A method and device for estimating the capacitance attenuation of a fusion terminal

Abstract

The present invention provides a method and device for estimating the capacitance attenuation of a capacitor based on a fusion terminal, which relates to the technical field of reactive power compensation in a distribution transformer area. The method includes continuously monitoring the switching position change of capacitors in a capacitor bank, and when the capacitor switch position changes each time, according to the change in reactive power capacity ΔQ on the grid system side S is approximately the actual effective reactive power output Q of the operating capacitor CO , and calculating the capacitance attenuation rate δ of the capacitor. The present invention can effectively warn of the capacitance attenuation of the capacitor, estimate the life of the capacitor, and lean the operation and maintenance of capacitor reactive power compensation. Thereby reducing the probability of capacitor failures, improving the power supply reliability of the transformer area, and ensuring the safe and stable operation of the power grid.

Description

Technical Field

[0001] The present invention relates to the technical field of reactive power compensation in distribution substations, and particularly to a method and device for estimating the attenuation of capacitor capacity. Technical Background

[0002] Most of the electrical loads are inductive and need to absorb reactive power. For on-site centralized compensation, reactive power compensation devices are generally installed on the low-voltage outgoing side of distribution substations to reduce power loss and improve the power quality of the power grid. Capacitor compensation has the advantages of simple principle, convenient use, economical operation, obvious improvement effect, etc., and has become the main reactive power compensation method in distribution substations.

[0003] During the operation life cycle of the capacitor, there is a situation of capacity attenuation. Excessive temperature of the capacitor will cause the aging of the insulating medium of the capacitor, the service life attenuation of the metallized film, and the capacity of the capacitor will attenuate. If the capacitor operates under overvoltage or overload for a long time, the internal temperature of the capacitor will rise, resulting in a shortened service life of the capacitor and a decrease in capacity at the same time. Now many low-voltage capacitors are self-healing capacitors. However, there is also capacity attenuation after the self-healing of metallized polypropylene film capacitors.

[0004] Distribution substations are characterized by a large number of points and wide areas, which brings pressure to the operation and maintenance of a large number of reactive power compensation capacitors on site. Most of the existing monitoring schemes for reactive power compensation capacitors only realize the information notification and reporting after the occurrence of faults, which belongs to post-treatment. At this time, equipment damage or power outage has already occurred. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to estimate the capacitor capacity and warn of the attenuation of capacitor capacity, and provides a method and device for monitoring and estimating the capacitor capacity based on a fusion terminal, which is applicable to low-voltage distribution substations equipped with fusion terminals and reactive power compensation capacitors.

[0006] The intelligent fusion terminal of the substation area (referred to as the fusion terminal) is designed based on the concept of "software-defined terminal" and an open platform architecture, with a hardware platform and software APP; it is a new generation of terminal product designed by using key technologies such as edge computing, containers, Internet of Things, and cloud-edge collaboration. The fusion terminal is the core device on the "edge" side of the power Internet of Things, and at the same time has the functions of device management, data acquisition and communication, collaborative computing, intelligent analysis and decision-making control, and can flexibly expand functions in a software-defined manner to support marketing, power distribution and emerging services.

[0007] Reactive power compensation is a technology that improves the power factor of the power grid, reduces the losses of transformers and transmission lines, improves the power supply efficiency, and improves the power supply quality in the power supply system.

[0008] The present invention provides a method for estimating the attenuation of capacitor capacity based on a fusion terminal, including the following steps:

[0009] Step 1: Continuously monitor the switching status of capacitors in the capacitor bank. Once a capacitor operates, proceed to Step 2;

[0010] Step 2: Obtain the change in reactive power capacity ΔQ on the grid system side before and after the operation S , when the operating capacitor is a single-phase shunt compensation type, ΔQ S = |Qs1 - Qs2|, where Qs1 is the reactive power of the corresponding phase obtained by AC sampling before the operation, and Qs2 is the reactive power of the corresponding phase obtained by AC sampling after the operation; when the operating capacitor is a three-phase common compensation type, ΔQ S = |Qs1' - Qs2'|, where Qs1' is the total reactive power obtained by AC sampling before the operation, and Qs2' is the total reactive power obtained by AC sampling after the operation;

[0011] Step 3: Obtain the current grid voltage U S , when the operation content of the operating capacitor is to be connected and the operating capacitor is a single-phase shunt compensation type, U S = Us2, where Us2 is the voltage of the corresponding phase obtained by AC sampling after the operation. When the operation content of the operating capacitor is to be connected and the operating capacitor is a three-phase common compensation type, U S = Us2', where Us2' is the AC line voltage Us2' obtained by AC sampling after the operation. When the operation content of the operating capacitor is to be disconnected and the operating capacitor is a single-phase shunt compensation type, U S = Us1, where Us1 is the voltage of the corresponding phase obtained by AC sampling before the operation. When the operation content of the operating capacitor is to be disconnected and the operating capacitor is a three-phase common compensation type, U S = Us1', where Us1' is the AC line voltage Us1' obtained by AC sampling before the operation;

[0012] Step 4: Obtain the current equivalent rated capacity Q of the operating capacitor CN_cale , the formula is , where U CN is the rated voltage of the operating capacitor, and K is the series reactance rate of the capacitor bank;

[0013] Step 5: Obtain the capacity attenuation rate δ of the operating capacitor, the formula is where Q CN is the rated capacity of the operating capacitor.

[0014] Furthermore, it also includes Step 6: When the capacity attenuation rate δ of a certain capacitor is continuously greater than δ set for N set times, send a capacity attenuation alarm signal, where N set is the set number of alarm judgment confirmation times, and δ set is the set capacity attenuation rate alarm threshold.

[0015] Further, it also includes a redundant verification step: verifying the data of the capacitor bank collected by the fusion terminal and the data of the outgoing line side of the distribution transformer collected by the fusion terminal. If the verification fails, an alarm indicating that the sampled data of the capacitor bank is inconsistent with the AC sampled data is issued, and at the same time, all other steps are locked.

[0016] The present invention also provides a capacitor capacity attenuation estimation device based on a fusion terminal, including the following modules:

[0017] Monitoring module: used to continuously monitor the switching position change of capacitors in the capacitor bank, and once a capacitor action occurs, proceed to other modules;

[0018] Grid reactive power change monitoring module: used to obtain the change in reactive power capacity ΔQ on the grid system side before and after the action S , when the action capacitor is a single-phase shunt compensation type, ΔQ S =|Qs1 - Qs2|, where Qs1 is the corresponding phase reactive power of the AC sampling before the action, and Qs2 is the corresponding phase reactive power of the AC sampling after the action; when the action capacitor is a three-phase common compensation type, ΔQ S =|Qs1’ - Qs2’|, where Qs1’ is the total reactive power of the AC sampling before the action, and Qs2’ is the total reactive power of the AC sampling after the action;

[0019] Grid-side voltage acquisition module: used to acquire the current grid-side voltage U S , when the action content of the action capacitor is to be put into operation and the action capacitor is a single-phase shunt compensation type, U S =Us2, where Us2 is the corresponding phase voltage of the AC sampling after the action; when the action content of the action capacitor is to be put into operation and the action capacitor is a three-phase common compensation type, U S =Us2’, where Us2’ is the AC line voltage Us2’ of the AC sampling after the action; when the action content of the action capacitor is to be cut off and the action capacitor is a single-phase shunt compensation type, U S =Us1, where Us1 is the corresponding phase voltage of the AC sampling before the action; when the action content of the action capacitor is to be cut off and the action capacitor is a three-phase common compensation type, U S =Us1’, where Us1’ is the AC line voltage Us1’ of the AC sampling before the action;

[0020] Current equivalent rated capacity acquisition module of the action capacitor: used to acquire the current equivalent rated capacity Q of the action capacitor CN_calc , and the formula is where U CN is the rated voltage of the action capacitor, and K is the series reactance rate of the capacitor bank;

[0021] Capacity attenuation rate acquisition module of the action capacitor: used to acquire the capacity attenuation rate δ of the action capacitor, and the formula is Among them, Q CN is the rated capacity of the reactive capacitor.

[0022] Furthermore, it also includes a capacity attenuation rate alarm module: used to send a capacity attenuation alarm signal when the capacity attenuation rate δ of a certain capacitor is continuously greater than δ set for N set times, where N set is the set number of alarm judgment confirmations, and δ set is the set capacity attenuation rate alarm threshold.

[0023] Furthermore, it also includes a redundant verification module: used to verify the data of the capacitor bank collected by the fusion terminal and the data of the outgoing line side of the distribution transformer collected by the fusion terminal. If the verification fails, an alarm indicating that the sampled data of the capacitor bank is inconsistent with the AC sampled data is sent, and at the same time, all other modules are locked.

[0024] Based on the platform of the intelligent fusion terminal in the substation area, the present invention proposes a method and device for estimating the capacitance capacity attenuation, which can effectively warn of the capacitance capacity attenuation of capacitors, estimate the life of capacitors, and perform lean operation and maintenance of capacitor reactive power compensation. Thereby reducing the probability of capacitor failures, improving the power supply reliability of the substation area, and ensuring the safe and stable operation of the power grid. The present invention can effectively estimate the capacitance of capacitors, warn of the life of capacitors, thereby reducing the probability of capacitor failures, improving the power supply reliability of the substation area, and ensuring the safe and stable operation of the power grid. Description of the Drawings

[0025] Figure 1 is the composition of the reactive power compensation system in the distribution substation area;

[0026] Figure 2 is the composition of the fusion terminal software APP;

[0027] Figure 3 is the calculation and alarm processing flow of capacitor capacity attenuation. Detailed Embodiment

[0028] The present invention will be further described below in conjunction with the drawings and specific embodiments:

[0029] As Figure 1 shown, the reactive power compensation system in the distribution substation area consists of a distribution transformer, a fusion terminal, and multiple capacitors. The fusion terminal and the capacitor bank are connected to the low-voltage outgoing line side of the distribution transformer through power cables. The fusion terminal collects the data of the capacitor bank through an RS485 communication line. The fusion terminal collects the data of the low-voltage outgoing line side of the distribution transformer through a PT and a CT.

[0030] As Figure 2As shown in the figure, the reactive power compensation APP and the AC acquisition APP are implemented by software in the integrated terminal. Among them, the reactive power compensation APP reads data such as the voltage, current, power, frequency, and power factor of the capacitor bank in a loop, as well as information data such as the switching status, fault and alarm signals, rated operating voltage, and rated capacity of each capacitor. The AC acquisition APP cyclically acquires electrical quantity data such as voltage, current, power, frequency, and power factor on the outgoing side of the distribution transformer. All the data collected by the APPs are written into the data center of the integrated terminal.

[0031] The specific process of the present invention is described below.

[0032] The integrated terminal establishes communication with the capacitor bank and cyclically acquires data such as the voltage, current, power, frequency, and power factor of the capacitor bank, as well as information data such as the switching status, fault and alarm signals, rated operating voltage, and rated capacity of each capacitor in the capacitor bank. At the same time, the integrated terminal cyclically acquires electrical quantity data such as voltage, current, power, frequency, and power factor on the outgoing side of the distribution transformer.

[0033] Redundant verification is performed on the acquired electrical quantity data. Since the data such as the voltage, current, power, frequency, and power factor of the capacitor bank collected by the integrated terminal (data collected by communicating with the capacitor), and the electrical quantity data such as the voltage, current, power, frequency, and power factor on the outgoing side of the distribution transformer collected by the integrated terminal (AC sampling data, abbreviated as AC sampling data) should theoretically be equal, the AC sampling data can be used to compare and verify the data collected by communicating with the capacitor. Continuously compare whether the error between the data collected by communicating with the capacitor and the AC sampling data is within the allowable error range to judge the validity of the sampling data, and prevent data calculation inconsistency problems caused by component failures, abnormal wiring, or incorrect parameter configuration. If the error exceeds the range, the subsequent capacity estimation process is locked (disabled), and an alarm indicating that the sampling data of the capacitor bank is inconsistent with the AC sampling data is reported to the master station.

[0034] When there is no alarm indicating that the sampling data of the capacitor bank is inconsistent with the AC sampling data, continuously monitor the switching status of the capacitor switches in the capacitor bank. Whenever a capacitor in the capacitor bank is put into or cut out according to the grid demand, a capacitor capacity estimation is performed once, and the process is as Figure 3 shown.

[0035] Ignore the change in the load of the substation area during the short process of putting into or cutting out the capacitor. At this time, it can be considered that the change in the reactive power capacity ΔQ S on the grid system side is approximately equal to the actual effective reactive power output capacity Q CO of the operating capacitor. That is, ΔQ S =Q CO , where the change in the reactive power capacity ΔQ S on the grid system side is the change in the reactive power of the grid system caused by putting into or cutting out.

[0036] If the series reactance rate of the capacitor bank is K, then the reactive power compensation circuit has Q L = K * Q C , and the actual effective reactive power output capacity Q of the operating capacitor CO is equal to the reactive power capacity Q generated by the operating capacitor C minus the reactive power capacity Q absorbed by the corresponding reactor L . That is, Q CO = Q C - Q L = (1 - K)Q C .

[0037] At the same time, the series voltage relationship of the compensation circuit has U S = U C (1 - K), and it is deduced that where U S is the current voltage on the grid side. The voltages across each capacitor in the capacitor bank are equal and equal to the current voltage U across the operating capacitor C , and KU C is the voltage across the reactor in the capacitor bank.

[0038] The actual effective reactive power output capacity of the operating capacitor where Q CN_calc is the current equivalent rated capacity of the operating capacitor, U C is the current voltage across the operating capacitor, U CN is the rated voltage of the operating capacitor, and U S is the current voltage on the grid side.

[0039] Calculate the current equivalent rated capacity of the operating capacitor

[0040] The calculation method of the final capacity attenuation rate δ of the operating capacitor is Store and record this result in the data center, where Q CN is the rated capacity of the operating capacitor.

[0041] The logic for reporting the early warning of capacitor capacity attenuation. When the calculation results of the capacity attenuation rate δ of a certain capacitor for N consecutive times are all greater than the set capacity attenuation rate alarm threshold δ set , and N is greater than or equal to N set , a capacity attenuation alarm signal is generated and reported to the master station. Where N set is the set number of times for alarm judgment confirmation.

[0042] In the actual calculation process, the shunt capacitors for reactive power compensation in the transformer substation area are of single-phase shunt compensation type and three-phase common compensation type. After the single-phase shunt compensation capacitors act, the corresponding phase voltage and the change in phase reactive power are required for calculation, while for the three-phase common compensation type, the line voltage and the total change in reactive power are required for calculation. Specifically, when the single-phase shunt compensation capacitors act and the action content is to be put into operation, the value of the current grid-side voltage U S is the corresponding phase voltage Us2 of the AC sampling after the action; when the action content is to be cut off, the value of the current grid-side voltage U S is the corresponding phase voltage Us1 of the AC sampling before the action. After the three-phase common compensation capacitors act and the action content is to be put into operation, the value of the current grid-side voltage U S is the AC line voltage Us2’ of the AC sampling after the action; when the action content is to be cut off, the value of the current grid-side voltage U S is the AC line voltage Us1’ of the AC sampling before the action. When the single-phase shunt compensation capacitors act, the change in the reactive power capacity ΔQ S on the grid system side is equal to the absolute value of the difference between the corresponding phase reactive power Qs1 of the AC sampling before the action and the corresponding phase reactive power Qs2 of the AC sampling after the action; after the three-phase common compensation capacitors act, the change in the reactive power capacity ΔQ S on the grid system side is equal to the absolute value of the difference between the total reactive power Qs1’ of the AC sampling before the action and the total reactive power Qs2’ of the AC sampling after the action.

Claims

1. A method for estimating the capacitance attenuation of a capacitor based on a fusion terminal, characterized in that It includes the following steps: Step 1: Continuously monitor the switching position change of capacitors in the capacitor bank. Once a capacitor operates, proceed to Step 2; Step 2: Obtain the change in the reactive power capacity ΔQ on the grid system side before and after the action S , when the action capacitor is single-phase shunt compensation type, ΔQ S = |Qs1 - Qs2|, where Qs1 is the corresponding phase-separated reactive power of the AC sampling before the action, and Qs2 is the corresponding phase-separated reactive power of the AC sampling after the action; when the action capacitor is three-phase common compensation type, ΔQ S = |Qs1' - Qs2'|, where Qs1' is the total reactive power of the AC sampling before the action, and Qs2' is the total reactive power of the AC sampling after the action; Step 3: Obtain the current grid-side voltage U S , when the action content of the action capacitor is to be switched in and the action capacitor is single-phase shunt compensation type, U S = Us2, where Us2 is the corresponding phase voltage of the AC sampling after the action. When the action content of the action capacitor is to be switched in and the action capacitor is three-phase common compensation type, U S = Us2', where Us2' is the AC line voltage Us2' of the AC sampling after the action. When the action content of the action capacitor is to be switched out and the action capacitor is single-phase shunt compensation type, U S = Us1, where Us1 is the corresponding phase voltage of the AC sampling before the action. When the action content of the action capacitor is to be switched out and the action capacitor is three-phase common compensation type, U S = Us1', where Us1' is the AC line voltage Us1' of the AC sampling before the action; Step 4: Obtain the current equivalent rated capacity Q of the switching capacitor CN_calc , and the formula is , where U CN is the rated voltage of the switching capacitor, and K is the series reactance rate of the capacitor bank; Step Five: Obtain the capacity attenuation rate δ of the operating capacitor, with the formula being where Q CN is the rated capacity of the operating capacitor.

2. The method for estimating the capacitance attenuation of a capacitor based on a fusion terminal according to claim 1, wherein It also includes Step Six: When the capacity attenuation rate δ of a certain capacitor is continuously greater than δ set for N set times, a capacity attenuation warning signal is issued, where N set is the set number of times for warning judgment confirmation, and δ set is the set warning threshold for capacity attenuation rate.

3. A method for estimating the capacitance attenuation of a capacitor based on a fusion terminal according to claim 1, characterized in that It also includes a redundant verification step: Verify the data of the capacitor bank collected by the fusion terminal and the data on the outgoing side of the distribution transformer collected by the fusion terminal. If the verification fails, issue an alarm indicating that the sampled data of the capacitor bank is inconsistent with the cross-sampled data, and at the same time lock all other steps.

4. A capacitor capacity attenuation estimation device based on a fusion terminal, characterized in that It includes the following modules: Monitoring module: Used to continuously monitor the switching position change of capacitors in the capacitor bank. Once a capacitor operates, proceed to other modules; Grid reactive power change monitoring module: used to obtain the change in reactive power capacity ΔQ on the grid system side before and after the action S , when the action capacitor is single-phase shunt compensation type, ΔQ S =|Qs1 - Qs2|, where Qs1 is the reactive power of the corresponding split phase in the AC sampling before the action, and Qs2 is the reactive power of the corresponding split phase in the AC sampling after the action; when the action capacitor is three-phase common compensation type, ΔQ S =|Qs1' - Qs2'|, where Qs1' is the total reactive power of the AC sampling before the action, and Qs2' is the total reactive power of the AC sampling after the action; Grid-side voltage acquisition module: used to acquire the current grid-side voltage U S , when the operation content of the operating capacitor is to be switched in and the operating capacitor is single-phase split-phase compensation type, U S = Us2, where Us2 is the corresponding split-phase voltage of the AC sampling after operation. When the operation content of the operating capacitor is to be switched in and the operating capacitor is three-phase common compensation type, U S = Us2', where Us2' is the AC line voltage Us2' of the AC sampling after operation. When the operation content of the operating capacitor is to be switched out and the operating capacitor is single-phase split-phase compensation type, U S = Us1, where Us1 is the corresponding split-phase voltage of the AC sampling before operation. When the operation content of the operating capacitor is to be switched out and the operating capacitor is three-phase common compensation type, U S = Us1', where Us1' is the AC line voltage Us1' of the AC sampling before operation; Operating capacitor current equivalent rated capacity acquisition module: used to acquire the current equivalent rated capacity Q of the operating capacitor CN_calc , and the formula is where U CN is the rated voltage of the operating capacitor, and K is the series reactance rate of the capacitor bank; Action capacitor capacity attenuation rate acquisition module: used to obtain the capacity attenuation rate δ of the action capacitor, and the formula is where Q CN is the rated capacity of the action capacitor.

5. The capacitor capacity attenuation estimation device based on a fusion terminal according to claim 4, characterized in that It further includes a capacity attenuation rate warning module: used for when the capacity attenuation rate δ of a certain capacitor is continuously greater than δ set for N set times, a capacity attenuation warning signal is issued, where N set is the set number of warning judgment confirmations, and δ set is the set capacity attenuation rate warning threshold.

6. The capacitor capacity attenuation estimation device based on a fusion terminal according to claim 4, characterized in that It also includes a redundant verification module: Used to verify the data of the capacitor bank collected by the fusion terminal and the data on the outgoing side of the distribution transformer collected by the fusion terminal. If the verification fails, issue an alarm indicating that the sampled data of the capacitor bank is inconsistent with the cross-sampled data, and at the same time lock all other modules.

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