CN110611304A - An online early warning method and system for low voltage risk in distribution network - Google Patents

Abstract

The invention provides an on-line early warning method and system for low-voltage risk of a distribution network, including: calculating the load moment of a preset line in the distribution network according to the real-time monitoring data and load prediction data of the distribution network; , calculate the voltage of the preset load point on the preset line, and judge whether there is a risk of low voltage overrun in the distribution network in the preset future time period according to the preset low voltage overrun warning judgment rule . The method and system provide a decision basis for rationally improving the power supply quality of the distribution network, can accurately warn the low-voltage risk of the distribution network, and have the advantages of good practicability, simple calculation and easy operation.

Description

An online early warning method and system for low voltage risk in distribution network

technical field

The invention belongs to the technical field of distribution network risk analysis and control, and in particular relates to an on-line early warning method and system for distribution network low voltage risk.

Background technique

In the distribution network, the line is too long, the load is heavy, the reactive power compensation is insufficient, the load distribution is unreasonable, the three-phase distribution transformer is unbalanced, the conductor cross section is too small, the distribution transformer is seriously deviated from the load center, and the power supply radius of the distribution transformer is too large, etc. It will cause the voltage to be low, the current to increase, and the line may be overloaded.

In the actual operation of the distribution network, when the distribution line load increases or is overloaded, the line voltage drop gradually increases, which exceeds the normal allowable range. If the line reactive power compensation is insufficient, the line load continues to increase, causing the voltage drop to continue for a long time. increase, there is a risk of low voltage at the end of the line. The occurrence of low voltage in the distribution network will greatly affect daily production and life. The occurrence of low line voltage will lead to the following consequences: (1) increase line loss and reduce efficiency; (2) electric appliances are difficult to start, and the temperature rise is too high; (3) Reduce the brightness of the incandescent lamp, so that the fluorescent lamp cannot be started; (4) It affects the image quality of the screen electrical appliances; (5) It affects the normal heating of the electric heating appliances.

At present, measures such as distribution transformer capacity increase, reactive power compensation, and heavy-load line shunt are usually adopted to control the low-voltage phenomenon of the distribution network.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned deficiencies of the prior art, the present invention proposes an online pre-warning method and system for low-voltage risk of a distribution network, which can pre-warn the amplitude of low-voltage drop in the distribution network.

The solutions used to achieve the above goals are:

An online early warning method for low voltage risk of distribution network, the improvement lies in:

According to the real-time monitoring data and load prediction data of the distribution network, the load moment of the preset line in the distribution network is calculated;

According to the load moment calculation result, the preset voltage of the preset load point on the line is calculated, and it is determined according to the preset low voltage over-limit early warning judgment rule that within a preset future time period, the distribution Whether there is a risk of low voltage exceeding the limit in the power grid.

The first preferred technical solution provided by the present invention is improved in that, according to the real-time monitoring data and load prediction data of the distribution network, the load moment of the preset line in the distribution network is calculated as follows:

M=∑P×L (1)

where M is the load moment of a line on a time node, P represents the obtained load prediction data of the preset load point at the time node on the line, and L represents the data obtained from the real-time monitoring data of the distribution network. The electrical distance from the load point on the line to the power supply, Σ represents the summation of the preset load points at the time node on the line.

The second preferred technical solution provided by the present invention is improved in that, according to the calculation result of the load moment, the preset voltage of the load point on the line is calculated, and the preset low voltage is calculated according to the preset low voltage. The over-limit warning judgment rule determines whether there is a low-voltage over-limit risk in the distribution network within a preset future time period, including:

According to the order of load torque from large to small, the preset voltage value of the line at the preset load point at the time node in the preset future time period is calculated in turn. When the voltage of the load point is lower than the preset voltage The limit value is determined, and it is judged that the line has a predicted low voltage exceeding the limit at the time node corresponding to the load moment, until the time node corresponding to the load moment does not have a predicted low voltage exceeding the limit;

According to the historical voltage data of the preset load point of the distribution network at the corresponding time of each time node in the preset future time period, it is determined whether the preset load point corresponds to the time point of each time node in the preset future time period. There is a historical low voltage limit;

When there is no predicted low voltage out-of-limit and historical low-voltage out-of-limit at the time node, the warning result is given as normal; otherwise, the warning result is given as a risk of low-voltage out-of-limit risk.

The third preferred technical solution provided by the present invention is improved in that the preset lines are sequentially calculated according to the load moment in descending order and are preset on time nodes within a preset future time period. The voltage value of the load point, when the voltage of a load point is lower than the preset lower voltage limit, it is determined that the line has a predicted low voltage exceeding the limit at the time node corresponding to the load torque, until the preset low voltage does not exist in the load torque Exceeding limits, including:

Select each time node of the preset line in the preset future time period in order according to the load moment from large to small, perform power flow calculation, obtain the voltage value of the preset load point, and make the following judgments:

If the voltage value of any load point is lower than the preset voltage lower limit value, it is determined that the line has a predicted low voltage exceeding the limit at the time node corresponding to the load moment;

Otherwise, the load moment is set as the standard load moment of the line, it is judged that there is no low voltage over-limit at the time node when the line load moment is less than the standard load moment, and the power flow calculation is stopped.

The fourth preferred technical solution provided by the present invention is improved in that the preset load point of the power distribution network is combined with the historical voltage data corresponding to each time node in the preset future time period to determine the preset load point. Whether there is a historical low voltage violation at each time node corresponding to the load point in the preset future time period, including:

Obtain the historical voltage data of each load point at the same moment of the day corresponding to each time node within the preset time period, and determine whether the historical voltage data is lower than the lower voltage limit value: if so, determine that the time node has historical low voltage higher Otherwise, there is no historical low voltage violation limit at the time node.

The fifth preferred technical solution provided by the present invention is improved in that, after the warning result is given, it also includes:

If the warning result is normal, the warning process ends, waiting for the next warning to start;

Otherwise, the warning information will be issued and the warning results will be tracked;

The early warning information includes time nodes, lines, load nodes and voltage amplitudes at which it is predicted that the low voltage exceeds the limit.

The sixth preferred technical solution provided by the present invention is improved in that the tracking and early warning results include:

When the topology of the distribution network changes, the low-voltage risk warning is re-executed according to the latest load forecast data. If the warning result is normal, the warning information is canceled, the warning process ends, and the next warning is activated; otherwise, a warning is issued. information, and track the warning results;

When the topology of the distribution network does not change, if the load changes, start the pre-warning process according to the latest load forecast, if the pre-warning result is normal, cancel the pre-warning information, end the pre-warning process, and wait for the next start; otherwise, The warning information is issued and the warning results are tracked;

When the topology and load of the distribution network have not changed, wait until the time when the low voltage exceeds the limit in the early warning. If the low voltage exceeds the limit, the warning information is canceled; otherwise, the low voltage exceeds the limit. Limit time and voltage amplitude, cancel the warning information.

An on-line early warning system for low voltage risk of a distribution network, which is improved in that it includes: a load moment calculation module and a risk prediction module;

The load torque calculation module is used to calculate the load torque of the preset line in the distribution network according to the real-time monitoring data and load prediction data of the distribution network;

The risk prediction module is used to calculate the voltage of the preset load point on the line according to the calculation result of the load moment, and to judge in the future time period according to the preset low voltage over-limit warning judgment rule. , whether there is a risk of low voltage over-limiting in the distribution network.

The seventh preferred technical solution provided by the present invention is improved in that the load moment calculation module includes: a data acquisition subunit and a load moment calculation subunit;

The data acquisition sub-unit is used to acquire the load prediction data of each time node in a preset time period, and acquire the electrical distance from the preset load point in the distribution network to the power supply from the real-time monitoring data of the distribution network;

The load moment calculation subunit is used to calculate the load moment of the preset lines on each time node in the distribution network as follows:

M=∑P×L (1)

where M is the load moment of a line on a time node, P represents the load prediction data of the preset load point at the time node on the line, and L represents the load moment on the line obtained from the real-time monitoring data of the distribution network. The electrical distance from the load point to the power source, Σ represents the summation of the preset load points at the time node on the line.

The eighth preferred technical solution provided by the present invention is improved in that the risk prediction module includes: a future judgment subunit, a historical judgment subunit and an early warning subunit;

The future judging subunit is used to sequentially calculate the voltage value of the preset load point at the time node of the line in the preset future time period according to the load moment in descending order, when there is a load point. When the voltage is lower than the preset voltage lower limit value, it is determined that the line has a predicted low voltage exceeding the limit at the time node corresponding to the load moment, until the time node corresponding to the load moment does not have a predicted low voltage exceeding the limit;

The historical judging subunit is used for judging that the preset load point is in the preset future time according to the historical voltage data corresponding to each time node in the preset future time period of the preset load point of the power distribution network Whether there is a historical low voltage violation at the corresponding time of each time node in the segment;

The pre-warning subunit is configured to give a warning result as normal when there is no predicted low-voltage out-of-limit and historical low-voltage out-of-limit at the time node; otherwise, the pre-warning result is given as a risk of low-voltage out-of-limit risk.

The ninth preferred technical solution provided by the present invention is improved in that it also includes a tracking module;

The tracking module is used to end the early warning process if the warning result is normal, and wait for the next warning to start;

Otherwise, the warning information will be issued and the warning results will be tracked;

The early warning information includes time nodes, lines, load nodes and voltage amplitudes at which it is predicted that the low voltage exceeds the limit.

The tenth preferred technical solution provided by the present invention is improved in that the tracking module includes: a topology change subunit, a load change subunit, and an invariant subunit;

The topology change subunit is used to re-run low-voltage risk warning according to the latest load forecast data when the topology of the distribution network changes, if the warning result is normal, cancel the warning information and wait for the next warning to start; otherwise , the warning information is issued and the warning results are tracked;

The load change sub-unit is used to start an early warning process according to the latest load forecast if the load changes when the topology of the distribution network does not change, and if the early warning result is normal, cancel the early warning information and end the early warning process , wait for the next startup; otherwise, issue warning information and track the warning results;

The invariant sub-unit is used to wait until the time when there is a low-voltage over-limit in the operation when the topology and load of the distribution network have not changed, and cancel the pre-warning if no low-voltage over-limit occurs. information; otherwise, the time and voltage amplitude when the low voltage exceeds the limit is obtained, and the warning information is cancelled.

Compared with the closest prior art, the present invention has the following beneficial effects:

The present invention proposes an on-line early warning method and system for low-voltage risk of distribution network, which aims to calculate the load moment according to the real-time monitoring data and load prediction data of the power grid, and calculate the preset node voltage on the preset line according to the calculation result of the load torque. The indicators are calculated and evaluated, and according to the preset low-voltage over-limit early warning judgment rules, it is judged whether there is a risk of over-voltage in the distribution network in the preset future time period, so as to provide a decision basis for reasonably improving the power supply quality of the distribution network. It can accurately warn the low voltage risk of distribution network, and has the advantages of good practicability, simple calculation and easy operation.

Description of drawings

FIG. 1 is a schematic flowchart of an online early warning method for low voltage risk of a distribution network provided by the present invention.

Detailed ways

The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

A schematic flowchart of a low-voltage risk monitoring and early-warning method for a distribution network provided by the present invention is shown in FIG. 1 , including:

According to the real-time monitoring data and load forecast data of the distribution network, the load moment of the preset lines in the distribution network is calculated;

According to the load moment calculation result, the voltage of the preset load point on the preset line is calculated, and according to the preset low voltage over-limit early warning judgment rule, it is judged whether the distribution network exists in the preset future time period. Risk of low voltage overrun.

Specifically, the specific steps of the online early warning method for low voltage risk of distribution network are as follows:

Step 1: Obtain the load prediction data of each time node in the future preset time period, and calculate the load moment M of the preset line at the time node as follows:

M=∑P×L (1)

Among them, the power of the load point is P, the electrical distance from the load point to the power point is L, and ∑ represents the summation of the preset load points at the same time node on the same line.

Step 2: Sort the load moments in the predicted time period of the line from large to small.

Step 3: Select the time node corresponding to the maximum load moment, perform power flow calculation, and save the voltage value of each load point.

Step 4: Judging whether the voltage of each load point is lower than the preset lower voltage limit at the time node corresponding to the maximum load moment.

Step 5: If the voltage of any load point is lower than the lower voltage limit, it is considered that the line has a predicted low voltage over-limit at the time node t' corresponding to the maximum load moment, and the corresponding load moment and voltage over-limit at this moment are recorded. time node, voltage amplitude and load node, go to step 6;

If the voltage is in the normal range, record the corresponding load moment, and use the load moment at this moment as the standard load moment of the line. It is judged that the time node when the line load moment is less than the standard load moment does not have a predicted low voltage exceeding the limit, and go to step 8.

Step 6: Select the time node corresponding to the next maximum load moment for power flow calculation.

Step 7: If there is a load point voltage lower than the lower voltage limit, it is considered that the line has a predicted low voltage over-limit at the time node t” corresponding to the load moment, and the corresponding load moment and voltage over-limit time node at this moment are recorded. Voltage amplitude and load node, return to step 6.

If the voltage is in the normal range, record the load moment, take the load moment at this moment as the standard load moment of the line, and go to step 8.

Step 8: According to the voltage situation of each load point at each time node in the predicted time period based on historical statistics, according to the low-voltage out-of-limit early warning judgment rule, determine whether the power grid has a voltage out-of-limit risk, and give an early warning result. Among them, the historical voltage data in the historical statistics is the voltage data at the same time in a day corresponding to each load point at each time node.

Determine whether the historical voltage data is lower than the lower voltage limit: if so, determine that the corresponding time node has a historical low voltage over-limit, otherwise there is no historical low-voltage over-limit at the corresponding time node;

When there is no predicted low voltage over-limit and historical under-voltage over-limit at this time node, the warning result is normal;

When there is any one of the predicted low voltage out-of-limit and the historical low-voltage out-of-limit at the time node, the warning result is that there is a low-voltage out-of-limit risk.

The low-voltage out-of-limit warning judgment rules are summarized in Table 1 below.

Table 1 Low-voltage out-of-limit warning judgment rules

Step 9: One line calculation ends.

Step 10: Repeat the above steps 1 to 9 for the preset line, and after the calculation is completed, save and statistically analyze the calculation result. After the calculation of all lines is completed, the same warning information is issued.

Step 11: If there is no warning, the warning process ends, waiting for the next warning to start.

Step 12: If there is an alert, track the alert result.

The tracking of low-voltage risk early warning results in distribution network needs to be tracked based on changes in network topology. The specific contents include:

When the topology changes, the load moment also changes accordingly. The judgment is divided into two situations as follows:

(1) When the topology changes, perform the low-voltage risk warning step again according to the latest load prediction result. If the result is that there is no low voltage, cancel the warning information, record the voltage amplitude of the current normal operation, end the warning process, and wait for the next If there is still low voltage, the warning information will still be issued, and the risk of low voltage will be tracked.

(2) When the topology does not change, if the load changes, start the early warning process according to the latest load forecast. If the result is that there is no low voltage, cancel the early warning information, and record the voltage amplitude of the current normal operation, and end the early warning process , wait for the next startup. If there is still a low voltage, a low voltage risk trace is performed. If the load does not change, wait until the time when the low voltage warning occurs. If the low voltage does not occur, record the voltage amplitude of the current normal operation and cancel the warning information; if the low voltage occurs, record the low voltage at this moment. Over the limit, and record the voltage amplitude, cancel the warning information.

Based on the same inventive concept, the present invention also provides an on-line early warning system for low-voltage risk of distribution network. Since the principle of these devices for solving technical problems is similar to the method of on-line early-warning of low-voltage risk of electrical distribution network, the repetition will not be repeated.

The system includes a load moment calculation module and a risk prediction module;

Wherein, the load torque calculation module is used to calculate the load torque of the preset lines in the distribution network according to the real-time monitoring data and load prediction data of the distribution network;

The risk prediction module is used to calculate the voltage of the preset load point on the preset line according to the calculation result of the load moment, and judge the power distribution network in the future time period according to the preset low-voltage over-limit early warning judgment rule. Whether there is a risk of low voltage overrun.

Wherein, the load moment calculation module includes: a data acquisition subunit and a load moment calculation subunit;

The data acquisition sub-unit is used to acquire the load prediction data of each time node in the preset time period, and obtain the electrical distance from the preset load point in the distribution network to the power source from the real-time monitoring data of the distribution network;

The load moment calculation subunit is used to calculate the load moment of the preset lines on each time node in the distribution network as follows:

M=∑P×L (1)

Among them, M is the load moment of a line on a time node, P represents the load prediction data of the preset load point on the line at this time node, L represents the electrical distance from the load point on the line to the power supply, and ∑ represents the load on the same line. The preset load points of the time nodes are summed.

The risk prediction module includes: a future judgment subunit, a historical judgment subunit, and an early warning subunit;

The future judgment subunit is used to calculate the voltage value of the preset load point on the preset line at the time node in the preset future time period in order according to the load moment from large to small, when the voltage of the load point is lower than the preset value. Set the lower limit of the voltage, and judge that the line has a predicted low voltage over-limit at the time node corresponding to the load moment, until the time node corresponding to the load moment does not have a predicted low voltage over-limit;

The historical judgment sub-unit is used for judging the preset load point at each time in the preset future time period according to the historical voltage data corresponding to each time node in the preset future time period of the preset load point of the distribution network Whether there is a historical low voltage violation at the time corresponding to the node;

The early warning subunit is used to give an early warning result when there is no predicted low voltage out-of-limit and historical low-voltage out-of-limit at the time node;

The system also includes a tracking module;

The tracking module is used to end the warning process if the warning result is normal, and wait for the next warning to start;

Otherwise, the warning information will be issued and the warning results will be tracked;

The early warning information includes time nodes, lines, load nodes and voltage amplitudes that are predicted to have low voltage violations.

Wherein, the tracking module includes: a topology change subunit, a load change subunit and an invariant subunit;

The topology change sub-unit is used to re-run low-voltage risk warning according to the latest load forecast data when the topology of the distribution network changes. If the warning result is normal, cancel the warning information, end the warning process, and wait for the next warning to start; otherwise , the warning information is issued and the warning results are tracked;

The load change sub-unit is used to start the early warning process according to the latest load forecast if the load changes when the topology of the distribution network does not change. If the early warning result is normal, cancel the early warning information, end the early warning process, and wait for the next time. Start; otherwise, the warning information will be issued and the warning results will be tracked;

The invariant sub-unit is used to wait when the topology and load of the distribution network have not changed, until the operation reaches the time when the low voltage exceeds the limit. If no low voltage exceeds the limit, the warning information is canceled; otherwise, the The time and voltage amplitude when the low voltage exceeds the limit will cancel the warning message.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application rather than limitations of its protection scope, although the present application has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand: After reading this application, those skilled in the art can still make various changes, modifications or equivalent replacements to the specific embodiments of the application, but these changes, modifications or equivalent replacements are all within the protection scope of the pending claims.

Claims (12)

1. an on-line early warning method for low voltage risk of distribution network, is characterized in that: According to the real-time monitoring data and load prediction data of the distribution network, the load moment of the preset line in the distribution network is calculated; According to the load moment calculation result, the preset voltage of the preset load point on the line is calculated, and it is determined according to the preset low voltage over-limit early warning judgment rule that within a preset future time period, the distribution Whether there is a risk of low voltage exceeding the limit in the power grid. 2. The method according to claim 1, wherein, according to the real-time monitoring data of the distribution network and the load prediction data, the load moment of the preset line in the distribution network is calculated as follows: M=∑P×L (1) where M is the load moment of a line on a time node, P represents the obtained load prediction data of the preset load point at the time node on the line, and L represents the data obtained from the real-time monitoring data of the distribution network. The electrical distance from the load point on the line to the power supply, Σ represents the summation of the preset load points at the time node on the line. 3 . The method according to claim 1 , wherein, according to the calculation result of the load moment, the preset voltage of the load point on the line is calculated, and the voltage of the preset low voltage is calculated according to the preset low voltage. 4 . The limit warning judgment rule judges whether there is a low voltage over-limit risk in the distribution network within a preset future time period, including: According to the order of load torque from large to small, the preset voltage value of the line at the preset load point at the time node in the preset future time period is calculated in turn. When the voltage of the load point is lower than the preset voltage The limit value is determined, and it is judged that the line has a predicted low voltage exceeding the limit at the time node corresponding to the load moment, until the time node corresponding to the load moment does not have a predicted low voltage exceeding the limit; According to the historical voltage data of the preset load point of the distribution network at the corresponding time of each time node in the preset future time period, it is determined whether the preset load point corresponds to the time point of each time node in the preset future time period. There is a historical low voltage limit; When there is no predicted low voltage out-of-limit and historical low-voltage out-of-limit at the time node, the warning result is given as normal; otherwise, the warning result is given as a risk of low-voltage out-of-limit risk. 4 . The method according to claim 3 , wherein, according to the load moment in descending order, the preset load of the line at the time node in the preset future time period is calculated sequentially. 4 . When the voltage at the load point is lower than the preset voltage lower limit value, it is determined that the line has a predicted low voltage exceeding the limit at the time node corresponding to the load torque, until the preset low voltage exceeds the limit when the load torque does not exist. limits, including: Select each time node of the preset line in the preset future time period in order according to the load moment from large to small, perform power flow calculation, obtain the voltage value of the preset load point, and make the following judgments: If the voltage value of any load point is lower than the preset voltage lower limit value, it is determined that the line has a predicted low voltage exceeding the limit at the time node corresponding to the load moment; Otherwise, the load moment is set as the standard load moment of the line, it is judged that there is no low voltage over-limit at the time node when the line load moment is less than the standard load moment, and the power flow calculation is stopped. 5 . The method according to claim 3 , wherein the predetermined load point of the power distribution network is combined with historical voltage data corresponding to each time node in a preset future time period to determine the preset value. 6 . Whether there is a historical low voltage violation at the corresponding time point of each time node in the preset future time period, including: Obtain the historical voltage data of each load point at the same moment of the day corresponding to each time node within the preset time period, and determine whether the historical voltage data is lower than the lower voltage limit value: if so, determine that the time node has historical low voltage higher Otherwise, there is no historical low voltage violation limit at the time node. 6. The method according to claim 3, characterized in that, after the warning result is given, further comprising: If the warning result is normal, the warning process ends, waiting for the next warning to start; Otherwise, the warning information will be issued and the warning results will be tracked; The early warning information includes time nodes, lines, load nodes and voltage amplitudes at which it is predicted that the low voltage exceeds the limit. 7. The method of claim 6, wherein the tracking and warning results comprise: When the topology of the distribution network changes, the low-voltage risk warning is re-executed according to the latest load forecast data. If the warning result is normal, the warning information is canceled, the warning process ends, and the next warning is activated; otherwise, a warning is issued. information, and track the warning results; When the topology of the distribution network does not change, if the load changes, start the pre-warning process according to the latest load forecast, if the pre-warning result is normal, cancel the pre-warning information, end the pre-warning process, and wait for the next start; otherwise, The warning information is issued and the warning results are tracked; When the topology and load of the distribution network have not changed, wait until the time when the low voltage exceeds the limit in the early warning. If the low voltage exceeds the limit, the warning information is canceled; otherwise, the low voltage exceeds the limit. Limit time and voltage amplitude, cancel the warning information. 8. An on-line early warning system for low voltage risk in a distribution network, characterized in that it comprises: a load moment calculation module and a risk prediction module; The load torque calculation module is used to calculate the load torque of the preset line in the distribution network according to the real-time monitoring data and load prediction data of the distribution network; The risk prediction module is used to calculate the voltage of the preset load point on the line according to the calculation result of the load moment, and to judge in the future time period according to the preset low voltage over-limit warning judgment rule. , whether there is a risk of low voltage over-limiting in the distribution network. 9. The system of claim 8, wherein the load moment calculation module comprises: a data acquisition subunit and a load moment calculation subunit; The data acquisition sub-unit is used to acquire the load prediction data of each time node in a preset time period, and acquire the electrical distance from the preset load point in the distribution network to the power supply from the real-time monitoring data of the distribution network; The load moment calculation subunit is used to calculate the load moment of the preset lines on each time node in the distribution network as follows: M=∑P×L (1) where M is the load moment of a line on a time node, P represents the load prediction data of the preset load point at the time node on the line, and L represents the load moment on the line obtained from the real-time monitoring data of the distribution network. The electrical distance from the load point to the power source, Σ represents the summation of the preset load points at the time node on the line. 10. The system of claim 8, wherein the risk prediction module comprises: a future judgment subunit, a historical judgment subunit, and an early warning subunit; The future judging subunit is used to sequentially calculate the voltage value of the preset load point at the time node of the line in the preset future time period according to the load moment in descending order, when there is a load point. When the voltage is lower than the preset voltage lower limit value, it is determined that the line has a predicted low voltage exceeding the limit at the time node corresponding to the load moment, until the time node corresponding to the load moment does not have a predicted low voltage exceeding the limit; The historical judging subunit is used for judging that the preset load point is in the preset future time according to the historical voltage data corresponding to each time node in the preset future time period of the preset load point of the power distribution network Whether there is a historical low voltage violation at the corresponding time of each time node in the segment; The pre-warning subunit is configured to give a warning result as normal when there is no predicted low-voltage out-of-limit and historical low-voltage out-of-limit at the time node; otherwise, the pre-warning result is given as a risk of low-voltage out-of-limit risk. 11. The system of claim 10, further comprising a tracking module; The tracking module is used to end the early warning process if the warning result is normal, and wait for the next warning to start; Otherwise, the warning information will be issued and the warning results will be tracked; The early warning information includes time nodes, lines, load nodes and voltage amplitudes at which it is predicted that the low voltage exceeds the limit. 12. The system of claim 11, wherein the tracking module comprises: a topology change subunit, a load change subunit, and an invariant subunit; The topology change subunit is used to re-run low-voltage risk warning according to the latest load forecast data when the topology of the distribution network changes, if the warning result is normal, cancel the warning information and wait for the next warning to start; otherwise , the warning information is issued and the warning results are tracked; The load change sub-unit is used to start an early warning process according to the latest load forecast if the load changes when the topology of the distribution network does not change, and if the early warning result is normal, cancel the early warning information and end the early warning process , wait for the next startup; otherwise, issue warning information and track the warning results; The invariant sub-unit is used to wait until the time when there is a low-voltage over-limit in the operation when the topology and load of the distribution network have not changed, and cancel the pre-warning if no low-voltage over-limit occurs. information; otherwise, the time and voltage amplitude when the low voltage exceeds the limit is obtained, and the warning information is cancelled.