Electrical fire early warning method based on single-phase residual current capacitive-resistive component calculation

Abstract

The invention discloses an electrical fire early warning method based on single-phase residual current capacitive-resistive component calculation. The method comprises the following steps: collecting residual current and live wire voltage in a single-phase distribution line; calculating a single-phase residual current capacitive component and a single-phase residual current resistive component according to the residual current and the live wire voltage; if the single-phase residual current capacitive component exceeds a preset first threshold value, judging that the cable is aged and higher harmonic and reactive loss exist, and not giving an alarm; and if the resistive component of the single-phase residual current exceeds a preset second threshold value, performing alarm or power-off protection to realize electrical fire early warning. According to the invention, the resistive component and the capacitive component of the single-phase residual current signal are calculated accurately, so that the capacitive component and the resistive component of the single-phase residual current are treated differently, and the practical difficulty that the conventional residual current detection equipment is interfered by a line and unnecessary alarms are frequently generated is solved.

Description

Technical Field

[0001] The invention relates to the technical field of electrical fire monitoring and detection, and in particular to an electrical fire early warning method based on calculation of single-phase residual current capacitive and resistive components. Background Art

[0002] Many fires are electrical fires, and it is necessary to determine whether there is leakage at the fire scene. Electrical fires are usually caused by faults in the electrical system, such as aging of wires, insulation damage, short circuits, overloads, etc. These problems may cause current leakage and then cause fires. Therefore, detecting leakage in the electrical system is crucial for preventing and controlling electrical fires. At present, the detection methods of electrical fires mainly include residual current detection, temperature monitoring, fault arc detection, pyrolysis particle detection, etc. Among them, residual current detection is one of the most commonly used methods. Residual current detection determines whether there is leakage by monitoring the residual current in the electrical circuit. However, there are some problems with the traditional residual current detection method, which leads to false alarms: First, the internal structure of wires and cables in the distribution system is complex, and distributed capacitance is widely present, and increases with the length and thickness of the wire. Second, there are loads such as inverters and switching power supplies in the distribution line that generate high-order harmonics and non-sinusoidal signals, which leads to a decrease in the capacitive reactance of the distributed capacitance and an increase in the leakage current. The detection of residual current in the traditional leakage detection method not only includes the resistive component of the residual current, but also includes the capacitive component of the residual current caused by the distributed capacitance, which leads to frequent false alarms of the detection equipment. In recent years, with the development of signal processing technology, Hilbert-Huang transform (HHT) has been widely used in the processing of nonlinear and non-stationary signals as an effective time-frequency analysis method. In order to more accurately detect leakage in electrical fires, it is necessary to develop a new detection method to overcome the limitations of existing technologies. Summary of the invention

[0003] Technical purpose: In view of the defects in the prior art, the present invention discloses an electrical fire warning method based on the calculation of the capacitive and resistive components of single-phase residual current. By accurately calculating the resistive and capacitive components of the single-phase residual current signal, the capacitive and resistive components of the single-phase residual current can be differentiated and managed, thus solving the practical difficulty that traditional residual current detection equipment frequently generates unnecessary alarms due to line interference.

[0004] Technical solution: In order to achieve the above technical objectives, the present invention adopts the following technical solution.

[0005] An electrical fire early warning method based on calculation of single-phase residual current capacitive and resistive components, comprising:

[0006] Collect the residual current and live line voltage of the single-phase distribution line;

[0007] The capacitive component of the single-phase residual current and the resistive component of the single-phase residual current are calculated according to the residual current and the live line voltage;

[0008] If the capacitive component of the single-phase residual current exceeds the preset first threshold, it is determined that the cable is aging and there are high-order harmonics and reactive power losses, and no alarm is issued;

[0009] If the resistive component of the single-phase residual current exceeds the preset second threshold, an alarm or power-off protection is issued to achieve electrical fire early warning.

[0010] Furthermore, the residual current and live line voltage in the single-phase distribution line are collected, including:

[0011] An external zero-sequence current transformer and voltage transformer are connected to the single-phase distribution line and connected to the ADC for synchronous sampling at an equal sampling rate to obtain the residual current and the live line voltage, that is, a number of residual current sampling values ​​and live line voltage sampling values.

[0012] Furthermore, the single-phase residual current resistive component is calculated based on the residual current and the live line voltage, including:

[0013] According to a number of residual current sampling values ​​and live line voltage sampling values, each cycle residual current vector and each cycle live line voltage vector are respectively formed;

[0014] Calculate the effective value of each cycle live line voltage according to each cycle live line voltage vector;

[0015] Calculate each cycle of leakage active power based on each cycle of residual current vector and each cycle of live line voltage vector;

[0016] The effective value of the resistive residual current per cycle is calculated based on the effective value of the live line voltage per cycle and the leakage active power per cycle as the resistive component of the single-phase residual current.

[0017] Furthermore, the capacitive component of the single-phase residual current is calculated based on the residual current and the live line voltage, including:

[0018] According to a number of residual current sampling values ​​and live line voltage sampling values, each cycle residual current vector and each cycle live line voltage vector are respectively formed;

[0019] Calculate the effective value of each cycle live line voltage according to each cycle live line voltage vector;

[0020] Design Hilbert digital filters;

[0021] Performing phase-shift filtering on each cycle live line voltage vector through a Hilbert digital filter to obtain each cycle live line voltage vector after phase-shift filtering;

[0022] Calculate the leakage reactive power of each cycle according to the residual current vector of each cycle and the live line voltage vector of each cycle after phase shift filtering;

[0023] The effective value of the capacitive residual current per cycle is calculated based on the leakage reactive power per cycle and the effective value of the live line voltage per cycle, which is used as the capacitive component of the single-phase residual current.

[0024] Furthermore, the Hilbert digital filter design process includes:

[0025] The ideal frequency response D(ω) of the Hilbert digital filter should be a 90° phase shift in the passband and zero in the stopband; the calculation formula for the ideal frequency response of the Hilbert digital filter includes:

[0026]

[0027] Among them, f p is the passband cutoff frequency, f s is the stopband cutoff frequency;

[0028] The error E(ω) between the actual frequency response H(ω) of the Hilbert digital filter and the ideal frequency response D(ω) is:

[0029] E(ω)=D(ω)-H(ω)

[0030] Let δ = max|E(ω)|, and repeatedly adjust the filter coefficients so that the error function satisfies the alternation condition at all frequency band boundary points, thereby finding a system function H(ω) that minimizes δ, and obtaining the optimal unit impulse response h(n), thus obtaining the required Hilbert digital filter.

[0031] Beneficial effects:

[0032] 1. The present invention can accurately calculate the effective value of the resistive component and the effective value of the capacitive component of the single-phase residual current at a site containing a large number of harmonic components, realize the differentiated management of the capacitive and resistive components of the single-phase residual current, suppress the interference caused by the combined management of the capacitive and resistive components of the residual current in the current technology to the electrical fire early warning system, improve the early warning efficiency, and reduce the false alarm rate of the fire alarm;

[0033] 2. The present invention designs a Hilbert digital filter based on the Hilbert-Huang transform to filter the live line voltage sampling value, which can effectively deal with the problems of high-order harmonics and non-sinusoidal signals that traditional residual current detection equipment cannot solve, and is more suitable for distribution lines with various types of power consumption, such as multiple types of harmonic source loads and complex electromagnetic interference source loads. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a flow chart of the method of the present invention;

[0035] Figure 2 This is a schematic diagram of live line voltage and residual current data collection according to an embodiment of the present invention;

[0036] Figure 3 It is a structural diagram of a FIR type Hilbert digital filter according to an embodiment of the present invention;

[0037] Figure 4 It is an amplitude-frequency characteristic diagram of a FIR type Hilbert digital filter according to an embodiment of the present invention;

[0038] Figure 5 It is a phase-frequency characteristic diagram of the FIR type Hilbert digital filter according to an embodiment of the present invention;

[0039] Figure 6 It is an impulse response diagram of a FIR type Hilbert digital filter according to an embodiment of the present invention;

[0040] Figure 7 This is a block diagram of the principle of calculating leakage reactive power per cycle using a Hilbert digital filter according to an embodiment of the present invention;

[0041] Figure 8 The figure is a flow chart of a method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0043] As attached Figure 1 As shown, the present invention provides an electrical fire early warning method based on calculation of single-phase residual current capacitive and resistive components, comprising:

[0044] Collect the residual current and live line voltage of the single-phase distribution line;

[0045] The capacitive component of the single-phase residual current and the resistive component of the single-phase residual current are calculated according to the residual current and the live line voltage;

[0046] If the capacitive component of the single-phase residual current exceeds the preset first threshold, it is determined that the cable is aging and there are high-order harmonics and reactive power losses, and no alarm is issued;

[0047] If the resistive component of the single-phase residual current exceeds the preset second threshold, an alarm or power-off protection is issued to achieve electrical fire early warning.

[0048] Among them, the first threshold value and the second threshold value are set according to actual working conditions and are not described in detail in the present invention.

[0049] The present invention achieves differentiated management of the capacitive and resistive components of single-phase residual current by accurately calculating the resistive and capacitive components of single-phase residual current. Exceeding the standard of the resistive component of the single-phase residual current usually means that a fire is approaching and an alarm is required immediately; exceeding the standard of the capacitive component of the single-phase residual current means that the cable is aging and there are a large number of high-order harmonics and reactive power losses in the load, and it is necessary to supplement harmonic management and reactive power compensation equipment. The present invention differentiates and manages the capacitive and resistive components of the single-phase residual current, solves the practical difficulties that traditional residual current detection equipment frequently generates unnecessary alarms due to line interference, and also provides a more scientific evaluation method for cables and loads in the use scenario. Therefore, the technical solution of the present invention can be applied to various electrical fire warning fields or equipment, such as household electrical fire monitoring detectors, combined electrical fire monitoring detectors, dangerous electrical appliances and electricity consumption behavior monitoring detectors, insulation performance detection electrical fire monitoring detectors, electrical fire protection current limiting protectors, etc.

[0050] like Figure 8 As shown, an electrical fire early warning method based on calculation of the capacitive resistive component of a single-phase residual current in one embodiment of the present invention is given below, comprising the following steps:

[0051] S1, sampling the residual current and live line voltage of the single-phase distribution line to obtain a number of residual current sampling values ​​and live line voltage sampling values;

[0052] In this embodiment, a zero-sequence current transformer and a voltage transformer can be connected to the single-phase distribution line, as shown in the attached Figure 2 As shown, the ADC is connected to perform synchronous sampling at the same sampling rate to obtain the residual current and the live line voltage, that is, a number of residual current sampling values ​​and live line voltage sampling values;

[0053] S2. According to a number of residual current sampling values ​​and live line voltage sampling values, each cycle residual current vector and each cycle live line voltage vector are respectively formed; wherein, each cycle residual current vector is The live line voltage vector per cycle is N is the number of sampling points per cycle.

[0054] S3, calculating the effective value of each cycle of the live line voltage according to each cycle of the live line voltage vector; calculating the root mean square of each cycle of the live line voltage vector to obtain the effective value of each cycle of the live line voltage;

[0055] Among them, the calculation formula for the effective value of the live line voltage per cycle UArms includes:

[0056]

[0057] S4, calculating each cycle leakage active power according to each cycle residual current vector and each cycle live line voltage vector;

[0058] Calculate the dot product of the live line voltage vector per cycle and the residual current vector per cycle, and then divide it by the number of sampling points per cycle (live line voltage or residual current) to obtain the leakage active power per cycle;

[0059] Among them, the calculation formula of each cycle leakage active power PLavr ​​includes:

[0060]

[0061] S5. Calculate the effective value of the resistive residual current per cycle according to the leakage active power per cycle and the effective value of the live line voltage per cycle, as the resistive component of the single-phase residual current;

[0062] Divide the leakage active power per cycle by the effective value of the live line voltage per cycle to obtain the effective value of the resistive residual current per cycle. The calculation formula for the effective value of the resistive residual current per cycle ILres includes:

[0063]

[0064] S6. Design the Hilbert digital filter. The implementation process includes:

[0065] The ideal frequency response D(ω) of the Hilbert digital filter should be a 90° phase shift in the passband and zero in the stopband. Specifically:

[0066]

[0067] Among them, f p is the passband cutoff frequency, f s is the stopband cutoff frequency.

[0068] The calculation formula for the error E(ω) between the actual frequency response H(ω) and the ideal frequency response D(ω) of the Hilbert digital filter is:

[0069] E(ω)=D(ω)-H(ω)

[0070] Let δ = max |E(ω)|, and adjust the filter coefficients repeatedly so that the error function satisfies the alternation condition at all frequency band boundary points, thereby finding a system function H(ω) that minimizes δ, and obtaining the optimal unit impulse response h(n), and obtaining the required FIR-type Hilbert digital filter, as shown in the attached figure. Figure 3 shown.

[0071] After simulation, we can get the amplitude-frequency characteristics, phase-frequency characteristics and impulse response simulation diagram of the FIR Hilbert digital filter, as shown in Figure 4 , Figure 5 and Figure 6 As shown;

[0072] S7, performing phase-shift filtering on each cycle live line voltage vector through a Hilbert digital filter to obtain each cycle live line voltage vector after phase-shift filtering;

[0073] Among them, the calculation formula of each cycle live line voltage vector after phase shift filtering includes:

[0074]

[0075] S8, calculating the leakage reactive power of each cycle according to the residual current vector of each cycle and the live line voltage vector of each cycle after phase shift filtering;

[0076] Calculate the dot product of each cycle live line voltage vector and each cycle residual current vector after phase shift filtering, and then divide it by the number of sampling points per cycle (live line voltage or residual current) to obtain the leakage reactive power per cycle;

[0077] The calculation formula for each cycle leakage reactive power QLavr includes:

[0078]

[0079] Attached Figure 7 The present invention is a process of calculating the reactive power of leakage current per cycle by using the Hilbert digital filter;

[0080] S9, calculating the effective value of the capacitive residual current per cycle according to the leakage reactive power per cycle and the effective value of the live line voltage per cycle, as the capacitive component of the single-phase residual current;

[0081] Divide the leakage reactive power per cycle by the effective value of the live line voltage per cycle to obtain the effective value of the capacitive residual current per cycle. The calculation formula for the effective value of the capacitive residual current per cycle ILcap includes:

[0082]

[0083] S10, if the capacitive component of the single-phase residual current exceeds the preset first threshold, it is determined that the cable is aged and there are high-order harmonics and reactive power losses, and no alarm is issued; if the resistive component of the single-phase residual current exceeds the preset second threshold, an alarm or power-off protection is issued to achieve electrical fire warning. The first threshold and the second threshold are set according to the actual working conditions and are not described in detail in the present invention.

[0084] The present invention can accurately calculate the resistive and capacitive components of a single-phase residual current at a site containing a large number of harmonic components, achieve differentiated management of the capacitive and resistive components of a single-phase residual current, suppress the interference to the early warning system of electrical fires caused by the combined management of the capacitive and resistive components of the residual current in the current technology, improve the early warning efficiency, and reduce the false alarm rate of fire alarms.

[0085] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An electrical fire early warning method based on calculation of single-phase residual current capacitive and resistive components, characterized in that: The method comprises: Collect the residual current and live line voltage in the single-phase distribution line; The capacitive component of the single-phase residual current and the resistive component of the single-phase residual current are calculated according to the residual current and the live line voltage; If the capacitive component of the single-phase residual current exceeds the preset first threshold, it is determined that the cable is aging and there are high-order harmonics and reactive power losses, and no alarm is issued; If the resistive component of the single-phase residual current exceeds the preset second threshold, an alarm or power-off protection is issued to achieve electrical fire early warning.

2. The electrical fire early warning method based on calculation of single-phase residual current capacitive and resistive components according to claim 1, characterized in that: Collect the residual current and live line voltage in the single-phase distribution line, including: An external zero-sequence current transformer and voltage transformer are connected to the single-phase distribution line and connected to the ADC for synchronous sampling at an equal sampling rate to obtain the residual current and the live line voltage, that is, a number of residual current sampling values ​​and live line voltage sampling values.

3. The electrical fire early warning method based on calculation of single-phase residual current capacitive and resistive components according to claim 1, characterized in that: The single-phase residual current resistive component is calculated based on the residual current and the live line voltage, including: According to a number of residual current sampling values ​​and live line voltage sampling values, each cycle residual current vector and each cycle live line voltage vector are respectively formed; Calculate the effective value of each cycle live line voltage according to each cycle live line voltage vector; Calculate each cycle of leakage active power based on each cycle of residual current vector and each cycle of live line voltage vector; The effective value of the resistive residual current per cycle is calculated based on the effective value of the live line voltage per cycle and the leakage active power per cycle as the resistive component of the single-phase residual current.

4. The electrical fire early warning method based on calculation of single-phase residual current capacitive and resistive components according to claim 1, characterized in that: The single-phase residual current capacitive component is calculated based on the residual current and the live line voltage, including: According to a number of residual current sampling values ​​and live line voltage sampling values, each cycle residual current vector and each cycle live line voltage vector are respectively formed; Calculate the effective value of each cycle live line voltage according to each cycle live line voltage vector; Design Hilbert digital filters; Performing phase-shift filtering on each cycle live line voltage vector through a Hilbert digital filter to obtain each cycle live line voltage vector after phase-shift filtering; Calculate the leakage reactive power of each cycle according to the residual current vector of each cycle and the live line voltage vector of each cycle after phase shift filtering; The effective value of the capacitive residual current per cycle is calculated based on the leakage reactive power per cycle and the effective value of the live line voltage per cycle, which is used as the capacitive component of the single-phase residual current.

5. The electrical fire early warning method based on calculation of single-phase residual current capacitive and resistive components according to claim 4, characterized in that: The Hilbert digital filter design process includes: The ideal frequency response D(ω) of the Hilbert digital filter should be a 90° phase shift in the passband and zero in the stopband; the calculation formula for the ideal frequency response of the Hilbert digital filter includes: Among them, f p is the passband cutoff frequency, f s is the stopband cutoff frequency; The error E(ω) between the actual frequency response H(ω) of the Hilbert digital filter and the ideal frequency response D(ω) is: E(ω)=D(ω)-H(ω) Let δ = max|E(ω)|, and repeatedly adjust the filter coefficients so that the error function satisfies the alternation condition at all frequency band boundary points, thereby finding a system function H(ω) that minimizes δ, and obtaining the optimal unit impulse response h(n), thus obtaining the required Hilbert digital filter.

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