurement
The simulation result shows that the positions of the current poles can influence the potentials at the grounding grid of the transformer substation and the grounding poles of the tower. The current division factor of the lightning conductor may differ depending on the position of the current pole. Therefore, it is necessary to know the influence rule of the current pole position on the shunt coefficient of the lightning conductor.
On the ground surface plane, 7 representative different positions 1(100,500), 2(-500, 0), 3(-300,400), 4(-100, 500), 5(0,500), 6(300,400), and 7(600,0) were selected as shown in fig. 4. (the black points in the figure are different current pole positions, and the current pole position 7 is the same direction as the lightning conductor pole position.)
The COMSOL Multiphysics simulation was performed for different current pole positions, respectively, and the shunt current value of the lightning conductor was calculated by software area integration, as shown in the table below.
Relationship between the shunt current and the current pole position of the lightning conductor
From the previous simulations and shown in the table above, we can see that the current value of the lightning conductor shunts at positions 1 to 6 does not vary much. However, when in position 7(600,0), we can find that the shunt current of the lightning conductor is much larger than in other cases. This is because the current flowing through the current pole is relatively close to the ground poles of the third and fourth towers, and the large potential drop is generated at the ground poles, and the attraction of the current by the return pole causes the current flowing through the lightning conductor to increase.
The potential values of the third base tower and the fourth base tower are compared with the potentials of the third base tower and the fourth base tower in the position 1. At the position 1, the electric potentials at the third base tower and the fourth base tower are 19.33V and 14.46V respectively; the third and fourth base towers at position 7 have potentials of 16.10V and 10.88V, respectively. It can be seen that the current poles generate a large negative potential at the third and fourth base tower, and this cannot be neglected.
As can be seen from the simulation result, the selection of the current pole position can significantly influence the shunting condition of the incoming line of the transformer substation. When the current pole is close to the power transmission line, the shunting effect is very strong, and the effect is most obvious when the pole tower is used as a backflow pole and the lightning conductor is not disconnected. At the transformer substation that has many inlet wires, the reposition of redundant personnel effect is more outstanding. When the backflow pole is far away from the power transmission line, the shunting effect is reduced. Therefore, in the arrangement selection of the return electrode, the return electrode should be far away from the power transmission line as far as possible, so that the influence caused by shunt can be reduced.
(3) Influence of line shunting on ground resistance measurement
And analyzing aiming at the simulation model. When the short-distance measurement method is adopted for measurement, the shunting effect of the lightning conductor is considered, and the accurate grounding resistance value can be measured through calculation of the compensation point. And (5) comparing by using a long line 0.618 method to obtain a measurement error range. The simulation condition is that the equivalent radius of the grounding grid is changed without changing the relevant parameters of the lightning conductor and the tower, the grounding resistance of the grounding grid is measured by a 0.618 method, and the grounding resistance is compared with the real resistance value of the grounding grid. Here we take the equivalent radii of the grounding grid as 40m, 45m, 50m, 55m, 60m, respectively.
Simulation and error of grounding resistance measurement of grounding grid
From the calculation results of the simulation model on the upper table, it can be seen that the error of the 0.618 method under the influence of one line is very large, between 10% and 20%, and if the ground resistance of a plurality of large-scale substations is measured, the error is larger and is hard to bear. The tower distribution condition of the grounding grid can be effectively established by using short-distance measurement, so that the shunt influence of the power transmission line is fully considered, and the actual potential value of the grounding grid is effectively measured. The difference between the 0.618 method and the potential compensation method is shown in fig. 5 by using a grounding grid with an equivalent radius of 50 m.
In field practice, the soil parameters and tower grounding impedance parameters may be different from each other, so that the model parameters are different from the actual parameters. The difference is inevitable, but the detection data of the tower grounding resistance of the transformer substation incoming line segment by the power department can be considered to be relatively accurate. In addition, the position and the trend of the power transmission line incoming line segment tower are established by adopting a satellite positioning system, and the model can be more practical by accurately establishing the simulation model, so that the accuracy of the calculation result is ensured.
(4) Numerical method derivation for compensating for shunt effects
① numerical calculation model
Because the field conditions may not have effective simulation means, the model of the power transmission line cannot be accurately established, and the influence of shunting cannot be effectively calculated and filtered. In this case, it is necessary to study a shunt value calculation correction method for the ground resistance measurement.
According to the model, the disc electrode is used for replacing grounding devices of a transformer substation grounding grid and a tower
The disc electrode earth surface potential calculation formula is as follows:
ground net potential with current injection:
Ixcurrent value passed to earth grid, I1….nThe current values from the first base tower to the nth base tower are different. D01Is the distance between the first base tower and the grounding grid, D02The distance from the second base tower to the center of the grounding grid, and similarly, D0nAnd the distance from the nth base tower to the center of the grounding grid. r is1、r2、......rnThe equivalent radius of the tower from the first base tower to the nth base tower. Similarly, we can also show the potential at the first base tower as shown in the following formula:
potential at the second base tower:
the electric potential of the nth base tower is as follows:
from the model constructed above, it is possible to further obtain an equivalent circuit diagram in consideration of the rise of the earth current to the earth potential, as shown in fig. 6.
Wherein delta UxThat is, the right side of the formula (3.6) is equivalent to removing RxIxThe sum of all external terms, when all tower grounding resistances pass through the current, the tower is groundedAn algebraic sum of potential rises is generated at the net. Delta U1The voltage drop generated by the tower grounding resistor itself is removed, and the potential generated by the grounding network and other tower grounding resistors at the first base tower rises when current flows; delta UnAnd so on.
If the return pole is not at infinity, then the return pole current-I the potential drop generated between the earth grid and the earth electrode of each base tower cannot be ignored. We can then get the potential at the ground net as:
where I is the total current injected from the earth grid, rcRadius of the disc equivalent to the return pole, D0cIs the distance between the current pole and the center of the grounding grid. We can also get the potential of each base tower in turn, taking into account the effect of the reflux pole on each base tower potential.
First base tower potential:
second base tower potential:
the electric potential of the nth base tower is as follows:
from the node voltage method, we can get the following expression:
there is also the formula for the current relationship:
I=Ix+I1+......+In(3.14)
by combining the above formula, theoretically, the expression of the current value of any point with respect to the Rx can be calculated, and then the value of the ground resistance Rx can be accurately calculated through the voltage value measured by the field voltage electrode.
② model simplification
The above has been specifically analyzed for the case of taking into account the shunt impedance of the lightning conductor when measuring the resistance of the earth mat. Corresponding software windows can be designed to calculate the shunt coefficient, so that the shunt current of the lightning conductor is obtained, and the accurate grounding resistance value is calculated.
But the formula is complex and is difficult to use in engineering actual estimation. It is required to simplify the processing thereof. Neglecting the smaller component, a simplified calculation method is formed.
Adopting the same line parameters as the finite element simulation model, wherein the lightning conductor impedance value of each span is as follows:
Zd2=Zd3=......=Zdn=0.6+j0.37Ω (3.15)
and (3) simulating the circuit by using Multisim, and calculating the total equivalent impedance of the lightning conductor tower and the current value flowing on each tower when the influence of the current in the ground is not considered. According to the Davining theorem, the complex parallel structure on the right side of the circuit is simplified to obtain the equivalent impedance. From this, equivalent impedance values at different numbers of pole bases of the lightning conductor can be obtained, and as shown in the following table, as shown in fig. 7, the equivalent impedance values are a circuit diagram of Multisim simulation.
Since the first span has a different line impedance than the rear span, which is only half the value of the rear span line impedance. The impedance value 2 in the table above is the equivalent impedance of the mast tower system when the impedance value of the first span line is not counted. As can be seen from the above table, the change rule of the equivalent impedance value of the tower-lightning conductor along with the increase of the tower base number is as follows: the impedance value is maximum when only one base tower is arranged at the beginning, and the equivalent impedance value is gradually reduced later; from the fifth base tower, the equivalent impedance value of the tower-lightning conductor changes little. And when the tower reaches the tenth base tower, the change rate of the equivalent impedance value of the tower lightning conductor is only 0.114%. The equivalent impedance of the tower can be expressed as:
Z=2.004+j0.663Ω (3.16)
③ circuit simplification without considering current pole under actual parameter
Next, we need to analyze and consider the influence of the current flowing into the ground on the potential of each point. We first analyze the case without considering the current pole, and let ρ be 100 Ω · m, r1=r2=r3=......=rn=2m,D01=100m,D02=D03=......=D0n200m can be simplified to formula (3.3) - (3.6):
and researching the influence of the tower cardinal number in the calculation model on the grounding grid shunting by adopting a method of equivalent parallel components on the right side. The simplified circuit was simulated using Multisim software and compared to the results of the COMSOL Multiphysics software simulation.
In the case where Rx is known to be 0.48 Ω, the potential distribution of each point on the ground can be obtained by simulation, as shown in fig. 8. The potential conditions of the substation grounding grid and the grounding pole of each base tower can be clearly seen from fig. 8.
As can be seen from fig. 8, the position at the earth mat is highest. We perform surface integration on the current density at the first base tower. The value of the current shunted by the tower in the COMSOL Multiphysics simulation can be obtained to be 14.68A. The potential values at each point along the tower (i.e. the positive x-axis in the simulation) can be obtained from comsolmutiphatics. As shown in fig. 8.
Then, we performed simulations using Multisim. We compare the case of considering only the first base tower, only the two base towers, three base towers and four base towers with the case of COMSOL Multiphysics simulation, respectively. If only one base tower is considered in fig. 9, the rear towers are equivalent by equivalent impedances.
The shunt current at the grounding grid is 85.367A when only one base tower is considered. The shunt value of the grounding grid is 85.563A when two base towers are considered; the obtained shunt current of the transformer substation grounding grid is 85.616A when three towers are considered; the substation grounding grid split when considering four base towers is 85.637 a. We can see that the shunt current of the substation grounding grid does not change much when considering one-base tower, two-base tower, three-base tower and four-base tower.
The comparison of the results obtained from Multisim simulation with the current values obtained from comsolmutics simulation shows that the error between the results obtained when using an equivalent circuit considering only one base tower and the actual (comsolmutics simulation) is small.
Therefore, the simplified calculation model can calculate the shunt coefficient by using the equivalent circuit only considering one base tower, and the error is not large.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (4)
1. The utility model provides a reverse short distance measurement circuit reposition of redundant personnel structure of ground net which characterized in that: including ground net (1), cable conductor (2) and base tower (3), ground net (1) surface is connected with a plurality of base tower (3) through cable conductor (2), the central point of ground net (1) is located same straight line with base tower (3), adjacent two distance between base tower (3) is 200m, is closest ground net (1) base tower (3) are 100m from the distance between ground net (1).
2. The reverse short distance measurement circuit shunting structure of ground net of claim 1, characterized in that: the grounding grid (1) adopts a disc electrode equivalent model, and the diameter of the grounding grid (1) is 100 m.
3. The reverse short distance measurement circuit shunting structure of ground net of claim 1, characterized in that: the base tower (3) is equivalent by adopting a corresponding disc electrode model with the radius of 2m, and the grounding resistance value of the base tower (3) is 8-10 omega.
4. The reverse short distance measurement circuit shunting structure of ground net of claim 1, characterized in that: the cable (2) is a steel stranded wire GJ-80 lightning conductor.
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Cited By (2)
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CN112924759A (en) * | 2020-12-30 | 2021-06-08 | 广东电网有限责任公司电力科学研究院 | Method and device for measuring grounding resistance of lightning tower |
CN113777441A (en) * | 2021-08-20 | 2021-12-10 | 云南电网有限责任公司楚雄供电局 | Lightning stroke same-jump evaluation method and platform considering height of coupling ground wire |
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Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
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CN112924759A (en) * | 2020-12-30 | 2021-06-08 | 广东电网有限责任公司电力科学研究院 | Method and device for measuring grounding resistance of lightning tower |
CN113777441A (en) * | 2021-08-20 | 2021-12-10 | 云南电网有限责任公司楚雄供电局 | Lightning stroke same-jump evaluation method and platform considering height of coupling ground wire |
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