RU2571513C2 - Method for prevention of fire in result of arcing in electrical mains or electrical installation and device for its implementation - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention is related to fire safety and electrical power industry, and namely to method and devices intended for prevention of fire (explosion) and failure of systems that lead to disasters and emergencies in structures, buildings, airplanes, vessels, railway transport and other facilities. The method is based on determination of parameters of spark gap resistance by measuring current of high-frequency components characterizing arc occurrence - arc quenching cycle at zero crossing of arcing current. Level of fire and explosion safety and failure-free performance of systems is assessed against integral factor of their dependency on arcing current value considering effect of shunting current, width of discharge gap and intensity of arcing as well as heat-removing properties of electric equipment and environment. According to results of control warning signal or command is generated to cut off the electric mains (installation).

EFFECT: improved accuracy for determining fire hazard level and reliability of the system as a whole.

2 cl, 5 dwg

Description

APPLICATION AREA

The invention relates to the field of fire safety and electric power, and in particular to methods and devices for preventing fires arising from sparking in an electrical circuit of an electrical network (ES) or electrical installations (EU) in rooms, structures, buildings, aircraft, ships, railway transport, and other objects.

Note. Hereinafter, fire safety refers to fire and / or explosion safety, as well as the failure of important functional systems leading to disaster or accident, for example, due to melting of insulation of wires or other elements of electrical equipment due to sparking (defective arc) in the spark gap without it fires. The operation of residential, domestic, industrial and other facilities is often accompanied by fires or explosions arising from sparking in electrical networks (ES) and electrical installations (ES).

In Russia, according to official statistics, a fire due to sparking in electrical equipment takes the second place in terms of the number and severity of consequences after careless handling of fire.

Particularly dangerous are the above failures, leading to incidents not only at facilities for the extraction, storage and transportation of petroleum products and gas and other fire hazardous facilities, but also causing disasters due to a violation of control systems for facilities in the air, space and at sea. For example, the death of aircraft in Surgut and Chelyabinsk, the death of the first Apollo-1 spacecraft, submarines and many other tragic events. Repeated failures of aircraft onboard batteries occur due to a connection failure with at least one jumper with one of several dozen batteries connected in series.

In order to improve this sad statistics, various methods and devices for protection against sparking used in ES and ES were developed.

BACKGROUND

The known "method for detecting a defective consecutive arc of an alternating current" [1], with which they detect and display the presence of a consecutive defective arc in an electric current supplied from an AC power source under an electric load. It includes two-time measurements (measurements of two periods of alternating current) of the values of its positive and negative half-periods and determination of their absolute values, then summing them up over each period and using the difference of two sums to establish the presence of a defective sequential arc in case this difference exceeds a predetermined threshold level .

Studies show that it is unreasonable to rely on the difference in the measurement results of the “sparking” periods, since, on the one hand, this difference may be absent, and, on the other hand, the difference in readings in comparing the two amounts can also occur for “non-sparking” periods alternating current. In addition, in this technical solution, the rationale is based on the analysis of signals of only industrial frequency (50, 60 Hz and other low frequencies) without taking into account the high-frequency components formed at the time of sparking and which are the main signs of this sparking.

Thus, the presence of sparking, of course, can be fixed, but without determining its level of danger and at the same time with a very low reliability indicator, i.e. some of the fire hazard situations will not be noticed, another, on the contrary, will give a danger signal in the absence of such in reality.

The known "method for determining the time of occurrence of the pre-fire situation from sparking in the electric network" [2], in which the AC voltage signal is rectified and converted into a half-wave signal. Each half-period of voltage is converted into a rectangular signal, along the leading edge of which a signal is generated corresponding to the zero voltage transition of the diagnosed network, a time interval equal in duration to the maximum distance between the maximum values of instantaneous power per half-period at the maximum possible angular phase difference between the current and voltage of the diagnosed network ...

The disadvantages of this method.

According to the characteristics set forth in the formula, the method does not include the operation of measuring any current in the network, which does not allow determining either the network power, the magnitude of the spark current, or the moment of its transition through zero. It follows that the use of this invention is not able to identify the danger of sparking.

The known "method and device for preventing fire from malfunctions in electrical networks and electrical installations" [3], which along with measuring the amplitude of the pulses at the damping and increasing stages of the cycle "occurrence - suppression of the spark" and the number of pulses at the increasing stage of this cycle additionally contains a measurement of one of the short circuit current, overload current, leakage current, the deviation of the mains voltage from the required values.

Moreover, the implementation of this method is also characterized in that it additionally contains at least one of the units for measuring the short circuit current, overload current, leakage current and measuring the magnitude of the deviation of the mains voltage from the required values.

However, this method does not take into account the influence of parallel currents (bypass currents) and the width of the spark gap on the accuracy of determining the level of danger of sparking.

Closest to the technical nature of the claimed invention is a "method of preventing fire from sparking in an electrical network or electrical installation and a device for its implementation" [4], which has a wider set of features, closest to the set of essential features of the invention. Therefore, this technical solution is selected as the closest analogue from among the known and taken as a prototype.

In accordance with this technical solution and according to the prior art [3], the electric current of the monitored section of the ES or EI is measured, the low-frequency component and high-frequency signals are formed from the measured current, characterizing the processes of electric breakdown of the spark gap and restoration of voltage across it in the region where the current passes through zero. In this time domain, processes of occurrence and attenuation of sparking (defective arc) are carried out. The parameters of the extracted signals are determined by the intensity and magnitude of this sparking current, which depends on the transition resistance. If necessary, the signal is amplified and rectified. In this case, the accumulation of thermal energy adequate to the cycle frequency and the sparking current is carried out taking into account the previously calculated value of this current. The magnitude of the spark current is calculated based on the measurement and subsequent calculation of the selected parameters of the cycle "occurrence - extinction of the spark" at its generating and decaying stages. These cycle parameters that determine the value of the sparking current include the amplitude of the generating and (or) decaying stages of the cycle, their duration and (or) the number of pulses at these stages of the cycle, the amplitude of which exceeds the set value. The result of the accumulation of the signal for a specified time is compared with a predetermined (given) its allowable values. At the same time, a warning signal is generated at the device output about the corresponding level of fire hazard and (or) a command to turn off the monitored section of the faulty ES or EA, coming to the information display unit and (or) to turn off the block to control the monitored section of the ES or ES.

A device for implementing this method is characterized in that it contains a unit for determining the magnitude of the spark current (FIGS. 2, 3 of the prior art [4]), which includes a signal-sign generation module 3 of the “occurrence - extinguishing of the spark” cycle at the time the current passes through zero, module 4 for measuring and calculating the parameters of the cycle (the frequency of the cycles, the duration of the generating and (or) decaying stages of the cycle; the number of pulses at the decaying stage of the cycle, the amplitude of which exceeds the set value), module 5 for calculating other sparking current, module 6 storing the calculated value of the sparking current and block 11 accumulation.

All commands to execute the given algorithm of the device are generated in the control unit 15, executed, for example, in the form of a microcontroller. The device is powered by the power supply unit 16 from the ES and (or) from an autonomous source.

When the condition of the monitored section of the electric network (electrical installation) is in good condition, there is no sparking at any point of the monitored section, therefore the value of the high-frequency component of the signal at the input of the correction device is zero.

When sparking occurs, associated with the formation of an ionized transition resistance R _junction in the place of, for example, a poor-quality contact, a spark current (free ion and electron current) appears in circuit 4, which manifests itself as a sequence of occurrence-extinguishing of the spark (electric arc) .

In accordance with the signal at the input of the unit for determining the magnitude of the sparking current in module 3, signal signs of the cycles are generated. According to the first pulse (the signal-sign of the cycle) in module 4, a time interval is formed and the incoming pulses of the signal-signs of the cycles are accumulated. After the set time has elapsed, the same module fixes the measured number of pulses and calculates the value of the cycle parameter (cycle frequency). The result obtained is transmitted to module 5. Here, according to a given functional, the argument of which is the cycle repetition rate, the magnitude of the spark current is calculated, which is stored in module 6. The calculation result is transmitted to accumulation unit 11, and a signal is transmitted to control unit 15 to form a command to conduct a new account of pulses of signal-signs of cycles that continue to arrive.

As a drawback of this technical solution, it should be noted that there is no measurement of the width of the spark gap, the gap value of which, together with the magnitude of the spark current, most fully determines the amount of thermal energy released in this spark gap, and therefore the accuracy of determining the level of fire hazard.

In addition, this technical solution does not take into account the effect of the shunt current (current parallel to the spark current) on the accuracy of determining the spark current in a branched electric circuit. Especially distorting the measurement results is the value of the shunt current, prevailing over the spark current.

These shortcomings in certain conditions significantly affect the accuracy of calculating the level of fire hazard, and therefore reduce the reliability of the prevention of an accident.

SUMMARY OF THE INVENTION

The aim of the invention is to increase the reliability and accuracy of measuring the level of fire hazard from sparking and other malfunctions in the ES and EU, aimed at improving the tactical and technical characteristics of the proposed technical solution.

The goal is achieved by the fact that the method of preventing fire from sparking in the electric circuit of the ES or EU contains a measurement of the electric current of the controlled area; the formation of low-frequency (industrial frequency) and high-frequency components from the signal of the measured current; if necessary, amplification and rectification of high-frequency signals; the formation of the pulse of the signal-sign of the cycle "occurrence - extinction of the spark" at the moment of transition of the current through zero; measurement and calculation of the frequency of repetition of cycles; measuring, if necessary, the amplitude of the pulses at the generating and (or) decaying stages of the cycle; measuring the duration of the generating and decaying stages of the cycle, as well as, if necessary, the number of pulses at these stages of the cycle, the amplitude of which exceeds the set value; measurement of at least one of the short circuit current, overload current, leakage current, the deviation of the mains voltage from the required values; display of measurement and calculation results and (or) shutdown of a controlled electrical network or electrical installation; control of the measurement and calculation process, for example, using a microcontroller; device power supply. At the same time, operations are introduced to determine the size of the spark gap formed at the place of the electric circuit rupture and the spark current, taking into account the influence of the shunt current on the accuracy of determining the parameters of the spark current.

Thus, in the well-known technical solution [4], along with the operations of measuring the electric current of the controlled area, generating low-frequency and high-frequency components from the measured current signal, operations are also introduced to determine the magnitude of the spark gap, and also determine the magnitude of the sparking current, taking into account the effect of the shunt current.

The presence in the claimed technical solution of a combination of distinctive features not known from the prior art allows us to conclude that it meets the condition of patentability “novelty”.

The set of essential features of the claimed invention, predetermining

the receipt of the specified technical result, obviously does not follow from the prior art, which allows us to conclude that the invention meets the condition of patentability "inventive step".

The patentability condition "industrial applicability" is confirmed by the example of a specific implementation.

DESCRIPTION OF DRAWINGS

The essence of the proposed technical solution is illustrated by drawings, which show:

FIG. 1 is a graph of the summation of the sparking current and the shunting current at the sensor input (1 - sparking current, 2 - shunting current, 3 - total load current);

FIG. 2 - graph of the signal of the total current at the output of the sensor (4 - the moment of formation of sparking (breakdown of the spark gap), 5 - the moment of attenuation of sparking);

FIG. 3 - interrelation of the spark current with the “dip” and the shunt current (4 - the moment of arcing, 5 - the moment of extinction of the spark, 6 - the shaded area of the spark current, 7 - the shaded area of the shunt current);

FIG. 4 - module for measuring the spark current taking into account the value of the shunt current (8 - unit for measuring the electric current of the controlled section, 9 - board for measuring and calculating the cycle parameter (from the prior art), 10 - board for calculating the value of the spark current (from the prior art), 11 - module for generating a signal-sign of the “occurrence - extinction” cycle of a spark (electric arc), 12 — module for measuring and calculating a cycle parameter, 13 — module for storing the value of the spark current, 14 — module for calculating the magnitude of the spark current, 15 — module for measuring the spark current values of w ntiruyuschego current (proposed), 16 - determining unit quantities sparking current (prior art);

FIG. 5 - board for determining the width of the spark gap (10 - board for calculating the magnitude of the spark current (from the prior art), 17 - module for generating a signal-sign of the cycle "occurrence - damping" of the spark, 18 - board for measuring the frequency of repetition of cycles, 19 - board for measuring the number of pulses 20 - a board for measuring the duration of the generating and decaying stages of the cycle, 21 - a board for determining the width of the spark gap, 22 - a board for measuring the moment of extinguishing of the spark of the first cycle and its conservation, 23 - board for measuring the moment of occurrence of the spark (breakdown) of the second cycle la adjacent current half-cycle, 24 - board for calculating the width of the spark gap, 25 - module for measuring and calculating cycle parameters).

DETAILED DESCRIPTION OF THE INVENTION

In FIG. Figure 1 shows the dependences of the sparking current and bypass current on time. When the spark current 1 passes through zero, a noticeable distortion of its sinusoidal shape, the so-called "dip", is observed. Due to the smallness of the current change in the border region with a zero value of the indicated section (“dip”), it is difficult to talk about the explicit parameters of this “dip”, especially taking into account the effect of the shunt current 2.

In order to better visualize the nature of the change in the dependence of the total current 3 on time and expand the possibilities of its analysis in the field of "failure", for example, by using a current transformer (sensor), its differentiation with respect to the first derivative is performed - measuring the slope of the change in the total load current on the secondary winding of this transformer, as shown in FIG. 2.

The signal of the total current at the output of the sensor is generated in the electric current measuring unit 8 of the controlled section, from the output of which it enters the spark current measuring module 15 taking into account the value of the shunt current.

In this module, the shaded areas are extracted from the signal of the first derivative in the “dip” region and their area (energy) is measured. The area of the shaded area 6 corresponds to the spark current, the area of the shaded area 7 corresponds to the shunt current.

By recalculating the ratios of the measured currents (spark current i _sparks and total current i _sum ) and shaded areas 6 and 7, the magnitude of the signal of the spark current is determined by the formula

Next, we consider the process of measuring the width of the spark gap. Hereinafter, by the medium of the spark gap, we mean an air or other dielectric medium.

By the spark gap we mean the corresponding distance between adjacent cycles “occurrence - quenching of the spark” (the so-called “dip”), equal to the time difference between the moments of occurrence of pulses at the decaying stage of one cycle before the current passes to zero (4) and the generatrix stage subsequent to it cycle of an adjacent half-cycle after a zero current transition (5), which corresponds to an air or other type of gap separating the electrodes in high or low voltage installations (at an electric up to 33 kV / cm and voltage at the electrodes up to 380 V, the gap width is not more than 115 microns).

The width of the spark gap is previously determined by the width of the "gap" between points 4 and 5 of FIG. 2, 3 as follows.

A module for determining the width of the spark gap is additionally introduced into the module 12 for measuring and calculating the parameters of the cycle (Fig. 5).

When the measurement of the duration of the generating (decaying) stages of the cycle of high-frequency signals appears on the board 20, they are recognized as signs of the sparking process and formed in the form of signal-signs of two successive cycles "occurrence - suppression of the spark", each of which belongs to one of the adjacent half-periods and further connecting this board to the spark gap width determining board 21. Moreover, according to FIG. 5 structural diagram of this board, perform the following operations:

- first, using the one shown in FIG. 5 card 22 measured at time t _gash sparks quench the first cycle and transmitting its stored charge 24 in calculating the width of the spark gap;

- then, using a plate 23 measured at time t _WHO sparks adjacent half cycle of the second cycle of current arcing fixed time t _cart and pass it on the same board 24, calculating the spark gap;

- using the board 24 calculate the width of the "failure" t _failure according to the formula

- determine the width of the spark gap t _clearance , for which

- with an active load of the sparking current, the spark gap corresponds to the width of the "dip" of the sparking current, i.e.

- with a reactive load of the sparking current, the spark gap accordingly changes by the amount of phase shift

$$t_{s\mathrm{but}s\mathrm{about}R}=k\cdot (t_{PR\mathrm{about}\mathrm{at}\mathrm{but}l}-\varphi ),(\mathrm{four})$$

where φ - the phase shift between the time point t _gash angle arcing current as it passes through the zero time point t and the electric _network voltage when it passes through zero;

k is a coefficient that establishes a relationship between the dependences of the voltage of the electric network on time and the electric field strength in the spark gap.

Finally, the result of calculating the width of the spark gap from the board 24 is transferred to the board 10 for calculating the magnitude of the spark current, together with which it is integrated into an integral indicator of the fire hazard level. This indicator is calculated on board 10 as the dependence of the fire hazard level on the magnitude of the spark current taking into account the shunt current, on the width of the spark gap and on the intensity of sparking, as well as on the characteristics of the heat-removing properties of electrical equipment and the environment.

The proposed technical solution for existing devices reduces the number of false reports and commands and increases the reliability indicator, which reduces the cost of implementing protection for the prevention of fires and explosions from sparking in electrical networks and electrical installations, and also increases the reliability of electrical systems in general.

The introduction of devices that implement the proposed method involves the use of existing technical solutions [3 and 4] with their minor circuit and software refinement.

It also does not require the restructuring of industrial enterprises and private firms to produce a new product range.

Thus, the economic and moral gain from the implementation of the invention is determined by the number of saved lives, as well as the number and cost of residential, industrial and other objects due to prevented fires by applying the proposed technical solution.

INFORMATION SOURCES

1. US patent US 7633729 from 12/15/2009 "Alternating current series ARC fault detection method". Priority from 10/22/2007. Publication of application No. 2009/0103216 A1 of 04/23/2009.

2. Russian patent RU 2309461 "Method for determining the time of occurrence of a pre-fire situation from sparking in the electric network and a device for its implementation." Priority dated 12/27/2005. Publication of application No. 2005141090/09 10/27/2007, bull. No. 30.

3. Application No.PCT / RU2005 / 000251 “Method and device for preventing fire from malfunctions in electric networks and electrical installations”. Priority dated May 6, 2005. Publication of application No. WO 2006/121364 A1 November 16, 2006.

4. Patent of Russia RU 2254615 dated 06/20/2005 “A method for preventing fire from sparking in an electric network or electrical installation and a device for its implementation”. Priority dated 10.07.2003. Publication of application No. 2003120730/09 02/10/2005, bull. Number 17.

Claims (2)

1. A method of preventing fire from sparking in an electrical network or electrical installation, comprising measuring the electric current of the controlled area; the formation of low-frequency and high-frequency components from the signal of the measured current; the formation of the pulse of the signal-sign of the cycle "occurrence - extinction of the spark" at the moment of transition of the current through zero; measurement and calculation of the frequency of repetition of cycles; measurement of the amplitude of the pulses at the generating and / or decaying stages of the cycle; measuring the duration of the generating and decaying stages of the cycle, as well as / or the number of pulses at these stages of the cycle, the amplitude of which exceeds the set value; measurement of at least one of the short circuit current, overload current, leakage current, the deviation of the mains voltage from the required values; display of measurement and calculation results and / or shutdown of a controlled electrical network or electrical installation, characterized in that they additionally determine the width of the spark gap formed at the place of integrity of the electrical circuit by determining the time difference between the moments of occurrence of sparking signals at the decaying stage of one cycle before the current transition zero value and after zero transition at the generating stage of the next cycle of the adjacent half-cycle following it; the value of the sparking current, taking into account the influence of the shunt current, by measuring the steepness of the change in the total load current in the region of the zero value of the sparking current, summing the obtained measurement results over time, and based on the summation results, determine the value of the sparking current. 2. The device for implementing the method of claim 1, comprising a unit for measuring the electric current of the controlled area, a unit for generating low-frequency and high-frequency components, a unit for generating pulses of a signal-sign of the “occurrence - extinguishing of the spark” cycle, a unit for measuring and calculating the repetition rate of the cycles, an amplitude measuring unit pulses at the generating and / or decaying stages of the cycle; a unit for measuring the duration of the generating and decaying stages of the cycle, as well as / or a unit for measuring the number of pulses at these stages of the cycle, the amplitude of which exceeds the set value; a unit for measuring at least one of the short-circuit current, overload current, leakage current, the deviation of the mains voltage from the required values, a display unit for information and / or disconnection of the electrical network or electrical installation, characterized in that an additional board for determining the width of the spark gap is introduced, an input which is connected to the output of the board for measuring the duration of the generating and decaying stages of the cycle, and the output is connected to the board for calculating the value of the spark current, in addition to the board for calculating the value of the spark current The spark current measurement module is finally introduced taking into account the effect of the shunt current, the input of which is connected to the electric current measuring unit of the controlled section, and the output is connected to the module for calculating the value of the spark current.

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