CN115275922A - Line interphase short-circuit fault property identification method and system by using energy storage capacitor - Google Patents
Line interphase short-circuit fault property identification method and system by using energy storage capacitor Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H1/00—Details of emergency protective circuit arrangements
- H02H1/0007—Details of emergency protective circuit arrangements concerning the detecting means
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/58—Testing of lines, cables or conductors
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/02—Details
- H02H3/06—Details with automatic reconnection
- H02H3/066—Reconnection being a consequence of eliminating the fault which caused disconnection
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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- Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
- Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
- Y04S10/00—Systems supporting electrical power generation, transmission or distribution
- Y04S10/50—Systems or methods supporting the power network operation or management, involving a certain degree of interaction with the load-side end user applications
- Y04S10/52—Outage or fault management, e.g. fault detection or location
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Abstract
A line interphase short circuit fault property identification method and system using an energy storage capacitor are disclosed, wherein a distribution line interphase short circuit fault property device using an energy storage capacitor discharge mode injects a probe signal into a distribution line after receiving protection action information of a line protection device, detects voltage change characteristics of the energy storage capacitor, and defines the voltage fluctuation rate of the end of the energy storage capacitor as lambda = delta udc/udcAfter the initial transient process waveform is filtered, if the voltage fluctuation rate lambda of the energy storage capacitor terminal voltage obtained by calculation is higher than the action threshold lambdaTIf yes, the distribution line is judged to be sentIf the fault is a permanent fault, a locking reclosing signal is sent to the protection device; otherwise, the locking reclosing signal is not sent to the protection device. According to the invention, signals are injected into the power distribution system by using the energy storage capacitor discharge mode, the fault characteristics are stable, the fault property identification criterion of the voltage change characteristics of the energy storage capacitor is combined, the judgment result accuracy is high, high-voltage and current sensors are not required to be configured, the implementation is simple, and the economical efficiency is good.
Description
Technical Field
The invention belongs to the technical field of power distribution network relay protection, and particularly relates to a distribution line interphase short-circuit fault property identification method and system by using an energy storage capacitor discharge mode.
Background
The power grid is used as a core platform for connecting power production and power consumption, and is a key link of sustainable development of power energy. The power distribution network is an important public infrastructure for national economy and social development, and along with the continuous increase of urban power utilization load, people put higher requirements on reliability, stability and safety of the power distribution network. In recent years, with gradual upgrading and transformation of a power distribution network in China, a large number of overhead and cable mixed lines emerge, the fault rate of the cable lines is extremely low, once the lines break down, the lines often have permanent faults, and therefore the success rate of traditional reclosure gradually decreases after the lines break down. According to the traditional reclosing device, a fixed delay time limit is set, a reclosing signal is sent after delay is finished, a breaker is closed again, the mode does not prejudge the fault property and is in blind reclosing, if the fault property is superposed on a permanent fault, secondary impact can be brought to a power distribution system and power equipment, and the safe and stable operation of a power distribution network is greatly influenced. Therefore, the research on the self-adaptive reclosing technology for judging the fault property in advance before reclosing has profound significance.
At present, the adaptive reclosing technology of a power transmission line is researched more, and the research can be divided into single-phase adaptive reclosing technology research and three-phase adaptive reclosing technology research according to different research objects. For a single phase, the main idea is to judge the fault by analyzing the electrical characteristics (such as recovery voltage characteristics and arc characteristics) reflected in the electromagnetic energy release process which is still remained after the fault line trips; for three phases, the fault property is judged by performing mode recognition on the inductance-capacitance parameters and the current characteristics of the system based on the power transmission line with the shunt reactor. However, residual electrical energy of the medium-low voltage distribution line after three-phase tripping due to phase-to-phase faults can be quickly attenuated, and the conventional adaptive reclosing research method of the transmission line is not applicable any more.
The existing research on the self-adaptive reclosing of the power distribution network is relatively less, and the methods in the existing documents can be divided into a passive method and an active method. In the passive method, typically, the following are included: (1) an additional circuit is adopted to directly add a system upstream power supply to a fault distribution circuit in a short time, so that electric quantity is generated, the characteristics of the electric quantity are analyzed to judge the fault property, and the method can impact an upstream system and a power-off line to a certain extent; (2) a traveling wave is generated by high-frequency oscillation discharge of the fault line based on the high-voltage capacitor on the fault line, and the characteristics of the traveling wave are identified to determine the nature of the fault. The above passive methods all require measuring and analyzing the short-time electrical quantity of the line itself to identify the fault property, and are limited by the structure of the distribution line itself and the line parameters, and the reliability of the obtained information needs to be discussed deeply. The active method is to inject a detection signal generated by a power electronic device into a fault line, and judge the fault property by analyzing the response characteristic of the line, typically: the low-voltage side of the distribution line is connected with an inverter power supply controlled by a thyristor, high-voltage pulse excitation is applied to the fault line, and fault identification is carried out by analyzing the characteristic that the harmonic impedance of the fault line changes along with the frequency. However, the response signal generated by applying the pulse excitation method has a large frequency randomness, and the characteristic frequency band is not fixed, which makes detection and analysis difficult, and when the frequency of the response signal is high, the line harmonic impedance characteristics deviate from the expected model, which may cause an error in the fault property identification result. In addition, the harmonic impedance characteristic identification requires that three-phase voltage and current signals are measured at an injection point, the requirement on the configuration of a transformer is high, and the application in an actual field is limited.
Disclosure of Invention
The invention aims to provide a distribution line interphase short circuit fault property identification method and a distribution line interphase short circuit fault property identification system in an energy storage capacitor discharge mode, which are used for solving the problem of difficult distribution line fault property identification.
In order to achieve the above purpose, the present invention specifically adopts the following technical scheme.
A line interphase short circuit fault property identification method using capacitor energy storage is characterized by comprising the following steps:
the power-taking TV is arranged on the upstream side of the line switch and is connected to the downstream side of the line switch sequentially through the power-taking loop switch, the rectifying circuit, the energy storage capacitor, the inverter circuit, the discharging loop switch and the step-up transformer;
when the circuit normally runs, the circuit switch CB is in a closed state, the discharge loop switch is in an open state, the voltage of the energy storage capacitor is detected in real time, and when the voltage of the energy storage capacitor is lower than a set value, the electricity taking loop switch is controlled to be closed to charge the energy storage capacitor;
when a line has a fault, the protection device acts to trip off a line switch CB, after the time delay is set, a discharge loop switch is closed, and the energy storage capacitor injects three-phase symmetrical alternating current signals to a line at the downstream side of the switch through an inverter circuit;
collecting alternating current pulse quantity delta u of energy storage capacitor terminal voltage during three-phase symmetrical alternating current signal injection period of linedcAnd the mean value udcAnd calculating the voltage fluctuation rate of the end of the energy storage capacitor: λ = Δ udc/udc；
If the calculated voltage fluctuation rate lambda of the energy storage capacitor terminal is higher than the action threshold lambdaTIf the fault is a permanent fault, a locking reclosing signal is sent to the protection device; otherwise, the locking reclosing signal is not sent to the protection device.
The present invention further includes the following preferred embodiments.
The specification of the energy storage capacitor is selected to be 0.12F/400V.
The control reference value of the effective value of the three-phase voltage output by the inverter is 100V, and the rated capacity of the inverter is 10kW.
The voltage set value of the energy storage capacitor is 0.98 times of the rated voltage value, when the voltage of the energy storage capacitor is lower than the set value, the switch of the electricity taking loop is controlled to be closed, the energy storage capacitor is charged through the rectifying circuit after electricity is taken from the secondary side of the electricity taking TV, and the switch of the electricity taking loop is disconnected until the voltage of the energy storage capacitor reaches the rated value.
The time delay setting time after the circuit switch CB is tripped is 0.5 s-1 s.
The frequency of the three-phase symmetrical alternating current signal injected into the line, namely the injection characteristic signal, is controlled between N and N +1 subharmonics through a reverse circuit.
Frequency f of the injected characteristic signalHThe selection was 230Hz.
Maximum capacity S of the injection characteristic signalNComprises the following steps:
SN＝100V*50A*1.732＝8.66kW。
the injection characteristic signal time is maintained for 180-220ms.
When calculating the ac pulsating quantity and the average value of the voltage across the energy storage capacitor, it is preferable to filter out a transient process waveform generated during the injection of the three-phase symmetric ac signal.
The motion threshold λTThe setting value is 0.45.
The application also discloses a line interphase short circuit fault property identification system based on the identification method, which comprises an instantaneous and permanent fault identification device, a detection unit and a control unit; the method is characterized in that:
the instantaneous and permanent fault recognition device comprises a power-taking TV, a rectification circuit, an energy storage capacitor, an inversion circuit, a step-up transformer, a power-taking loop switch and a discharge loop switch, wherein the power-taking TV is arranged on the upstream side of the line switch, the secondary side of the power-taking TV is connected to the input end of the rectification circuit through the power-taking loop switch, the output end of the rectification circuit is connected with the input end of the inversion circuit after passing through the energy storage capacitor, the output end of the inversion circuit is connected to the step-up transformation input end through the discharge loop switch, and the output end of the step-up transformer is connected to a line on the downstream side of the line switch;
the detection unit is used for detecting the voltage at two ends of the energy storage capacitor;
the control unit comprises a power-taking loop switch control module, a discharging loop switch control module, an inverter drive control module, an energy storage capacitor terminal voltage fluctuation rate calculation module and a line fault property judgment module, and when the energy storage capacitor needs to be charged, the power-taking loop switch control module controls a power-taking loop switch to be closed to charge the energy storage capacitor; when the line switch has inter-phase fault tripping and delays for a set time, the inverter driving control module is used for modulating the inverter loop to generate a three-phase symmetrical alternating current signal; the discharge loop switch is controlled to be closed by the discharge loop switch control module, and three-phase symmetrical alternating current signals generated by the inverter circuit are injected into a circuit after passing through the step-up transformer; the energy storage capacitor end voltage fluctuation rate calculation module receives the voltages at the two ends of the energy storage capacitor detected by the detection unit and calculates the energy storage capacitor end voltage fluctuation rate during the signal injection period; and the line fault property judging module is used for judging whether the line inter-phase fault is a permanent fault or an instantaneous fault according to the comparison of the voltage fluctuation rate of the energy storage capacitor and a set action threshold value.
Compared with the prior art, the invention has the following beneficial technical effects:
according to the invention, signals are injected into the power distribution system by using the energy storage capacitor discharge mode, the fault characteristics are stable, the fault property identification criterion of the voltage change characteristics of the energy storage capacitor is combined, the judgment result accuracy is high, high-voltage and current sensors are not required to be configured, the implementation is simple, and the economical efficiency is good.
Drawings
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and together with the description serve to explain the invention and not to limit the invention.
FIG. 1 is a schematic diagram of the structure of the instantaneous and permanent fault recognition device using capacitive energy storage discharge according to the present invention;
FIG. 2 is a schematic flow chart of a method for identifying the inter-phase short circuit fault property of the capacitive energy storage circuit according to the present invention;
FIG. 3 shows the short-circuit fault property identification method applied to a 10kV distribution network simulation model; fig. 4 (a) -4 (c) are graphs of simulation results in a three-phase balanced load transient fault state, where 4 (a) is a graph of positive-negative sequence current output by the inverter circuit, 4 (b) is a graph of instantaneous positive-negative sequence power output by the inverter circuit, and 4 (c) is a graph of storage capacitor voltage;
fig. 5 (a) -5 (c) are simulation results of transient fault states of three-phase unbalanced loads, where 5 (a) is a positive-negative sequence current diagram output by the inverter circuit, 5 (b) is a transient positive-negative sequence power diagram output by the inverter circuit, and 5 (c) is a voltage diagram of the storage capacitor;
fig. 6 (a) -6 (c) are simulation results in a permanent fault state, where 6 (a) is a positive-negative sequence current diagram output by the inverter circuit, 6 (b) is an instantaneous positive-negative sequence power diagram output by the inverter circuit, and 6 (c) is a storage capacitor voltage diagram.
Detailed Description
In order to make the technical solutions of the present invention better understood, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, shall fall within the protection scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and claims of the present invention and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are capable of operation in other sequences than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
As shown in fig. 1, the distribution line interphase short circuit fault property identification device using the energy storage capacitor discharge mode according to the present invention includes a power-taking TV, a rectification circuit, an energy storage capacitor, an inverter circuit, a step-up transformer, a power-taking loop switch and a discharge loop switch, wherein the power-taking TV is disposed on an upstream side of the line switch, a secondary side of the power-taking TV is connected to an input end of the rectification circuit through the power-taking loop switch, an output end of the rectification circuit is connected to an input end of the inverter circuit after passing through the energy storage capacitor, an output end of the inverter circuit is connected to a step-up voltage transformation input end through the discharge loop switch, and an output end of the step-up transformer is connected to a line on a downstream side of the line switch. When the circuit normally runs, the circuit switch CB is in a closed state, if the capacitor voltage is detected to be lower than a set value by utilizing the instantaneous and permanent fault recognition device for capacitor energy storage discharge, the circuit switch S1 is controlled to be closed, the rectifying circuit obtains electricity from the secondary side (220V) of the electricity obtaining TV, charges the energy storage capacitor C after rectification, and disconnects the electricity obtaining circuit switch S1 after the charging is finished. When the distribution line breaks down, the protection device acts to trip off the circuit switch CB, a certain time is delayed, the discharging circuit switch S2 is closed, the inverter circuit is put into operation, and the energy storage capacitor discharges to the distribution line.
As shown in fig. 2, the method for identifying the interphase short-circuit fault property by using the capacitive energy storage line specifically includes the following steps:
an electricity-taking TV is arranged on the upstream side of the line switch and is connected to the downstream side of the line switch sequentially through an electricity-taking loop switch, a rectifying circuit, an energy storage capacitor, an inverter circuit, a discharging loop switch and a step-up transformer.
The typical storage capacitor has a specification of 0.12F/400V.
The inverter circuit, namely the inverter, selects a constant-voltage current-limiting control strategy, sets an effective value control reference value of three-phase voltage output by the inverter to be 100V, and simultaneously, in order to prevent the phenomenon that the inverter output current is overlarge when a near-end short-circuit fault occurs at an access point of the device, adds a current-limiting strategy in the inverter control strategy, limits the maximum effective value of the inverter output current not to exceed 50A, and then can determine the maximum capacity of an injection signal as follows:
SN＝100V*50A*1.732＝8.66kW
considering a certain margin, the rated capacity of the inverter can be 10kW.
When the circuit normally runs, the circuit switch CB is in a closed state, the discharge loop switch is in an open state, the voltage of the energy storage capacitor is detected in real time, and when the voltage of the energy storage capacitor is lower than a set value, the electricity taking loop switch is controlled to be closed to charge the energy storage capacitor;
when a line has a fault, the protection device acts to trip off a line switch CB, after the time delay is set, a discharge loop switch is closed, and the energy storage capacitor injects three-phase symmetrical alternating current signals to a line at the downstream side of the switch through an inverter circuit; the direct current electric energy that energy storage capacitor C stored is converted into three-phase symmetry alternating current signal by the inverter and pours into the distribution lines into, need solve the frequency of pouring into the signal at first and select the problem, mainly considers the factor in two aspects: (1) To avoid confusion with conducted or coupled interference signals inherent in the power distribution system, the frequency of the injected signature signal is selected to be between the N and N +1 harmonics. (2) If the frequency of the injected characteristic signal is too high, on one hand, the capacitive reactance of the distribution line to the ground is significantly reduced, which may adversely affect the fault property identification, and on the other hand, the rate requirement for signal acquisition and processing is increased. Taking into account the above two aspects, the frequency f of the injection characteristic signalHThe selection was 230Hz.
In the preferred embodiment of the invention, after receiving the line protection action information sent by the protection device, delaying for a certain time (usually 0.5S-1S), closing S2, controlling the inverter loop to work, and injecting the frequency f into the distribution lineHThe injection signal process lasts 200ms. Collecting alternating current pulse quantity delta u of energy storage capacitor terminal voltage during three-phase symmetrical alternating current signal injection period of linedcAnd the mean value udcAnd calculating the voltage fluctuation rate of the end terminal of the energy storage capacitor: λ = Δ udc/udc(ii) a When the alternating current pulse quantity and the average value of the voltage of the energy storage capacitor are calculated, the transient process waveform generated during the injection of the three-phase symmetrical alternating current signal is preferably filtered.
If the calculated voltage fluctuation rate lambda of the energy storage capacitor terminal is higher than the action threshold lambdaTIf the distribution line is judged to have a permanent fault, a locking reclosing signal is sent to the protection device;otherwise, the locking reclosing signal is not sent to the protection device. Wherein the action threshold λTThe setting value is 0.45.
The application also discloses a line interphase short circuit fault property identification system based on the identification method, which comprises an instantaneous and permanent fault identification device, a detection unit and a control unit.
As described above, the instantaneous and permanent fault recognition device includes the electricity-taking TV, the rectification circuit, the energy storage capacitor, the inverter circuit, the step-up transformer, the electricity-taking loop switch and the discharge loop switch, the electricity-taking TV is disposed on the upstream side of the line switch, the secondary side of the electricity-taking TV is connected to the input end of the rectification circuit through the electricity-taking loop switch, the output end of the rectification circuit is connected to the input end of the inverter circuit through the energy storage capacitor, the output end of the inverter circuit is connected to the step-up voltage transformation input end through the discharge loop switch, and the output end of the step-up transformer is connected to the line on the downstream side of the line switch;
the detection unit is used for detecting the voltage at two ends of the energy storage capacitor;
the control unit comprises a power taking loop switch control module, a discharging loop switch control module, an inverter driving control module, an energy storage capacitor terminal voltage fluctuation rate calculation module and a line fault property judgment module, and when the energy storage capacitor needs to be charged, the power taking loop switch control module controls the power taking loop switch to be closed to charge the energy storage capacitor; when the line switch has interphase fault tripping and delays for a set time, the inverter driving control module is used for modulating an inverter loop to generate a three-phase symmetrical alternating current signal; the discharge loop switch is controlled to be closed by the discharge loop switch control module, and three-phase symmetrical alternating current signals generated by the inverter circuit are injected into a circuit after passing through the step-up transformer; the energy storage capacitor end voltage fluctuation rate calculation module receives the voltages at the two ends of the energy storage capacitor detected by the detection unit and calculates the energy storage capacitor end voltage fluctuation rate during the signal injection period; and the line fault property judging module is used for judging whether the line phase-to-phase fault is a permanent fault or a transient fault according to the comparison of the voltage fluctuation rate of the energy storage capacitor end and a set action threshold value. Fig. 3 shows a 10kV distribution network simulation model, and system parameters of the distribution network are shown in table 1.
TABLE 1 Power distribution grid System parameters
In simulation, a distribution line has a fault at the time of 0.01s, a line protection action cuts off the fault line, and the interphase short circuit fault property of the distribution line in an energy storage capacitor discharge mode is identified to enter an injection signal mode at the time of 0.06 s.
Example 1 transient fault: three-phase balanced load
The method comprises the steps of distributing 80% of load of a power line, enabling the total length of an L1 overhead line to be 10km, enabling the tail end of the line to have an instantaneous fault, putting a fault property recognition device into the line, and detecting the positive and negative sequence current, the instantaneous positive and negative sequence power and the change characteristics of direct current bus capacitance voltage output by an inverter within the characteristic signal injection duration, wherein after the signal is stabilized, the positive sequence current output by the inverter is about 30A, the negative sequence current is close to 0, the instantaneous positive sequence power output by the inverter is about 100W, the instantaneous negative sequence power is close to 0, the voltage waveform fluctuation quantity of the direct current bus is small, and the voltage waveform fluctuation quantity of the direct current bus is close to 0 after the signal is stabilized, as shown in figures 4 (a) -4 (c).
Example 2 transient fault: three-phase unbalanced load
According to the national standard of unbalance degree, the A-phase load impedance and the B-phase load impedance are kept unchanged, the C-phase load impedance is changed into 4.033 omega/6.217 mH, and the tail end of the L1 overhead line is set to have instantaneous fault. The method comprises the steps of detecting the positive and negative sequence current, instantaneous positive and negative sequence power and the change characteristics of the direct current bus capacitor voltage output by an inverter, wherein after signals are stabilized, the positive sequence current output by the inverter is about 20A, the negative sequence current output by the inverter is about 10A, the instantaneous positive sequence power output by the inverter is about 400W, the instantaneous negative sequence power periodically fluctuates between-1500W and +1500W according to a sine wave rule, the direct current bus voltage waveform has certain pulsation, and the voltage fluctuation rate of the end terminal of an energy storage capacitor is about 0.35 percent, as shown in figures 5 (a) -5 (c).
EXAMPLE 3 permanent phase-to-phase failure
The method comprises the steps of setting the tail end of an L1 km overhead line to have a permanent phase-to-phase fault, and detecting the change characteristics of positive and negative sequence current, instantaneous positive and negative sequence power and direct current bus capacitor voltage output by an inverter within the injection duration of a characteristic signal, wherein after the signal is stabilized, the positive sequence current output by the inverter is about 40A, the negative sequence current is about 10A, the instantaneous positive sequence power output by the inverter is within 100W, the instantaneous negative sequence power periodically fluctuates between-2000W and +2000W according to a sine wave rule, the voltage waveform of the direct current bus has a certain fluctuation quantity, and the voltage fluctuation rate of the end of an energy storage capacitor is about 0.55%, as shown in figures 6 (a) -6 (c).
According to the comprehensive comparison of the three situations, under the condition that the permanent phase-to-phase fault occurs at the tail end of the line L1, the fluctuation rate of the direct-current bus capacitor voltage is 0.55%, and under the condition of the transient fault, even if the three-phase load unbalance degree is severe, the fluctuation rate of the direct-current voltage is 0.35%, so that 0.45% of the threshold value of the fluctuation rate of the end voltage of the energy storage capacitor is given as the fault property criterion.
Finally, it should be noted that: although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.
Claims (10)
1. A line interphase short circuit fault property identification method using capacitor energy storage is characterized by comprising the following steps:
the power-taking TV is arranged on the upstream side of the line switch and is connected to the downstream side of the line switch sequentially through a power-taking loop switch, a rectifying circuit, an energy storage capacitor, an inverter circuit, a discharging loop switch and a step-up transformer;
when the circuit normally runs, the circuit switch CB is in a closed state, the discharge loop switch is in an open state, the voltage of the energy storage capacitor is detected in real time, and when the voltage of the energy storage capacitor is lower than a set value, the electricity taking loop switch is controlled to be closed to charge the energy storage capacitor;
when a line has a fault, the protection device acts to trip off a line switch CB, after the time delay is set, a discharge loop switch is closed, and the energy storage capacitor injects three-phase symmetrical alternating current signals to a line at the downstream side of the switch through an inverter circuit;
collecting alternating current pulse quantity delta u of energy storage capacitor terminal voltage during three-phase symmetrical alternating current signal injection period of linedcAnd the mean value udcAnd calculating the voltage fluctuation rate of the end of the energy storage capacitor: λ = Δ udc/udc；
If the calculated voltage fluctuation rate lambda of the energy storage capacitor terminal is higher than the action threshold lambdaTIf the fault is a permanent fault, a locking reclosing signal is sent to the protection device; otherwise, the locking reclosing signal is not sent to the protection device.
2. The line interphase short-circuit fault property identification method according to claim 1, characterized in that:
the specification of the energy storage capacitor is selected to be 0.12F/400V.
3. The line interphase short-circuit fault property identification method according to claim 1, characterized in that:
the control reference value of the effective value of the three-phase voltage output by the inverter is 100V, and the rated capacity of the inverter is 10kW.
4. The line interphase short-circuit fault property identification method according to claim 1 or 2, characterized in that:
the set value of the energy storage capacitor is 0.98 times of the rated voltage value, when the voltage of the energy storage capacitor is lower than the set value, the switch of the electricity taking loop is controlled to be closed, the energy storage capacitor is charged through the rectifying circuit after electricity is taken from the secondary side of the electricity taking TV, and the switch of the electricity taking loop is disconnected until the voltage of the energy storage capacitor reaches the rated value.
5. The line inter-phase short-circuit fault property identification method according to claim 1, characterized in that:
the time delay setting time after the circuit switch CB is tripped is 0.5 s-1 s.
6. The line inter-phase short-circuit fault property identification method according to claim 1 or 5, characterized in that:
the frequency of the three-phase symmetrical alternating current signal injected into the line, namely the injection characteristic signal, is controlled between N and N +1 subharmonics through a reverse circuit.
7. The line inter-phase short-circuit fault property identification method according to claim 6, characterized in that:
frequency f of the injected characteristic signalHThe selection was 230Hz.
8. The line interphase short-circuit fault property identification method according to claim 6, characterized in that:
maximum capacity S of injected characteristic signalNComprises the following steps:
SN＝100V*50A*1.732＝8.66kW。
the injection characteristic signal time is maintained for 180-220ms.
9. The line interphase short-circuit fault property identification method according to claim 1 or 8, characterized in that:
when calculating the ac pulsating quantity and the average value of the voltage across the energy storage capacitor, it is preferable to filter out a transient process waveform generated during the injection of the three-phase symmetric ac signal.
The motion threshold λTThe setting value is 0.45.
10. A line interphase short-circuit fault property identification system based on the identification method of any one of claims 1 to 9, comprising an instantaneous and permanent fault identification device, a detection unit and a control unit; the method is characterized in that:
the instantaneous and permanent fault recognition device comprises a power-taking TV, a rectification circuit, an energy storage capacitor, an inverter circuit, a step-up transformer, a power-taking loop switch and a discharge loop switch, wherein the power-taking TV is arranged on the upstream side of the line switch, the secondary side of the power-taking TV is connected to the input end of the rectification circuit through the power-taking loop switch, the output end of the rectification circuit is connected with the input end of the inverter circuit after passing through the energy storage capacitor, the output end of the inverter circuit is connected to the step-up voltage transformation input end through the discharge loop switch, and the output end of the step-up transformer is connected to a line on the downstream side of the line switch;
the detection unit is used for detecting the voltage at two ends of the energy storage capacitor;
the control unit comprises a power taking loop switch control module, a discharging loop switch control module, an inverter driving control module, an energy storage capacitor terminal voltage fluctuation rate calculation module and a line fault property judgment module, and when the energy storage capacitor needs to be charged, the power taking loop switch control module controls the power taking loop switch to be closed to charge the energy storage capacitor; when the line switch has inter-phase fault tripping and delays for a set time, the inverter driving control module is used for modulating the inverter loop to generate a three-phase symmetrical alternating current signal; the discharge loop switch control module controls the discharge loop switch to be closed, and three-phase symmetrical alternating current signals generated by the inverter circuit are injected into a circuit after passing through the step-up transformer; the energy storage capacitor end voltage fluctuation rate calculation module receives the voltages at the two ends of the energy storage capacitor detected by the detection unit and calculates the energy storage capacitor end voltage fluctuation rate during the signal injection period; and the line fault property judging module is used for judging whether the line phase-to-phase fault is a permanent fault or a transient fault according to the comparison of the voltage fluctuation rate of the energy storage capacitor end and a set action threshold value.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115549439A (en) * | 2022-11-29 | 2022-12-30 | 东南大学 | MMC (Modular multilevel converter) switching loss optimization method and equipment under low-power operation |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115549439A (en) * | 2022-11-29 | 2022-12-30 | 东南大学 | MMC (Modular multilevel converter) switching loss optimization method and equipment under low-power operation |
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Application publication date: 20221101 |