Leakage protector in effective power detection mode

Abstract

The invention provides a leakage protector in an effective power detection mode, which is characterized in that an MCU (Microprogrammed Control Unit) is arranged in the leakage protector, mains supply voltage and residual current are respectively acquired, and active power current is identified after ADC (Analog to Digital Converter) signal conversion, digital correlation function filtering processing, digital integral filtering and threshold judgment processing, so as to trigger an electromagnetic switch to act. The leakage protector can work normally in a limited or invalid environment of a traditional leakage protector.

Description

Technical Field

[0001] The invention relates to the technical field of leakage protectors, and in particular to a leakage protector in an effective power detection mode. Background Art

[0002] Electricity safety accidents happen from time to time. This is due to inadequate management and environmental restrictions. For example, urban street lamp power supply systems rarely install leakage protectors because the urban street lamp power supply system has a long circuit and large inherent capacitance. During operation, there is a large leakage capacitance, and conventional leakage protectors cannot be used.

[0003] First of all, leakage is the leakage of electric power rather than current leakage. The secondary disasters caused by electric power leakage are the consequences of active power, while the reactive power included in the leakage has no effect or influence on the outside world: power leakage is converted into local thermal power release, which will produce local high temperature that causes fire, while reactive power has no such mechanism; power leakage is converted into local thermal power release of the human body, and electrochemical reactions with organisms will cause life disorders, while reactive power has no such mechanism. Its power conversion conforms to the law of conservation of energy, so only power leakage is harmful. Active power formula: Since the analog circuit of the traditional leakage protector cannot identify active power and reactive power, the use of traditional leakage protectors is limited or even unusable in special power usage occasions. For example, in the power supply system of urban road lamps, the power supply circuit is long and the cable has a large capacitance. The traditional leakage protector with a residual current triggering standard of 30mA·s cannot be used. Summary of the invention

[0004] The present invention aims to provide a leakage protector in an effective power detection mode, which can work normally in an environment where a traditional leakage protector is limited or fails.

[0005] The present invention specifically adopts the following technical solutions:

[0006] A leakage protector with an effective power detection mode is characterized in that: an MCU is built into the leakage protector to collect the mains voltage and residual current respectively, convert them by ADC signals, filter them by digital correlation functions, and then process them by digital integral filtering and threshold judgment to identify the active power current to trigger the action of the electromagnetic switch.

[0007] Furthermore, the voltage-current correlation coefficient is calculated first, and then the residual current effective value is calculated. The sliding window integration is used to obtain the residual current effective value, and then it is determined whether the integral of the residual current effective value exceeds the limit. If it does not exceed the limit, it returns to recalculate the voltage-current correlation coefficient. If it exceeds the limit, the protection is triggered and the power supply is cut off.

[0008] Furthermore, the correlation coefficient between the residual current I and the mains voltage V is obtained in the following manner: suppose the AC voltage VAC is sampled by the ADC built into the MCU to generate a data sequence V(n); the residual current ISEN is sampled by the ADC built into the MCU to generate a data sequence I(n);

[0009] Correlation coefficient formula:

[0010] Current RMS formula:

[0011] Effective residual current formula: I 有效 =ρ·I

[0012] V i As a voltage channel sampling sequence, I i As the current channel sampling value; calculate the effective value of the AC signal part of sequence I to obtain ρ·I, and then get the effective component of the residual current. Then use the window function to calculate the integral of the effective part of the residual current, and then determine whether to trigger the protection action.

[0013] Furthermore, the inductor T1 collects the leakage current and voltage, and transmits the residual current and mains voltage signals to the MCU after dual operational amplifier amplification. The MCU performs digital correlation function filtering and digital integral filtering to analyze whether the residual current is an active power current. If it is analyzed to be an active power residual current and exceeds the set threshold, the MCU sends a signal to the thyristor D2 to disconnect the electromagnetic switch K1.

[0014] In summary, the active power leakage protector provided by the present invention and its preferred solution can accurately detect the residual current of active power and identify harmful leakage current, and is more suitable for application in long circuit and multi-load power applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0016] Figure 1 This is a reference diagram for a single-phase 3-wire power supply circuit;

[0017] Figure 2 The working principle block diagram of the traditional leakage protector;

[0018] Figure 3 Traditional leakage protector action curve diagram;

[0019] Figure 4 A block diagram of the working principle of the active power leakage protector according to an embodiment of the present invention;

[0020] Figure 5The embodiment of the present invention does not include a circuit diagram of an active power mode leakage protector for digital processing of an auxiliary power supply;

[0021] Figure 6 Flowchart of the digital signal processing part of the embodiment of the present invention. DETAILED DESCRIPTION

[0022] In order to make the features and advantages of this patent more obvious and easy to understand, the following embodiments are specifically described in detail with the accompanying drawings as follows:

[0023] This embodiment makes a detailed analysis of the traditional leakage protector and the proposed leakage protector with effective power detection mode.

[0024] Take a single-phase power supply circuit as an example. Figure 1 As shown, it is assumed that the distributed capacitance of the power supply circuit wire LN to the ground is equal (the measured distributed capacitance of the wire LN to the ground is shown in Table 1), and the internal Y capacitor of the load is also equal to the ground capacitance. However, due to the 220V difference between the LN line and the ground, the current flowing through C N and C L The current to ground is different. This causes the traditional residual current detection circuit to measure a considerable residual current. Due to the orthogonal relationship between the driving voltage of the capacitor and the working current, this residual current reflects the power supply as mostly reactive power. Taking the street light power supply system as an example, assuming that the cable length of a loop is 1000 meters, and there are 30 street lights with 60 lamps. With reference to the data in Table 1 and Table 2, its distributed capacitance to ground is about 400nF. The imaginary residual current generated is about 27mA. Therefore, the traditional residual current trigger standard of the leakage protector is 30mA·s and cannot be used.

[0025] Table 1. Measurement of cable-to-ground distributed capacitance

[0026] Cable Model Cable length Distributed electricity to ground Test Equipment YJV5*16 20 2.7 Delixi YJV5*25 1014 187 Delixi YJV4*150 28 6.1 Delixi FVL2*2.5 10 0.5 FLUKE

[0027] Table 2. Load-to-ground capacitance

[0028] Power supply model brand Power(W) Load to ground Test Equipment EBD-255S105DV Infit 255 1.5 FLUKE EUM-200S105DG Infit 200 2.2 FLUKE EBC-060S105DV Infit 60 1.4 FLUKE EBD-075S105DV Infit 75 1.4 FLUKE EUM-100S105DG Infit 100 1.9 FLUKE EBC-042S105DV Infit 42 1.4 FLUKE EBD-150S105DVA Infit 150 1.5 FLUKE EUM-150S105DG Infit 150 1.9 FLUKE EUD-320S150DV Infit 320 3 FLUKE X6-200M286 Maoshuo 200 3.1 FLUKE

[0029] The working principle of traditional leakage protector is as follows Figure 2As shown, the principle is to amplify the residual current, detect, low-pass filter, and then make a threshold judgment. The protection is triggered according to whether it exceeds the limit. The advantages are simplicity and low cost. The disadvantage is that it cannot meet the relevant provisions of the construction industry standard JGJ46-2005 "Technical Specifications for Temporary Power Safety at Construction Sites", and the trigger standard is 30mA·s. (Refer to Article 8.2.11 of the construction industry standard JGJ46-2005 "Technical Specifications for Temporary Power Safety at Construction Sites": "The rated leakage action current of the leakage protector in the main distribution box should be greater than 30mA, and the rated leakage action time should be greater than 0.1s, but the product of the rated leakage action current and the rated leakage action time should not be greater than 30mA·s", such as Figure 3 As shown). Based on this "30mA" current, it can be concluded that when the leakage power reaches 6.6w, the leakage protector cannot protect. At this time, a large amount of heat has been generated locally, which will further spread and cause a fire. When a human body flows through 8mA current for a long time, it may be life-threatening. Therefore, the current traditional leakage protector cannot strictly meet the industry standards and cannot eliminate all safety hazards.

[0030] The following is a leakage protection countermeasure based on active power / effective current detection provided by an embodiment of the present invention: Figure 4 As shown in the figure, the MCU is built into the leakage protector to collect the mains voltage and residual current respectively, convert them by ADC signals, filter them by digital correlation function, and then filter them by digital integration and safety regulation to identify the active power current, thereby triggering the electromagnetic switch action. The residual current trigger standard of 30mA·s specified in the industry standard can be achieved.

[0031] The active power leakage protection circuit provided by the above scheme is as follows Figure 5 As shown: Inductor T1 collects leakage current and voltage, and after being amplified by dual op amp LMV358, the residual current and mains voltage signals are transmitted to U1 respectively. U1 performs digital correlation function filtering and digital integral filtering to analyze whether the residual current is active power current. If it is analyzed as active power residual current and exceeds the set threshold, U1 sends a signal to thyristor D2 to disconnect electromagnetic switch K1. Among them, C2 plays a phase compensation role, D3 and D4 play a lightning protection role, and the 3.3V power supply voltage forms a midpoint voltage after being divided by R5 and R6, so that the voltage collected by the fifth foot of LMV358 is a positive number. In the mains environment, this circuit can not only realize active power mode leakage protection, but also be reverse compatible with traditional national standard leakage protectors after removing the active power digital signal processing, but it is more accurate than the traditional analog circuit signal processing and can fully meet the relevant standards.

[0032] The following is the technical content of the digital signal processing part of this solution:

[0033] Concept of correlation function: Correlation function is a function that describes signal X (s) , Y (t) (these two signals can be random or deterministic), the degree of correlation between the values ​​of s and t at any two different times. The similarity between two signals is measured by the correlation coefficient. Definition: ρ xy It is called the correlation coefficient of variables X and Y. If the correlation coefficient is equal to 0, then X and Y are said to be uncorrelated. The larger the correlation coefficient, the greater the correlation, but it is definitely less than or equal to 1. Correlation functions are divided into autocorrelation and cross-correlation: The autocorrelation function is a function that describes the random signal x. (t) The degree of correlation between the values ​​at any different times t1 and t2; the cross-correlation function is a function that describes the random signal x (t) ,y (t) The degree of correlation between the values ​​of s and t at any two different times.

[0034] Therefore, the following correlation coefficient between the residual current I and the mains voltage V is obtained: Assume that the AC voltage VAC is sampled by the ADC built into the MCU to generate a data sequence V(n); the residual current ISEN is sampled by the ADC built into the MCU to generate a data sequence I(n);

[0035] Correlation coefficient formula:

[0036] Current RMS formula:

[0037] Effective residual current formula: I 有效 =ρ·I

[0038] Therefore, the correlation coefficient can be calculated by the built-in software program. i As a voltage channel sampling sequence, I i As the current channel sampling value. Calculate the effective value of the AC signal part of sequence I to obtain ρ·I to get the effective component of the residual current. Use the window function to calculate the integral of the effective part of the residual current, and then determine whether to trigger the protection action. Experimental process: Use a 1uF capacitor and a 100KΩ resistor in parallel as a load, and the sampling rate n is 16 times. The generated voltage ADC sampling value and residual current ADC sampling value are as follows:

[0039] Table 3. Voltage ADC sampling value, residual current ADC sampling value

[0040]

[0041] The calculation shows that the imaginary residual current is 69.12mA, the real residual current is 2.2mA, the phase angle is 88.18°, and the total residual current is 68.15mA. By changing the capacitance value of the load, the following experimental data are obtained:

[0042] Table 4. Experimental data of different load capacitances

[0043] Capacitance(μF) 0.1 0.5 1 2 3 Leakage resistance kΩ 100 100 100 100 100 Supply voltage V 220 220 220 220 220 Imaginary residual current (mA) 6.91 34.56 69.12 138.23 207.35 Real residual current (mA) 2.2 2.2 2.2 2.2 2.2 Phase(°) 72.34 86.36 88.18 89.09 89.39 Total residual current (mA) 7.25 34.63 69.15 138.24 207.36

[0044] It can be seen from the data in the above table that when the load capacitance is changed, the imaginary residual current changes accordingly, while the real residual current remains unchanged, which shows that the design provided by the embodiment of the present invention can accurately identify the leakage current of active power.

[0045] Further, the digital signal processing software program provided is as Figure 6 As shown: first calculate the voltage-current correlation coefficient, then calculate the residual current effective value, use the sliding window integration to obtain the residual current effective value, and further determine whether the integral of the residual current effective value exceeds the limit. If it does not exceed the limit, return to calculate the voltage-current correlation coefficient. If it exceeds the limit, the protection is triggered and the power is cut off. The program ends after the power is cut off.

[0046] This patent is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of leakage protectors with effective power detection modes based on the inspiration of this patent. All equivalent changes and modifications made within the scope of the patent application of the present invention should fall within the scope of this patent.

Claims

1. A leakage protector in effective power detection mode, characterized in that: The leakage protector has a built-in MCU, which collects the mains voltage and residual current respectively, converts them into ADC signals, filters them through digital correlation functions, and then processes them through digital integration filtering and threshold judgment to identify the active power current and trigger the electromagnetic switch.

2. The leakage protector in the effective power detection mode according to claim 1, characterized in that: First, the voltage-current correlation coefficient is calculated, and then the residual current effective value is calculated. The sliding window integration is used to obtain the residual current effective value, and then it is determined whether the integral of the residual current effective value exceeds the limit. If it does not exceed the limit, it returns to recalculate the voltage-current correlation coefficient. If it exceeds the limit, the protection is triggered and the power supply is cut off.

3. The leakage protector in the effective power detection mode according to claim 2, characterized in that: The correlation coefficient between the residual current I and the mains voltage V is obtained in the following way: suppose the AC voltage VAC is sampled by the ADC built into the MCU to generate a data sequence V(n); the residual current ISEN is sampled by the ADC built into the MCU to generate a data sequence I(n); Correlation coefficient formula: Current RMS formula: Effective residual current formula: I 有效 =ρ·I V i As a voltage channel sampling sequence, I i Considered as the current channel sampling value; The effective value of the AC signal part of sequence I is calculated to obtain ρ·I, and the effective component of the residual current is obtained. Then, the integral of the effective part of the residual current is calculated using the window function, and then it is determined whether the protection action is triggered.

4. The leakage protector in the effective power detection mode according to claim 1, characterized in that: Inductor T1 collects leakage current and voltage, and transmits the residual current and mains voltage signals to MCU after dual operational amplifier amplification. MCU performs digital correlation function filtering and digital integral filtering to analyze whether the residual current is active power current. If it is analyzed to be residual current of active power and exceeds the set threshold, MCU sends a signal to thyristor D2 to disconnect electromagnetic switch K1.

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