A power grid accident under generator isolated grid operation control method and device

Abstract

The application provides a power grid accident generator isolated grid operation control method and device, and belongs to the technical field of relay protection. The method comprises the following steps: connecting a standby tripping outlet of a main transformer main protection device of a power system to a high-level feeder circuit breaker tripping control loop of a generator grid-connected cabinet; classifying all power consumption loads on the bus side; configuring low-frequency low-voltage load shedding setting and power balance checking logic for non-essential loads; triggering the disconnection of the circuit breaker through the main protection linkage when the system loses power, realizing the electrical isolation of the generator and the external power grid; collecting system frequency, voltage and various power parameters after isolation, performing power balance checking and low-frequency low-voltage load shedding, and cutting off non-essential loads to ensure that the total load of the isolated grid is not more than the rated output of the generator. The application does not need to add hardware devices, can quickly build a stable isolated grid, effectively guarantees the continuous power supply of core production loads and auxiliary power, and has strong economy and reliability.

Description

Technical Field

[0001] This application belongs to the field of relay protection technology, specifically relating to a generator islanding operation control method and device under power grid fault conditions. Background Technology

[0002] Currently, large industrial enterprises generally configure dedicated load stabilization control systems for their power systems. When internal or external power supply failures occur in the power system, precise load shedding operations can be performed through preset control strategies to ensure system frequency and voltage stability and maintain continuous power supply to core production loads.

[0003] In existing technologies, industrial enterprises equipped with their own generator sets mainly adopt two types of technical solutions to cope with power supply accidents such as external power grid failures and main transformer malfunctions. The first type involves configuring a dedicated load stabilization control device. This device centrally collects the bus voltage, frequency, load power of each branch, and generator operating parameters of the entire system. According to a preset control strategy, it tieredly disconnects the corresponding loads during faults to maintain system power balance and stable operation. The second type relies on existing outgoing line relay protection devices, configuring conventional low-frequency, low-voltage load shedding protection in each load circuit. This protection uses only system frequency and bus voltage falling below preset values ​​as activation criteria, triggering the load circuit breaker to trip after the activation time limit is reached.

[0004] Existing technologies suffer from two main problems: Firstly, dedicated load stabilization control devices require additional hardware procurement and control cabling, resulting in high construction and maintenance costs. Secondly, for small-to-medium-sized industrial power supply systems with single-bus architecture and small capacity, the equipment suffers from high functional redundancy and low return on investment, hindering widespread application. Thirdly, conventional low-frequency, low-voltage load shedding protection lacks time-series linkage with the main transformer protection on the power supply side. After a grid failure, generator reverse power and out-of-step protection prioritizing action can easily lead to unit shutdowns, making it impossible to quickly establish a stable isolated grid. Furthermore, the lack of real-time power matching logic during load shedding makes it prone to erroneous or insufficient shedding of core loads, failing to guarantee continuous and reliable power supply to critical production loads such as blast furnaces and oxygen plants. Summary of the Invention

[0005] The purpose of this invention is to provide a method and apparatus for controlling generator isolated operation under power grid faults, in order to solve the problems in the prior art.

[0006] In a first aspect, embodiments of this application provide a generator islanded operation control method under power grid fault conditions, the method comprising the following steps: S1. Connect the standby tripping output of the main protection device of the main transformer of the power system to the tripping control circuit of the upstream incoming circuit breaker of the generator grid connection cabinet. Classify all electrical loads on the generator bus side according to the importance of the load, and configure low-frequency low-voltage load shedding action settings and power balance verification logic for the protection devices corresponding to non-important loads. S2. Real-time acquisition of electrical and non-electrical signals of the main transformer through the main transformer protection device to continuously monitor the power supply operation status of the system power supply side. S3. When the main transformer protection device determines that a power failure has occurred on the power supply side of the system, it generates an instantaneous trip command, which is transmitted to the upstream incoming circuit breaker through the backup trip output, triggering the circuit breaker to open, so that the generator and the load on the bus are electrically isolated from the external power grid. S4. After completing grid isolation, collect the real-time frequency, bus voltage, generator output, power of important loads, plant power and auxiliary equipment load power of the isolated grid system in real time. S5. Based on the real-time frequency, bus voltage, generator output, power of each important load, plant power and auxiliary equipment load power collected, perform power balance verification and low-frequency low-voltage load reduction, cut off corresponding non-important loads, so that the total power load of the islanded grid system does not exceed the generator's rated output, and maintain the stable operation of the islanded grid system.

[0007] Further, in step S1, the constraint formula for the power balance verification logic is:

[0008] In the formula, For the real-time active power output of the generator, The total active power of all critical loads. This refers to the total active power of the plant's power load and the load of the generator set's auxiliary equipment local electrical control system. This is the pre-set active power reserve margin for isolated network operation; In step S1, non-critical loads are divided into multiple load shedding cycles according to their importance from low to high. The low-frequency, low-voltage load shedding action setting adopts a multi-parameter joint criterion of frequency, voltage, and frequency change rate. Specifically, the load shedding action is triggered when any of the following conditions are met: Condition one: and and ; Condition two: and ; In the formula, For the real-time frequency of the isolated network system, The threshold value is set for low frequency. This refers to the real-time bus voltage of the isolated grid system. The low-voltage setting threshold; For the duration of the parameter exceeding the limit, For the action time limit; The system frequency change rate, This is the frequency change rate setting value. This is the frequency offset buffer value; When condition one is met, the tiered load reduction is triggered according to the normal time limit; when condition two is met, it is determined that there is a large power shortage in the system, and the accelerated load reduction action is triggered, directly cutting off the first level of non-critical loads; during the load reduction process, after each level of load is cut off, the power balance check is re-executed, and the load reduction is terminated immediately if the constraint is met.

[0009] Furthermore, step S1 also includes a relay protection setting timing matching algorithm to ensure the timing coordination between isolation actions and island network construction when the system loses power. The specific setting constraint formula is as follows:

[0010] In the formula, The instantaneous tripping time of the main transformer's main protection device. This refers to the inherent tripping time of the upstream incoming circuit breaker of the generator grid-connected cabinet. This refers to the operating time of the generator reverse power protection or out-of-step protection.

[0011] Furthermore, in step S5, the specific process of performing the power balance verification is as follows: S51. After grid isolation is completed, the current generator output will be collected in real time. The power of each important load, the power of plant power and the power of auxiliary equipment load are substituted into the constraint formula of the power balance verification logic for verification; S52. If the formula is true, the load reduction action will not be triggered. If the formula is false, the low-frequency and low-voltage load reduction logic will be started, and non-critical loads will be cut off according to priority. After each level of load is cut off, the formula will be re-submitted for verification until the constraint conditions are met.

[0012] Furthermore, in step S5, when performing low-frequency, low-voltage load shedding, the dynamic load shedding calculation method is used to determine the single load shedding capacity. The calculation formula is as follows:

[0013] In the formula, The total active power load to be removed. The total active power load of the isolated network system. For the current active power output of the generator, This is the preset active power reserve margin; Non-critical loads are classified according to their importance from low to high as follows: N There are several load shedding cycles, each corresponding to a preset load capacity. Load shedding occurs sequentially according to the cycle order, and the total system load is updated after each cycle is shedding. And recalculate using the formula until... Stop unloading; If the power balance constraint is still not met after all non-critical loads are removed, the generator overload protection alarm will be triggered, and a warning signal will be output to the operation monitoring system.

[0014] Secondly, embodiments of this application also provide a generator islanded operation control device under power grid fault conditions, the device comprising: Main transformer protection unit, grid connection isolation execution unit, bus parameter acquisition unit, load classification and shedding unit, and core logic control unit; The core logic control unit establishes signal connections with the main transformer protection unit, grid-connected isolation execution unit, bus parameter acquisition unit, and load graded load reduction unit through control cables, respectively. The main transformer protection unit is located on the main transformer side of the power system. The signal output terminal of the main transformer protection unit is divided into two paths: the first path is connected to the core logic control unit and is used to collect the main transformer's electrical quantity and non-electrical quantity operation signals in real time, determine the power failure status of the system power supply side, and output a fault signal to the core logic control unit; the second path is directly connected to the trip control circuit of the upstream incoming circuit breaker of the grid-connected isolation execution unit through its own backup trip output and is used to output an instantaneous trip command when a power failure is determined. The grid-connected isolation execution unit includes an upstream incoming circuit breaker of the generator grid-connected cabinet, which is used to quickly trip after receiving a trip command to achieve electrical isolation between the generator bus and the external power grid; The bus parameter acquisition unit is located on the generator bus side and is used to collect system frequency, bus voltage and active power data of each branch in real time under isolated grid operation, and transmit the collected data to the core logic control unit. The load grading and load reduction unit is electrically connected to the protection devices of each load level on the bus side, and is used to receive load reduction control commands from the core logic control unit and cut off non-critical loads of the corresponding level according to a preset strategy.

[0015] Furthermore, the core logic control unit has a built-in power balance verification module, which pre-stores power balance constraint formulas and load classification lists; The power balance constraint formula is:

[0016] in, For the real-time active power output of the generator, The total active power of all critical loads. This refers to the total active power of the plant's power supply and generator auxiliary equipment. Pre-set active power reserve margin; The power balance verification module receives real-time power data transmitted by the bus parameter acquisition unit, substitutes it into the constraint formula to complete the verification, and outputs the verification result to the core logic control unit as the trigger basis for load reduction action.

[0017] Furthermore, the load grading and load reduction unit incorporates a multi-parameter joint criterion module, which employs a frequency-voltage-frequency change rate joint criterion algorithm and presets two sets of action triggering conditions: Condition one: and and ; Condition two: and ; In the formula, For the real-time frequency of the isolated network system, The threshold value is set for low frequency. This refers to the real-time bus voltage of the isolated grid system. The low-voltage setting threshold; For the duration of the parameter exceeding the limit, For the action time limit; The system frequency change rate, This is the frequency change rate setting value. This is the frequency offset buffer value; The multi-parameter joint criterion module receives real-time frequency and voltage data transmitted by the bus parameter acquisition unit, calculates the frequency change rate in real time, and outputs a load reduction trigger signal to the core logic control unit when any trigger condition is met, and outputs a regular load reduction or accelerated load reduction command according to the trigger condition type.

[0018] Furthermore, the load grading and load reduction unit also incorporates a dynamic load reduction calculation module and a round execution module; The dynamic load reduction calculation module has a preset formula for calculating the load shedding amount:

[0019] in, The required total active power load to be removed. The total active power load of the isolated network system. For the current active power output of the generator, Pre-set active power reserve margin; The execution module stores a table of non-critical load shedding cycles sorted by importance from low to high, with each cycle corresponding to a fixed load capacity. The dynamic load shedding calculation module calculates the required load shedding amount in real time. The execution module issues trip commands sequentially according to the cycle order. After each load shedding cycle, a feedback signal is sent to the dynamic load shedding calculation module for recalculation until the power balance constraint is met, at which point the load shedding is terminated.

[0020] Furthermore, the core logic control unit also incorporates a setpoint timing matching module and a plant power supply guarantee module; The fixed-value timing matching module has a pre-defined timing constraint formula:

[0021] in, The main transformer's main protection instantaneous tripping time. The inherent tripping time of the upstream incoming circuit breaker. This is the operating time for generator reverse power or out-of-step protection; the setting value timing matching module is used to verify the operating settings of each protection device to ensure that grid isolation is completed before the generator's own protection operates. The plant power supply protection module is electrically connected to the power supply circuit of the plant transformer and the local electrical control system of the generator set auxiliary equipment. It is used to monitor the power supply status of the plant power circuit in real time and lock the plant power and generator set auxiliary equipment circuits into an uncuttable state during load reduction.

[0022] As can be seen from the above technical solutions, the present invention has the following advantages: The generator islanded operation control method and device under power grid faults of the present invention only requires wiring modification of the backup trip outlet of the existing main transformer main protection device, and can achieve the function by optimizing the setting value and logic configuration of the existing load protection device. This reduces construction and operation and maintenance costs and avoids the functional redundancy and resource waste of configuring dedicated stability control equipment in small and medium-sized industrial power supply systems. By directly linking the main transformer main protection device to the tripping of the upstream incoming circuit breaker of the generator grid-connected cabinet, the electrical isolation of the power grid can be completed quickly in the instant of power failure. This ensures that the isolation action sequence precedes the generator reverse power and out-of-step protection action, avoids generator false shutdown under faults, and improves the success rate of islanded operation construction. By linking power balance verification with low-frequency low-voltage load reduction logic, non-critical loads are cut off as needed based on the real-time output of the generator and the load classification results. This ensures that the total load of the islanded grid does not exceed the rated output of the generator, and can reliably guarantee the continuous power supply of core production loads such as blast furnaces and oxygen production, as well as plant power, thus taking into account both the stability of power system operation and the reliability of core load power supply. Attached Figure Description

[0023] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart illustrating the generator isolated grid operation control method under power grid fault conditions as described in this application. Figure 2 This is a schematic diagram of the trip control circuit of the main protection device of the main transformer in the power system of this application, which is connected to the upstream incoming circuit breaker of the generator grid-connected cabinet. Figure 3 This is a schematic diagram of the generator islanding sequence in this application. Detailed Implementation

[0025] The various embodiments of the present invention will be described more fully in the following detailed description of the generator islanding operation control method and apparatus under power grid faults. The present invention may have various embodiments, and adjustments and modifications may be made therein. However, it should be understood that there is no intention to limit the various embodiments of the present invention to the specific embodiments disclosed herein, but rather the present invention should be understood to cover all adjustments, equivalents, and / or alternatives falling within the spirit and scope of the various embodiments of the present invention.

[0026] To make the objectives, features, and advantages of this invention more apparent and understandable, specific embodiments and accompanying drawings will be used to clearly and completely describe the technical solutions protected by this invention. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0027] Please see Figure 1 The diagram shows a flowchart of a generator islanded operation control method under power grid fault conditions. The method includes the following steps: S1. Connect the standby tripping output of the main protection device of the main transformer of the power system to the tripping control circuit of the upstream incoming circuit breaker of the generator grid connection cabinet. Classify all electrical loads on the generator bus side according to the importance of the load, and configure low-frequency low-voltage load shedding action settings and power balance verification logic for the protection devices corresponding to non-important loads. S2. Real-time acquisition of electrical and non-electrical signals of the main transformer through the main transformer protection device to continuously monitor the power supply operation status of the system power supply side. S3. When the main transformer protection device determines that a power failure has occurred on the power supply side of the system, it generates an instantaneous trip command, which is transmitted to the upstream incoming circuit breaker through the backup trip output, triggering the circuit breaker to open, so that the generator and the load on the bus are electrically isolated from the external power grid. S4. After completing grid isolation, collect the real-time frequency, bus voltage, generator output, power of important loads, plant power and auxiliary equipment load power of the isolated grid system in real time. S5. Based on the real-time frequency, bus voltage, generator output, power of each important load, plant power and auxiliary equipment load power collected, perform power balance verification and low-frequency low-voltage load reduction, cut off corresponding non-important loads, so that the total power load of the islanded grid system does not exceed the generator's rated output, and maintain the stable operation of the islanded grid system.

[0028] As a refinement and extension of the specific implementation of the above embodiments, in order to fully illustrate the specific implementation process in this embodiment, another generator islanded operation control method under power grid faults is provided, which includes the following steps: S1. Connect the standby tripping output of the main protection device of the main transformer of the power system to the tripping control circuit of the upstream incoming circuit breaker of the generator grid connection cabinet. Classify all electrical loads on the generator bus side according to the importance of the load, and configure low-frequency low-voltage load shedding action settings and power balance verification logic for the protection devices corresponding to non-important loads. The standby trip output of the main protection device of the main transformer in the power system is connected to the trip control circuit of the upstream incoming circuit breaker of the generator grid-connected cabinet, such as... Figure 2 As shown; In step S1, the constraint formula for the power balance verification logic is:

[0029] In the formula, For the real-time active power output of the generator, The total active power of all critical loads. This refers to the total active power of the plant's power load and the load of the generator set's auxiliary equipment local electrical control system. This is the pre-set active power reserve margin for isolated network operation; In step S1, non-critical loads are divided into multiple load shedding cycles according to their importance from low to high. The low-frequency, low-voltage load shedding action setting adopts a multi-parameter joint criterion of frequency, voltage, and frequency change rate. Specifically, the load shedding action is triggered when any of the following conditions are met: Condition one: and and ; Condition two: and ; In the formula, For the real-time frequency of the isolated network system, The low-frequency tuning threshold is set to 48.5Hz; This refers to the real-time bus voltage of the isolated grid system. The low-voltage setting threshold is set to 85% of the rated bus voltage. For the duration of the parameter exceeding the limit, This is the action duration, with a value of 0.2s. The system frequency change rate, This is the frequency change rate setting value. This is the frequency offset buffer value; When condition one is met, the tiered load shedding is triggered according to the normal time limit; when condition two is met, it is determined that there is a large power shortage in the system, and the accelerated load shedding action is triggered to directly cut off the first level of non-critical loads to avoid the system frequency from dropping and collapsing rapidly; during the load shedding process, the power balance check is re-executed after each level of load is cut off, and the load shedding is terminated immediately if the constraints are met.

[0030] Step S1 also includes a relay protection setting timing matching algorithm to ensure the timing coordination between isolation actions and island network construction when the system loses power. The specific setting constraint formula is as follows:

[0031] In the formula, The instantaneous tripping time of the main transformer's main protection device. This refers to the inherent tripping time of the upstream incoming circuit breaker of the generator grid-connected cabinet. This refers to the operating time of the generator reverse power protection or out-of-step protection.

[0032] It should be noted that by setting the instantaneous trip setting of the main protection and the circuit breaker tripping speed, grid isolation is ensured before the generator's own protection operates, preventing the generator from tripping due to reverse power or loss of synchronism, thus ensuring the success rate of islanded operation; at the same time, the low-frequency low-voltage load shedding action time limit is set. Greater than the total duration of grid isolation action This prevents voltage frequency fluctuations during isolation from erroneously triggering load shearing actions.

[0033] S2. Real-time acquisition of electrical and non-electrical signals of the main transformer through the main transformer protection device to continuously monitor the power supply operation status of the system power supply side. S3. When the main transformer protection device determines that a power failure has occurred on the power supply side of the system, it generates an instantaneous trip command, which is transmitted to the upstream incoming circuit breaker through the backup trip output, triggering the circuit breaker to open, so that the generator and the load on the bus are electrically isolated from the external power grid. like Figure 3 As shown, when the system loses power, "Protection Device-1" trips "Protection Device-2" instantly; "Protection Devices-3 and-5" operate normally; "Protection Device-4" activates the low-frequency and low-voltage tripping function; "Blast Furnace System, Oxygen Inhalation System, Generator Grid Connection Cabinet, and Plant Auxiliary Transformer Ticket" operate normally; and the generator set auxiliary equipment local electrical control system operates normally.

[0034] S4. After completing grid isolation, collect the real-time frequency, bus voltage, generator output, power of important loads, plant power and auxiliary equipment load power of the isolated grid system in real time. S5. Based on the real-time frequency, bus voltage, generator output, power of each important load, plant power and auxiliary equipment load power collected, perform power balance verification and low-frequency low-voltage load reduction, cut off corresponding non-important loads, so that the total power load of the islanded grid system does not exceed the generator's rated output, and maintain the stable operation of the islanded grid system.

[0035] In step S5, the specific process of performing the power balance verification is as follows: S51. After grid isolation is completed, the current generator output will be collected in real time. The power of each important load, the power of plant power and the power of auxiliary equipment load are substituted into the constraint formula of the power balance verification logic for verification; S52. If the formula is true, the load reduction action will not be triggered. If the formula is false, the low-frequency and low-voltage load reduction logic will be started, and non-critical loads will be cut off according to priority. After each level of load is cut off, the formula will be re-submitted for verification until the constraint conditions are met.

[0036] It should be noted that important loads and non-important loads are classified according to GB 50052 "Code for Design of Power Supply and Distribution System" and GB / T 50655 "Electricity Design Standard for Iron and Steel Enterprises". Blast furnace system and oxygen production system are classified as important loads that cannot be cut off, while auxiliary production loads such as sintering system are classified as non-important loads that can be cut off. Plant power load and generator auxiliary load are included in the scope of guaranteed loads and are not included in the sequence of loads that can be cut off.

[0037] In step S5, when performing low-frequency, low-voltage load shedding, the dynamic load shedding calculation method is used to determine the single load shedding capacity. The calculation formula is as follows:

[0038] In the formula, The total active power load to be removed. The total active power load of the isolated network system. For the current active power output of the generator, This is the preset active power reserve margin; Non-critical loads are classified according to their importance from low to high as follows: N There are several load shedding cycles, each corresponding to a preset load capacity. Load shedding occurs sequentially according to the cycle order, and the total system load is updated after each cycle is shedding. And recalculate using the formula until... Stop unloading; If the power balance constraint is still not met after all non-critical loads are removed, the generator overload protection alarm will be triggered, and a warning signal will be output to the operation monitoring system.

[0039] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0040] The following embodiment is a generator islanded operation control device under power grid fault conditions. The device includes: The device includes: Main transformer protection unit, grid connection isolation execution unit, bus parameter acquisition unit, load classification and shedding unit, and core logic control unit; The core logic control unit establishes signal connections with the main transformer protection unit, grid-connected isolation execution unit, bus parameter acquisition unit, and load graded load reduction unit through control cables, respectively. The main transformer protection unit is located on the main transformer side of the power system. The signal output terminal of the main transformer protection unit is divided into two paths: the first path is connected to the core logic control unit and is used to collect the main transformer's electrical quantity and non-electrical quantity operation signals in real time, determine the power failure status of the system power supply side, and output a fault signal to the core logic control unit; the second path is directly connected to the trip control circuit of the upstream incoming circuit breaker of the grid-connected isolation execution unit through its own backup trip output and is used to output an instantaneous trip command when a power failure is determined. The grid-connected isolation execution unit includes an upstream incoming circuit breaker of the generator grid-connected cabinet, which is used to quickly trip after receiving a trip command to achieve electrical isolation between the generator bus and the external power grid; The bus parameter acquisition unit is located on the generator bus side and is used to collect system frequency, bus voltage and active power data of each branch in real time under isolated grid operation, and transmit the collected data to the core logic control unit. The load grading and load reduction unit is electrically connected to the protection devices of each load level on the bus side, and is used to receive load reduction control commands from the core logic control unit and cut off non-critical loads of the corresponding level according to a preset strategy.

[0041] As a refinement and extension of the specific implementation of the above embodiments, in order to fully illustrate the specific implementation process of this embodiment, another generator islanded operation control device under power grid fault conditions is provided, which includes: Main transformer protection unit, grid connection isolation execution unit, bus parameter acquisition unit, load classification and shedding unit, and core logic control unit; The core logic control unit establishes signal connections with the main transformer protection unit, grid-connected isolation execution unit, bus parameter acquisition unit, and load graded load reduction unit through control cables, respectively. The core logic control unit has a built-in power balance verification module, which pre-stores power balance constraint formulas and load classification lists. The power balance constraint formula is:

[0042] in, For the real-time active power output of the generator, The total active power of all critical loads. This refers to the total active power of the plant's power supply and generator auxiliary equipment. Pre-set active power reserve margin; The power balance verification module receives real-time power data transmitted by the bus parameter acquisition unit, substitutes it into the constraint formula to complete the verification, and outputs the verification result to the core logic control unit as the trigger basis for load reduction action.

[0043] The core logic control unit also has a built-in setpoint timing matching module and a plant power supply guarantee module. The fixed-value timing matching module has a pre-defined timing constraint formula:

[0044] in, The main transformer's main protection instantaneous tripping time. The inherent tripping time of the upstream incoming circuit breaker. This is the operating time for generator reverse power or out-of-step protection; the setting value timing matching module is used to verify the operating settings of each protection device to ensure that grid isolation is completed before the generator's own protection operates. The plant power supply protection module is electrically connected to the power supply circuit of the plant transformer and the local electrical control system of the generator set auxiliary equipment. It is used to monitor the power supply status of the plant power circuit in real time and lock the plant power and generator set auxiliary equipment circuits into an uncuttable state during the load reduction process.

[0045] The main transformer protection unit is located on the main transformer side of the power system. The signal output terminal of the main transformer protection unit is divided into two paths: the first path is connected to the core logic control unit and is used to collect the main transformer's electrical quantity and non-electrical quantity operation signals in real time, determine the power failure status of the system power supply side, and output a fault signal to the core logic control unit; the second path is directly connected to the trip control circuit of the upstream incoming circuit breaker of the grid-connected isolation execution unit through its own backup trip output and is used to output an instantaneous trip command when a power failure is determined. The grid-connected isolation execution unit includes an upstream incoming circuit breaker of the generator grid-connected cabinet, which is used to quickly trip after receiving a trip command to achieve electrical isolation between the generator bus and the external power grid; The bus parameter acquisition unit is located on the generator bus side and is used to collect system frequency, bus voltage and active power data of each branch in real time under isolated grid operation, and transmit the collected data to the core logic control unit. The load grading and load reduction unit is electrically connected to the protection devices of each load level on the bus side, and is used to receive load reduction control commands from the core logic control unit and cut off non-critical loads of the corresponding level according to a preset strategy.

[0046] The load grading and load reduction unit has a built-in multi-parameter joint criterion module, which uses a frequency-voltage-frequency change rate joint criterion algorithm and presets two sets of action triggering conditions: Condition one: and and ; Condition two: and ; In the formula, For the real-time frequency of the isolated network system, The low-frequency tuning threshold is set to 48.5Hz; This refers to the real-time bus voltage of the isolated grid system. The low-voltage setting threshold is set to 85% of the rated bus voltage. For the duration of the parameter exceeding the limit, This is the action duration, with a value of 0.2s. The system frequency change rate, This is the frequency change rate setting value. This is the frequency offset buffer value; The multi-parameter joint criterion module receives real-time frequency and voltage data transmitted by the bus parameter acquisition unit, calculates the frequency change rate in real time, and outputs a load reduction trigger signal to the core logic control unit when any trigger condition is met, and outputs a regular load reduction or accelerated load reduction command according to the trigger condition type.

[0047] The load grading and load reduction unit also has a built-in dynamic load reduction calculation module and a round execution module; The dynamic load reduction calculation module has a preset formula for calculating the load shedding amount:

[0048] in, The required total active power load to be removed. The total active power load of the isolated network system. For the current active power output of the generator, Pre-set active power reserve margin; The execution module stores a table of non-critical load shedding cycles sorted by importance from low to high, with each cycle corresponding to a fixed load capacity. The dynamic load shedding calculation module calculates the required load shedding amount in real time. The execution module issues trip commands sequentially according to the cycle order. After each load shedding cycle, a feedback signal is sent to the dynamic load shedding calculation module for recalculation until the power balance constraint is met, at which point the load shedding is terminated.

[0049] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling generator isolated operation under power grid faults, characterized in that, The method includes the following steps: S1. Connect the standby tripping output of the main protection device of the main transformer of the power system to the tripping control circuit of the upstream incoming circuit breaker of the generator grid connection cabinet. Classify all electrical loads on the generator bus side according to the importance of the load, and configure low-frequency low-voltage load shedding action settings and power balance verification logic for the protection devices corresponding to non-important loads. S2. Real-time acquisition of electrical and non-electrical signals of the main transformer through the main transformer protection device to continuously monitor the power supply operation status of the system power supply side. S3. When the main transformer protection device determines that a power failure has occurred on the power supply side of the system, it generates an instantaneous trip command, which is transmitted to the upstream incoming circuit breaker through the backup trip output, triggering the circuit breaker to open, so that the generator and the load on the bus are electrically isolated from the external power grid. S4. After completing grid isolation, collect the real-time frequency, bus voltage, generator output, power of important loads, plant power and auxiliary equipment load power of the isolated grid system in real time. S5. Based on the real-time frequency, bus voltage, generator output, power of each important load, plant power and auxiliary equipment load power collected, perform power balance verification and low-frequency low-voltage load reduction, cut off corresponding non-important loads, so that the total power load of the islanded grid system does not exceed the generator's rated output, and maintain the stable operation of the islanded grid system.

2. The generator islanded operation control method under power grid faults according to claim 1, characterized in that, In step S1, the constraint formula for the power balance verification logic is: In the formula, For the real-time active power output of the generator, The total active power of all critical loads. This refers to the total active power of the plant's power load and the load of the generator set's auxiliary equipment local electrical control system. This is the pre-set active power reserve margin for isolated network operation; In step S1, non-critical loads are divided into multiple load shedding cycles according to their importance from low to high. The low-frequency, low-voltage load shedding action setting adopts a multi-parameter joint criterion of frequency, voltage, and frequency change rate. Specifically, the load shedding action is triggered when any of the following conditions are met: Condition one: and and ; Condition two: and ; In the formula, For the real-time frequency of the isolated network system, The threshold value is set for low frequency. This refers to the real-time bus voltage of the isolated grid system. The low-voltage setting threshold; For the duration of the parameter exceeding the limit, For the action time limit; The system frequency change rate, This is the frequency change rate setting value. This is the frequency offset buffer value; When condition one is met, the tiered load reduction is triggered according to the normal time limit; when condition two is met, it is determined that there is a large power shortage in the system, and the accelerated load reduction action is triggered, directly cutting off the first level of non-critical loads; during the load reduction process, after each level of load is cut off, the power balance check is re-executed, and the load reduction is terminated immediately if the constraint is met.

3. The generator islanded operation control method under power grid faults according to claim 1, characterized in that, Step S1 also includes a relay protection setting timing matching algorithm to ensure the timing coordination between isolation actions and island network construction when the system loses power. The specific setting constraint formula is as follows: In the formula, The instantaneous tripping time of the main transformer's main protection device. This refers to the inherent tripping time of the upstream incoming circuit breaker of the generator grid-connected cabinet. This refers to the operating time of the generator reverse power protection or out-of-step protection.

4. The generator islanded operation control method under power grid faults according to claim 1, characterized in that, In step S5, the specific process of performing the power balance verification is as follows: S51. After grid isolation is completed, the current generator output will be collected in real time. The power of each important load, the power of plant power and the power of auxiliary equipment load are substituted into the constraint formula of the power balance verification logic for verification; S52. If the formula is true, the load reduction action will not be triggered. If the formula is false, the low-frequency and low-voltage load reduction logic will be started, and non-critical loads will be cut off according to priority. After each level of load is cut off, the formula will be re-submitted for verification until the constraint conditions are met.

5. The generator islanded operation control method under power grid faults according to claim 4, characterized in that, In step S5, when performing low-frequency, low-voltage load shedding, the dynamic load shedding calculation method is used to determine the single load shedding capacity. The calculation formula is as follows: In the formula, The total active power load to be removed. The total active power load of the isolated network system. For the current active power output of the generator, This is the preset active power reserve margin; Non-critical loads are classified according to their importance from low to high as follows: N There are several load shedding cycles, each corresponding to a preset load capacity. Load shedding occurs sequentially according to the cycle order, and the total system load is updated after each cycle is shedding. And recalculate using the formula until... Stop unloading; If the power balance constraint is still not met after all non-critical loads are removed, the generator overload protection alarm will be triggered, and a warning signal will be output to the operation monitoring system.

6. A generator islanded operation control device under power grid fault conditions, characterized in that, The apparatus is used to implement the method as described in any one of claims 1-5, the apparatus comprising: Main transformer protection unit, grid connection isolation execution unit, bus parameter acquisition unit, load classification and shedding unit, and core logic control unit; The core logic control unit establishes signal connections with the main transformer protection unit, grid-connected isolation execution unit, bus parameter acquisition unit, and load graded load reduction unit through control cables, respectively. The main transformer protection unit is located on the main transformer side of the power system. The signal output terminal of the main transformer protection unit is divided into two paths: the first path is connected to the core logic control unit and is used to collect the main transformer's electrical quantity and non-electrical quantity operation signals in real time, determine the power failure status of the system power supply side, and output a fault signal to the core logic control unit; the second path is directly connected to the trip control circuit of the upstream incoming circuit breaker of the grid-connected isolation execution unit through its own backup trip output and is used to output an instantaneous trip command when a power failure is determined. The grid-connected isolation execution unit includes an upstream incoming circuit breaker of the generator grid-connected cabinet, which is used to quickly trip after receiving a trip command to achieve electrical isolation between the generator bus and the external power grid; The bus parameter acquisition unit is located on the generator bus side and is used to collect system frequency, bus voltage and active power data of each branch in real time under isolated grid operation, and transmit the collected data to the core logic control unit. The load grading and load reduction unit is electrically connected to the protection devices of each load level on the bus side, and is used to receive load reduction control commands from the core logic control unit and cut off non-critical loads of the corresponding level according to a preset strategy.

7. The generator islanded operation control device under power grid fault conditions according to claim 6, characterized in that, The core logic control unit has a built-in power balance verification module, which pre-stores power balance constraint formulas and load classification lists. The power balance constraint formula is: in, For the real-time active power output of the generator, The total active power of all critical loads. This refers to the total active power of the plant's power supply and generator auxiliary equipment. Pre-set active power reserve margin; The power balance verification module receives real-time power data transmitted by the bus parameter acquisition unit, substitutes it into the constraint formula to complete the verification, and outputs the verification result to the core logic control unit as the trigger basis for load reduction action.

8. The generator islanded operation control device under power grid accident as described in claim 6, characterized in that, The load grading and load reduction unit has a built-in multi-parameter joint criterion module, which uses a frequency-voltage-frequency change rate joint criterion algorithm and presets two sets of action triggering conditions: Condition one: and and ; Condition two: and ; In the formula, For the real-time frequency of the isolated network system, The threshold value is set for low frequency. This refers to the real-time bus voltage of the isolated grid system. The low-voltage setting threshold; For the duration of the parameter exceeding the limit, For the action time limit; The system frequency change rate, This is the frequency change rate setting value. This is the frequency offset buffer value; The multi-parameter joint criterion module receives real-time frequency and voltage data transmitted by the bus parameter acquisition unit, calculates the frequency change rate in real time, and outputs a load reduction trigger signal to the core logic control unit when any trigger condition is met, and outputs a regular load reduction or accelerated load reduction command according to the trigger condition type.

9. The generator islanded operation control device under power grid fault conditions according to claim 8, characterized in that, The load grading and load reduction unit also has a built-in dynamic load reduction calculation module and a round execution module; The dynamic load reduction calculation module has a preset formula for calculating the load shedding amount: in, The required total active power load to be removed. The total active power load of the isolated network system. For the current active power output of the generator, Pre-set active power reserve margin; The execution module stores a table of non-critical load shedding cycles sorted by importance from low to high, with each cycle corresponding to a fixed load capacity. The dynamic load shedding calculation module calculates the required load shedding amount in real time. The execution module issues trip commands sequentially according to the cycle order. After each load shedding cycle, a feedback signal is sent to the dynamic load shedding calculation module for recalculation until the power balance constraint is met, at which point the load shedding is terminated.

10. The generator islanded operation control device under power grid accident as described in claim 6, characterized in that, The core logic control unit also has a built-in setpoint timing matching module and a plant power supply guarantee module. The fixed-value timing matching module has a pre-defined timing constraint formula: in, The main transformer's main protection instantaneous tripping time. The inherent tripping time of the upstream incoming circuit breaker. This is the operating time for generator reverse power or out-of-step protection; the setting value timing matching module is used to verify the operating settings of each protection device to ensure that grid isolation is completed before the generator's own protection operates. The plant power supply protection module is electrically connected to the power supply circuit of the plant transformer and the local electrical control system of the generator set auxiliary equipment. It is used to monitor the power supply status of the plant power circuit in real time and lock the plant power and generator set auxiliary equipment circuits into an uncuttable state during load reduction.

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