Improved method for low voltage ride through protection of coal feeder based on dcs logic control

Abstract

An improved method of low-voltage ride-through protection of a coal feeder based on DCS logic control.The prior art has frequent large changes in the rotating speed of the coal feeder during coal cutting; when the rotating speed signal detected in the coal feeder changes greatly, the internal program judges that the rotating speed is abnormal, which causes the coal feeder to trigger a trip signal by mistake, and brings great safety hazards to the normal operation of the unit.The present application comprises the following steps: (1) an internal program modification method of the coal feeder microcomputer board; (2) a low-voltage judgment method of the coal feeder control loop; (3) a logic configuration method of the self-starting of the low-voltage fault of the coal feeder; (4) a fault simulation method of the internal program of the coal feeder; (5) a setting method of the internal parameters of the frequency converter of the coal feeder; an alternative control method of the low-voltage ride-through control device of the coal feeder is proposed, which solves the problem of the coal feeder tripping by mistake due to the rotating speed during coal cutting.The present application is used for the improved method of low-voltage ride-through protection of the coal feeder based on DCS logic control.

Description

Technical Field

[0001] This invention relates to the field of electronic weighing coal feeder technology in power plant boilers, and specifically to an improved method for low voltage ride-through protection of coal feeders based on DCS logic control. Background Technology

[0002] Most coal feeders are belt feeders with microcomputer-controlled electronic weighing and automatic speed regulation devices. When the coal feeder trips for some reason, the microcomputer board detects the trip signal and the coal feeder will automatically switch to local operation, disconnecting the internal electrical circuit and preventing it from starting automatically remotely.

[0003] In recent years, abnormal incidents of coal feeder tripping due to voltage fluctuations have occurred frequently in various regions. In response to this situation, this method proposes a control method that can quickly start the coal feeder when the grid voltage drops instantaneously without changing the original coal feeder control circuit or adding equipment, so as to improve the reliability of the equipment and ensure the safe operation of the unit.

[0004] Currently, existing technologies are exploring methods for blending and burning coal. During this exploration process, coal feeders inevitably experience frequent coal shortages due to coal quality issues. Most coal feeders control coal quantity by multiplying the weight of a unit belt by its rotational speed to calculate the feed rate. Therefore, during coal shortages, the feeder speed often fluctuates significantly. When the feeder detects a significant change in the speed signal, the internal program judges the speed as abnormal, causing the feeder to erroneously trigger a trip signal, posing a significant safety hazard to the normal operation of the unit.

[0005] In response to the above three situations, this application proposes a control method that can replace the low voltage ride-through control device of the coal feeder, and solves the problem of the coal feeder tripping erroneously due to its speed, thereby improving the stability of the coal feeder. Summary of the Invention

[0006] The purpose of this invention is to provide an improved method for low voltage ride-through protection of a coal feeder based on DCS logic control. This method is mainly applied to a coal feeder control system with frequency conversion regulation function and the frequency converter has a fault self-reset function. It proposes a control method that can replace the low voltage ride-through control device of the coal feeder and solves the problem of the coal feeder tripping erroneously due to speed reasons during the coal cutting process, thereby improving the reliability of the coal feeder.

[0007] The above objectives are achieved through the following technical solutions:

[0008] An improved method for low-voltage ride-through protection of a coal feeder based on DCS logic control, the method comprising the following steps:

[0009] Step 1: Method for modifying the internal program of the coal feeder's microcomputer board;

[0010] Step 2: Method for determining low voltage in the coal feeder control circuit;

[0011] Step 3: Logic configuration method for automatic restart of coal feeder under low voltage fault;

[0012] Step 4: Simulation method for internal program faults in the coal feeder;

[0013] Step 5: How to set the internal parameters of the coal feeder frequency converter;

[0014] Step one, modifying the internal program of the coal feeder's microcomputer board, includes:

[0015] (1) Cancel the internal trip fault code of the coal feeder and merge the trip fault code and alarm fault code; for example, there are 7 fault codes that are ORed from 1 to 7 respectively, and 4 trip fault codes that are ORed from 8 to 11 respectively. These 11 fault codes can be output as a single comprehensive fault code. All 11 fault codes are ORed and are only used as fault alarms. The trip fault code is canceled.

[0016] Step two, the method for determining low voltage in the coal feeder control circuit, includes: the method for installing a coal feeder incoming line voltage monitor and the method for installing a control circuit voltage monitor, specifically including the following conditions:

[0017] (1) The bus voltage of the PC section where the coal feeder is located is lower than the incoming line voltage;

[0018] (2) Low voltage in the power circuit of the coal feeder;

[0019] (3) Low voltage in the coal feeder control circuit;

[0020] To ensure the reliability of the low voltage judgment condition for the coal feeder, the low voltage of the coal feeder inlet line is judged when any two of the above three conditions are met.

[0021] Step three, the logic configuration method for automatic restart of the coal feeder in case of low voltage fault;

[0022] (1) When the low voltage condition of the coal feeder is met in step two, the automatic start condition of the coal feeder is triggered;

[0023] (2) When the condition in (1) is met, a 10s pulse signal is triggered and the automatic start of the coal feeder fails within 10s, the logic is reset once and the automatic start of the coal feeder is performed again; where (1) and (2) are OR relationships;

[0024] Step four: Method for simulating internal program faults in the coal feeder;

[0025] (1) Implementation method of auxiliary logic:

[0026] A. The power plant boiler has a coal feeder complete shutdown protection logic in the loss of all fuel. In order to prevent the coal feeder from tripping abnormally due to a large reduction in the power grid in extreme cases, which would lead to boiler MFT, the low voltage judgment condition can be used as the assignment value of the coal feeder complete shutdown delay. The judgment condition in step two is the low voltage judgment condition of each coal feeder. The low voltage requirement of the coal feeder complete shutdown protection requires all operating coal feeders to meet the conditions in step two to trigger the change of the delay time.

[0027] B. Add a low voltage delay to the coal feeder full stop protection. The delay time is set to 1 second under normal conditions. When condition A is detected, the delay time parameter will be automatically set to 3 seconds.

[0028] (2) Simulation of coal feeder fault codes;

[0029] To prevent the coal feeder from failing to trip in a faulty state, which could lead to unit malfunctions, simulations need to be performed in the DCS logic.

[0030] A. Add a coal feeder trip judgment to the DCS logic, and make a judgment based on the actual situation;

[0031] a. The deviation between the coal feeder command and the coal quantity feedback signal is greater than ±5t / h;

[0032] b. The coal feeder fault signal is triggered, where a and b are ANDed and used as the judgment for the coal feeder tripping;

[0033] B. Add a first-level alarm to the DCS logic;

[0034] The deviation between the coal feeder command and the coal quantity feedback signal is greater than ±10t / h;

[0035] Step five: Method for setting the internal parameters of the coal feeder frequency converter;

[0036] The inverter's overcurrent reset, overvoltage reset, undervoltage reset, analog input fault, and external fault reset functions are all enabled. The inverter fault reset parameters are set to multiple reset times, greater than 10 seconds, and 0.1 seconds fault reset delay time. This ensures that the inverter will reset immediately when a fault occurs. The inverter fault start prohibition function is set to allow start, so that the inverter can start automatically as soon as it is activated after an automatic fault reset. Beneficial effects

[0037] 1. This invention is an improved method for low voltage ride-through protection of coal feeders based on DCS logic control. This method proposes a control method that can quickly start the coal feeder when the grid voltage drops instantaneously without changing the original coal feeder control circuit or adding low voltage ride-through equipment, so as to improve the reliability of the equipment and ensure the safe operation of the unit.

[0038] 2. This invention solves the problem that during the coal feeder's shutdown process, the internal program misjudges the abnormal speed and triggers the trip signal due to the large change in the feeder's speed, thus improving the reliability of the coal feeder equipment.

[0039] 3. This invention utilizes this method to move the internal fault codes of the coal feeder to the DCS for display according to actual needs, making fault diagnosis clearer and more accurate. Attached Figure Description

[0040] Figure 1 is a schematic diagram of the principle of the coal feeder of the present invention;

[0041] Figure 2 is one of the diagrams illustrating the method for determining and assigning values ​​to the coal feeder complete stop delay time under low voltage according to the present invention;

[0042] Figure 3 is the second diagram of the method for determining and assigning values ​​to the coal feeder complete stop delay time under low voltage according to the present invention;

[0043] Figure 4 is one of the configuration method diagrams for the automatic start-up conditions of the coal feeder according to the present invention;

[0044] Figure 5 is a second configuration diagram of the conditions for automatic start-up of the coal feeder according to the present invention;

[0045] Figure 6 is one of the method diagrams for adding tripping logic to the DCS of the present invention;

[0046] Figure 7 is a second diagram illustrating the method of adding tripping logic to the DCS of the present invention. Detailed Implementation Example

[0047] An improved method for low voltage ride-through protection of a coal feeder based on DCS logic control is proposed. The method mainly includes the following steps: adding a voltage monitoring transmitter to the coal feeder, judging the low voltage of the coal feeder, judging the automatic start of the coal feeder, and judging the protection logic of the coal feeder.

[0048] Referring to Figure 1, in this example, the coal feeder control power supply is 110V, which is derived from the 380V power supply through a 110V transformer. The internal operation of the coal feeder is controlled by a self-holding circuit, and the relay uses an AC 110V coil. In order to reliably monitor the changes in the internal voltage of the coal feeder, voltage monitoring points can be added to any two incoming lines in the power circuit of the coal feeder, and voltage monitoring points can be added to the control power supply.

[0049] In this example, there are a total of 11 fault codes for the coal feeder, ranging from 01 to 11. There are 7 alarm codes. When the coal feeder alarms, only the alarm signal is triggered; the feeder does not trip, and the control circuit does not switch to local control. There are 4 shutdown codes. When a fault code is triggered, the feeder switches to local control, and it cannot be restarted remotely. To solve this problem, the program on the feeder's microcomputer board is modified in this example, merging the 4 shutdown codes and alarm codes, and changing the shutdown codes into alarm codes.

[0050] Refer to Figure 2 for the method of determining the delay time for the complete shutdown of the coal feeder when the voltage is low. The low voltage determination only illustrates the determination for one coal feeder. Since two voltage monitoring points are already installed inside the coal feeder, the following method can be used:

[0051] ① The coal feeder's inlet voltage is low;

[0052] ② The coal feeder has low power supply;

[0053] ③ The control power supply of the coal feeder is low. This is used as the judgment for low voltage of each coal feeder. The low voltage values ​​for the coal feeder's input line voltage and power supply voltage are 300V, and the low voltage value for the control power supply is 100V. To ensure that the judgment settings are accurate and reliable, two out of three (①②③) can be used for judgment, which will be used as the judgment for low voltage of each coal feeder.

[0054] See Figure 3 If the voltage of the coal feeder bus drops, it will cause the coal feeder to stop instantly and the unit to trip. The low voltage judgment condition of the coal feeder can be used to assign a delay time value to the coal feeder stop protection. The T block in Figure 4 is the switching block. The normal delay time is 1 second. When the low voltage of the coal feeder is detected, the delay time is assigned to 3 seconds. After the coal feeder stops for 3 seconds, the unit will trip.

[0055] Refer to Figure 4 for the automatic start-up judgment method of the coal feeder. The low voltage of the coal feeder is output 1 in Figure 1. Since the fluctuation of the grid voltage will affect the fluctuation of the 6kV system voltage, the 6kV bus voltage can be used as the judgment condition for low grid voltage. Consideration should be given to the reliable start-up of the coal feeder under low voltage.

[0056] The following conditions apply:

[0057] ① The line voltage of the PTs on the A and B sections of the 6kV operating bus is less than 5.5kV;

[0058] ②The bus voltage of the boiler PC section is less than 300V;

[0059] ③ The coal feeder voltage is low;

[0060] When any one of the conditions ①②③ is met, a 3s pulse command and the upper feeder running signal are triggered, and the feeder is automatically started once.

[0061] The reverse delay TD OFF after the coal feeder operation signal means that the coal feeder operation signal disappears after a 10-second delay.

[0062] See Figure 5. ① When the coal feeder voltage is low; ② When the coal feeder fails to start; When both conditions ① and ② are met, the coal feeder will be automatically started again; The low voltage signal of the coal feeder is followed by a reverse delay TD OFF, which means that the coal feeder running signal will disappear after a 10-second delay; The coal feeder protection logic has been changed to an alarm, and the coal feeder tripping condition needs to be added to the DCS logic.

[0063] Currently, most coal feeders control the coal quantity by multiplying the weight of a unit belt by the belt speed to calculate the coal feed rate; and using the deviation of the coal quantity as the DCS logic judgment.

[0064] Referring to Figure 6, in this practical example, an alarm condition is added to the DCS logic: when the deviation between the actual coal feed rate and the coal feed rate command is greater than ±10t / h, it serves as the coal feeder alarm condition; when the coal feed rate deviation is greater than ±10t / h and the coal feeder malfunctions, it serves as the coal feeder trip condition. Regarding inverter parameter settings, this example requires an inverter with a fault self-reset function, using the ABB ACS510 inverter as an example. The inverter's automatic fault reset function is as follows: Enable all inverter functions: 3104 Overcurrent Reset, 3105 Overvoltage Reset, 3106 Undervoltage Reset, 3107 Analog Input Fault, and 3108 External Fault Reset. Inverter fault reset parameter 3101 is the number of inverter fault resets, which can be set to 5 times; parameter 3102 is the inverter reset time, which can be set to 30s, so that when the inverter detects a fault, it can continuously reset the inverter 5 times within this time period; parameter 3103... The fault reset delay time can be set to 0.1s, so that when the inverter fails, it will immediately reset other inverter functions; the inverter's internal undervoltage control function parameter is 2106, which enables the undervoltage control function; when the inverter detects a voltage drop, it will automatically adjust the frequency to a suitable value; the start-disable function parameter is 2108, which sets the start-disable function to 0, so that after the inverter fault is reset, the inverter can be restarted immediately as long as the function is activated;

[0065] The control method described in this example has been practically applied in the field. Through modifications and experiments to the above method, the coal feeder can start quickly after a voltage drop, which fully meets the requirements of the field conditions. In addition, by modifying the internal logic of the coal feeder using the above method, the faults of the coal feeder can be made more visible and the fault diagnosis can be more accurate, which greatly reduces the frequency of abnormal tripping of the coal feeder due to speed.

Claims

1. An improved method for low-voltage ride-through protection of a coal feeder based on DCS logic control, characterized in that, Includes the following steps: Step 1: Method for modifying the internal program of the coal feeder's microcomputer board; The internal trip fault codes of the coal feeder are cancelled. All trip fault codes and alarm fault codes are merged into a single comprehensive fault code. All fault codes are ORed, and only alarm signals are triggered. The coal feeder will not trip. The fault codes include 7 alarm codes and 4 trip codes, for a total of 11. Step two, the method for determining low voltage in the coal feeder control circuit, includes: the method for installing a coal feeder incoming line voltage monitor, and the method for installing a control circuit voltage monitor, specifically including the following conditions: (1) The bus voltage of the PC section where the coal feeder is located is lower than the incoming line voltage; (2) Low voltage in the power circuit of the coal feeder; (3) Low voltage in the coal feeder control circuit; To ensure the reliability of the low voltage judgment condition for the coal feeder, the low voltage of the coal feeder inlet line is judged when any two of the above three conditions are met. Step 3: Logic configuration method for automatic restart of coal feeder under low voltage fault; When the low voltage condition in step two is met, a pulse signal lasting 10 seconds is triggered to drive the coal feeder to start automatically; if the automatic start fails within 10 seconds, the logic is reset and the automatic start is executed again. Step 4: Simulation method for internal program faults in the coal feeder; (1) Implementation method of auxiliary logic: A. The power plant boiler has a coal feeder complete shutdown protection logic in the loss of all fuel. In order to prevent the coal feeder from tripping abnormally due to a large reduction in the power grid in extreme cases, which would lead to boiler MFT, the low voltage judgment condition is used as the assignment value of the coal feeder complete shutdown delay. The judgment condition in step two is the low voltage judgment condition of each coal feeder. The low voltage requirement of the coal feeder complete shutdown protection requires all operating coal feeders to meet the conditions in step two to trigger the delay time change. B. Add a low voltage delay to the coal feeder full stop protection. The delay time is set to 1 second under normal conditions. When condition A is detected, the delay time parameter will be automatically set to 3 seconds. (2) Simulation of coal feeder fault codes; To prevent the coal feeder from failing to trip in a faulty state, which could lead to unit malfunctions, simulations need to be performed in the DCS logic. A. Add a coal feeder trip judgment to the DCS logic, and make a judgment based on the actual situation; a. The absolute value of the deviation between the coal feeder command and the coal quantity feedback signal is greater than 5t / h; b. The coal feeder fault signal is triggered, where a and b are ANDed and used as the judgment for the coal feeder tripping; B. Add a first-level alarm to the DCS logic; The absolute value of the deviation between the coal feeder command and the coal quantity feedback signal is greater than 10 t / h; Step 5: How to set the internal parameters of the coal feeder frequency converter; Enable all inverter functions: overcurrent reset, overvoltage reset, undervoltage reset, analog input fault reset, and external fault reset. Set the number of fault resets to multiple. Set the inverter reset time to greater than 10 seconds. Set the fault reset delay time to 0.1 seconds. Set the inverter fault start prohibition function to start.

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