Automatic isolation grounding system and method for operation and maintenance of distribution transformer areas with a large number of distributed photovoltaic power access

Abstract

The present invention discloses an automatic isolation grounding system and method for operation and maintenance of a large number of distributed photovoltaic access substations, mainly including a control module, a signal source, a disconnector and its control device, a grounding switch and its control device, and a signal measurement component; the control module is used to control the disconnection of the disconnector, the closing of the grounding switch, and the injection of the signal source, determine the reliability of the switch opening and closing through the collected detection signals, and control the closing of the disconnector, the disconnection of the grounding switch, and the withdrawal of the signal source after the maintenance is completed; the signal source injects a capacitor discharge signal, and then realizes the grounding reliability analysis through the differential smoothing comparison of the current sequences on both sides of the grounding switch; realizes the automatic high-reliability safety isolation and grounding of the equipment to be detected and maintained, greatly improves the safety guarantee of the operation and maintenance personnel while improving the operation and maintenance efficiency, improves the automation degree of the substation operation and maintenance, and ensures the stable operation of the substation.

Description

Technical Field

[0001] The present invention belongs to the field of power automation, and particularly relates to an automatic isolation and grounding system and method for operation and maintenance of a large number of distributed photovoltaic access substations. Background Art

[0002] With the proposal of the "dual carbon" goal, the operation and maintenance work mode of the original distribution substation has been changed after a large number of distributed photovoltaics are connected to the substation. The problem of reverse power transmission caused by the connection of a large number of distributed photovoltaics makes a large amount of preparatory work required for routine inspection or replacement of equipment. To ensure reliable isolation and grounding of the components to be repaired, while spending a large amount of manpower and working time, it also brings greater potential safety hazards to maintenance personnel.

[0003] Since the voltage level of the distribution substation is low (less than 10 kV), the equipment in the substation belongs to normal electrical equipment, with relatively low cost and no particularity. Therefore, the overall automation level of the current substation is low, and there is no large-scale configuration of automated monitoring equipment, resulting in the operation and maintenance efficiency of the current distribution substation completely relying on on-site operation and mainly relying on manpower. Traditional operation and maintenance mainly include sectional search and elimination, single-phase switching off for power outage isolation, manual grounding operation, etc. It not only consumes a lot of manpower and has low efficiency, but on the other hand, the low-voltage substation lines have the characteristics of strong user dispersion. The overall maintenance work of a large number of substations is more onerous. Manual operation and maintenance lead to a sharp increase in labor costs. At the same time, the frequent power outages for maintenance of each substation are relatively long, which is likely to affect the normal electricity use of residents, is not conducive to people's lives and social and economic activities, and also affects the normal operation of the power grid. When maintenance personnel lack professional knowledge, it is also easy to cause safety accidents. The low maintenance efficiency may further lead to an increasing number of faults year by year, further threatening the production and life of residents. With the improvement of the country's requirements for power supply reliability, especially the need for the construction of smart grids, it is urgent to solve this problem. How to improve the operation and maintenance efficiency and ensure the safety of personnel during the maintenance process is a difficult problem in the operation and maintenance of distribution substations for many years. Improving the automation level of operation and maintenance is an effective way to solve this difficult problem. Incorporating the necessary steps of daily operation and maintenance into automated management can better solve the common problems faced by a large number of transformer operation and maintenance tasks, improve the professional level of operation and maintenance, and at the same time greatly ensure the safety of personnel and enhance the reliability of power grid operation. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides an automatic isolation and grounding system and method for operation and maintenance of a large number of distributed photovoltaic access substations.

[0005] To achieve the above object, the technical solutions adopted by the present invention include:

[0006] An automatic isolation grounding system for operation and maintenance of a large number of distributed photovoltaic access substations, including a control module, a disconnector, a grounding switch, an electrical detection module, and a signal source, where:

[0007] The disconnector is used to isolate the maintenance point and the load, and the grounding switch is used to ground the maintenance point;

[0008] The control module judges the opening or closing state of the disconnector and the grounding switch according to the collected signals and outputs a control signal. Under normal conditions, the disconnector and the signal source power switch are closed, and the grounding switch and the signal source injection switch are opened; when maintenance starts, the disconnector and the signal source power switch are opened, and the grounding switch and the signal source injection switch are closed;

[0009] The electrical detection module is used to collect the current signals on both sides of the disconnector and the grounding switch and send them to the control module;

[0010] The signal source includes a signal source power switch connected to the power grid, a signal source injection switch connected to the branch where the grounding switch is located, and a grounded capacitor. In the normal state without maintenance, the signal source power switch is closed and connected, and the signal source injection switch is opened, for charging the capacitor. When maintenance starts, the signal source power switch is opened, the signal source injection switch is closed and connected, for discharging the branch where the grounding switch is located, and sends a cut-off signal to the control module at the moment when the capacitor voltage is 0.

[0011] Further, the control module includes a control decision unit and a on-off determination unit. The on-off determination unit analyzes the signals collected by the electrical detection module to judge the opening and closing of the disconnector and the grounding switch; the control decision unit issues a control signal according to the opening or closing state judged by the on-off determination unit, and through the control signal, the disconnector and the signal source power switch are opened when maintenance starts, and the grounding switch and the signal source injection switch are closed.

[0012] Further, judging the opening or closing state of the disconnector specifically includes: after the disconnector opening command is issued, using the set current signal sequence with a fixed duration as the judgment basis, forming the current sequences on both sides S1 = {I r11 , I r12 , …, I r1n} and S2 = {I r21 , I r22 , …, I r2n}, where n is the number of collected current signals, performing root mean square processing on the sequences S1 and S2 to form the sequence judgment values S 1r and S 2r , that is:

[0013]

[0014] Set a threshold value S r , S r is set to a value approximately 0 according to the accuracy of the electrical detection module; the sequence judgment value S 1r and S 2r are AND-operated with the comparison result with the threshold value and the disconnection switch signal of the disconnector to obtain the judgment result of the disconnector, that is:

[0015] S 1r <S r ∩S 2r <S r ∩G

[0016] where G is the disconnection switch signal of the auxiliary contact of the disconnector, 1 represents disconnection, 0 represents connection, and the judgment result of the disconnector being 1 represents disconnection and 0 represents connection.

[0017] Furthermore, judging the disconnection or closing state of the earthing switch specifically includes: using the current sequences S3 = {Ig11, Ig12,..., Ig1m} and S4 = {Ig21, Ig22,..., Ig2m} on both sides of the earthing switch during the capacitor discharge stage as the analysis basis, where m is the number of collected current signals, performing differential smoothing processing on S3 and S4 to form new sequences S5 = {Ig11p, Ig12p,..., Ig1mp} and S6 = {Ig21p, Ig22p,..., Ig2mp};

[0018] Subtracting the corresponding elements with the same time in sequences S5 and S6 to form a new sequence S7, and calculating the root mean square value S7r of S7,

[0019]

[0020] where ΔIrm is the element of sequence S7 formed by subtracting S5 and S6;

[0021] Set a threshold value Srg, which is set to a value approximately 0 according to the accuracy of the electrical detection module; the AND operation is performed on the comparison result of the sequence judgment value with the threshold value and the closing switch signal sent by the auxiliary contact of the earthing switch to obtain the judgment result of the reliable closing of the earthing switch, that is:

[0022] S 7r <S rg ∩W

[0023] where W is the closing switch signal of the auxiliary contact of the earthing switch; the judgment result of the disconnector being 1 represents disconnection and 0 represents connection.

[0024] Furthermore, the elements of sequences S5 and S6 obtained by performing differential smoothing processing on S3 and S4 are:

[0025]

[0026] Further, it further includes a human - machine interaction interface for data display and human - machine interaction.

[0027] Further, the control module, the electrical detection module and the human - machine interaction interface are integrally installed in the control cabinet.

[0028] Further, when the signal source charges the capacitor and discharges the branch where the grounding switch is located, it specifically includes: in the normal state without maintenance, the signal source power switch is closed and the signal source injection switch is open, taking power from the surrounding power grid, converting three - phase electricity into direct current through a rectifier circuit to charge the capacitor, and stopping charging after the capacitor reaches the preset voltage value; at the beginning of maintenance, the signal source power switch is open and the signal source injection switch is closed, starting to discharge the branch where the grounding switch is located, and sending a cut - off signal to the control module at the moment when the capacitor voltage is 0.

[0029] Further, the preset voltage value does not exceed 100 volts.

[0030] An automatic isolation grounding method based on the automatic isolation grounding system includes the steps:

[0031] The electrical detection module collects the current signals on both sides of the disconnector and the grounding switch and sends them to the control module;

[0032] The control module judges the opening or closing state of the disconnector and the signal source power switch according to the collected signals and outputs control signals; in the normal state, it issues control signals to close the disconnector and the signal source power switch and open the grounding switch and the signal source injection switch; in the case of starting maintenance, it issues control signals to open the disconnector and the signal source power switch and close the grounding switch and the signal source injection switch;

[0033] The switches in the disconnector, the grounding switch and the signal source are automatically opened or closed according to the control signals.

[0034] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: Aiming at the problems of heavy maintenance tasks, low automation level, poor professionalism and low safety guarantee faced after a large number of distributed photovoltaics are connected to the substation area, the present invention realizes the automatic operation of isolation and grounding operations at the maintenance points through switch control, adopts the method of injecting signals into the grounding point by capacitor discharge and performing differential smoothing data processing, strengthens the grounding reliability, realizes the automatic and reliable isolation grounding of the operation and maintenance of a large number of distributed photovoltaics connected to the substation area, improves the intelligent operation level of the substation area, improves the operation and maintenance efficiency of the distribution substation area, greatly enhances the safety and reliability of operation and maintenance, and ensures the safe and stable operation of the power grid. Description of the Drawings

[0035] Figure 1 It is a diagram of an automatic isolation grounding system for operation and maintenance of a large number of distributed photovoltaic access substations. Specific implementation manner

[0036] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and cannot be used to limit the protection scope of the present invention.

[0037] A diagram of an automatic isolation grounding system for operation and maintenance of a large number of distributed photovoltaic access substations, as Figure 1 shown, where K1 is a grounding switch, K2 is a disconnector, I g1 , I g2 are the currents on both sides of the grounding switch, and I r1 , I r2 are the currents on both sides of the disconnector; the technical solutions adopted by the present invention include:

[0038] 1) The automatic isolation grounding system for operation and maintenance of a large number of distributed photovoltaic access substations mainly includes a device control cabinet, a signal source, a disconnector, and a grounding switch; among them, the disconnector is used to isolate the maintenance point and the load, and the grounding switch is used to ensure that the maintenance point is grounded, so as to ensure the safety of personnel and equipment;

[0039] 2) The device control cabinet mainly includes functions of a human-machine interface, control decision-making, electrical detection, and on-off determination; the human-machine interface is used to receive the start and end of maintenance, give a determination of reliable on-off, etc. for human-machine interaction; the control decision-making, according to the current working state, disconnects the disconnector and the signal source power switch when starting maintenance, and closes the grounding switch and the signal source injection switch; the electrical detection collects the current signal on both sides of the disconnector and the grounding switch; the on-off determination analyzes the collected signal to determine the reliable disconnection and closing of the switch;

[0040] 3) In the normal state without maintenance, the signal source takes power from the adjacent power grid, and through the rectification part, converts the three-phase power into direct current to charge the capacitor. After the capacitor reaches the preset voltage value, the charging stops. The preset voltage value generally does not exceed 100 volts; at the start moment of maintenance, the switch connecting the signal source to the power grid is disconnected, and the switch connecting to the branch where the grounding switch is located is closed, and the branch where the grounding switch is located starts to discharge. When the capacitor voltage is 0, a cut-off signal is sent to the device control cabinet, and the current signal sequence collected during the capacitor discharge time is used as the judgment basis for the reliable grounding of the grounding switch; the signal source is well-known in the art, and its internal circuit structure will not be described in detail here;

[0041] 4) Reliable disconnection judgment of the disconnector: After the disconnection command of the disconnector is issued, a current signal sequence of a fixed duration is used as the judgment basis to form the current sequences on both sides S1 = {I r11 , Ir12 ,…,I r1n}, and S2 = {I r21 , I r22 ,…,I r2n}, where n is the number of collected current signals. Perform root-mean-square processing on sequences S1 and S2 as shown in Equation (1) to form sequence judgment values S 1r and S 2r . Set the threshold S r . Since the currents on both sides of the disconnector should be close to 0 after reliable isolation, S r should be set to a value close to 0 according to the accuracy of the measuring component;

[0042]

[0043] Perform an AND operation on the comparison result of the sequence judgment value and the threshold with the disconnection switch signal sent by the auxiliary contact of the disconnector as the judgment result for reliable disconnection of the disconnector, as shown in Equation (2).

[0044] S 1r < S r ∩ S 2r < S r ∩ G(2)

[0045] where G is the disconnection switch signal of the auxiliary contact of the disconnector, 1 represents disconnection, and 0 represents connection;

[0046] The value of Equation (2) being 1 represents disconnection, and 0 represents connection.

[0047] 5) Reliable closing judgment of the earthing switch: Use the current sequences S3 = {I g11 , I g12 ,…,I g1m} and S4 = {I g21 , I g22 ,…,I g2m} on both sides of the earthing switch during the capacitor discharge stage as the analysis basis, where m is the number of collected current signals. Perform differential smoothing processing on S3 and S4 as shown in Equation (3) to form new sequences S5 = {I g11p , I g12p ,…,I g1mp} and S6 = {I g21p , I g22p ,…,I g2mp}.

[0048]

[0049] Subtract the corresponding elements with the same time in sequences S5 and S6 to form a new sequence S7, and calculate the root-mean-square value S of S7 through Equation (4) 7r, set the threshold value S rg , since the difference between the currents on both sides of the earthing switch should be close to 0 after reliable earthing, S rg should be set to a value close to 0 according to the accuracy of the measuring component.

[0050]

[0051] Among them, ΔI rm is an element of the sequence S7 formed by subtracting S6 from S5.

[0052] Perform an AND operation on the comparison result between the sequence judgment value and the threshold value and the closing switch signal sent by the auxiliary contact of the earthing switch as the judgment result for reliable closing of the earthing switch, as shown in formula (5).

[0053] S 7r <S rg ∩W(5)

[0054] Among them, W is the closing switch signal of the auxiliary contact of the earthing switch;

[0055] The value of formula (5) being 1 indicates disconnection, and 0 indicates connection.

[0056] An automatic isolation earthing method based on the automatic isolation earthing system includes the steps of:

[0057] The electrical detection module collects the current signals on both sides of the disconnector and the earthing switch and sends them to the control module;

[0058] The control module judges the opening or closing state of the disconnector and the signal source power switch according to the collected signals and outputs control signals; under normal conditions, it issues control signals to close the disconnector and the signal source power switch and open the earthing switch and the signal source injection switch; in the case of starting maintenance, it issues control signals to open the disconnector and the signal source power switch and close the earthing switch and the signal source injection switch;

[0059] The switches in the disconnector, the earthing switch and the signal source are automatically opened or closed according to the control signals.

[0060] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can still be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. An automatic isolation grounding system for operation, maintenance and inspection of a large number of distributed photovoltaic access stations, characterized by: It includes a control module, an isolating switch, a grounding switch, an electrical detection module and a signal source, wherein: The isolating switch is used to isolate the maintenance point from the load, and the grounding switch is used to ground the maintenance point; The control module determines the disconnection or closing state of the isolating switch and the grounding switch according to the collected signal, and outputs a control signal. In a normal state, the isolating switch and the signal source power switch are closed, and the grounding switch and the signal source injection switch are disconnected; when starting maintenance, the isolating switch and the signal source power switch are disconnected, and the grounding switch and the signal source injection switch are closed; The electrical detection module is used to collect current signals on both sides of the isolating switch and the grounding switch, and send them to the control module; The signal source includes a signal source power switch connected to the power grid, a signal source injection switch connected to the branch where the grounding switch is located, and a grounded capacitor. In a normal state without maintenance, the signal source power switch is closed and connected, and the signal source injection switch is disconnected, so as to charge the capacitor. At the beginning of maintenance, the signal source power switch is disconnected, and the signal source injection switch is closed and connected, so as to discharge the branch where the grounding switch is located, and send a cutoff signal to the control module when the capacitor voltage is 0; Determining the disconnection or closing state of the isolating switch specifically includes: after the disconnection command of the isolating switch is issued, taking the current signal sequence of the set fixed time length as the judgment basis, forming the current sequence S1 on both sides = {I r11 ,I r12 ,…,I r1n } and S2={I r21 ,I r22 ,…,I r2n }, where n is the number of collected current signals, and the sequences S1 and S2 are processed by RMS to form the sequence judgment value S 1r and S 2r ,Right now: Set the threshold S r , S r According to the accuracy of the electrical detection module, it is set to a value close to 0; the sequence judgment value S 1r and S 2r The comparison result with the threshold is operated with the disconnect switch signal of the disconnect switch as the judgment result of the disconnect switch, that is: S 1r <S r ∩S 2r <S r ∩G Among them, G is the disconnect switch signal of the auxiliary contact of the isolating switch, 1 represents disconnection, and 0 represents connection. The judgment result of the isolating switch is 1 represents disconnection, and 0 represents connection.

2. According to claim 1, an automatic isolation grounding system for operation, maintenance and inspection of a large number of distributed photovoltaic access stations is characterized by: The control module includes a control decision unit and an on-off judgment unit. The on-off judgment unit analyzes the signal collected by the electrical detection module to determine whether the disconnecting switch and the earthing switch are opened or closed. The control decision unit sends a control signal according to the open or closed state determined by the on-off judgment unit. Through the control signal, the disconnecting switch and the signal source power switch are disconnected, and the earthing switch and the signal source injection switch are closed when the maintenance starts.

3. According to claim 1, an automatic isolation grounding system for operation, maintenance and inspection of a large number of distributed photovoltaic access stations is characterized by: Determining the disconnection or closing state of the grounding switch specifically includes: taking the current sequences S3 = {Ig11, Ig12, ..., Ig1m} and S4 = {Ig21, Ig22, ..., Ig2m} on both sides of the grounding switch in the capacitor discharge stage as analysis basis, where m is the number of collected current signals, performing differential smoothing processing on S3 and S4 to form new sequences S5 = {Ig11p, Ig12p, ..., Ig1mp} and S6 = {Ig21p, Ig22p, ..., Ig2mp}; Subtract the elements of sequences S5 and S6 that have the same corresponding time to form a new sequence S7, and calculate the root mean square value S7r of S7. Where ΔIrm is the element of sequence S7 formed by subtracting S5 and S6; The threshold Srg is set to a value close to 0 according to the accuracy of the electrical detection module; the comparison result between the sequence judgment value and the threshold is ANDed with the closed switch signal sent by the auxiliary contact of the grounding switch as the judgment result of the reliable closure of the grounding switch, that is: S 7r <S rg ∩W Wherein, W is the closing switch signal of the auxiliary contact of the grounding switch; the judgment result of the isolating switch is 1 for disconnection and 0 for connection.

4. According to claim 3, an automatic isolation grounding system for operation, maintenance and inspection of a large number of distributed photovoltaic access stations is characterized by: The elements of the sequences S5 and S6 obtained by performing differential smoothing on S3 and S4 are:

5. According to claim 1, an automatic isolation grounding system for operation, maintenance and inspection of a large number of distributed photovoltaic access stations is characterized by: It also includes a human-computer interaction interface for receiving maintenance tasks and displaying data.

6. According to claim 5, an automatic isolation grounding system for operation, maintenance and inspection of a large number of distributed photovoltaic access stations is characterized by: The control module, electrical detection module and human-machine interaction interface are integrated and installed in a control cabinet.

7. According to claim 1, an automatic isolation grounding system for operation, maintenance and inspection of a large number of distributed photovoltaic access stations is characterized by: The signal source charges the capacitor and discharges the branch where the grounding switch is located, specifically including: in a normal state without maintenance, the signal source power switch is closed and connected, the signal source injection switch is disconnected, power is taken from the surrounding power grid, and the three-phase power is converted into direct current through a rectifier circuit to charge the capacitor, and charging is stopped after the capacitor reaches a preset voltage value; at the beginning of maintenance, the signal source power switch is disconnected, the signal source injection switch is closed and connected, and the branch where the grounding switch is located begins to be discharged, and a cutoff signal is sent to the control module when the capacitor voltage is 0.

8. The automatic isolation grounding system for operation, maintenance and inspection of a large number of distributed photovoltaic access stations according to claim 7 is characterized by: The preset voltage value does not exceed 100 volts.

9. An automatic isolation grounding method based on the automatic isolation grounding system according to any one of claims 1 to 8, characterized in that: Includes steps: The electrical detection module collects current signals on both sides of the isolating switch and the grounding switch and sends them to the control module; The control module determines the disconnection or closing state of the isolation switch and the signal source power switch according to the collected signal, and outputs a control signal; Under normal conditions, a control signal is sent to close the isolating switch and the signal source power switch, and to disconnect the grounding switch and the signal source injection switch; When starting maintenance, a control signal is issued to disconnect the isolating switch and the signal source power switch, and to close the grounding switch and the signal source injection switch; The isolating switch, the earthing switch and the switches in the signal source are automatically opened or closed according to the control signal.

Images