Method and device for reducing loss, preventing explosion and prolonging service life of cable sheath protector

Abstract

The invention discloses a method and device for reducing loss, preventing explosion and prolonging the service life of a cable sheath protector, and the method comprises the steps: S1, constructing a protection device voltage reduction circuit which comprises a resistor Rg and a capacitor Cg connected with the resistor Rg in parallel, the resistor Rg has a preset resistance characteristic, and the capacitor Rg has a preset capacitance characteristic; s2, constructing an equivalent circuit of the cable sheath protector, wherein the equivalent circuit of the cable sheath protector comprises an equivalent resistor Rcsp and an equivalent capacitor Ccsp connected with the equivalent resistor Rcsp in parallel; and S3, the protection device step-down circuit and the cable sheath protector circuit are connected in series, so that the voltage at the two ends of the cable sheath protector can be automatically adjusted according to the preset resistance characteristic and capacitance characteristic. According to the invention, the operation loss of the cable sheath protector can be reduced, misoperation during power frequency overvoltage and lightning overvoltage is prevented, and the service life of the cable sheath protector is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of electric power, and in particular relates to a method and a device for reducing damage, preventing explosion and extending service life of a cable sheath protector. Background Art

[0002] A protector is a device used to provide power safety protection for power equipment. A cable sheath protector is a protective device installed in the connecting section of an overhead line cable. It plays a protective role when the cable is subjected to lightning overvoltage and prevents the cable sheath from being punctured. When the cable system is subjected to power frequency overvoltage, the short-circuit current borne by the cable sheath protector can reach several seconds, which will cause the cable sheath protector to overheat and explode in a short time, seriously threatening the operation safety of the cable. In addition, when the cable is operating normally, the protector is constantly subjected to alternating AC sheath voltage, which will cause loss and shorten the service life of the cable sheath protector. Therefore, it is of great significance to study a method for reducing the loss and explosion of a cable sheath protector to prevent the protector from exploding due to short-term overheating under power frequency overvoltage, reduce the power frequency loss of the cable sheath protector, and extend its service life. Summary of the invention

[0003] The first purpose of the invention is to overcome the shortcomings and deficiencies in the prior art and to provide a method for reducing damage, preventing explosions and extending the life of a cable sheath protector, which can reduce the operating loss of the cable sheath protector, prevent false operation during power frequency overvoltage and lightning overvoltage, and increase its service life.

[0004] The second purpose of the present invention is to provide a device for reducing damage, preventing explosion and extending the service life of a cable sheath protector.

[0005] The purpose of the present invention is achieved through the following technical solution: A method for reducing the damage and explosion-proofing of a cable sheath protector and extending its service life, comprising the steps of: S1. Construct a voltage-reducing circuit for a protection device, wherein the voltage-reducing circuit for the protection device includes a resistor R g And the capacitor C in parallel g , resistor R g With preset resistance characteristics, capacitor R g Having preset capacitance characteristics; S2, constructing a cable sheath protector equivalent circuit, the cable sheath protector equivalent circuit includes an equivalent resistor R csp And the equivalent capacitance C in parallel csp ; S3. Connect the step-down circuit of the protection device and the cable sheath protector circuit in series to automatically adjust the voltage across the cable sheath protector according to preset resistance characteristics and capacitance characteristics.

[0006] Preferably, in the cable sheath protector loss reduction and explosion-proof device, the voltage U at both ends of the cable sheath protector circuit is csp The calculation formula is: , formula (1), Among them, U a is the cable sheath voltage, B csp is the susceptance of the equivalent capacitor, f l is the voltage frequency of the cable sheath.

[0007] Preferably, the determination of the preset resistance characteristic and the preset capacitance characteristic range specifically includes the steps of: S11. When the cable sheath is subjected to the power frequency induced voltage, the cable sheath protector is subject to the maximum loss constraint condition, so as to calculate the first range of the resistance characteristic: S12, when the cable sheath is subjected to power frequency overvoltage, the cable sheath protector does not operate, and the operating voltage constraint condition is obtained, thereby calculating the second range of the resistance characteristic; S13, combining the first range of resistance characteristics and the second range of resistance characteristics, the resistance R is obtained by analysis g The resistance characteristics of S14. When the cable sheath is subjected to lightning overvoltage, the cable sheath protector needs to operate normally, and the action voltage correction constraint condition is obtained to calculate the capacitance C. g Capacitance characteristics.

[0008] Preferably, step S11 specifically includes the steps of: S111. Under the power frequency induced voltage, the capacitor and equivalent capacitor are regarded as open circuit, and the voltage calculation formula of the two ends of the cable sheath protector is: , formula (2); Among them, U a0 is the power frequency induced voltage on the cable sheath, R csp is the internal resistance of the cable sheath protector; S112. The maximum loss constraint condition expression is: , formula (3), Among them, P csp is the actual power loss of the cable sheath protector, P max The maximum designed power loss of the cable sheath protector; S113. Combining equation (2) and equation (3), the first range of resistance characteristics is obtained: , formula (4).

[0009] Preferably, step S12 specifically includes the steps of: S121. Under power frequency overvoltage, the capacitor and equivalent capacitor are regarded as open circuit, and the voltage calculation formula of the two ends of the cable sheath protector is: , formula (5), Then we have: , formula (6); Among them, U aOV , U aOV.max are the power frequency overvoltage amplitude and the maximum power frequency overvoltage borne by the cable sheath, U csp.max For U aOV.max When the corresponding cable sheath protector has overvoltage at both ends; S122, the action voltage constraint condition expression is: , formula (7), Among them, U csp.max For U aOV.max The corresponding overvoltage at both ends of the cable sheath protector is U act is the operating voltage of the cable sheath protector; S123. Combining equation (6) and equation (7), the second range of resistance characteristics is obtained: , formula (8).

[0010] Preferably, in step S13, the resistor R g The resistance characteristics are: , formula (9).

[0011] Preferably, step S14 specifically includes the steps of: S131. Under lightning overvoltage, the resistor R g is regarded as a short circuit, and the equivalent resistance R csp Ignoring it, the voltage calculation formula at both ends of the cable sheath protector is: , formula (10), Among them, U l Lightning overvoltage borne by the cable sheath; Since the cable sheath protector can identify the fundamental frequency voltage more accurately when it is in action, the fundamental frequency component of the minimum lightning overvoltage is used to calculate the voltage division of the cable sheath protector, and then formula (10) becomes: , formula (11), Among them, U l.min(1) is the fundamental frequency component of the minimum lightning overvoltage, U csp.min The voltage across the cable sheath protector corresponding to the minimum lightning overvoltage of the cable sheath; S132, the action voltage correction constraint condition is: , formula (12), Among them, 30 is the preset over-limit coefficient, which is used to ensure that the cable sheath protector acts quickly when the cable sheath is subjected to the minimum lightning overvoltage; S133. Combining equation (11) and equation (12), the capacitance characteristic is obtained: , formula (13).

[0012] Preferably, after step S14, the method further comprises the following steps: S15, calculate the resistance R according to the preset resistance cost g The maximum value R g.max , combined with the resistance characteristic in step S13, to obtain a final value range of the resistance characteristic; S16. Calculate the capacitance C based on the maximum harmless electric field effect of the preset capacitance g The maximum value of C g.max , combined with the capacitance characteristic in step S14, the final value range of the capacitance characteristic is obtained.

[0013] A device for reducing damage and explosion-proofing a cable sheath protector and extending its service life comprises a protective device step-down circuit and a cable sheath protector circuit connected in series therewith, wherein the protective device step-down circuit comprises a resistor R g And the capacitor C in parallel g , resistor R g With preset resistance characteristics, capacitor R g It has a preset capacitance characteristic; the cable sheath protector equivalent circuit includes an equivalent resistor R csp And the equivalent capacitance C in parallel csp .

[0014] Preferably, the determination of the preset resistance characteristic and the preset capacitance characteristic range specifically includes the steps of: When the cable sheath is subjected to the power frequency induced voltage, the cable sheath protector is subject to the maximum loss constraint condition, so the first range of the resistance characteristic is calculated: When the cable sheath is subjected to power frequency overvoltage, the cable sheath protector does not operate, and the operating voltage constraint condition is obtained, thereby calculating the second range of the resistance characteristic; Combining the first range of resistance characteristics and the second range of resistance characteristics, the resistance R g The resistance characteristics of According to the cable sheath protector needs to operate normally when the cable sheath is subjected to lightning overvoltage, the action voltage correction constraint condition is obtained, and the capacitance C is calculated g Capacitance characteristics.

[0015] Compared with the prior art, the present invention has the following advantages and effects: (1) The present invention provides a method for reducing the loss, preventing explosion and extending the service life of a cable sheath protector, by constructing a step-down circuit of a protection device and a cable sheath protector circuit, and connecting the two in series, so as to automatically adjust the voltage at both ends of the cable sheath protector according to preset resistance characteristics and capacitance characteristics. The present invention adjusts the voltage division of the cable sheath protector through the step-down circuit of the protection device, which can reduce the operating loss of the cable sheath protector, prevent malfunction during power frequency overvoltage and lightning overvoltage, and increase its service life.

[0016] (1) The determination of the preset resistance and capacitance characteristic ranges in the present invention is based on the voltage division calculation of the cable sheath protector, and is obtained by combining the maximum loss constraint conditions, action voltage constraint conditions and action voltage correction constraint conditions of the cable sheath protector under power frequency voltage, power frequency overvoltage and lightning overvoltage. It is achieved to reduce the voltage at both ends of the cable sheath protector during normal power frequency operation, reduce losses and prevent false operation; when there is power frequency overvoltage, reduce the voltage at both ends of the cable sheath protector to prevent the power frequency overvoltage from causing the cable sheath protector to malfunction or even explode; under lightning overvoltage, it does not affect the normal operation of the cable sheath protector, thereby increasing the service life of the cable sheath protector.

[0017] (3) The present invention provides a device for reducing damage, preventing explosion and extending the service life of a cable sheath protector, the device comprising a protection device step-down circuit and a cable sheath protector circuit connected in series therewith, the protection device step-down circuit comprising a resistor R g And the capacitor C in parallel g , with preset resistance and capacitance characteristics. The device has simple structure, good economy and strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart of a method for reducing damage, preventing explosion and extending the service life of a cable sheath protector according to Example 1 of the present invention.

[0019] Figure 2 This is a schematic diagram of the circuit principle of a device for reducing damage, preventing explosion and extending the service life of a cable sheath protector according to embodiment 2 of the present invention.

[0020] Figure 3 A logic schematic diagram for selecting the resistance and capacitance characteristic ranges of a cable sheath protector loss reduction, explosion prevention and life extension device of the present invention.

[0021] Figure 4 The present invention is a schematic diagram of the operating performance principle of a device for reducing damage, preventing explosion and extending the service life of a cable sheath protector. DETAILED DESCRIPTION

[0022] The present invention will be further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0023] Example 1 like Figure 1 The figure shows a flow chart of a method for reducing the damage and explosion-proofing of a cable sheath protector and extending its service life, comprising the steps of: S1. Construct a voltage-reducing circuit for a protection device, wherein the voltage-reducing circuit for the protection device includes a resistor R g And the capacitor C in parallel g , resistor R g With preset resistance characteristics, capacitor R g Having preset capacitance characteristics; S2, constructing a cable sheath protector equivalent circuit, the cable sheath protector equivalent circuit includes an equivalent resistor R csp And the equivalent capacitance C in parallel csp ; S3. Connect the step-down circuit of the protection device and the cable sheath protector circuit in series to automatically adjust the voltage across the cable sheath protector according to preset resistance characteristics and capacitance characteristics.

[0024] Specifically, the present invention constructs a protection device step-down circuit and a cable sheath protector circuit, connects one end of the protection device (i.e., the protection device step-down circuit) to the cable sheath, and the other end to the cable sheath protector, so as to divide the voltage at both ends of the cable sheath protector according to the preset resistance characteristics and capacitance characteristics, thereby realizing the function of reducing the voltage at both ends of the cable sheath protector. The protection device is composed of a resistor and a capacitor connected in parallel, such as Figure 2 shown.

[0025] Usually, the cable sheath protector has a large resistance under normal power frequency voltage, and the current flowing through the cable sheath protector is very small, at the microampere level; under overvoltage, the resistance of the cable sheath protector decreases, and the current increases, thereby releasing the charge on the cable sheath to protect the cable sheath. This resistance change characteristic of the cable sheath protector is due to its core functional component, the zinc oxide valve plate. According to the nonlinear characteristics of its volt-ampere curve, in this embodiment, it is regarded as an equivalent resistor. R csp and equivalent capacitance C csp A parallel circuit such as Figure 2 The present invention reduces the voltage at both ends of the cable sheath protector through the step-down circuit of the protection device, which can reduce the operation loss of the cable sheath protector, prevent malfunction during power frequency overvoltage and lightning overvoltage, and increase its service life.

[0026] In the cable sheath protector loss reduction and explosion-proof device, the voltage U at both ends of the cable sheath protector circuit iscsp The calculation formula is: , formula (1), Among them, U a is the cable sheath voltage, B csp is the susceptance of the equivalent capacitor, f l is the voltage frequency of the cable sheath.

[0027] Specifically, Figure 2 The circuit principle diagram of the present invention is shown in FIG. In this embodiment, according to the characteristics that the cable sheath protector only acts on overvoltage but has no selectivity for overvoltage frequency, it is approximately considered that the equivalent capacitor C csp The susceptance does not change with frequency, so use B csp Represents the susceptance of the equivalent capacitor. The grounding grid resistance is too small compared to the cable sheath protector and can be ignored. According to the circuit principle analysis, the voltage division calculation formula of the cable sheath protector in the circuit is shown in formula (1).

[0028] The determination of the preset resistance characteristic and the preset capacitance characteristic range specifically includes the steps of: S11. When the cable sheath is subjected to the power frequency induced voltage, the cable sheath protector is subject to the maximum loss constraint condition, so as to calculate the first range of the resistance characteristic: S12, when the cable sheath is subjected to power frequency overvoltage, the cable sheath protector does not operate, and the operating voltage constraint condition is obtained, thereby calculating the second range of the resistance characteristic; S13, combining the first range of resistance characteristics and the second range of resistance characteristics, the resistance R is obtained by analysis g The resistance characteristics of S14. When the cable sheath is subjected to lightning overvoltage, the cable sheath protector needs to operate normally, and the action voltage correction constraint condition is obtained to calculate the capacitance C. g Capacitance characteristics.

[0029] Specifically, the preset resistance characteristics and capacitance characteristics in the step-down circuit of the protection device are closely related to the operation of the cable sheath protector. In this embodiment, the determination of the preset resistance characteristics and capacitance characteristics is constrained mainly from three purposes, including: (a) reducing the voltage across the cable sheath protector under the power frequency sheath induced voltage, thereby reducing its loss and extending the service life of the cable sheath protector; (b) reducing the voltage across the cable sheath protector under the power frequency overvoltage, so that the cable sheath protector does not operate, thereby preventing the cable sheath protector from overheating and explosion; (c) under the lightning overvoltage, the cable sheath protector reduces the voltage division of the protector through the protection device, and does not affect the normal operation of the cable sheath protector.

[0030] Before calculating the resistance characteristics and capacitance characteristics according to the maximum loss constraint, action voltage constraint and action voltage correction constraint of the cable sheath protector, the various electrical parameters of the cable sheath under the operation state of the cable line and the design parameters of the cable sheath protector itself are first obtained. The electrical parameters include the power frequency induced voltage U of the cable sheath obtained through the historical operation data of the target cable line. a0 , Maximum power frequency overvoltage U aOV.max and the minimum fundamental value of lightning overvoltage; the design parameters include the resistance R of the cable sheath protector obtained from the nameplate csp 、Susceptance B csp And the operating voltage U act In addition, the maximum design loss P of the cable sheath protector is determined according to the on-site environment (including local temperature and ventilation conditions of the grounding box, etc.). max , the design is determined according to actual usage requirements.

[0031] like Figure 3 A logical schematic diagram is provided for selecting the resistance and capacitance characteristic range of a cable sheath protector for reducing damage, preventing explosion and extending service life of the present invention. Figure 4 The schematic diagram of the operating performance principle of a device for reducing loss, preventing explosion and extending the life of a cable sheath protector of the present invention. The determination of the preset resistance and capacitance characteristic ranges in the present invention is based on the voltage division calculation of the cable sheath protector, and is obtained by combining the maximum loss constraint conditions, action voltage constraint conditions and action voltage correction constraint conditions of the cable sheath protector under power frequency voltage, power frequency overvoltage and lightning overvoltage. It can reduce the voltage across the cable sheath protector during normal power frequency operation, reduce losses and prevent false operation; reduce the voltage across the cable sheath protector during power frequency overvoltage to prevent the power frequency overvoltage from causing the cable sheath protector to malfunction or even explode; and do not affect the normal operation of the cable sheath protector under lightning overvoltage, thereby increasing the service life of the cable sheath protector.

[0032] Step S11 specifically includes the following steps: S111. Under the power frequency induced voltage, the capacitor and equivalent capacitor are regarded as open circuit, and the voltage calculation formula of the two ends of the cable sheath protector is: , formula (2); Among them, U a0 is the power frequency induced voltage on the cable sheath, R csp is the internal resistance of the cable sheath protector; S112. The maximum loss constraint condition expression is: , formula (3), Among them, P cspis the actual power loss of the cable sheath protector, P max The maximum designed power loss of the cable sheath protector; S113. Combining equation (2) and equation (3), the first range of resistance characteristics is obtained: , formula (4).

[0033] Specifically, the resistance characteristics of the resistor in the protection device are preliminarily determined through the maximum loss constraint of the cable sheath protector. The main contents are as follows: Under the power frequency sheath induced voltage, the capacitor C g The reactance is large, and the cable sheath protector has not reached the action threshold. In this embodiment, the capacitor C g and equivalent capacitance C csp Considered as an open circuit, according to the circuit principle, the voltage division of the cable sheath protector is approximately determined by the resistance R g and equivalent resistance R csp Ratio of resistance R g Can be the equivalent resistance R csp The voltage is divided, so that the voltage at both ends of the cable sheath protector is U csp reduce.

[0034] Combined with the maximum loss constraint: the actual loss of the cable sheath protector does not exceed the maximum loss P max , preliminarily determine the resistance in the protection device R g The internal resistance characteristics of this are called the first range of resistance characteristics.

[0035] Step S12 specifically includes the following steps: S121. Under power frequency overvoltage, the capacitor and equivalent capacitor are regarded as open circuit, and the voltage calculation formula of the two ends of the cable sheath protector is: , formula (5), Then we have: , formula (6); Among them, U aOV , U aOV.max are the power frequency overvoltage amplitude and the maximum power frequency overvoltage borne by the cable sheath, U csp.max For U aOV.max When the corresponding cable sheath protector has overvoltage at both ends; S122, the action voltage constraint condition expression is: , formula (7), Among them, U csp.max For U aOV.max The corresponding overvoltage at both ends of the cable sheath protector is U act is the operating voltage of the cable sheath protector; S123. Combining equation (6) and equation (7), the second range of resistance characteristics is obtained: , formula (8).

[0036] Specifically, the resistance characteristics of the resistor in the protection device are determined secondary through the action voltage constraint conditions during power frequency overvoltage. The specific contents are as follows: In this embodiment, when the cable sheath is subjected to power frequency overvoltage, the capacitor C g The reactance is very large, and the cable sheath protector has not reached the action threshold. C g and C csp Considered as a circuit breaker, the voltage division of the cable sheath protector depends approximately on the resistance R g and equivalent resistance R csp proportion.

[0037] After the protection device is connected in series, in order to ensure that the cable sheath protector does not operate and avoid its explosion, the operating voltage constraint condition that the cable sheath protector needs to meet is: the maximum value of the power frequency overvoltage U aOV.max Under this condition, the corresponding overvoltage at both ends of the cable sheath protector is U csp.max Less than the starting voltage U act , and then combine the voltage division calculation formula to determine the resistance in the protection device R g The internal resistance characteristics of this are called the second range of resistance characteristics.

[0038] In step S13, the resistor R g The resistance characteristics are: , formula (9).

[0039] Step S14 specifically includes the following steps: S131. Under lightning overvoltage, the resistor R g is regarded as a short circuit, and the equivalent resistance R csp Ignoring it, the voltage calculation formula at both ends of the cable sheath protector is: , formula (10), Among them, U l Lightning overvoltage borne by the cable sheath; Since the cable sheath protector can identify the fundamental frequency voltage more accurately when it is in action, the fundamental frequency component of the minimum lightning overvoltage is used to calculate the voltage division of the cable sheath protector, and then formula (10) becomes: , formula (11), Among them, U l.min(1) is the fundamental frequency component of the minimum lightning overvoltage, U csp.min The voltage across the cable sheath protector corresponding to the minimum lightning overvoltage of the cable sheath; S132, the action voltage correction constraint condition is: , formula (12), Among them, 30 is the preset over-limit coefficient, which is used to ensure that the cable sheath protector acts quickly when the cable sheath is subjected to the minimum lightning overvoltage; S133. Combining equation (11) and equation (12), the capacitance characteristic is obtained: , formula (13).

[0040] Specifically, the protection device is allowed to operate normally when there is a lightning overvoltage through the fundamental wave value of the minimum lightning overvoltage exceeding the limit starting constraint condition, that is, the action voltage correction constraint condition, and the capacitance characteristics of the capacitor in the protection device are designed and determined. The specific contents are as follows: In this embodiment, when the cable sheath is subjected to lightning overvoltage, the equivalent frequency of the lightning overvoltage is about 2.08*10 5 Hz, much larger than the power frequency, capacitor C g The reactance is very small, which is approximately equivalent to R g short circuit; and when the cable sheath protector operates normally, the equivalent capacitance C csp Conductive leakage, resistance R of cable sheath protector csp The voltage division of the cable sheath protector under high equivalent frequency lightning voltage is calculated according to formula (10), and its voltage division mainly depends on the capacitance C g and equivalent capacitance C csp It should be noted that in order not to affect the normal operation of the cable sheath protector, according to formula (10), 2πf l C g Should be much greater than B csp To ensure Ucsp and U l Not much difference.

[0041] Cable sheath protector according to the minimum lightning overvoltage U l.min Over-limit start constraint conditions, because the cable sheath protector action can more accurately identify the fundamental frequency voltage, the minimum lightning overvoltage is obtained according to the fast Fourier transform FFT U l.min The fundamental frequency component U l.min（1） ,use U l.min（1） The voltage division formula of the protector is as shown in formula (11). In order to make the voltage protection reliability of the cable sheath protector higher, 30* U act The value is used as the minimum threshold of the protector voltage division, and the limiting condition of the cable sheath protector voltage division is obtained as shown in formula (12). Finally, the capacitance range selection formula is calculated as shown in formula (13).

[0042] After step S14, the method further includes the following steps: S15, calculate the resistance R according to the preset resistance cost g The maximum value R g.max , combined with the resistance characteristic in step S13, to obtain a final value range of the resistance characteristic; S16. Calculate the capacitance C based on the maximum harmless electric field effect of the preset capacitance g The maximum value of C g.max , combined with the capacitance characteristic in step S14, the final value range of the capacitance characteristic is obtained.

[0043] Specifically, the minimum values ​​of the preset resistance characteristics and capacitance characteristics are determined through steps S11-S13. In this embodiment, in order to take into account both cost and electric field effect, the maximum values ​​of resistance and capacitance are considered, so as to comprehensively obtain the value range of the preset resistance characteristics and capacitance characteristics, thereby increasing rationality and practicality.

[0044] In order to further explain the method of the present invention, specific examples are provided below for illustration.

[0045] First, obtain the voltage parameters of the cable sheath protector under the operation state of the cable line, as well as other design parameters of the cable sheath protector: 110kV cable sheath power frequency induced voltage U a0 =100V, maximum power frequency overvoltage U aOV.max =6* U a0 , the fundamental component of the minimum lightning overvoltageU l.min（1） =10kV, maximum loss P 1 =3*10 -4 W; other parameters of cable sheath protector are R csp =15MΩ, C csp =0.72nF, B csp =0.226uΩ, action voltage U act =250V; at high frequency f l =2.08*10 5 At Hz, the capacitance of the cable sheath protector decreases slightly, making B csp A slight increase in the partial pressure of the cable sheath protector is conducive to normal operation, so it does not affect the calculation of the appropriate range of parameters.

[0046] The first step is to preliminarily determine the internal resistance characteristics of the device through loss constraints. When the cable is working normally, according to formula (4), R g ≥7.36MΩ.

[0047] The second step is to determine the internal resistance characteristics of the device through the power frequency overvoltage division constraint condition. When the cable is subjected to the maximum power frequency overvoltage, according to formula (8), R g >21MΩ.

[0048] The third step is to determine the internal capacitance characteristics of the device through the minimum lightning overvoltage fundamental value over-limit startup constraint condition. When the cable is subjected to the minimum lightning overvoltage, according to formula (13) C g >0.52pF.

[0049] Comprehensive comparison, the resistance R g The resistance characteristic is R g >21MΩ, capacitance C g The capacitance characteristic is C g >0.52pF.

[0050] In this embodiment, the resistor R is finally calculated based on the preset resistor cost. g The maximum value R g.max , the final value range of the resistance characteristic is: 21MΩ< Rg <R g.max ; Calculate the capacitance C based on the maximum harmless electric field effect of the preset capacitor g The maximum value of C g.max ,get The final value range of the capacitance characteristic is: 0.52pF< R g <C g.max .

[0051] Example 2 A device for reducing damage and explosion-proofing a cable sheath protector and extending its service life comprises a protective device step-down circuit and a cable sheath protector circuit connected in series therewith, wherein the protective device step-down circuit comprises a resistor R g And the capacitor C in parallel g , resistor R g With preset resistance characteristics, capacitor R g It has a preset capacitance characteristic; the cable sheath protector equivalent circuit includes an equivalent resistor R csp And the equivalent capacitance C in parallel csp .

[0052] When the cable sheath is subjected to the power frequency induced voltage, the cable sheath protector is subject to the maximum loss constraint condition, so the first range of the resistance characteristic is calculated: When the cable sheath is subjected to power frequency overvoltage, the cable sheath protector does not operate, and the operating voltage constraint condition is obtained, thereby calculating the second range of the resistance characteristic; Combining the first range of resistance characteristics and the second range of resistance characteristics, the resistance R g The resistance characteristics of According to the cable sheath protector needs to operate normally when the cable sheath is subjected to lightning overvoltage, the action voltage correction constraint condition is obtained, and the capacitance C is calculated g Capacitance characteristics.

[0053] Specifically, the present invention provides a device for reducing damage, preventing explosion and extending service life of a cable sheath protector, the device comprising a protection device step-down circuit and a cable sheath protector circuit connected in series therewith, the protection device step-down circuit comprising a resistor R g And the capacitor C in parallel g , with preset resistance and capacitance characteristics. The device has simple structure, good economy and strong practicality.

[0054] The above embodiments are preferred implementations of the present invention and are not intended to limit the present invention. Any other changes or other equivalent replacement methods that do not deviate from the technical solutions of the present invention are included in the protection scope of the present invention.

Claims

1. A method for reducing damage, preventing explosion and extending service life of a cable sheath protector, characterized in that: Includes steps: S1. Construct a voltage-reducing circuit for a protection device, wherein the voltage-reducing circuit for the protection device includes a resistor R g And the capacitor C in parallel g , resistor R g With preset resistance characteristics, capacitor R g Having preset capacitance characteristics; S2, constructing a cable sheath protector equivalent circuit, the cable sheath protector equivalent circuit includes an equivalent resistor R csp And the equivalent capacitance C in parallel csp ; S3. Connect the step-down circuit of the protection device and the cable sheath protector circuit in series to automatically adjust the voltage across the cable sheath protector according to preset resistance characteristics and capacitance characteristics.

2. A method for reducing damage, preventing explosion and extending service life of a cable sheath protector according to claim 1, characterized in that: In the cable sheath protector loss reduction and explosion-proof device, the voltage U at both ends of the cable sheath protector circuit is csp The calculation formula is: , formula (1), Among them, U a is the cable sheath voltage, B csp is the susceptance of the equivalent capacitor, f l is the voltage frequency of the cable sheath.

3. The method for reducing damage, preventing explosion and extending service life of a cable sheath protector according to claim 1, characterized in that: The determination of the preset resistance characteristic and the preset capacitance characteristic range specifically includes the steps of: S11. When the cable sheath is subjected to the power frequency induced voltage, the cable sheath protector is subject to the maximum loss constraint condition, so as to calculate the first range of the resistance characteristic: S12, when the cable sheath is subjected to power frequency overvoltage, the cable sheath protector does not operate, and the operating voltage constraint condition is obtained, thereby calculating the second range of the resistance characteristic; S13, combining the first range of resistance characteristics and the second range of resistance characteristics, the resistance R is obtained by analysis g The resistance characteristics of S14. When the cable sheath is subjected to lightning overvoltage, the cable sheath protector needs to operate normally, and the action voltage correction constraint condition is obtained to calculate the capacitance C. g Capacitance characteristics.

4. A method for reducing damage, preventing explosion and extending service life of a cable sheath protector according to claim 3, characterized in that: Step S11 specifically includes the following steps: S111. Under the power frequency induced voltage, the capacitor and equivalent capacitor are regarded as open circuit, and the voltage calculation formula of the two ends of the cable sheath protector is: , formula (2); Among them, U a0 is the power frequency induced voltage on the cable sheath, R csp is the internal resistance of the cable sheath protector; S112. The maximum loss constraint condition expression is: , formula (3), Among them, P csp is the actual power loss of the cable sheath protector, P max The maximum designed power loss of the cable sheath protector; S113. Combining equation (2) and equation (3), the first range of resistance characteristics is obtained: , formula (4).

5. A method for reducing damage, preventing explosion and extending service life of a cable sheath protector according to claim 4, characterized in that: Step S12 specifically includes the following steps: S121. Under power frequency overvoltage, the capacitor and equivalent capacitor are regarded as open circuit, and the voltage calculation formula of the two ends of the cable sheath protector is: , formula (5), Then we have: , formula (6); Among them, U aOV , U aOV.max are the power frequency overvoltage amplitude and the maximum power frequency overvoltage borne by the cable sheath, U csp.max For U aOV.max When the corresponding cable sheath protector has overvoltage at both ends; S122, the action voltage constraint condition expression is: , formula (7), Among them, U csp.max For U aOV.max The corresponding overvoltage at both ends of the cable sheath protector is U act is the operating voltage of the cable sheath protector; S123. Combining equation (6) and equation (7), the second range of resistance characteristics is obtained: , formula (8).

6. A method for reducing damage, preventing explosion and extending service life of a cable sheath protector according to claim 5, characterized in that: In step S13, the resistor R g The resistance characteristics are: , formula (9).

7. The method for reducing damage, preventing explosion and extending service life of a cable sheath protector according to claim 3, characterized in that: Step S14 specifically includes the following steps: S131. Under lightning overvoltage, the resistor R g is regarded as a short circuit, and the equivalent resistance R csp Ignoring it, the voltage calculation formula at both ends of the cable sheath protector is: , formula (10), Among them, U l Lightning overvoltage borne by the cable sheath; Since the fundamental frequency voltage can be more accurately identified when the cable sheath protector is in action, the fundamental frequency component of the minimum lightning overvoltage is used to calculate the voltage division of the cable sheath protector, and then formula (10) becomes: , formula (11), Among them, U l.min(1) is the fundamental frequency component of the minimum lightning overvoltage, U csp.min The voltage across the cable sheath protector corresponding to the minimum lightning overvoltage of the cable sheath; S132, the action voltage correction constraint condition is: , formula (12), Among them, 30 is the preset over-limit coefficient, which is used to ensure that the cable sheath protector acts quickly when the cable sheath is subjected to the minimum lightning overvoltage; S133. Combining equation (11) and equation (12), the capacitance characteristic is obtained: , formula (13).

8. The method for reducing damage, preventing explosion and extending service life of a cable sheath protector according to claim 3, characterized in that: After step S14, the method further includes the following steps: S15, calculate the resistance R according to the preset resistance cost g The maximum value R g.max , combined with the resistance characteristic in step S13, to obtain a final value range of the resistance characteristic; S16. Calculate the capacitance C based on the maximum harmless electric field effect of the preset capacitance g The maximum value of C g.max , combined with the capacitance characteristic in step S14, the final value range of the capacitance characteristic is obtained.

9. A device for reducing damage, preventing explosion and extending service life of a cable sheath protector, characterized in that: It includes a protection device step-down circuit and a cable sheath protector circuit connected in series, wherein the protection device step-down circuit includes a resistor R g And the capacitor C in parallel g , resistor R g With preset resistance characteristics, capacitor R g It has a preset capacitance characteristic; the cable sheath protector equivalent circuit includes an equivalent resistor R csp And the equivalent capacitance C in parallel csp .

10. A device for reducing damage, preventing explosion and extending service life of a cable sheath protector according to claim 9, characterized in that: The determination of the preset resistance characteristic and the preset capacitance characteristic range specifically includes the steps of: When the cable sheath is subjected to the power frequency induced voltage, the cable sheath protector is subject to the maximum loss constraint condition, so the first range of the resistance characteristic is calculated: When the cable sheath is subjected to power frequency overvoltage, the cable sheath protector does not operate, and the operating voltage constraint condition is obtained, thereby calculating the second range of the resistance characteristic; Combining the first range of resistance characteristics and the second range of resistance characteristics, the resistance R g The resistance characteristics of According to the cable sheath protector needs to operate normally when the cable sheath is subjected to lightning overvoltage, the action voltage correction constraint condition is obtained, and the capacitance C is calculated g Capacitance characteristics.

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