Low-voltage and low-frequency load shedding function test method and test device

Abstract

The invention relates to the technical field of electric power detection, and provides a low-voltage and low-frequency load shedding function test method and a test device, in the on-site real-model test process, the test method and the test device are hung on a grid along with an FTU, the voltage and frequency change of the power grid and the action of the FTU are recorded in real time, a broken line graph is generated through upper computer software, and the action process of on-site low-voltage and low-frequency detection is displayed. Whether the device correctly executes the low-voltage and low-frequency load shedding action or not is visually observed, and the method has high practical significance (fault prevention), asset configuration optimization (service life prolonging) and final service for efficient, reliable and economical operation of a power grid.

Description

Technical Field

[0001] This application belongs to the field of power testing technology, specifically relating to a low-voltage, low-frequency load shedding function test method and test device. Background Technology

[0002] FTU, also known as a feeder terminal unit, is an intelligent terminal device specifically designed for 10kV power distribution systems. Through digital and network communication technologies, it enables remote monitoring and control of the power distribution system. Using built-in sensors and data processing modules, it collects key data such as voltage, current, power, and temperature in the power distribution system in real time, processes, stores, and uploads this data, and uses parameters to determine the operating status of the power grid. In the event of abnormal grid operation, it controls the pole-mounted circuit breaker (also known as a switch, hereinafter referred to as the switch) to trip, thus protecting the 10kV line.

[0003] The low-voltage, low-frequency load shedding algorithm is a protection algorithm that runs on the FTU. It is mainly used to deal with the risk of frequency or voltage collapse caused by active / reactive power deficit. Its core principle is to quickly restore system balance by tiered load shedding.

[0004] When applying low-voltage, low-frequency load shedding algorithms in the field, on-site grid testing is required before formal operation. However, existing testing equipment is easily affected by line power quality and switch malfunctions, which prolongs the testing time and affects the accuracy of the test. Summary of the Invention

[0005] This application provides a low-voltage, low-frequency load shedding function test method and test device to solve or partially solve the problems mentioned in the background art.

[0006] This application provides a method for testing the low-voltage, low-frequency load shedding function, including the following steps:

[0007] S1: Real-time acquisition of line voltage signals, generation of digital voltage and frequency signals, and recording of voltage and frequency signals;

[0008] S2: Acquire the opening and closing signals transmitted by the FTU device and record the opening and closing signals;

[0009] S3: Generate low-frequency and low-voltage events based on digital voltage, frequency, and opening / closing signals, then generate a low-frequency and low-voltage line graph, and determine whether the low-frequency and low-voltage judgment algorithm is qualified.

[0010] Preferably, in step S1, the method for acquiring the line voltage signal in real time and generating the digital voltage signal and frequency signal is as follows:

[0011] S101: Inputs the line voltage signal to the voltage sampling interface and steps it down through a voltage transformer;

[0012] S102: Input the low - voltage signal output by the voltage transformer into the internal ADC of the MCU to obtain a digital voltage signal;

[0013] S103: Input the low - voltage signal output by the voltage transformer into the sine - wave - to - square - wave circuit to convert the voltage sine wave into a square wave of the same frequency, and then connect the square wave to the MCU. Through the internal edge - triggered timer, measure the time difference Δt between two edges, and then calculate the voltage frequency. The formula is:

[0014]

[0015] Preferably, in the step S2, the specific method for obtaining the closing and tripping signals transmitted by the FTU device is as follows:

[0016] The MCU accesses the closing and tripping status telecontrol interface of the FTU. The signal is first isolated by an optocoupler. When there is a closing or tripping signal at the input point, the optocoupler controls the triode to conduct, and the input to the MCU is a positive voltage signal. When there is no closing or tripping signal at the input point, the triode is cut off, and the input to the MCU is a negative signal. The MCU records the closing and tripping signals according to the edge of the input signal.

[0017] Preferably, in the steps S1 and S2, the sampled voltage and frequency signals are temporarily saved. After a tripping event occurs, the signals and the tripping event within a preset time period before and after the trip are permanently saved.

[0018] Preferably, the specific method of the step S3 is as follows:

[0019] The standard secondary - side voltage of the FTU is 220V. Set the low - voltage load - shedding threshold to t1V and the tripping delay to xS. When the current voltage V on the secondary side of the FTU < t1V and lasts for xS, the FTU triggers a low - voltage load - shedding action to control the switch to trip. When testing the low - voltage load - shedding algorithm of the FTU, the specific steps are as follows:

[0020] S301: First, configure the voltage recording duration wS1 according to the tripping delay xS configured by the FTU, where wS1 > xS;

[0021] S302: Calculate the sampled voltage once every cycle and temporarily store the sampled voltage;

[0022] S303: When the FTU has a low - voltage load - shedding action, the FTU controls the switch to trip. At this time, the switch opening signal is synchronously input to the MCU. The MCU records the opening signal and permanently stores the tripping event and all voltage sampling points within wS1 before and after the event occurs;

[0023] S304: After the test, the host computer software reads the tripping event and related voltage samples, determines the low-voltage load shedding event and automatically generates a line graph. When all low-voltage load shedding events meet the condition that the voltage during the low-voltage period is less than t1 and the tripping event occurs xS after the start time of the low-voltage period, the low-voltage load shedding algorithm is deemed qualified; otherwise, it is deemed unqualified.

[0024] The standard voltage frequency of the FTU is 50Hz. The low-frequency load shedding threshold is set to t2Hz, and the trip delay is xS. When the current frequency on the secondary side of the FTU is less than t2Hz and lasts for xS, the FTU triggers the low-frequency load shedding action and controls the switch to trip. The specific steps for testing the low-frequency load shedding algorithm of the FTU are as follows:

[0025] S311: Configure the electrical frequency recording duration wS2 according to the trip delay xS configured by the FTU, where wS2>xS;

[0026] S312: Calculate the sampling frequency once every cycle and temporarily store the sampling frequency;

[0027] S313: When the FTU performs a low-frequency load shedding action, the FTU controls the switch to trip. At this time, the switch tripping signal is synchronously input to the MCU. The MCU records the tripping signal and permanently stores the tripping event and all frequency sampling points within wS2 before and after the event.

[0028] S314: After the test, the host computer software reads the tripping events and related frequency samples to determine the low-frequency load shedding events and automatically generates a line graph. When all low-frequency load shedding events meet the condition that the frequency of the low-frequency period is less than t2 and the tripping event occurs xS after the start time of the low-frequency period, the low-frequency load shedding algorithm is deemed qualified; otherwise, it is deemed unqualified.

[0029] Preferably, in steps S304 and S314, an error threshold ±x-er is added to the verification of the trip delay xS.

[0030] This application also provides a low-voltage, low-frequency load shedding function test device, including: a sampling input circuit, a switching signal input circuit, an MCU, host computer software, and a storage module;

[0031] The sampling input circuit, including a voltage sampling input circuit and a sine wave to square wave circuit, inputs the collected voltage signal into the MCU;

[0032] The circuit for inputting opening and closing signals of the FTU is used to input the opening and closing signals to the MCU.

[0033] The MCU generates digital voltage and frequency signals based on the acquired voltage signals, receives the opening and closing signals from the FTU, and stores the digital voltage signals, frequency signals, and opening and closing signals.

[0034] The host computer software generates low-frequency and low-voltage events based on digital voltage signals, frequency signals, and opening and closing signals, and then generates a low-frequency and low-voltage line graph, and determines whether the low-frequency and low-voltage judgment algorithm is qualified.

[0035] The storage module is used to temporarily or permanently store digital voltage signals, frequency signals, and opening / closing signals.

[0036] Preferably, the voltage sampling input circuit includes a voltage transformer that converts a large voltage signal into a small voltage signal;

[0037] The sine wave to square wave circuit is a signal conversion circuit based on a Schmitt trigger.

[0038] The MCU communicates with the host computer software via an RS485 serial port.

[0039] Preferably, the MCU is an STM32F103RET6; the storage module is a FLASH memory, model W25Q64.

[0040] Compared with the prior art, the beneficial effects of this application are as follows:

[0041] (1) This application proposes a low-voltage and low-frequency load shedding function test method and device. During the field real-world test, the device is connected to the grid along with the FTU and records the voltage and frequency changes of the grid and the actions of the FTU in real time. The upper computer software generates a line graph to show the action process of low-voltage and low-frequency detection on site. It can be seen more intuitively whether the device correctly performs the low-voltage and low-frequency load shedding action, which has high practical significance (fault prevention), optimizes asset allocation (extends life), and ultimately serves the efficient, reliable and economical operation of the power grid.

[0042] (2) This application converts the voltage signal into a digital voltage signal and frequency signal that can be directly recognized by the MCU through the sampling input circuit. The circuit structure is simple and reliable, the sampling accuracy is high, and the test accuracy is improved.

[0043] (3) The test method of this application can effectively avoid interference with the test accuracy by using threshold control and delay logic.

[0044] (4) By setting up temporary and permanent storage of sampling data in stages and categories, this application effectively reduces the storage space occupied, facilitates the use of FLASH flash memory with faster storage speed, improves the overall testing efficiency, and effectively reduces the cost of testing equipment. Attached Figure Description

[0045] The present application will be further described below with reference to the accompanying drawings and embodiments.

[0046] Figure 1This is a schematic diagram of the voltage sampling input circuit of the test device in this application.

[0047] Figure 2 This is a schematic diagram of the sine wave to square wave conversion circuit of the test device in this application.

[0048] Figure 3 This is a schematic diagram of the storage module circuit of the test device of this application.

[0049] Figure 4 This is a schematic diagram of the opening and closing signal input circuit of the test device of this application.

[0050] Figure 5 This is a schematic diagram of the low-voltage load shedding in this application.

[0051] Figure 6 This is a schematic diagram of the low-frequency load shedding in this application. Detailed Implementation

[0052] The specification and claims use certain terms to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The term "comprising" throughout the specification and claims is an open-ended term and should be interpreted as "comprising but not limited to." "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error.

[0053] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "horizontal", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0054] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0055] Example 1

[0056] like Figures 1 to 6As shown, this application provides a low-voltage, low-frequency load shedding function test method, including the following steps:

[0057] S1: Real-time acquisition of line voltage signals, generation of digital voltage and frequency signals, and recording of voltage and frequency signals;

[0058] S2: Acquire the opening and closing signals transmitted by the FTU device and record the opening and closing signals;

[0059] S3: Generate low-frequency and low-voltage events based on digital voltage, frequency, and opening / closing signals, then generate a low-frequency and low-voltage line graph, and determine whether the low-frequency and low-voltage judgment algorithm is qualified.

[0060] Specifically, in step S1, the method for acquiring the line voltage signal in real time and generating the digital voltage signal and frequency signal is as follows:

[0061] S101: Inputs the line voltage signal to the voltage sampling interface and steps it down through a voltage transformer;

[0062] S102: Input the low-voltage signal output from the voltage transformer to the ADC inside the MCU to obtain the digital voltage signal;

[0063] S103: The low-voltage signal output from the voltage transformer is input to the sine wave to square wave circuit, which converts the voltage sine wave into a square wave of the same frequency. The square wave is then connected to the MCU, and through the internal edge-triggered timer, the time difference Δt between the two edges is measured to calculate the voltage frequency. The formula is as follows:

[0064]

[0065] Specifically, in step S2, the method for obtaining the opening and closing signals transmitted by the FTU device is as follows:

[0066] The MCU connects to the remote signaling interface for the opening and closing status of the FTU. The signal is first isolated by an optocoupler. When there is an opening or closing signal at the input point, the optocoupler controls the transistor to conduct, and the input to the MCU is a positive voltage signal. When there is no opening or closing signal at the input point, the transistor is cut off, and the input to the MCU is a negative signal. The MCU triggers the recording of the opening and closing signal based on the edge of the input signal.

[0067] Specifically, in steps S1 and S2, the sampled voltage and frequency signals are temporarily saved, and after a tripping event occurs, the signals and the tripping event within a preset time period before and after the tripping event are permanently saved.

[0068] Specifically, the method for step S3 is as follows:

[0069] Regarding the low-voltage load shedding algorithm, the FTU adopts the method of threshold + delay (to prevent the switch from tripping due to instantaneous fluctuations). The standard secondary voltage of the FTU is 220V. The low-voltage load shedding threshold is set to t1V, and the tripping delay is xS. When the current voltage V on the secondary side of the FTU is < t1V and lasts for xS, the FTU triggers the low-voltage load shedding action to control the switch to trip. When testing the low-voltage load shedding algorithm of the FTU, the specific steps are as follows:

[0070] S301: First, configure the voltage recording duration wS1 according to the tripping delay xS configured in the FTU, where wS1 > xS;

[0071] S302: Calculate the sampled voltage once every other cycle and temporarily store the sampled voltage;

[0072] S303: When the FTU undergoes a low-voltage load shedding action, the FTU controls the switch to trip. At this time, the switch opening signal is synchronously input to the MCU. The MCU records the opening signal and permanently stores the tripping event and all voltage sampling points within wS1 before and after the event occurs;

[0073] S304: After the test, the upper computer software reads the tripping event and related voltage samples, determines the low-voltage load shedding event, and automatically generates a line chart. When all low-voltage load shedding events meet the condition that the voltage during the low-voltage period is less than t1 and the tripping event occurs xS after the start time of the low-voltage period, it is determined that the low-voltage load shedding algorithm is qualified; otherwise, it is determined to be unqualified;

[0074] Regarding the low-frequency load shedding algorithm, the FTU adopts the method of threshold + delay (to prevent the switch from tripping due to instantaneous fluctuations). The standard voltage frequency of the FTU is 50Hz. The low-frequency load shedding threshold is set to t2Hz, and the tripping delay is xS. When the current frequency on the secondary side of the FTU is less than t2Hz and lasts for xS, the FTU triggers the low-frequency load shedding action to control the switch to trip. When testing the low-frequency load shedding algorithm of the FTU, the specific steps are as follows:

[0075] S311: Configure the electrical frequency recording duration wS2 according to the tripping delay xS configured in the FTU, where wS2 > xS;

[0076] S312: Calculate the sampled frequency once every other cycle and temporarily store the sampled frequency;

[0077] S313: When the FTU undergoes a low-frequency load shedding action, the FTU controls the switch to trip. At this time, the switch opening signal is synchronously input to the MCU. The MCU records the opening signal and permanently stores the tripping event and all frequency sampling points within wS2 before and after the event occurs;

[0078] S314: After the test, the host computer software reads the tripping events and related frequency samples to determine the low-frequency load shedding events and automatically generates a line graph. When all low-frequency load shedding events meet the condition that the frequency of the low-frequency period is less than t2 and the tripping event occurs xS after the start time of the low-frequency period, the low-frequency load shedding algorithm is deemed qualified; otherwise, it is deemed unqualified.

[0079] Specifically, in steps S304 and S314, an error threshold ±x-er is added to the verification of the trip delay xS.

[0080] This application also provides a low-voltage, low-frequency load shedding function test device, including: a sampling input circuit, a switching signal input circuit, an MCU, host computer software, and a storage module;

[0081] The sampling input circuit, including a voltage sampling input circuit and a sine wave to square wave circuit, inputs the collected voltage signal into the MCU;

[0082] The circuit for inputting opening and closing signals of the FTU is used to input the opening and closing signals to the MCU.

[0083] The MCU generates digital voltage and frequency signals based on the acquired voltage signals, receives the opening and closing signals from the FTU, and stores the digital voltage signals, frequency signals, and opening and closing signals.

[0084] The host computer software generates low-frequency and low-voltage events based on digital voltage signals, frequency signals, and opening and closing signals, and then generates a low-frequency and low-voltage line graph, and determines whether the low-frequency and low-voltage judgment algorithm is qualified.

[0085] The storage module is used to temporarily or permanently store digital voltage signals, frequency signals, and opening / closing signals.

[0086] The low-voltage, low-frequency load shedding test device provided in this application is connected to the grid together with the FTU during on-site full-scale grid connection testing. The device measures the grid frequency and voltage in real time. When the grid voltage or frequency changes, it records the voltage, frequency, and occurrence time of the event. The FTU connects the opening and closing feedback remote signaling contact to the test device. When the switch opens and closes, it records the grid voltage, frequency, and occurrence time of the event. When the grid connection test is completed, the host computer reads the event records and generates a line graph. Users can use the line graph to determine whether the low-voltage, low-frequency load shedding action is a normal protection action, a false trip, or a failure to trip.

[0087] Specifically, the voltage sampling input circuit includes a voltage transformer that converts a large voltage signal into a small voltage signal, and the small voltage signal is converted into a digital signal by the ADC inside the MCU.

[0088] Specifically, the sine wave to square wave circuit is a signal conversion circuit based on a Schmitt trigger. A Schmitt trigger is a threshold switching circuit with hysteresis characteristics (hysteresis voltage). Its core principle is to achieve signal shaping, noise suppression, and level conversion through dual threshold voltages. When the input voltage rises from a low level to the positive threshold voltage VT+, the output jumps from a high level to a low level; when the input voltage falls from a high level to the negative threshold voltage VT+, the output jumps from a high level to a low level. - When the output changes from low to high, the input signal at VT... - When the voltage fluctuates between VT and VT+, the output state remains unchanged, thereby converting the sine wave of the AC voltage into a square wave of the corresponding frequency.

[0089] Specifically, the MCU communicates with the host computer software via an RS485 serial port.

[0090] Specifically, the storage module uses FLASH (W25Q64) as the event recording storage element. The sampled voltage and frequency are temporarily saved after sampling. After a tripping event occurs, the records and tripping events before and after the tripping event are permanently saved.

[0091] Preferably, the MCU is an STM32F103RET6.

[0092] The embodiments of this application have been described in detail above with reference to the accompanying drawings. However, this application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of this application.

Claims

1. A method for testing low-voltage, low-frequency load shedding function, characterized in that, It includes the following steps: S1: Obtain the line voltage signal in real time, generate a digital voltage signal and a frequency signal, and record the voltage and frequency signals; S2: Obtain the opening and closing signals transmitted by the FTU device and record the opening and closing signals; S3: Generate a low-frequency and low-voltage event based on the digital voltage, frequency, and opening and closing signals, and then generate a low-frequency and low-voltage broken line graph, and determine whether the low-frequency and low-voltage judgment algorithms are qualified.

2. A low-voltage and low-frequency load shedding function test method according to claim 1, wherein: In the step S1, the method for obtaining the line voltage signal in real time and generating a digital voltage signal and a frequency signal is as follows: S101: Input the line voltage signal into the voltage sampling interface and step down the voltage through a voltage transformer; S102: Input the low-voltage signal output by the voltage transformer into the internal ADC of the MCU to obtain a digital voltage signal; S103: Input the low-voltage signal output by the voltage transformer into the sine wave to square wave circuit, convert the voltage sine wave into a square wave of the same frequency, and then connect the square wave to the MCU. Through the internal edge trigger timer, measure the time difference Δt between two edges, and then calculate the voltage frequency. The formula is:

3. A low-voltage and low-frequency load shedding function test method according to claim 1, wherein: In the step S2, the specific method for obtaining the opening and closing signals transmitted by the FTU device is as follows: The MCU accesses the opening and closing status telecontrol interface of the FTU. The signal is first isolated through an optocoupler. When there is an opening and closing signal at the input point, the optocoupler controls the triode to conduct, and the input to the MCU is a positive voltage signal. When there is no opening and closing signal at the input point, the triode is cut off, and the input to the MCU is a negative signal. The MCU records the opening and closing signals according to the edge of the input signal.

4. A low-voltage and low-frequency load shedding function test method according to claim 1, wherein: In the steps S1 and S2, the sampled voltage and frequency signals are temporarily saved. After a tripping event occurs, the signals within a preset time period before and after the trip and the tripping event are permanently saved.

5. A low-voltage and low-frequency load shedding function test method according to any one of claims 1 or 4, wherein: The specific method of the step S3 is as follows: The secondary standard voltage of the FTU is 220V. Set the low-voltage load shedding threshold to t1V and the tripping delay to xS. When the current voltage V of the secondary side of the FTU < t1V and lasts for xS, the FTU triggers a low-voltage load shedding action to control the switch to trip. When testing the low-voltage load shedding algorithm of the FTU, the specific steps are as follows: S301: First, configure the voltage recording duration wS1 according to the tripping delay xS configured by the FTU, wS1 > xS; S302: Calculate the sampled voltage once every other cycle and temporarily store the sampled voltage; S303: When the FTU has a low-voltage load shedding action, the FTU controls the switch to trip. At this time, the switch opening signal is synchronously input to the MCU. The MCU records the opening signal and permanently stores the tripping event and all voltage sampling points within wS1 before and after the event occurs. S304: After the test, the host computer software reads the tripping event and related voltage samples, determines the low-voltage load shedding event and automatically generates a line graph. When all low-voltage load shedding events meet the condition that the voltage during the low-voltage period is less than t1 and the tripping event occurs xS after the start time of the low-voltage period, the low-voltage load shedding algorithm is deemed qualified; otherwise, it is deemed unqualified. The standard voltage frequency of the FTU is 50Hz. The low-frequency load shedding threshold is set to t2Hz, and the trip delay is xS. When the current frequency on the secondary side of the FTU is less than t2Hz and lasts for xS, the FTU triggers the low-frequency load shedding action and controls the switch to trip. The specific steps for testing the low-frequency load shedding algorithm of the FTU are as follows: S311: Configure the electrical frequency recording duration wS2 according to the trip delay xS configured by the FTU, where wS2>xS; S312: Calculate the sampling frequency once every cycle and temporarily store the sampling frequency; S313: When the FTU performs a low-frequency load shedding action, the FTU controls the switch to trip. At this time, the switch tripping signal is synchronously input to the MCU. The MCU records the tripping signal and permanently stores the tripping event and all frequency sampling points within wS2 before and after the event. S314: After the test, the host computer software reads the tripping events and related frequency samples to determine the low-frequency load shedding events and automatically generates a line graph. When all low-frequency load shedding events meet the condition that the frequency of the low-frequency period is less than t2 and the tripping event occurs xS after the start time of the low-frequency period, the low-frequency load shedding algorithm is deemed qualified; otherwise, it is deemed unqualified.

6. The low-voltage, low-frequency load shedding function test method according to claim 5, characterized in that: In steps S304 and S314, an error threshold ±x-er is added to the verification of the trip delay xS.

7. A low-voltage, low-frequency load shedding function testing device, characterized in that, include: Sampling input circuit, opening and closing signal input circuit, MCU, host computer software, and storage module; The sampling input circuit, including a voltage sampling input circuit and a sine wave to square wave circuit, inputs the collected voltage signal into the MCU; The circuit for inputting opening and closing signals of the FTU is used to input the opening and closing signals to the MCU. The MCU generates digital voltage and frequency signals based on the acquired voltage signals, receives the opening and closing signals from the FTU, and stores the digital voltage signals, frequency signals, and opening and closing signals. The host computer software generates low-frequency and low-voltage events based on digital voltage signals, frequency signals, and opening and closing signals, and then generates a low-frequency and low-voltage line graph, and determines whether the low-frequency and low-voltage judgment algorithm is qualified. The storage module is used to temporarily or permanently store digital voltage signals, frequency signals, and opening / closing signals.

8. The low-voltage, low-frequency load shedding function testing device according to claim 7, characterized in that: The voltage sampling input circuit includes a voltage transformer that converts a large voltage signal into a small voltage signal; The sine wave to square wave circuit is a signal conversion circuit based on a Schmitt trigger. The MCU communicates with the host computer software via an RS485 serial port.

9. A low-voltage, low-frequency load shedding function testing device according to any one of claims 7 or 8, characterized in that: The MCU model is STM32F103RET6; The storage module is a FLASH flash memory, model W25Q64.

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