Method for judging voltage phase sequence of high-voltage side of transformer during grid connection of low-voltage lines of interconnected power grid

Abstract

The invention discloses a method for judging a voltage phase sequence of a high-voltage side of a transformer during grid connection of a low-voltage line of an interconnected power grid. The method comprises the following steps of: setting a maximum value theta m of an absolute value of a phase angle difference of phase voltages of nodes to be connected in parallel of two lines; a phase sequence indicator is used for determining the phase sequence of phase voltages of nodes to be connected in two lines, one line with the phase voltages of the nodes to be connected in the positive phase sequence is set as a line LL1, and the other line is set as a line LL2; the phase sequence of the voltage of the high-voltage side of the transformer connected with the line LL1 is A-B-C; measuring the phase difference delta between the a-phase voltage of the to-be-paralleled node of the line LL2 and the a-phase voltage of the to-be-paralleled node of the line LL1; and the phase sequence of the high-voltage side voltage of the transformer connected with the line LL2 is judged by comparing the angle interval where the phase angle difference delta is located. Detection is only carried out on the low-voltage line side, the phase sequence of the voltage on the high-voltage side of the transformer does not need to be directly detected, and the convenient and safe low-voltage line grid connection condition detection method is provided for electric power system dispatching personnel.

Description

Technical Field

[0001] The invention relates to a method for detecting grid-connected conditions of an electric power system, in particular to a method for judging the voltage phase sequence on the high-voltage side of a Yd11 group transformer when low-voltage lines of the same interconnected power grid are connected to the grid. Background Art

[0002] Grid-connected operation is an operation frequently performed by power system operators. When a power system is connected to the grid, certain conditions must be met, such as whether the phase sequence, frequency, and voltage are the same. The phases of the three-phase voltages of the power system differ by 120°. When the voltage of phase B lags behind phase A by 120°, and the voltage of phase C lags behind phase B by 120°, it is called a positive phase sequence, and there are three types: ABC, CAB, and BCA; when the voltage of phase B leads phase A by 120°, and the voltage of phase C leads phase B by 120°, it is called a reverse phase sequence, and there are three types: CBA, ACB, and BAC. For the phase sequence conditions of grid-connected operation, two independent power systems are connected to the grid or a generator is connected to a power system, as long as both are in a positive phase sequence; when two lines are connected to the grid within the same interconnected power grid, not only are both required to be in a positive phase sequence, but also the A, B, and C phases of the two must correspond one to one. For example Figure 1 The 10kV line grid connection schematic diagram is shown in the figure. L1 , L L2 They are two 10kV lines to be connected to the grid, B1 and B2 are line L L1 , L L2 The grid-connected nodes of line L are T1 and T2 respectively. L1 , L L2 Connected step-down transformer, L H1 , L H2 They are the high-voltage incoming lines of transformers T1 and T2 respectively. The 10kV voltage level of the power grid is obtained by stepping down the voltage level of a higher level through a step-down transformer. When the high-voltage three-phase line is arranged in a triangle, it is easier to have a phase sequence error. When the three-phase line is arranged horizontally or vertically, in order to ensure the symmetry of the three-phase parameters, it is necessary to transpose, which may also cause a phase sequence error in the high-voltage transmission line. The phase sequence error of the high-voltage line will cause the phase sequence error of the low-voltage line. When the low-voltage side lines of two transformers are connected to the grid, if the high-voltage side incoming lines of the two transformers are in the same interconnected power grid, it is necessary to determine whether the phase sequence of the high-voltage side voltages of the two transformers is the same, that is, whether the A, B, and C phases of the two correspond one to one. The two transformers may be far apart, and it is difficult to directly determine the phase sequence of the high-voltage side voltage of the transformer.

[0003] The primary and secondary windings of a three-phase transformer may be connected in star or triangle. The national standard stipulates that when the windings of a three-phase transformer are connected in star, they are labeled Y (primary winding) and y (secondary winding). When the neutral point is led out, they are labeled YN or yn; when the windings are connected in triangle, they are labeled D (primary winding) and d (secondary winding).

[0004] Since the primary and secondary windings of a three-phase transformer may be connected in star or triangle, different connection methods of the primary and secondary windings of a three-phase transformer can result in a variety of combinations. The numbers of the three-phase transformer connection group number are represented by the clock ordinal number of the phase difference. The new national standard uses the phase difference of the phase voltage phasor corresponding to the primary and secondary sides to judge, with the primary phase voltage phasor as the reference to the clock 0, and the clock point number pointed to by the secondary phase voltage phasor is the three-phase transformer connection group number, and the virtual neutral point of the triangle is the center of the triangle. The same connection method is used on both sides of the three-phase transformer, that is, when Yy and Dd, the even-numbered points are 0, 2, 4, 6, 8, and 10; one side of the three-phase transformer uses a star connection and the other side uses a triangle connection, that is, when Yd and Dy, the odd-numbered points are 1, 3, 5, 7, 9, and 11.

[0005] The power grid can be divided into two parts: the transmission network and the distribution network. The transmission network consists of 220~1000kV transmission lines and regional substations, which deliver electric energy to various local power supply networks or directly to large users. The distribution network consists of 110kV~220 / 380V distribution lines and step-down substations, which distribute electric energy to various types of users. In the distribution network, the connection group of 110kV / 10kV transformers is usually YNd11, and the connection group of 66kV / 10kV transformers and 35kV / 10kV transformers is usually Yd11. The difference between YNd11 and Yd11 connection group transformers is only whether the neutral point of the primary side of the transformer is grounded. The primary and secondary phase relationship of the two is the same, and the secondary phase voltage leads the primary phase voltage by 30°, see Figure 2 The following are the wiring diagram and phase diagram of the primary and secondary sides of the Yd11 transformer when the primary phase sequence is ABC. If the phase sequence of the high voltage side of the transformer is not ABC, the phase relationship between the primary and secondary sides of the transformer will not be that the secondary side phase voltage leads the primary side phase voltage by 30°. Figure 3 The primary and secondary phase diagrams of the Yd11 transformer are shown when the primary phase sequence is not ABC. In these cases, the primary phases A, B, and C of the transformer do not correspond to the secondary phases a, b, and c, and the primary voltage phase sequence cannot be directly determined from the secondary voltage phase sequence of the transformer. Summary of the invention

[0006] In order to solve the above-mentioned problems existing in the grid connection of the power system, the present invention proposes a method for determining the phase sequence of the voltage on the high-voltage side of the transformer when the low-voltage lines of the interconnected power grid are connected to the grid. The phase sequence of the voltage on the high-voltage side of the transformer is determined by the phase difference of the phase voltages of the nodes to be connected of the two low-voltage lines. This method is easy to implement and relatively safe.

[0007] The basic idea of ​​the present invention is: firstly, a phase sequence indicator is used to determine the phase sequence of the phase voltages of the nodes to be connected to the grid of two low-voltage lines to be connected to the grid, and a line whose phase voltage of the node to be connected is a positive phase sequence is selected as line L.L1 , the other line is line L L2 , then detect line L L2 The voltage of phase a of the node B2 to be connected is proportional to the voltage of line L L1 The phase difference of the a-phase voltage of the node B1 to be connected is used to determine the phase sequence of the high-voltage side of the transformer. In the present invention, the three-phase labels of the primary side (high-voltage side) of the transformer are represented by capital letters A, B, and C, and the three-phase labels of the secondary side (low-voltage side) of the transformer are represented by lowercase letters a, b, and c.

[0008] Depend on Figure 2 It can be seen that for the transformer of Yd11 (or YNd11) connection group, if the primary phase sequence is ABC, the secondary phase voltage of the transformer leads the corresponding primary phase voltage by 30°; the low-voltage side of the transformer is still defined as a, b, and c phases from left to right. If the phase sequence of the high-voltage side voltage is not ABC, the secondary phase voltage of the transformer is not 30° ahead of the corresponding primary phase voltage, and the phase difference between the primary and secondary phase voltages of each phase is also different. Figure 3 In these cases, the primary side A, B, C phases of the transformer do not correspond to the secondary side a, b, c phases, and the primary side voltage phase sequence cannot be directly determined from the secondary side voltage phase sequence of the transformer.

[0009] Depend on Figure 3 (a) It can be seen that when the primary voltage phase sequence of the transformer is CAB, the secondary phase voltage leads the corresponding phase voltage of the primary side by 150°; Figure 3 (b) It can be seen that when the primary voltage phase sequence of the transformer is BCA, the secondary phase voltage leads the corresponding phase voltage of the primary by -90°, that is, lags by 90°. Figure 3 (c) It can be seen that when the primary voltage phase sequence of the transformer is CBA, the secondary phase a voltage leads the primary phase A voltage by 90°, the secondary phase b voltage leads the primary phase B voltage by -30°, and the secondary phase c voltage leads the primary phase C voltage by -150°. Figure 3 (d) It can be seen that when the primary voltage phase sequence of the transformer is ACB, the secondary phase a voltage leads the primary phase A voltage by -30°, the secondary phase b voltage leads the primary phase B voltage by -150°, and the secondary phase c voltage leads the primary phase C voltage by 90°. Figure 3 (e) It can be seen that when the primary voltage phase sequence of the transformer is BAC, the secondary phase a voltage leads the primary phase A voltage by -150°, the secondary phase b voltage leads the primary phase B voltage by 90°, and the secondary phase c voltage leads the primary phase C voltage by -30°. Under various phase sequences of the transformer primary voltage, the phase angle of the transformer secondary phase voltage leading the corresponding phase voltage of the primary is shown in Table 1.

[0010] Table 1 The phase angle of the transformer secondary phase voltage leading the primary corresponding phase voltage

[0011] Primary phase voltage phase sequence Phase A Phase B Phase C ABC 30° 30° 30° CAB 150° 150° 150° BCA -90° -90° -90° CBA 90° -30° -150° ACB -30° -150° 90° BAC -150° 90° -30°

[0012] Table 2 shows the voltage on the high voltage side of transformer T2 under various phase sequences of line L L2 The phase voltage of the node to be connected B2 is ahead of line L L1 The phase angle of the phase voltage of the node B1 to be connected is δ0. This phase angle is the result of assuming that the phase sequence of the high-voltage side voltage of the two transformers is ABC and the phase difference of the low-voltage line node to be connected is 0. In fact, there is a certain phase difference between the nodes of the power system. Assuming that the phase sequence of the high-voltage side voltage of the transformer is ABC, in the two 10kV lines to be connected to the grid, line L L2 The voltage of the node to be connected B2 is ahead of the line L L1 The angle of the phase voltage of the node B1 to be connected is θ (this angle may be negative), then the data in Table 2 should be added with angle θ to obtain the actual phase angle δ. If the maximum absolute value of angle θ is θ m , then when the voltage phase sequence on the high voltage side of transformer T2 is CAB, there is 120°-θ m ≤δ≤120°+θ m By analogy, when the voltage phase sequence on the high-voltage side of transformer T2 is other values, line L L2 The phase voltage of the node to be connected B2 is ahead of line L L1 The phase angle δ of the phase voltage of the node to be connected is B1. As can be seen from Table 2, the phase sequence of the voltage on the high-voltage side of transformer T2 is different. L2 The phase voltage of the node to be connected B2 is ahead of line L L1 The phase angle δ of the phase voltage of the node B1 to be connected is also different, so the phase sequence of the voltage on the high-voltage side of the transformer T2 can be determined based on this phase angle δ. When determining, only any one of the phases a, b, and c needs to be determined.

[0013] Table 2 Transformer T2 high voltage side voltage line L under various phase sequences L2 Phase voltage leads line L L1 Phase angle of phase voltage

[0014] Primary phase voltage phase sequence a phase Phase b Phase C ABC 0° 0° 0° CAB 120° 120° 120° BCA -120° -120° -120° CBA 60° -60° 180° ACB -60° 180° 60° BAC 180° 60° -60°

[0015] The technical solution of the present invention is as follows: A method for determining the voltage phase sequence on the high-voltage side of a transformer when a low-voltage line of an interconnected power grid is connected to the grid comprises the following steps:

[0016] The technical solution of the present invention is as follows: A method for determining the voltage phase sequence on the high-voltage side of a transformer when a low-voltage line of an interconnected power grid is connected to the grid comprises the following steps:

[0017] A. Set the maximum value of the absolute value of the phase angle difference between the two lines to be connected at the node m ;

[0018] B. Use the phase sequence indicator to determine the phase sequence of the phase voltages at the nodes to be connected. Assume that the line with the positive phase sequence of the phase voltage at the node to be connected is line L. L1 , the other line is line L L2 ;

[0019] C. Set line L L1 The phase sequence of the high voltage side voltage of the connected transformer is ABC;

[0020] D. Measurement circuit L L2 The voltage of phase a of the node to be connected leads the voltage of line L L1 The phase difference δ of the phase a voltage of the node to be connected;

[0021] E. By comparing the angle interval of the phase angle difference δ, determine the line L L2 The phase sequence of the high voltage side voltage of the connected transformer; the angle interval includes -θ m ~θ m , 120°-θ m ~120°+θ m 、-120°-θ m ~-120°+θ m , 60°-θ m ~60°+θ m 、-60°-θ m ~-60°+θ m , 180°-θ m ~180°+θ m There are six intervals in total.

[0022] Furthermore, the maximum value θ in step A m The setting method is as follows:

[0023] Since transformers and lines will produce voltage drops, when the phase sequence of each node is ABC, there is also a phase difference between the voltages of each node in the power system. The maximum absolute value of the phase angle difference is set to θ m is 20°.

[0024] Furthermore, the definition of the phase sequence described in step B is as follows: the phases of the three-phase voltages of the power system differ by 120° respectively. When the voltage of phase B lags behind phase A by 120°, and the voltage of phase C lags behind phase B by 120°, it is called a positive phase sequence, and there are three types: ABC, CAB, and BCA; when the voltage of phase B leads phase A by 120°, and the voltage of phase C leads phase B by 120°, it is called a reverse phase sequence, and there are three types: CBA, ACB, and BAC.

[0025] Furthermore, in step E, the judgment line L L2 The phase sequence of the high voltage side voltage of the connected transformer is as follows:

[0026] E1. Determine whether the phase angle difference δ is greater than or equal to -θ m and less than or equal to θ m , if not, go to step E2; if satisfied, then line L L2 The phase sequence of the high-voltage side voltage of the connected transformer is ABC, go to step E7;

[0027] E2. Determine whether the phase angle difference δ is greater than or equal to 120°-θ m And less than or equal to 120°+θ m , if not, go to step E3; if satisfied, then line L L2 The phase sequence of the high-voltage side voltage of the connected transformer is CAB, go to step E7;

[0028] E3. Determine whether the phase angle difference δ is greater than or equal to -120°-θ m And less than or equal to -120°+θ m , if not, go to step E4; if satisfied, then line L L2 The phase sequence of the high-voltage side voltage of the connected transformer is BCA, go to step E7;

[0029] E4. Determine whether the phase angle difference δ is greater than or equal to 60°-θ m And less than or equal to 60°+θ m , if not, go to step E5; if satisfied, then line L L2 The phase sequence of the high-voltage side voltage of the connected transformer is CBA, go to step E7;

[0030] E5. Determine whether the phase angle difference δ is greater than or equal to -60°-θ m And less than or equal to -60°+θ m , if not, go to step E6; if satisfied, then line L L2 The phase sequence of the high-voltage side voltage of the connected transformer is ACB, go to step E7;

[0031] E6. Determine whether the phase angle difference δ is greater than or equal to 180°-θ m And less than or equal to 180°+θ m , if satisfied, then line L L2 The phase sequence of the high voltage side voltage of the connected transformer is BAC;

[0032] E7. End.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The method for judging the phase sequence of the voltage on the high-voltage side of the transformer when the low-voltage line of the interconnected power grid is connected to the grid proposed by the present invention only detects on the low-voltage line side and does not need to directly detect the phase sequence of the voltage on the high-voltage side of the transformer, thus providing a convenient and safe method for detecting the grid-connected conditions of the low-voltage line for power system dispatchers. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention has attached Figure 4 Zhang, among which:

[0036] Figure 1 This is a wiring diagram for 10kV line grid connection.

[0037] Figure 2 It is the Yd11 transformer wiring diagram and primary-secondary phase diagram when the primary phase sequence of the transformer is ABC.

[0038] Figure 3 This is the primary-secondary phasor diagram of the Yd11 transformer when the primary side of the transformer has a phase sequence other than ABC.

[0039] Figure 4 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with the accompanying drawings. Figure 1 The wiring diagram of the 10kV line grid connection is shown in the figure. The transformer connection group is Yd11, the high-voltage incoming line voltage is 35kV, and the low-voltage line voltage is 10kV. Assume that the maximum absolute value of the phase angle difference between the two nodes to be connected is θ m is 20°.

[0041] Example 1

[0042] First, use the phase sequence indicator to determine the phase sequence of the two lines. Suppose any line with a positive phase sequence is line L. L1 , and assume that its phase sequence is ABC, then the other line is line L L2 .

[0043] Measure line L again L2 The voltage of phase a of the node to be connected leads the voltage of line L L1 The phase difference δ of the phase a voltage of the node to be connected is 40°≤δ≤80°, for example, δ=63°, then 60°-θ is satisfied. m ≤δ≤60°+θ m The conditions can be used to determine the line L L2 The phase sequence of the high-voltage side voltage of the connected transformer is CBA.

[0044] Example 2

[0045] First, use the phase sequence indicator to determine the phase sequence of the two lines. Suppose any line with a positive phase sequence is line L. L1 , and assume that its phase sequence is ABC, then the other line is line L L2 .

[0046] Measure line L again L2 The voltage of phase a of the node to be connected leads the voltage of line L L1 The phase difference δ of the phase a voltage of the node to be connected is 160°≤δ≤200°, for example, δ=183°, then 180°-θ is satisfied. m ≤δ≤180°+θ m The conditions can be used to determine the line L L2 The phase sequence of the high voltage side voltage of the connected transformer is BAC.

[0047] Example 3

[0048] First, use the phase sequence indicator to determine the phase sequence of the two lines. Suppose any line with a positive phase sequence is line L. L1 , and assume that its phase sequence is ABC, then the other line is line L L2 .

[0049] Measure line L again L2 The voltage of phase a of the node to be connected leads the voltage of line L L1 The phase difference δ of the phase a voltage of the node to be connected is -140°≤δ≤-100°, for example, δ=-117°, then -120°-θ is satisfied m ≤δ≤-120°+θ m The conditions can be used to determine the line L L2 The phase sequence of the high-voltage side voltage of the connected transformer is BCA.

[0050] The present invention is applicable to determining the voltage phase sequence on the high-voltage side of a transformer of a Yd11 or YNd11 group when a low-voltage line of the same interconnected power grid is connected to the grid. In addition to using the phase angle difference of the a-phase voltage at the node to be connected between the two lines to determine the voltage phase sequence on the high-voltage side of the transformer, the phase angle difference of the b-phase voltage or the phase angle difference of the c-phase voltage at the node to be connected between the two lines can also be used to determine the voltage phase sequence on the high-voltage side of the transformer.

[0051] The present invention is not limited to this embodiment, and any equivalent concepts or changes within the technical scope disclosed by the present invention are included in the protection scope of the present invention.

Claims

1. A method for determining the voltage phase sequence on the high-voltage side of a transformer when a low-voltage line of an interconnected power grid is connected to the grid, characterized in that: The following steps are involved: A. Set the maximum value of the absolute value of the phase angle difference between the two lines to be connected at the node m ; B. Use the phase sequence indicator to determine the phase sequence of the phase voltages at the nodes to be connected. Assume that the line with the positive phase sequence of the phase voltage at the node to be connected is line L. L1 , the other line is line L L2 ; C. Set line L L1 The phase sequence of the high voltage side voltage of the connected transformer is ABC; D. Measurement circuit L L2 The voltage of phase a of the node to be connected leads the voltage of line L L1 The phase difference δ of the phase a voltage of the node to be connected; E. By comparing the angle interval of the phase angle difference δ, determine the line L L2 The phase sequence of the high voltage side voltage of the connected transformer; the angle interval includes -θ m ~θ m , 120°-θ m ~120°+θ m 、-120°-θ m ~-120°+θ m , 60°-θ m ~60°+θ m 、-60°-θ m ~-60°+θ m , 180°-θ m ~180°+θ m There are six intervals in total.

2. According to the method for determining the phase sequence of the voltage on the high-voltage side of the transformer when the low-voltage line of the interconnected power grid is connected to the grid according to claim 1, it is characterized in that: The maximum value θ in step A m The setting method is as follows: Since transformers and lines will produce voltage drops, when the phase sequence of each node is ABC, there is also a phase difference between the voltages of each node in the power system. The maximum absolute value of the phase angle difference is set to θ m is 20°.

3. According to the method for determining the phase sequence of the voltage on the high-voltage side of the transformer when the low-voltage line of the interconnected power grid is connected to the grid as described in claim 1, it is characterized in that: The definition of the phase sequence described in step B is as follows: the phases of the three-phase voltages of the power system differ by 120° respectively. When the voltage of phase B lags behind phase A by 120°, and the voltage of phase C lags behind phase B by 120°, it is called a positive phase sequence, and there are three types: ABC, CAB, and BCA; when the voltage of phase B leads phase A by 120°, and the voltage of phase C leads phase B by 120°, it is called a reverse phase sequence, and there are three types: CBA, ACB, and BAC.

4. According to claim 1, the method for determining the voltage phase sequence on the high-voltage side of a transformer when the low-voltage line of an interconnected power grid is connected to the grid is characterized in that: Step E: Determine line L L2 The phase sequence of the high voltage side voltage of the connected transformer is as follows: E1. Determine whether the phase angle difference δ is greater than or equal to -θ m and less than or equal to θ m , if not, go to step E2; if satisfied, then line L L2 The phase sequence of the high-voltage side voltage of the connected transformer is ABC, go to step E7; E2. Determine whether the phase angle difference δ is greater than or equal to 120°-θ m And less than or equal to 120°+θ m , if not, go to step E3; if satisfied, then line L L2 The phase sequence of the high-voltage side voltage of the connected transformer is CAB, go to step E7; E3. Determine whether the phase angle difference δ is greater than or equal to -120°-θ m And less than or equal to -120°+θ m , if not, go to step E4; if satisfied, then line L L2 The phase sequence of the high-voltage side voltage of the connected transformer is BCA, go to step E7; E4. Determine whether the phase angle difference δ is greater than or equal to 60°-θ m And less than or equal to 60°+θ m , if not, go to step E5; if satisfied, then line L L2 The phase sequence of the high-voltage side voltage of the connected transformer is CBA, go to step E7; E5. Determine whether the phase angle difference δ is greater than or equal to -60°-θ m And less than or equal to -60°+θ m , if not, go to step E6; if satisfied, then line L L2 The phase sequence of the high-voltage side voltage of the connected transformer is ACB, go to step E7; E6. Determine whether the phase angle difference δ is greater than or equal to 180°-θ m And less than or equal to 180°+θ m , if satisfied, then line L L2 The phase sequence of the high voltage side voltage of the connected transformer is BAC; E7. End.

Images