CN113922383A - Distributed low-voltage load shedding acceleration action method and device considering load characteristics - Google Patents

Distributed low-voltage load shedding acceleration action method and device considering load characteristics Download PDF

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CN113922383A
CN113922383A CN202111348300.5A CN202111348300A CN113922383A CN 113922383 A CN113922383 A CN 113922383A CN 202111348300 A CN202111348300 A CN 202111348300A CN 113922383 A CN113922383 A CN 113922383A
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voltage
low
load shedding
line
condition
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CN113922383B (en
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张华杰
周文越
刘明忠
王利平
杨琪
赵子涵
向博
朱童
张纯
曾雪洋
李小鹏
吴杰
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Electric Power Research Institute of State Grid Sichuan Electric Power Co Ltd
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Electric Power Research Institute of State Grid Sichuan Electric Power Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
    • H02J3/14—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by switching loads on to, or off from, network, e.g. progressively balanced loading
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2310/00—The network for supplying or distributing electric power characterised by its spatial reach or by the load
    • H02J2310/50—The network for supplying or distributing electric power characterised by its spatial reach or by the load for selectively controlling the operation of the loads
    • H02J2310/56—The network for supplying or distributing electric power characterised by its spatial reach or by the load for selectively controlling the operation of the loads characterised by the condition upon which the selective controlling is based
    • H02J2310/58—The condition being electrical
    • H02J2310/60—Limiting power consumption in the network or in one section of the network, e.g. load shedding or peak shaving
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/30—Systems integrating technologies related to power network operation and communication or information technologies for improving the carbon footprint of the management of residential or tertiary loads, i.e. smart grids as climate change mitigation technology in the buildings sector, including also the last stages of power distribution and the control, monitoring or operating management systems at local level
    • Y02B70/3225—Demand response systems, e.g. load shedding, peak shaving
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • 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
    • Y04S20/00—Management or operation of end-user stationary applications or the last stages of power distribution; Controlling, monitoring or operating thereof
    • Y04S20/20—End-user application control systems
    • Y04S20/222—Demand response systems, e.g. load shedding, peak shaving

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  • Power Engineering (AREA)
  • Supply And Distribution Of Alternating Current (AREA)

Abstract

The invention discloses a distributed low-voltage load shedding acceleration action method and a distributed low-voltage load shedding acceleration action device considering load characteristics, wherein the method comprises the following steps: acquiring three-phase line voltage and line current data of a line where a protection device is located in real time; according to the obtained three-phase line voltage and line current data, judging that the voltage of the power system cannot be quickly recovered, and recovering the voltage of the power system in a low-voltage load shedding mode; the judgment basis comprises a first judgment condition and a second judgment condition; judging and identifying voltage sensitive loads according to the change characteristics of the electrical quantity; wherein the judgment identification basis is a third judgment condition; and when the first judgment condition, the second judgment condition and the third judgment condition are all met, executing low-pressure load shedding acceleration action. The method has the advantages that the situation that the power grid cannot be quickly recovered due to insufficient dynamic voltage support capability after the power grid has a serious fault is realized, the voltage sensitive load is quickly and accurately cut off through low-voltage load shedding when the voltage of the power grid is quickly reduced, the safe and stable operation of the power grid is guaranteed, and the possibility of misoperation is reduced.

Description

Distributed low-voltage load shedding acceleration action method and device considering load characteristics
Technical Field
The invention relates to the technical field of operation and control of power systems, in particular to a distributed low-voltage load shedding acceleration action method and device considering load characteristics.
Background
The load center area has less power supplies, the problem of 'hollowing' of the power supplies exists, the dynamic voltage supporting capacity is limited after a near-area line or a main transformer has a serious fault, the voltage recovery speed is slow or the voltage cannot be recovered to a normal level, and great risks are brought to the operation of a power grid. The safe and stable operation of the power grid is maintained through low-voltage load shedding, the safety problem after the power grid is seriously failed can be guaranteed, and the major power failure event caused by system voltage collapse is avoided. The low-voltage load shedding is a basic and effective control measure for solving the problem of voltage stability, at present, a low-voltage load shedding strategy integrated in a power distribution network line protection device (hereinafter referred to as a distributed low-voltage load shedding device) only achieves a load shedding function through a preset voltage threshold value and meets the requirement of prolonging time, and due to the fact that the difference of voltage dynamic change processes excited by different loads is large, the current load shedding device does not consider the influence of load characteristics, cannot give full play to the low-voltage load shedding function, cannot accurately cut voltage sensitive loads when insufficient voltage support occurs, and the power failure range is expanded.
Therefore, there is a need for a distributed low-voltage load shedding acceleration method and device considering load characteristics, which can quickly identify voltage-sensitive loads, quickly cut off the voltage-sensitive loads when the system is at low voltage and cannot be recovered, reduce the power failure range, and ensure the quick recovery of the system voltage.
Disclosure of Invention
The invention aims to provide a distributed low-voltage load shedding acceleration action method and device considering load characteristics, which can quickly and accurately cut off voltage sensitive loads through low-voltage load shedding when the power grid is in serious failure and the power grid cannot be quickly recovered due to insufficient dynamic voltage support capability after the power grid is in serious failure, so that the safe and stable operation of the power grid is guaranteed, and the possibility of misoperation is reduced.
The invention is realized by the following technical scheme:
in a first aspect, the present invention provides a distributed low-voltage load shedding acceleration action method considering load characteristics, including:
step 1, acquiring three-phase line voltage and line current data of a line where a protection device is located in real time, and preprocessing the three-phase line voltage and line current data;
step 2, judging that the voltage of the power system cannot be quickly recovered according to the acquired three-phase line voltage and line current data, and recovering the voltage of the power system in a low-voltage load shedding mode; wherein, the voltage of the power system is quickly recovered after being quickly reduced as a first judgment condition; the minimum effective value of the interphase voltage of the power system is smaller than the low-voltage load shedding action threshold value and meets the set time as a second judgment condition;
step 3, judging and identifying voltage sensitive loads according to the change characteristics of the electrical quantity; wherein, the power factor change rate is larger than a third preset value as a third judgment condition;
and 4, executing low-pressure load shedding acceleration action when the first judgment condition, the second judgment condition and the third judgment condition are all met.
Further, in the step 1, a three-phase line voltage and a line current of a line where the protection device is located are obtained in real time, and preprocessing is performed; the method specifically comprises the following steps:
the three-phase line voltage and line current data of a line where the protection device is located are obtained in real time through the obtaining unit and processed, the protection device is connected to a power distribution network system, the three-phase line voltage and line current data of a power system can be obtained in real time through a Potential Transformer (PT) element and a Current Transformer (CT) element of the line where the protection device is located, and an interphase voltage effective value U is calculated in real timeab、Ubc、UcaLine current effective value, line power factor cos θ and rate of change of voltage dU/dt.
Specifically, the calculation method of the voltage change rate is an effective value U of the interphase voltageab、Ubc、UcaThe voltage change rate dU/dt is calculated as the maximum of the voltage change amplitude within any 100ms as follows:
Figure BDA0003354783830000021
wherein, Uabt1、Ubct1、Ucat1Respectively at t1 times AB, BC, CA phase voltage effective value, Uabt0、Ubct0、Ucat0The effective values of the interphase voltages AB, BC and CA at the time t0 are respectively, and the time from t0 to t1 is a fixed time window of 100 ms; min [ 2 ]]To take the minimum function (since the voltage drop is monitored, the voltage value at time t1 should be less than at time t0, so that the voltage drop dU/dt is negative in V/s).
Further, in step 2, it is determined that the voltage of the power system cannot be recovered quickly according to the acquired three-phase line voltage and line current data, and the specific method for recovering the voltage of the power system in a low-voltage load shedding manner needs to be analyzed and considered as follows:
the low-voltage load shedding is used as a third defense line of the power system, and the voltage cannot be recovered after a serious fault occurs, so that the protection device needs to effectively identify the fault occurrence and removal process, and the purpose of accurate response is achieved. In order to realize the criterion that the system voltage cannot be recovered to normal quickly, the protection device can quickly lock the device when the system fails, so that the load loss caused by low-voltage load shedding misoperation due to the failure outside the area is avoided; when the voltage of the power system is in a slow recovery state after the fault is judged to be cut off, the device can effectively identify and open the low-voltage load shedding action logic.
The maximum change of the effective value of the fundamental wave of the interphase voltage collected by the protection device within any 100ms can be defined as voltage slip, dU/dt is used as an effective criterion for fault criterion and fault removal, when the value of dU/dt is large, the voltage drop speed of the power system is too high, the power system is considered to have a fault, and low-voltage load shedding logic is locked; when the voltage of the power system recovers to a certain level or the voltage recovery change dU/dt reaches a certain fixed value, the fault is judged to be removed by combining the lower content of the negative sequence and the zero sequence components of the system voltage, and the state is used as the starting condition of the low-voltage load-shedding acceleration action.
Further preferably, the power system voltage is rapidly reduced and then rapidly recovered as the first determination condition; the method specifically comprises the following steps:
when the power system is in fault, the voltage drops rapidly, and when the voltage change rate is less than a first preset value (dU/dt)<K1) When the low-voltage load shedding function is locked; after the fault is removed, when the voltage change rate is larger than a second preset value (dU/dt)>K2) Low pressure deloading accelerated start, and at TjsReturning to locking acceleration action after the moment, wherein the condition is a first judgment condition of a low-pressure load shedding acceleration action method;
the first preset value K1 is a low-pressure load shedding slip locking fixed value, and the fixed value setting method refers to a system stability calculation result or a common low-pressure load shedding device fixed value parameter; the second preset value is a low-pressure deloading slip unlocking fixed value.
More preferably, the minimum effective value of the inter-phase voltage of the power system is smaller than the low-voltage load shedding action threshold value, and the set time is satisfied as a second judgment condition (i.e. the low-voltage load shedding action condition); the second judgment condition has the following discrimination formula:
Umin＝MIN[Uab，Ubc，Uca]；
Umin<Udyzd；
wherein, MIN 2]To take the minimum contentCounting; u shapeab，Ubc，UcaDividing the voltage into three-phase interphase voltage effective values; u shapeminThe minimum effective value of the interphase voltage; u shapedyzdSetting a value for the low-pressure load shedding action;
this condition is the second determination condition of the low-pressure load shedding acceleration operation method.
Further, in step 3, judging and identifying voltage-sensitive loads according to the electrical quantity change characteristics; the method for judging the voltage-sensitive load through the electric quantity change characteristics takes the induction motor load which occupies a larger part in the industrial load as an analysis object, and details the voltage-sensitive characteristics and the judging method. The specific analysis is as follows:
an induction motor electromagnetic torque expression can be deduced according to the induction motor principle:
Figure BDA0003354783830000031
wherein: te is the electromagnetic torque of the induction motor; p is the number of pole pairs of the induction motor; s is the slip of the induction motor; u is the voltage of the power grid side; r1、X1The impedance and leakage reactance of the network side of the motor are shown; r'2Is the equivalent impedance of the rotor side of the induction motor.
According to the formula of T, when the voltage on the power grid side is reduced in the normal operating voltage range of the induction motor, the rotor e is used
The induction motor has certain inertia characteristic, the slip cannot change suddenly at the moment, the electromagnetic torque is reduced at the moment, the rotation speed of the motor is continuously reduced because the load on the rotor side is not changed and is smaller than the mechanical torque, the electromagnetic torque of the induction motor is increased along with the increase of the slip, and when the motor is balanced with the mechanical torque, the motor is stabilized at a new operation point again.
The slip of the motor is increased and the reactive power of the motor for establishing the magnetic field of the stator is increased in order to maintain the electromagnetic torque constant, resulting in a rapid reduction of the power factor of the motor in low voltage operation.
When the voltage at the side of the power grid is reduced by an amplitude which exceeds the critical voltage of the induction motor, the rotating speed of the motor is rapidly reduced to cause the motor to be locked, the power factor is extremely low when the motor is locked, the current (called locked-rotor current) during locked-rotor can reach 3-7 times of the rated current, and a large amount of reactive power can be injected into the system in the process.
The induction motor is used as a main dynamic load of the power system, occupies a large area, is a key factor causing voltage instability, and can cause the slip ratio of the induction motor to be increased and the reactive power to be remarkably increased when the voltage of the power system is reduced, so that the voltage is further reduced. Therefore, it is necessary to cut off the voltage sensitive load as soon as possible and ensure the system voltage to recover as soon as possible by reducing the power factor as a necessary condition for the low-voltage load-shedding acceleration outlet. Therefore, voltage sensitive loads can be accurately identified through power factor changes before and after system faults, and the fact that the system voltage cannot be quickly recovered is effectively identified in combination with the step 2, and relevant branch loads are quickly cut off.
Preferably, the power factor change rate before and after the fault collected by the protection device is used as a voltage sensitive load criterion condition, and when the voltage sensitive load is judged, the power factor change rate is used as a device load shedding action condition.
Wherein, the calculation formula of the power factor change rate is as follows:
Figure BDA0003354783830000041
where δ is the power factor rate of change, cos θ0Representing the line power factor before the fault occurs, cos θ1Representing the line power factor after fault recovery.
The existing low-voltage load shedding function integrated in the line protection device comprises the following steps: 1) when the maximum line voltage of the system is smaller than the low-voltage load shedding fixed value and meets a certain time delay, starting a low-voltage load shedding action; 2) when the system fails, the low-voltage load shedding misoperation is avoided, the function is locked through the voltage slip, and the function is unlocked when the voltage meets a certain condition; 3) the function is locked by means of negative sequence voltage, PT disconnection logic, soft and hard pressure plates or line current magnitude and the like.
In a second aspect, the present invention further provides a distributed low-voltage load shedding and accelerating device considering load characteristics, which supports any one of the described distributed low-voltage load shedding and accelerating methods considering load characteristics, the device comprising:
the acquisition unit is used for acquiring three-phase line voltage and line current data of a line where the protection device is located in real time and preprocessing the three-phase line voltage and line current data;
the first and second condition judgment units are used for judging that the voltage of the power system cannot be quickly recovered according to the acquired three-phase line voltage and line current data, and the system voltage needs to be recovered in a low-voltage load shedding mode; wherein, the voltage of the power system is quickly recovered after being quickly reduced as a first judgment condition; the minimum effective value of the interphase voltage of the power system is smaller than the low-voltage load shedding action threshold value and meets the set time as a second judgment condition;
the third condition judging unit judges and identifies the voltage sensitive load according to the change characteristics of the electrical quantity; wherein, the power factor change rate is larger than a third preset value as a third judgment condition;
and the low-pressure load shedding acceleration action unit executes low-pressure load shedding acceleration action when the first judgment condition, the second judgment condition and the third judgment condition are all met.
Further, the obtaining unit executes the following processes:
the method comprises the steps of acquiring three-phase line voltage and line current data of a power system in real time through a PT element and a CT element of a line voltage transformer of a line where a protection device is located, and calculating an interphase voltage effective value U in real timeab、Ubc、UcaInformation such as line current effective value, line power factor cos θ and voltage change rate dU/dt;
the calculation mode of the voltage change rate is an interphase voltage effective value Uab、Ubc、UcaThe voltage change rate dU/dt is calculated as the maximum of the voltage change amplitude within any 100ms as follows:
Figure BDA0003354783830000051
wherein, Uabt1、Ubct1、Ucat1Respectively at t1 times AB, BC, CA phase voltage effective value, Uabt0、Ubct0、Ucat0The effective values of the interphase voltages AB, BC and CA at the time t0 are respectively, and the time from t0 to t1 is a fixed time window of 100 ms; min [ 2 ]]To take the minimum function (since the voltage drop is monitored, the voltage value at time t1 should be less than at time t0, so that the voltage drop dU/dt is negative in V/s).
Further, the first and second condition judging units include a first condition judging subunit and a second condition judging subunit;
the first condition judging subunit, when the power system is in fault, the voltage drops rapidly, and when the voltage change rate is less than a first preset value (dU/dt)<K1) When the low-voltage load shedding function is locked; after the fault is removed, when the voltage change rate is larger than a second preset value (dU/dt)>K2) Low pressure deloading accelerated start, and at TjsReturning to locking acceleration action after the moment, wherein the condition is a first judgment condition of a low-pressure load shedding acceleration action method; the first preset value K1 is a low-pressure load shedding slip locking fixed value, and the fixed value setting method refers to a system stability calculation result or a common low-pressure load shedding device fixed value parameter; the second preset value is a low-pressure load shedding slip unlocking fixed value;
the discrimination formula of the second judgment condition in the second condition judgment subunit is as follows:
Umin＝MIN[Uab，Ubc，Uca]；
Umin<Udyzd；
wherein, MIN 2]Is to take the minimum function; u shapeab，Ubc，UcaDividing the voltage into three-phase interphase voltage effective values; u shapeminThe minimum effective value of the interphase voltage; u shapedyzdThe low pressure load shedding action is fixed.
Further, the calculation formula of the power factor change rate in the third condition judgment unit is as follows:
Figure BDA0003354783830000052
where δ is the power factor rate of change, cos θ0Representing the line power factor before the fault occurs, cos θ1Representing the line power factor after fault recovery.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. the method and the device can preferentially cut off the voltage sensitive load, reduce the load loss and avoid the load amount from being cut off due to unreasonable system round setting.
2. The method and the device can quickly respond, improve the voltage recovery speed of the system and avoid the voltage breakdown of the system.
3. The method and the device can adapt to different operation modes of the power grid, and reduce systematic risks.
4. The method and the device of the invention carry out the low-voltage load reduction action outlet according to the line power factor, thereby reducing the possibility of misoperation.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
fig. 1 is a flowchart of a distributed low-pressure load shedding acceleration method considering load characteristics according to the present invention.
Fig. 2 is an operation logic diagram of a distributed low-voltage load shedding acceleration operation method in consideration of load characteristics according to an embodiment of the present invention.
Fig. 3 is a schematic structural diagram of a distributed low-pressure load-shedding acceleration operation device in consideration of load characteristics according to the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Example 1
As shown in fig. 1, fig. 1 is a flowchart of a distributed low-voltage load shedding and accelerating method in consideration of load characteristics, and fig. 2 is a logic diagram of an operation of a distributed low-voltage load shedding and accelerating method in consideration of load characteristics.
The method comprises the following steps:
step 1, acquiring three-phase line voltage and line current data of a line where a protection device is located in real time through an acquisition unit, and preprocessing the three-phase line voltage and line current data;
the three-phase line voltage and line current data of the power system can be obtained in real time through a PT element and a CT element of a line voltage transformer of a line where the protection device is located, and the interphase voltage effective value U is calculated in real timeab、Ubc、UcaLine current effective value, line power factor cos θ and rate of change of voltage dU/dt.
Specifically, the calculation method of the voltage change rate is an effective value U of the interphase voltageab、Ubc、UcaThe voltage change rate dU/dt is calculated as the maximum of the voltage change amplitude within any 100ms as follows:
Figure BDA0003354783830000061
wherein, Uabt1、Ubct1、Ucat1Respectively at t1 times AB, BC, CA phase voltage effective value, Uabt0、Ubct0、Ucat0The effective values of the interphase voltages AB, BC and CA at the time t0 are respectively, and the time from t0 to t1 is a fixed time window of 100 ms; min [ 2 ]]To take the minimum function (since the voltage drop is monitored, the voltage value at time t1 should be less than at time t0, so that the voltage drop dU/dt is negative in V/s).
Step 2, judging that the voltage of the power system cannot be quickly recovered according to the acquired three-phase line voltage and line current data, and recovering the voltage of the power system in a low-voltage load shedding mode; wherein, the voltage of the power system is quickly recovered after being quickly reduced as a first judgment condition; the minimum effective value of the interphase voltage of the power system is smaller than the low-voltage load shedding action threshold value and meets the set time as a second judgment condition;
when the dU/dt value is large, the voltage drop speed of the power system is too high, the power system is considered to be in fault, and the low-voltage load shedding logic is locked; when the voltage of the power system recovers to a certain level or the voltage recovery change dU/dt reaches a certain fixed value, the fault is judged to be removed by combining the lower negative sequence and zero sequence component contents of the system voltage, and the state is used as the starting condition of the low-voltage load-shedding acceleration action, which is specifically represented as follows:
when the power system is in fault, the voltage drops rapidly, and when the voltage change rate is less than a first preset value (dU/dt)<K1) When the low-voltage load shedding function is locked; after the fault is removed, when the voltage change rate is larger than a second preset value (dU/dt)>K2) Low pressure deloading accelerated start, and at TjsReturning to locking acceleration action after the moment, wherein the condition is a first judgment condition of a low-pressure load shedding acceleration action method;
the first preset value K1 is a low-pressure load shedding slip locking fixed value, and the fixed value setting method refers to a system stability calculation result or a common low-pressure load shedding device fixed value parameter; the second preset value is a low-pressure deloading slip unlocking fixed value.
Within the acceleration action starting time, if the voltage of the power system is judged to meet the low-voltage load shedding condition, the voltage of the power system is considered to be incapable of being quickly recovered, the low-voltage load shedding condition is that the minimum effective value of the interphase voltage of the system is smaller than the threshold value of the low-voltage load shedding action, and a certain time (namely, set time) is met, and the judgment formula of the second judgment condition is as follows:
Umin＝MIN[Uab，Ubc，Uca]；
Umin<Udyzd；
wherein, MIN 2]Is to take the minimum function; u shapeab，Ubc，UcaDividing the voltage into three-phase interphase voltage effective values; u shapeminThe minimum effective value of the interphase voltage; u shapedyzdSetting a value for the low-pressure load shedding action;
this condition, i.e., the low-pressure load shedding operation condition, is the second determination condition of the low-pressure load shedding acceleration operation method.
Step 3, judging and identifying voltage sensitive loads according to the change characteristics of the electrical quantity; wherein, the power factor change rate is larger than a third preset value as a third judgment condition;
based on the description of the load power factor change rate, the induction motor is used as a main dynamic load of a power system, occupies a large area, is a key factor causing voltage instability, and when the system voltage is reduced, the slip ratio of the induction motor is increased, the reactive power is obviously increased, and the voltage is further reduced. Therefore, it is necessary to cut off the voltage sensitive load as soon as possible and ensure the system voltage to recover as soon as possible by reducing the power factor as a necessary condition for the low-voltage load-shedding acceleration outlet. The line power factor change rate before the fault occurs and after the fault is removed can be judged as the device action condition, and the calculation formula of the power factor change rate is as follows:
Figure BDA0003354783830000071
where δ is the power factor rate of change, cos θ0Representing the line power factor before the fault occurs, cos θ1Representing the line power factor after fault recovery.
By judging the variation of the line power factor before and after the low-voltage load shedding acceleration function is started, if the power factor variation rate delta is greater than a third preset value K3, the condition is a third judgment condition of the low-voltage load shedding acceleration action method.
The locking condition is explained, the low-voltage load reduction can be locked in various modes such as PT disconnection, composite voltage (including negative sequence voltage and zero sequence voltage), circuit no-current and the like, and the misoperation of the low-voltage load reduction accelerating device is avoided.
And 4, executing low-pressure load shedding acceleration action when the first judgment condition, the second judgment condition and the third judgment condition are all met.
Through the implementation processes of the steps 1 to 4, firstly, the voltage sensitive load can be cut off preferentially, the load loss is reduced, and the load amount is prevented from being cut due to unreasonable system round setting; secondly, the system can respond quickly, the voltage recovery speed of the system is improved, and the system voltage breakdown is avoided; thirdly, the method can adapt to different operation modes of the power grid, and systematic risks are reduced; and the fourth low-voltage load reduction action outlet is carried out according to the power factor of the line, so that the possibility of misoperation is reduced.
Example 2
As shown in fig. 3, the present embodiment is different from embodiment 1 in that the present embodiment provides a distributed low-voltage load shedding acceleration operation device considering load characteristics, which supports the distributed low-voltage load shedding acceleration operation method considering load characteristics described in embodiment 1, and the device includes:
the acquisition unit is used for acquiring three-phase line voltage and line current data of a line where the protection device is located in real time and preprocessing the three-phase line voltage and line current data;
the first and second condition judgment units are used for judging that the voltage of the power system cannot be quickly recovered according to the acquired three-phase line voltage and line current data, and the system voltage needs to be recovered in a low-voltage load shedding mode; wherein, the voltage of the power system is quickly recovered after being quickly reduced as a first judgment condition; the minimum effective value of the interphase voltage of the power system is smaller than the low-voltage load shedding action threshold value and meets the set time as a second judgment condition;
the third condition judging unit judges and identifies the voltage sensitive load according to the change characteristics of the electrical quantity; wherein, the power factor change rate is larger than a third preset value as a third judgment condition;
and the low-pressure load shedding acceleration action unit executes low-pressure load shedding acceleration action when the first judgment condition, the second judgment condition and the third judgment condition are all met.
In this embodiment, the execution process of the obtaining unit is as follows:
the method comprises the steps of acquiring three-phase line voltage and line current data of a power system in real time through a PT element and a CT element of a line voltage transformer of a line where a protection device is located, and calculating an interphase voltage effective value U in real timeab、Ubc、UcaInformation such as line current effective value, line power factor cos θ and voltage change rate dU/dt;
meter of the rate of change of the voltageThe calculation mode is interphase voltage effective value Uab、Ubc、UcaThe voltage change rate dU/dt is calculated as the maximum of the voltage change amplitude within any 100ms as follows:
Figure BDA0003354783830000081
wherein, Uabt1、Ubct1、Ucat1Respectively at t1 times AB, BC, CA phase voltage effective value, Uabt0、Ubct0、Ucat0The effective values of the interphase voltages AB, BC and CA at the time t0 are respectively, and the time from t0 to t1 is a fixed time window of 100 ms; min [ 2 ]]To take the minimum function (since the voltage drop is monitored, the voltage value at time t1 should be less than at time t0, so that the voltage drop dU/dt is negative in V/s).
In this embodiment, the first and second condition determining units include a first condition determining subunit and a second condition determining subunit;
the first condition judging subunit, when the power system is in fault, the voltage drops rapidly, and when the voltage change rate is less than a first preset value (dU/dt)<K1) When the low-voltage load shedding function is locked; after the fault is removed, when the voltage change rate is larger than a second preset value (dU/dt)>K2) Low pressure deloading accelerated start, and at TjsReturning to locking acceleration action after the moment, wherein the condition is a first judgment condition of a low-pressure load shedding acceleration action method; the first preset value K1 is a low-pressure load shedding slip locking fixed value, and the fixed value setting method refers to a system stability calculation result or a common low-pressure load shedding device fixed value parameter; the second preset value is a low-pressure load shedding slip unlocking fixed value;
the discrimination formula of the second judgment condition in the second condition judgment subunit is as follows:
Umin＝MIN[Uab，Ubc，Uca]；
Umin<Udyzd；
wherein, MIN 2]Is to take the minimum function; u shapeab，Ubc，UcaDivided into three-phase interphase powerPressing the effective value; u shapeminThe minimum effective value of the interphase voltage; u shapedyzdThe low pressure load shedding action is fixed.
In this embodiment, a calculation formula of the power factor change rate in the third condition determining unit is as follows:
Figure BDA0003354783830000091
where δ is the power factor rate of change, cos θ0Representing the line power factor before the fault occurs, cos θ1Representing the line power factor after fault recovery.
The distributed low-voltage load shedding acceleration action device considering the load characteristics fully considers the influence of the load characteristics, fully plays the role of low-voltage load shedding, and can accurately cut off voltage sensitive loads when insufficient voltage support occurs, so that the power failure range is expanded.
Compared with the prior art, the method has the following advantages: (1) voltage sensitive loads can be cut off preferentially, load loss is reduced, and load amount over-cutting caused by unreasonable system round setting is avoided; (2) the system can respond quickly, the voltage recovery speed of the system is improved, and the system voltage breakdown is avoided; (3) the method can adapt to different operation modes of the power grid, and reduce systematic risks; (4) the low-voltage load reduction action outlet is carried out according to the line power factor, and the possibility of misoperation is reduced.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A distributed low-pressure load shedding acceleration action method considering load characteristics, comprising:
acquiring three-phase line voltage and line current data of a line where a protection device is located in real time;
according to the obtained three-phase line voltage and line current data, judging that the voltage of the power system cannot be quickly recovered, and recovering the voltage of the power system in a low-voltage load shedding mode; wherein, the voltage of the power system is quickly recovered after being quickly reduced as a first judgment condition; the minimum effective value of the interphase voltage of the power system is smaller than the low-voltage load shedding action threshold value and meets the set time as a second judgment condition;
judging and identifying voltage sensitive loads according to the change characteristics of the electrical quantity; wherein, the power factor change rate is larger than a third preset value as a third judgment condition;
and when the first judgment condition, the second judgment condition and the third judgment condition are all met, executing low-pressure load shedding acceleration action.
2. The distributed low-voltage load shedding and accelerating action method considering the load characteristics as claimed in claim 1, wherein the three-phase line voltage and the line current of the line on which the protection device is located are obtained in real time; the method specifically comprises the following steps:
the method comprises the steps of acquiring three-phase line voltage and line current data of a power system in real time through a PT element and a CT element of a line voltage transformer of a protection device, and calculating an interphase voltage effective value, a line current effective value, a line power factor and voltage change rate information in real time.
3. The distributed low-voltage load shedding and accelerating method according to claim 2, wherein the voltage change rate is calculated as an effective phase-to-phase voltage value Uab、Ubc、UcaThe voltage change rate dU/dt is calculated as the maximum of the voltage change amplitude within any 100ms as follows:
Figure FDA0003354783820000011
wherein, Uabt1、Ubct1、Ucat1Are respectively provided withEffective value of interphase voltage AB, BC and CA at t1 time, Uabt0、Ubct0、Ucat0The effective values of the interphase voltages AB, BC and CA at the time t0 are respectively, and the time from t0 to t1 is a fixed time window of 100 ms; min [ 2 ]]Is a function of taking the minimum value.
4. The distributed low-voltage load shedding and accelerating method considering the load characteristics as claimed in claim 1, wherein the first determination condition is that the voltage of the power system is rapidly reduced and then rapidly restored; the method specifically comprises the following steps:
when the power system breaks down, the voltage drops rapidly, and when the voltage change rate is smaller than a first preset value, the low-voltage load shedding function is locked; after the fault is removed, when the voltage change rate is greater than a second preset value, the low-voltage load shedding is accelerated to start, and the voltage is controlled to be at TjsReturning to locking acceleration action after the moment, wherein the condition is a first judgment condition of a low-pressure load shedding acceleration action method;
wherein, the first preset value K1 is a low-pressure deloading slip locking fixed value; the second preset value is a low-pressure deloading slip unlocking fixed value.
5. The distributed low-voltage load shedding and accelerating method considering the load characteristics as claimed in claim 1, wherein the minimum effective value of the inter-phase voltage of the power system is smaller than the threshold value of the low-voltage load shedding operation and meets the set time as a second judgment condition; the second judgment condition has the following discrimination formula:
Umin＝MIN[Uab，Ubc，Uca]；
Umin<Udyzd；
wherein, MIN 2]Is to take the minimum function; u shapeab，Ubc，UcaDividing the voltage into three-phase interphase voltage effective values; u shapeminThe minimum effective value of the interphase voltage; u shapedyzdSetting a value for the low-pressure load shedding action;
this condition is the second determination condition of the low-pressure load shedding acceleration operation method.
6. The distributed low-voltage load shedding acceleration action method considering the load characteristics as claimed in claim 1, wherein the power factor change rate is greater than a third preset value as a third judgment condition; the calculation formula of the power factor change rate is as follows:
Figure FDA0003354783820000021
where δ is the power factor rate of change, cos θ0Representing the line power factor before the fault occurs, cos θ1Representing the line power factor after fault recovery.
7. A distributed low-pressure load shedding acceleration operation device considering load characteristics, which supports a distributed low-pressure load shedding acceleration operation method considering load characteristics according to any one of claims 1 to 6, the device comprising:
the acquisition unit is used for acquiring three-phase line voltage and line current data of a line where the protection device is located in real time;
the first and second condition judgment units are used for judging that the voltage of the power system cannot be quickly recovered according to the acquired three-phase line voltage and line current data, and the system voltage needs to be recovered in a low-voltage load shedding mode; wherein, the voltage of the power system is quickly recovered after being quickly reduced as a first judgment condition; the minimum effective value of the interphase voltage of the power system is smaller than the low-voltage load shedding action threshold value and meets the set time as a second judgment condition;
the third condition judging unit judges and identifies the voltage sensitive load according to the change characteristics of the electrical quantity; wherein, the power factor change rate is larger than a third preset value as a third judgment condition;
and the low-pressure load shedding acceleration action unit executes low-pressure load shedding acceleration action when the first judgment condition, the second judgment condition and the third judgment condition are all met.
8. The distributed low-pressure load shedding and accelerating device considering the load characteristics as claimed in claim 7, wherein the acquiring unit performs the following processes:
acquiring three-phase line voltage and line current data of a power system in real time through a PT element and a CT element of a line voltage transformer of a protection device, and calculating an interphase voltage effective value, a line current effective value, a line power factor and voltage change rate information in real time;
the calculation mode of the voltage change rate is an interphase voltage effective value Uab、Ubc、UcaThe voltage change rate dU/dt is calculated as the maximum of the voltage change amplitude within any 100ms as follows:
Figure FDA0003354783820000031
wherein, Uabt1、Ubct1、Ucat1Respectively at t1 times AB, BC, CA phase voltage effective value, Uabt0、Ubct0、Ucat0The effective values of the interphase voltages AB, BC and CA at the time t0 are respectively, and the time from t0 to t1 is a fixed time window of 100 ms; min [ 2 ]]Is a function of taking the minimum value.
9. The distributed low-pressure load shedding and accelerating device considering the load characteristics as claimed in claim 7, wherein the first and second condition determining units comprise a first condition determining subunit and a second condition determining subunit;
when the power system fails, the voltage drops rapidly, and when the voltage change rate is smaller than a first preset value, the low-voltage load shedding function is locked; after the fault is removed, when the voltage change rate is greater than a second preset value, the low-voltage load shedding is accelerated to start, and the voltage is controlled to be at TjsReturning to locking acceleration action after the moment, wherein the condition is a first judgment condition of a low-pressure load shedding acceleration action method; wherein, the first preset value K1 is a low-pressure deloading slip locking fixed value; the second preset value is a low-pressure load shedding slip unlocking fixed value;
the discrimination formula of the second judgment condition in the second condition judgment subunit is as follows:
Umin＝MIN[Uab，Ubc，Uca]；
Umin<Udyzd；
wherein, MIN 2]Is to take the minimum function; u shapeab，Ubc，UcaDividing the voltage into three-phase interphase voltage effective values; u shapeminThe minimum effective value of the interphase voltage; u shapedyzdThe low pressure load shedding action is fixed.
10. A distributed low-pressure load shedding and accelerating device according to claim 7, wherein the third condition determining unit calculates the rate of change of the power factor by:
Figure FDA0003354783820000032
where δ is the power factor rate of change, cos θ0Representing the line power factor before the fault occurs, cos θ1Representing the line power factor after fault recovery.
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