Self-checking method and system for a maintenance and power preservation integrated device

Abstract

The application discloses a self-checking method and system of a maintenance and power supply integrated device, and belongs to the technical field of power grid switching. The self-checking method comprises the following steps: disconnecting a first circuit breaker, a third circuit breaker, a first switch and a second switch, and providing a detection voltage by a second power supply; acquiring second signal data; sending a first closing instruction to the second switch by a master control unit, acquiring third signal data and a second closing time of the second switch; sending a second closing instruction to the first switch by the master control unit, acquiring first signal data and a first closing time; and checking relevant data. The first circuit breaker is disconnected with the first power supply, the third circuit breaker is disconnected with a load, the second power supply is used as a working voltage, the key switches and monitoring data of synchronous grid connection are checked, the mechanical performance of the switches is determined to be consistent with the design, and the effectiveness of different power supply signal data is determined, thereby providing reliability and safety guarantee for synchronous grid connection.

Description

Technical Field

[0001] This invention relates to the field of power grid switching technology, specifically to a self-testing method and system for an integrated maintenance and power protection device. Background Technology

[0002] With economic and social development and the improvement of people's living standards, electricity users have increasingly higher requirements for the continuity and reliability of power supply systems. In particular, some major events and important conference venues have a more urgent need for continuous power supply and are very sensitive to power outages, even short-term power outages and insufficient power supply. The social impact of insufficient power supply during peak electricity consumption periods has long been a major concern for power supply companies.

[0003] Insufficient power supply causes voltage drops, preventing related loads from functioning properly and even damaging the equipment. This severely impacts normal business production and causes considerable inconvenience to people's lives. Major events and important conference venues are particularly sensitive to power demand.

[0004] Therefore, in order to solve the problems of load capacity expansion and power supply maintenance in important locations, it is necessary to improve the reliability and safety of uninterrupted power supply capacity expansion of the distribution network through synchronous grid connection. The consistency of the mechanical performance of the switches and the different power signal data of synchronous grid connection are of great significance to successful grid connection. Summary of the Invention

[0005] To address the aforementioned technical problems in the existing technology, this invention provides a self-testing method and system for an integrated maintenance and power protection device, which verifies the signal data and switches of the integrated maintenance and power protection device, thereby ensuring the reliability and safety of simultaneous grid connection.

[0006] This invention discloses a self-testing method for an integrated maintenance and power protection device. The integrated maintenance and power protection device includes a main control unit, a first switch, a first circuit breaker, a third circuit breaker, and a second switch.

[0007] The first switch K1 is connected to the first power supply T via the first circuit breaker M1, and the second switch K2 is connected to the second power supply G. The output terminals of the first switch K1 and the second switch K2 are connected to the load via the third circuit breaker M3. The main control unit C is connected to the control terminals of the first switch K1, the second switch K2, the first circuit breaker, and the third circuit breaker. The main control unit C is connected to the sensors at the input terminals of the first switch K1, the second switch K2, and the third circuit breaker, respectively, and obtains the first signal data of the first power supply T, the second signal data of the second power supply G, and the third signal data of the input terminal of the third circuit breaker.

[0008] The self-testing method includes: disconnecting the first circuit breaker, the third circuit breaker, the first switch, and the second switch; providing a detection voltage from the second power supply; acquiring second signal data; sending a first closing command to the second switch through the main control unit, acquiring third signal data, and obtaining the second closing time of the second switch based on the initiation time of the closing command and the change time of the third signal data; sending a second closing command to the first switch through the main control unit, acquiring first signal data, and obtaining the first closing time of the first switch based on the initiation time of the first closing command and the change time of the first signal data; and after verifying the second signal data, the first signal data, the third signal data, the first closing time, and the second closing time, disconnecting the first switch and the second switch.

[0009] Preferred methods for preheating include:

[0010] Disconnect the first circuit breaker and the third circuit breaker, and open the first switch and the second switch to preheat;

[0011] After preheating, perform the self-test method described above;

[0012] Alarm methods include:

[0013] Determine whether the second signal data, first signal data, third signal data, first closing time, and second closing time are abnormal;

[0014] If so, generate the corresponding alarm information.

[0015] Preferred grid connection testing method:

[0016] Disconnect the third circuit breaker and the second switch K2, and close the first circuit breaker M1 and the first switch K1;

[0017] Acquire the first signal data of the first power source and the second signal data of the second power source;

[0018] Based on the algorithm of synchronous grid connection, the second switch is closed according to the first signal data and the second signal data, and the third signal data of the third circuit breaker and the second closing time of the second switch are obtained.

[0019] The third signal data and closing time are verified.

[0020] Preferred algorithms for simultaneous grid connection include the sliding algorithm:

[0021] Obtain the first phase of the first power supply and the second phase of the second power supply within the sliding window, and calculate the phase difference between the first phase and the second phase;

[0022] Obtain the difference between adjacent phase differences to achieve phase slip;

[0023] Obtain the sum of phase sliding within the sliding window;

[0024] If the sum of phase slips does not exceed the first threshold, the second switch will be closed.

[0025] Preferably, the phase difference is expressed as:

[0026] NR i =N i -R i (1)

[0027] The sum of phase slips is expressed as:

[0028]

[0029] NR i Let N represent the phase difference, Th represent the sum of phase slips, and N represent the phase difference. i Represented as the i-th value of the first phase, R i This represents the i-th value of the second phase, and n represents the total number of values ​​within the window.

[0030] Preferably, the algorithm for simultaneous grid connection includes the average sliding algorithm:

[0031] Obtain the first phase of the first power supply and the second phase of the second power supply within the sliding window, and calculate the phase difference between the first phase and the second phase;

[0032] Obtain the difference between adjacent phase differences to achieve phase slip;

[0033] Obtain the sum of phase sliding within the sliding window;

[0034] If the average value of the sum of phase slips does not exceed the first threshold, the second switch is closed.

[0035] Preferably, the average value of the sum of phase slips is calculated as follows:

[0036] NR i =N i -R i (1)

[0037]

[0038] Avg=Th / (n×cyc) (3)

[0039] Among them, NR i Let N represent the phase difference, Th represent the sum of phase slips, and N represent the phase difference. i Represented as the i-th value of the first phase, R i Let represent the i-th value of the second phase, n represent the total number of values ​​within the window, Avg represent the average value of the phase sliding sum, and cyc represent the number of cycles calculated.

[0040] The present invention also provides a system for implementing the above self-testing method, including an integrated maintenance and power protection device, a first power supply, and a second power supply;

[0041] The first circuit breaker M1 of the integrated power protection device is connected to the first power supply T.

[0042] The input terminal of the second switch of the integrated maintenance and power protection device is connected to the second power supply G.

[0043] Preferably, the first and second switches employ DC excitation drive circuits.

[0044] The first power supply line of the DC excitation drive circuit is connected to the positive terminal of the first rectifier diode group, and the negative terminal of the first rectifier diode group is connected to the positive terminal of the first capacitor group through the first metal-oxide-semiconductor field-effect transistor.

[0045] The first power line is connected to the negative terminal of the second rectifier diode group, and the positive terminal of the second rectifier diode group is connected to the negative terminal of the second capacitor group through the second metal-oxide-semiconductor field-effect transistor.

[0046] The negative terminal of the first capacitor bank and the positive terminal of the second capacitor bank are connected to the second power supply line;

[0047] The positive terminal of the first capacitor bank and the negative terminal of the second power supply bank are connected to the excitation discharge circuit.

[0048] Preferably, the first power supply is electrically connected to the load via a third switch QF;

[0049] The first circuit breaker M1 is connected to the input terminal of the third switch QF through the first grid-connected switch QF1, and the third circuit breaker M3 is connected to the input terminal of the load through the second grid-connected switch QF2.

[0050] The first power supply is connected to the third switch QF via an isolation switch QS.

[0051] Compared with the prior art, the beneficial effects of the present invention are as follows: by disconnecting the connection with the first power supply through the first circuit breaker and disconnecting the connection with the load through the third circuit breaker, and using the second power supply as the working voltage, the key switches and monitoring data of synchronous grid connection are tested to determine the consistency of the mechanical performance of the switches with the design and the validity of different power supply signal data, thus providing a guarantee of reliability and safety for synchronous grid connection. Attached Figure Description

[0052] Figure 1 This is the circuit diagram of the integrated power protection and maintenance device;

[0053] Figure 2 This is a flowchart of the self-inspection method for the integrated power protection device.

[0054] Figure 3 This is a flowchart of the testing method for simultaneous grid connection;

[0055] Figure 4 Schematic diagram of phase sliding calculation in Example 2;

[0056] Figure 5 This is a circuit diagram of a DC excitation drive circuit;

[0057] Figure 6 This is the circuit diagram for Example 5;

[0058] Figure 7 This is a schematic diagram of the box structure in Example 5. Detailed Implementation

[0059] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] The present invention will now be described in further detail with reference to the accompanying drawings:

[0061] A self-testing method for an integrated maintenance and power protection device, such as Figure 1 As shown, the integrated maintenance and power protection device includes a main control unit C, a first switch K1, a first circuit breaker M1, a third circuit breaker M3, and a second switch K2. The first switch K1 is connected to a first power supply T through the first circuit breaker M1, and the second switch K2 is connected to a second power supply G. The output terminals of the first switch K1 and the second switch K2 are connected to the load through the third circuit breaker M3. The main control unit C is connected to the control terminals of the first switch K1, the second switch K2, the first circuit breaker M1, and the third circuit breaker M3. The main control unit C is connected to the sensors at the input terminals of the first switch K1, the second switch K2, and the third circuit breaker, respectively, and obtains the first signal data of the first power supply T, the second signal data of the second power supply G, and the third signal data of the input terminal of the third circuit breaker.

[0062] like Figure 2 As shown, the self-testing method includes:

[0063] Step 101: Disconnect the first circuit breaker M1, the third circuit breaker M3, the first switch K1, and the second switch K2, and provide the detection voltage / operating voltage from the second power supply.

[0064] Step 102: Acquire the second signal data of the second power supply;

[0065] Step 103: The main control unit sends a first closing command to the second switch, acquires the third signal data, and obtains the second closing time of the second switch based on the initiation time of the closing command and the reception or change time of the third signal data. After closing, the voltage of the third signal data changes; the closing time can be estimated using the change time and initiation time.

[0066] Step 104: Send a second closing command to the first switch through the main control unit, obtain the first signal data, and obtain the first closing time of the first switch according to the initiation time of the first closing command and the reception / change time of the first signal data.

[0067] Step 105: After verifying the second signal data, the first signal data, the third signal data, the first closing time, and the second closing time, disconnect the first switch and the second switch. For example, determine whether the values ​​of the second signal data, the first signal data, and the third signal data are within the normal range, and whether the first closing time and the second closing time are within the normal range.

[0068] By disconnecting the connection to the first power source through the first circuit breaker and disconnecting the connection to the load through the third circuit breaker, and using the second power source as the operating voltage, the key switches and monitoring data for synchronous grid connection are tested to confirm that the mechanical performance of the switches is consistent with the design and the validity of different power source signal data, thus providing reliability and safety for successful synchronous grid connection.

[0069] The present invention also includes methods for preheating and alarm.

[0070] Methods for warming up before self-test include:

[0071] Disconnect the first circuit breaker and the third circuit breaker, and open the first switch and the second switch to preheat;

[0072] After preheating, perform the self-test method. Preheating the equipment ensures that all components reach optimal performance before performing the self-test.

[0073] Alarm methods include:

[0074] Step 106: Determine whether the verification of the second signal data, the first signal data, the third signal data, the first closing time, and the second closing time is abnormal;

[0075] If so, step 107: Generate corresponding alarm information and proceed to step 108. The alarm information includes the type / component of the error, such as an error in the closing time of the first switch, and prompts for maintenance or a second self-test.

[0076] If not, proceed to step 108: Generate a self-test report.

[0077] Example 1

[0078] This embodiment provides a method for detecting simultaneous grid connection, such as... Figure 3 :

[0079] Step 201: Disconnect the third circuit breaker M3 and the second switch K2, and close the first circuit breaker M1 and the first switch K1.

[0080] Step 202: Obtain the first signal data of the first power supply and the second signal data of the second power supply.

[0081] Step 203: Based on the algorithm of synchronous grid connection, close the second switch according to the first signal data and the second signal data, and obtain the third signal data of the third circuit breaker and the second closing time of the second switch;

[0082] Step 204: Verify the third signal data and the closing time. For example, verify whether the second closing time is within the preset range, and verify whether changes in the third signal data impact the load.

[0083] Example 2

[0084] A synchronous grid connection algorithm includes a sliding algorithm:

[0085] Step 201: Obtain the first phase of the first power supply and the second phase of the second power supply within the sliding window, and calculate the phase difference NR between the first phase N and the second phase R.

[0086] For example, using a 128-point phase detection method, the phase data might be obtained by converting the acquired current signal into an analog-to-digital converter (DAC). Taking a sampling frequency of 12kHz as an example, the angular resolution of the phase detection is 1.5°.

[0087] Step 203: Obtain the difference between adjacent phase differences to achieve phase slip.

[0088] Step 204: Obtain the phase sliding sum (SUM) within the sliding window.

[0089] Step 205: If the sum of the phase slips does not exceed the first threshold, close the second switch.

[0090] Figure 4 The diagram illustrates the phase difference between the first and second phases, and how the phase slip is calculated. The sum of the phase difference and the phase slip can be expressed as:

[0091] NR i =N i -R i (1)

[0092]

[0093] Among them, NR iLet N represent the phase difference, Th represent the sum of phase slips, and N represent the phase difference. i Represented as the i-th value of the first phase, R i It represents the i-th value of the second phase, and n represents the total number of values ​​within the window, i.e., the window width.

[0094] The circuit breaker is closed when the sum of the phase slips does not exceed or is less than the first threshold, such as when there are no more than 4 points, i.e., the average phase difference does not exceed 6°. It should be noted that the sum of the phase slips of the first and second power supplies being less than the first threshold is an important condition for synchronous grid connection, but not the only condition. For example, the voltage difference between the first and second power supplies may be less than the second threshold, and the frequency difference may be less than the third threshold.

[0095] The sliding window includes the values ​​of the last 128 points before the last value of the period. The last value of the period can be obtained from the index number, that is, the index number is used as the last phase value of the period.

[0096] Example 3

[0097] Unlike Example 2, the grid connection calculation is performed using the values ​​at point n after the cycle. The average value of the sum of phase slips is calculated using the following formula:

[0098] NR i =N i -R i (1)

[0099]

[0100] Avg=Th / (n×cyc) (3)

[0101] Among them, NR i Let N represent the phase difference, Th represent the sum of phase slips, and N represent the phase difference. i Represented as the i-th value of the first phase, R i Let represent the i-th value of the second phase, n represent the total number of values ​​within the window, Avg represent the average of the phase sliding sums, and cyc represent the number of cycles to be calculated. If only data within the current cycle is calculated, then cyc is 1.

[0102] If the average value Avg of the sum of phase slips does not exceed the first threshold, the second switch is closed for grid connection. For example, no more than 4 points.

[0103] In a specific test, the angle difference at the closing point was -1, or -1.5 degrees. The waveforms of the first and second signal data basically overlapped during grid connection, which greatly reduced the power flow impact at the time of grid connection and met the requirements of grid connection.

[0104] Example 4

[0105] This embodiment constructs a self-testing system for implementing the above self-testing method, such as... Figure 1 As shown, the device includes an integrated maintenance and power protection device 1, a first power supply T, and a second power supply G. The first circuit breaker M1 of the integrated maintenance and power protection device 1 is connected to the first power supply T. The input terminal of the second switch of the integrated maintenance and power protection device is connected to the second power supply G. The first power supply is electrically connected to the load via a third switch QF.

[0106] Because AC excitation drive has a certain degree of instability and cannot guarantee consistency in each closing operation, a DC excitation drive circuit for the first and second switches was designed. For example... Figure 5 As shown, the first power line UA_IN is connected to the positive terminal of the first rectifier diode group (D3-D6). The negative terminal of the first rectifier diode group is connected to the positive terminal of the first capacitor group (C22-C25) through the first MOSFET Q1. The first power line UA_IN is connected to the negative terminal of the second rectifier diode group (D7-D10). The positive terminal of the second rectifier diode group is connected to the negative terminal of the second capacitor group (C28-C31) through the second MOSFET Q2. The negative terminals of the first and second capacitor groups are connected to the second power line UB_IN. The positive terminal of the first capacitor group serves as the DC positive terminal DC+, and the negative terminal of the second power line serves as the DC negative terminal DC-, and is connected to the excitation discharge circuit. In a specific embodiment, the AC voltage between UA_IN and UA_B is 380V, and the DC voltage between DC+ and DC- is 750V. The DC excitation drive circuit can stabilize the switching drive time, making the measurement results more accurate. In a specific test, the closing time of the switch was 25-36ms.

[0107] Example 5

[0108] Unlike Example 4, as Figure 6 and Figure 7 This embodiment constructs a mobile integrated maintenance and power supply device, comprising a housing 1. A first power supply T is electrically connected to the load via a third switch QF; a first circuit breaker M1 is connected to the input terminal of the third switch QF via a first grid-connected switch QF1; a third circuit breaker M3 is connected to the input terminal (output terminal of the third switch QF) of the load via a second grid-connected switch QF2; the first power supply T is connected to the third switch QF via a disconnecting switch QS. The first grid-connected switch QF1 and the second grid-connected switch QF2 are deployed within the distribution box / room of the first power supply T for manual operation.

[0109] A connector is arranged on one side of the enclosure 1, including a second connector S2, a third connector S3, and a fourth connector S4. The first circuit breaker M1 is connected to the first power supply T via the second connector S2, the second circuit breaker M2 is connected to the second power supply G via the third connector S3, and the output terminal of the third circuit breaker M3 is connected to the load via the fourth connector S4. The circuit breakers can be molded case circuit breakers to ensure operational reliability and stability; the first switch K1 and the second switch K2 can be changeover switches.

[0110] The first switch K1, the first circuit breaker M1, the second switch K2, the second circuit breaker M2, and the main control unit C are encapsulated within the enclosure 1. The original power distribution network can be configured with a quick connection between the first and second connectors, and a quick connection between the fifth and fourth connectors. Specifically, the first power supply T is connected to the first grid-connected switch QF1, and the first grid-connected switch QF1 is connected to the second connector S2 via the first connector S1; the fifth connector S5 is connected to the input terminal of the load via the second grid-connected switch QF2.

[0111] Figure 7 The structure of enclosure 1 is shown: a second connector S2, a third connector S3, and a fourth connector S4 are provided on the side; an alarm 12 is provided at the top of the enclosure; multiple casters 11 are provided at the bottom; and control buttons 14 and a tilted display 13 are arranged on the front. The connectors are suitable for three-phase four-wire low-voltage electricity. The enclosure adopts a mobile design.

[0112] In one specific embodiment, the first power source includes mains power, and the second power source includes a generator vehicle. Using the synchronization algorithm in Embodiment 4, functional tests were conducted: bypass low-voltage circuit breaker closing (first switch K1) test, synchronization check grid connection switching to generator test, synchronization check grid connection return to mains power test, fault protection test, status indication test, and 48-hour continuous operation assessment test. The standards used were BG / T 7261-2016 19, GB / T 3797-2016 7.12, and GB / T14048.11-2016 8.2, and the test results were all compliant.

[0113] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A self-inspection method for an integrated maintenance and power protection device, characterized in that, The integrated maintenance and power protection device includes a main control unit, a first switch, a first circuit breaker, a third circuit breaker, and a second switch. The first switch is connected to the first power supply via the first circuit breaker, and the second switch is connected to the second power supply; the output terminals of the first and second switches are connected to the load via the third circuit breaker; the main control unit is connected to the control terminals of the first switch, the second switch, the first circuit breaker, and the third circuit breaker; the main control unit is connected to the sensors at the input terminals of the first switch, the second switch, and the third circuit breaker, respectively, and obtains the first signal data of the first power supply, the second signal data of the second power supply, and the third signal data of the input terminal of the third circuit breaker. The self-test method includes: Disconnect the first circuit breaker, the third circuit breaker, the first switch, and the second switch, and the detection voltage is provided by the second power supply; Acquire second signal data; The main control unit sends a first closing command to the second switch, obtains the third signal data, and obtains the second closing time of the second switch based on the initiation time of the closing command and the change time of the third signal data. The main control unit sends a second closing command to the first switch, obtains the first signal data, and obtains the first closing time of the first switch based on the initiation time of the first closing command and the change time of the first signal data. After verifying the second signal data, the first signal data, the third signal data, the first closing time, and the second closing time, the first switch and the second switch are disconnected.

2. The self-testing method according to claim 1, characterized in that, It also includes methods for preheating and alarms. Preheating methods include: Disconnect the first circuit breaker and the third circuit breaker, and close the first switch and the second switch to preheat; After preheating, perform the self-test method described above; Alarm methods include: Determine whether the second signal data, first signal data, third signal data, first closing time, and second closing time are abnormal; If so, generate the corresponding alarm information.

3. The self-testing method according to claim 1, characterized in that, It also includes grid connection testing methods: Disconnect the third circuit breaker and the second switch, and close the first circuit breaker and the first switch; Acquire the first signal data of the first power source and the second signal data of the second power source; Based on the algorithm of synchronous grid connection, the second switch is closed according to the first signal data and the second signal data, and the third signal data of the third circuit breaker and the second closing time of the second switch are obtained. The third signal data and the second closing time are verified.

4. The self-testing method according to claim 3, characterized in that, Simultaneous grid connection algorithms include the sliding algorithm: Obtain the first phase of the first power supply and the second phase of the second power supply within the sliding window, and calculate the phase difference between the first phase and the second phase; Obtain the difference between adjacent phase differences to achieve phase slip; Obtain the sum of phase sliding within the sliding window; If the sum of phase slips does not exceed the first threshold, the second switch will be closed.

5. The self-testing method according to claim 4, characterized in that, The phase difference is expressed as: （1）； The sum of phase slips is expressed as: （2）； Represented as phase difference, Expressed as the sum of phase slips, Represented as the first phase i A number, Represented as the second phase i A number, n This represents the total value within the window.

6. The self-testing method according to claim 3, characterized in that, The algorithms for simultaneous grid connection include the average sliding algorithm: Obtain the first phase of the first power supply and the second phase of the second power supply within the sliding window, and calculate the phase difference between the first phase and the second phase; Obtain the difference between adjacent phase differences to achieve phase slip; Obtain the sum of phase sliding within the sliding window; If the average value of the sum of phase slips does not exceed the first threshold, the second switch is closed.

7. The self-testing method according to claim 6, characterized in that, The average value of the sum of phase slips is calculated as follows: （1）； （2）； （3）； in, Represented as phase difference, Expressed as the sum of phase slips, Represented as the first phase i A number, Represented as the second phase i A number, n This is represented as the total value within the window. Avg It is expressed as the average of the sum of phase slips. cyc This indicates the number of cycles in the calculation.

8. A system for implementing the self-testing method as described in any one of claims 1-7, characterized in that, This includes an integrated power protection and maintenance device, a primary power supply, and a secondary power supply. The first circuit breaker of the integrated power protection device is connected to the first power source. The input terminal of the second switch of the integrated maintenance and power protection device is connected to the second power supply.

9. The system according to claim 8, characterized in that, The first and second switches use DC excitation drive circuits. The first power supply line of the DC excitation drive circuit is connected to the positive terminal of the first rectifier diode group, and the negative terminal of the first rectifier diode group is connected to the positive terminal of the first capacitor group through the first metal-oxide-semiconductor field-effect transistor. The first power line is connected to the negative terminal of the second rectifier diode group, and the positive terminal of the second rectifier diode group is connected to the negative terminal of the second capacitor group through the second metal-oxide-semiconductor field-effect transistor. The negative terminal of the first capacitor bank and the positive terminal of the second capacitor bank are connected to the second power supply line; The positive terminal of the first capacitor bank and the negative terminal of the second capacitor bank are connected to the excitation discharge circuit.

10. The system according to claim 8, characterized in that, The first power source is electrically connected to the load via a third switch; The first circuit breaker is connected to the input terminal of the third switch via the first grid-connected switch, and the third circuit breaker is connected to the input terminal of the load via the second grid-connected switch; The first power supply is connected to the third switch via an isolating switch.

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