A method and device for reducing loss, preventing explosion and prolonging the service life of a cable sheath protector

Abstract

The present invention discloses a method and device for reducing loss, preventing explosion and prolonging the service life of a cable sheath protector. The method includes the steps of: S1, constructing a voltage reduction circuit for the protection device, where the voltage reduction circuit for the protection device includes a resistor R g and a capacitor C connected in parallel therewith g , the resistor R g has a preset resistance characteristic, and the capacitor C g has a preset capacitance characteristic; S2, constructing a circuit for the cable sheath protector, where the circuit for the cable sheath protector includes an equivalent resistor R csp and an equivalent capacitor C connected in parallel therewith csp ; S3, connecting the voltage reduction circuit for the protection device and the circuit for the cable sheath protector in series to automatically adjust the voltage across the cable sheath protector according to the preset resistance characteristic and capacitance characteristic. The present invention can reduce the operating loss of the cable sheath protector, prevent misoperation during power frequency overvoltage and lightning overvoltage, and improve its service life.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric power, and specifically relates to a method and device for reducing loss, explosion-proof and extending the service life of a cable sheath protector. Background Art

[0002] A protector refers to a device used to provide electrical safety protection for electrical equipment. A cable sheath protector is a protection device installed on the connecting section cable of an overhead line, which plays a protective role when the cable withstands lightning overvoltage and prevents the cable sheath from being punctured; when the cable system withstands power frequency overvoltage, the short-circuit current time 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 safe operation of the cable; in addition, when the cable is operating normally, the protector continuously bears the alternating-direction AC sheath voltage, which will cause losses and shorten the service life of the cable sheath protector. Therefore, it is of great significance to study a method for reducing loss, explosion-proof and extending the service life 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 object of the invention is to overcome the disadvantages and deficiencies existing in the prior art, and provide a method for reducing loss, explosion-proof and extending the service life of a cable sheath protector, which can reduce the operating loss of the cable sheath protector, prevent misoperation under power frequency overvoltage and lightning overvoltage, and improve its service life.

[0004] The second object of the present invention is to provide a device for reducing loss, explosion-proof and extending the service life of a cable sheath protector.

[0005] The object of the present invention is achieved by the following technical solutions: A method for reducing loss, explosion-proof and extending the service life of a cable sheath protector includes the steps:

[0006] S1. Construct a voltage-reducing circuit for the protection device, and the voltage-reducing circuit for the protection device includes a resistor R g and a capacitor C g connected in parallel therewith, the resistor R g has a preset resistance characteristic, and the capacitor C g has a preset capacitance characteristic;

[0007] S2. Construct a cable sheath protector circuit, and the cable sheath protector circuit includes an equivalent resistor R csp and an equivalent capacitor C csp connected in parallel therewith;

[0008] S3. Connect the protection device step-down circuit and the cable sheath protector circuit in series to automatically adjust the voltage across the cable sheath protector according to the preset resistance characteristics and capacitance characteristics.

[0009] Preferably, the voltage U across the cable sheath protector circuit csp is calculated by the formula:

[0010] , Equation (1),

[0011] where U a is the cable sheath voltage, B csp is the susceptance of the equivalent capacitance, f l is the voltage frequency of the cable sheath.

[0012] Preferably, the determination of the preset resistance characteristics and the preset capacitance characteristics range specifically includes the steps:

[0013] S11. According to the condition that the cable sheath protector is restricted by the maximum loss constraint when the cable sheath bears the power frequency induced voltage, calculate the first range of the resistance characteristics:

[0014] S12. According to the condition that the cable sheath protector does not operate when the cable sheath bears the power frequency overvoltage, obtain the operating voltage constraint condition, and then calculate the second range of the resistance characteristics;

[0015] S13. Combine the first range of the resistance characteristics and the second range of the resistance characteristics, and analyze to obtain the resistance characteristics of the resistor R g ;

[0016] S14. According to the condition that the cable sheath protector needs to operate normally when the cable sheath bears the lightning overvoltage, obtain the operating voltage correction constraint condition, and then calculate the capacitance characteristics of the capacitor C g .

[0017] Preferably, step S11 specifically includes the steps:

[0018] S111. Under the power frequency induced voltage, regard the capacitor and the equivalent capacitor as open circuits. The formula for calculating the voltage across the cable sheath protector is:

[0019] , Equation (2);

[0020] where U a0 is the power frequency induced voltage of the cable sheath, and R csp is the internal resistance of the cable sheath protector;

[0021] S112. The expression of the maximum loss constraint condition is:

[0022] , Equation (3),

[0023] where, P csp is the actual loss power of the cable sheath protector, and P max is the designed maximum loss power of the cable sheath protector;

[0024] S113. Combining Equation (2) and Equation (3), the first range of the resistance characteristic is obtained:

[0025] , Equation (4).

[0026] Preferably, step S12 specifically includes the steps:

[0027] S121. Under power frequency overvoltage, regarding the capacitor and the equivalent capacitor as open circuits, the calculation formula for the voltage at both ends of the cable sheath protector is:

[0028] , Equation (5),

[0029] then there is: , Equation (6);

[0030] where, U aOV , U aOV.max are respectively the amplitude and the maximum value of the power frequency overvoltage borne by the cable sheath, and U csp.max is the overvoltage at both ends of the cable sheath protector corresponding to U aOV.max ;

[0031] S122. The expression of the operating voltage constraint condition is:

[0032] , Equation (7),

[0033] where, U csp.max is the overvoltage at both ends of the cable sheath protector corresponding to U aOV.max , and U act is the operating voltage of the cable sheath protector;

[0034] S123. Combining Equation (6) and Equation (7), the second range of the resistance characteristic is obtained:

[0035] , Equation (8).

[0036] Preferably, in step S13, the resistance characteristic of the resistor R g is:

[0037] , Equation (9).

[0038] Preferably, step S14 specifically includes the steps:

[0039] S131. Under lightning overvoltage, the resistor R in the protection device step-down circuit is regarded as a short circuit, and the equivalent resistor R in the cable sheath protector circuit is ignored. Then, the calculation formula for the voltage at both ends of the cable sheath protector is: g csp

[0040] , Equation (10),

[0041] where, U l is the lightning overvoltage borne by the cable sheath;

[0042] Since the cable sheath protector can identify the fundamental frequency voltage more accurately when it operates, the fundamental frequency component of the minimum lightning overvoltage is used to calculate the voltage division of the cable sheath protector. Then, Equation (10) becomes:

[0043] , Equation (11),

[0044] where, U l.min(1) is the fundamental frequency component of the minimum lightning overvoltage, and U csp.min is the voltage at both ends of the cable sheath protector corresponding to the minimum lightning overvoltage borne by the cable sheath;

[0045] S132. The operating voltage correction constraint condition is:

[0046] , Equation (12),

[0047] where, 30 is a preset over-limit coefficient used to ensure that the cable sheath protector operates quickly when the cable sheath bears the minimum lightning overvoltage;

[0048] S133. Combining Equation (11) and Equation (12), the capacitance characteristics are obtained:

[0049] , Equation (13).

[0050] Preferably, after step S14, the following steps are further included:

[0051] S15. Calculate the maximum value R g of the resistor R according to the preset resistor cost, and combine the resistor characteristics in step S13 to obtain the final value range of the resistor characteristics; g.max

[0052] S16. Calculate the maximum value C g of the capacitor C according to the maximum harmless electric field effect of the preset capacitor, and combine the capacitance characteristics in step S14 to obtain the final value range of the capacitance characteristics. g.max

[0053] ​​​​A device for reducing loss, explosion-proof and extending the service life of a cable sheath protector, comprising a voltage reduction circuit of a protection device and a cable sheath protector circuit connected in series therewith. The voltage reduction circuit of the protection device includes a resistor R g and a capacitor C connected in parallel therewith g . The resistor R g has a preset resistance characteristic, and the capacitor R g has a preset capacitance characteristic; the cable sheath protector circuit includes an equivalent resistor R csp and an equivalent capacitor C connected in parallel therewith csp .

[0054] Preferably, the determination of the ranges of the preset resistance characteristic and the preset capacitance characteristic specifically includes the steps of:

[0055] According to when the cable sheath bears the power frequency induced voltage, the cable sheath protector is restricted by the maximum loss constraint condition, so as to calculate the first range of the resistance characteristic:

[0056] According to when the cable sheath bears the power frequency overvoltage, the cable sheath protector does not act, so as to obtain the action voltage constraint condition, and then calculate the second range of the resistance characteristic;

[0057] Combining the first range of the resistance characteristic and the second range of the resistance characteristic, analyze to obtain the resistance characteristic of the resistor R g ;

[0058] According to when the cable sheath bears the lightning overvoltage, the cable sheath protector needs to act normally, so as to obtain the action voltage correction constraint condition, and then calculate the capacitance characteristic of the capacitor C g .

[0059] The present invention has the following advantages and effects compared with the prior art:

[0060] (1) The present invention provides a method for reducing loss, explosion-proof and extending the service life of a cable sheath protector. By constructing a voltage reduction circuit of a protection device and a cable sheath protector circuit and connecting the two in series, the voltage at both ends of the cable sheath protector is automatically adjusted according to the preset resistance characteristic and capacitance characteristic. The present invention adjusts the voltage division of the cable sheath protector through the voltage reduction circuit of the protection device, can reduce the operating loss of the cable sheath protector, prevent misoperation during power frequency overvoltage and lightning overvoltage, and improve its service life.

[0061] (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 comprehensively obtained by combining the maximum loss constraint condition, the operating voltage constraint condition, and the operating voltage correction constraint condition that the cable sheath protector is respectively subjected to under power frequency voltage, power frequency overvoltage, and lightning overvoltage. It realizes reducing the voltage across the cable sheath protector during normal power frequency operation, reducing losses and preventing misoperation; during power frequency overvoltage, reducing the voltage across the cable sheath protector to prevent the power frequency overvoltage from causing misoperation or even explosion of the cable sheath protector; under lightning overvoltage, it does not affect the normal operation of the cable sheath protector, thereby improving the service life of the cable sheath protector.

[0062] (3) The present invention provides a device for reducing losses, preventing explosion, and extending the life of a cable sheath protector. The device includes a protection device step-down circuit and a cable sheath protector circuit connected in series therewith. The protection device step-down circuit includes a resistor R g and a capacitor C connected in parallel therewith g , which has preset resistance and capacitance characteristics. The device has a simple structure, good economy, and strong practicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 is a schematic flow chart of a method for reducing losses, preventing explosion, and extending the life of a cable sheath protector according to Embodiment 1 of the present invention.

[0064] Figure 2 is a schematic circuit principle diagram of a device for reducing losses, preventing explosion, and extending the life of a cable sheath protector according to Embodiment 2 of the present invention.

[0065] Figure 3 is a schematic diagram of the logic for selecting the resistance and capacitance characteristic ranges of a device for reducing losses, preventing explosion, and extending the life of a cable sheath protector according to the present invention.

[0066] Figure 4 is a schematic diagram of the operating performance principle of a device for reducing losses, preventing explosion, and extending the life of a cable sheath protector according to the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0067] The present invention will be further described in detail below in conjunction with the embodiments and the drawings, but the embodiments of the present invention are not limited thereto.

[0068] Embodiment 1

[0069] As Figure 1 shown is a schematic flow chart of a method for reducing losses, preventing explosion, and extending the life of a cable sheath protector, including the steps:

[0070] S1. Construct a protection device step-down circuit, where the protection device step-down circuit includes a resistor R g and a capacitor C connected in parallel therewith g , and the resistor Rg has a preset resistance characteristic, capacitor R g has a preset capacitance characteristic;

[0071] S2. Construct a cable sheath protector circuit, and the cable sheath protector circuit includes an equivalent resistance R csp and an equivalent capacitance C connected in parallel therewith csp ;

[0072] S3. Connect the protection device step-down circuit and the cable sheath protector circuit in series to automatically adjust the voltage across the cable sheath protector according to the preset resistance and capacitance characteristics.

[0073] 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, and divides the voltage across the cable sheath protector according to the preset resistance and capacitance characteristics to realize the function of reducing the voltage across the cable sheath protector. Among them, the protection device is composed of a resistor and a capacitor connected in parallel, as Figure 2 shown.

[0074] Generally, the cable sheath protector has a very large resistance under normal power frequency voltage, and the current flowing through the cable sheath protector is very small, at the microampere level; while under overvoltage, the resistance of the cable sheath protector becomes smaller and the current increases, so as to release the charge on the cable sheath to play a role in protecting the cable sheath. This resistance change characteristic of the cable sheath protector benefits from its core functional element, the zinc oxide varistor. According to the non-linear characteristic of its volt-ampere curve, in this embodiment, it is regarded as an equivalent resistance R csp and an equivalent capacitance C csp parallel circuit, as Figure 2 shown. The present invention reduces the voltage across the cable sheath protector through the protection device step-down circuit, which can reduce the operating loss of the cable sheath protector, prevent misoperation during power frequency overvoltage and lightning overvoltage, and improve its service life.

[0075] The formula for the voltage U csp across both ends of the cable sheath protector circuit is:

[0076] , Equation (1),

[0077] where U a is the cable sheath voltage, B csp is the susceptance of the equivalent capacitance, f l is the voltage frequency of the cable sheath.

[0078] Specifically,Figure 2 The following is a schematic diagram of the circuit principle of the present invention. In this embodiment, according to the characteristic that the cable sheath protector only acts on overvoltage and has no selectivity for the overvoltage frequency, it is approximately considered that the susceptance of this equivalent capacitance C csp will not change with frequency, and B csp is used to represent the susceptance of this equivalent capacitance. The resistance of the grounding grid is too small compared with the cable sheath protector and is ignored. According to the analysis of circuit principles, the voltage division calculation formula of the cable sheath protector in the circuit is shown in Equation (1).

[0079] The determination of the preset resistance characteristic and the preset capacitance characteristic range specifically includes the following steps:

[0080] S11. When the cable sheath bears the power frequency induced voltage, the cable sheath protector is restricted by the maximum loss constraint condition, so as to calculate the first range of the resistance characteristic:

[0081] S12. When the cable sheath bears the power frequency overvoltage, the cable sheath protector does not act, and the action voltage constraint condition is obtained, so as to calculate the second range of the resistance characteristic;

[0082] S13. Combining the first range of the resistance characteristic and the second range of the resistance characteristic, the resistance characteristic of the resistor R g is analyzed;

[0083] S14. When the cable sheath bears the lightning overvoltage, the cable sheath protector needs to act normally, and the action voltage correction constraint condition is obtained, so as to calculate the capacitance characteristic of the capacitor C g ;

[0084] Specifically, the preset resistance characteristic and capacitance characteristic in the step-down circuit of the protection device are closely related to the operation of the cable sheath protector. In this embodiment, mainly starting from three purposes, the determination of the preset resistance characteristic and capacitance characteristic is restricted, 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 protector does not act, thereby preventing the cable sheath protector from overheating and exploding; (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 action of the cable sheath protector.

[0085] Before calculating the resistance characteristics and capacitance characteristics according to the maximum loss constraint condition, operating voltage constraint condition, and operating voltage correction constraint condition of the cable sheath protector respectively, the electrical parameters of the cable sheath under the operating state of the cable line and the design parameters of the cable sheath protector itself are obtained first. The electrical parameters include the power frequency induced voltage U of the cable sheath obtained from the historical operating data of the target cable line a0 , the maximum value U of the power frequency overvoltage aOV.max and the minimum value of the fundamental wave of the lightning overvoltage; the design parameters include the resistance R of the cable sheath protector obtained from the nameplate csp , the susceptance B csp and the operating voltage U act ; in addition, the designed maximum loss P of the cable sheath protector is determined according to the on-site environment (including local temperature, ventilation of the grounding box, etc.) max , which is determined according to the actual use requirements.

[0086] Such as Figure 3 is a schematic diagram of the selection logic of the resistance and capacitance characteristic ranges of a device for reducing loss, explosion protection, and extending the service life of a cable sheath protector according to the present invention. Such as Figure 4 is a schematic diagram of the operating performance principle of a device for reducing loss, explosion protection, and extending the service life of a cable sheath protector according to 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 condition, operating voltage constraint condition, and operating voltage correction constraint condition respectively suffered by the cable sheath protector under power frequency voltage, power frequency overvoltage, and lightning overvoltage. It realizes reducing the voltage at both ends of the cable sheath protector during normal power frequency operation, reducing loss and preventing misoperation; during power frequency overvoltage, reducing the voltage at both ends of the cable sheath protector to prevent the power frequency overvoltage from causing misoperation or even explosion of the cable sheath protector; under lightning overvoltage, it does not affect the normal operation of the cable sheath protector, thereby improving the service life of the cable sheath protector.

[0087] Step S11 specifically includes the steps:

[0088] S111. Under the power frequency induced voltage, regarding the capacitor and the equivalent capacitor as open circuits, the voltage calculation formula at both ends of the cable sheath protector is:

[0089] , formula (2);

[0090] Among them, U a0 is the power frequency induced voltage of the cable sheath, and R csp is the internal resistance of the cable sheath protector;

[0091] S112. The expression of the maximum loss constraint condition is:

[0092] , Equation (3),

[0093] where P csp is the actual loss power of the cable sheath protector, and P max is the designed maximum loss power of the cable sheath protector;

[0094] S113. Combining Equation (2) and Equation (3), the first range of resistance characteristics is obtained:

[0095] , Equation (4).

[0096] Specifically, the resistance characteristics of the resistor in the protection device are initially determined through the maximum loss constraint condition of the cable sheath protector. The main content is as follows:

[0097] Under the power frequency sheath induced voltage, the reactance of the capacitor C g is very large, and the cable sheath protector has not reached the action threshold. In this embodiment, the capacitor C g and the equivalent capacitor C csp are regarded as open circuits. According to the circuit principle, the voltage division of the cable sheath protector approximately depends on the ratio of the resistor R g and the equivalent resistor R csp . The resistor R g can divide the voltage of the equivalent resistor R csp , so that the voltage U csp at both ends of the cable sheath protector during normal operation is reduced.

[0098] Combined with the maximum loss constraint condition: the actual loss of the cable sheath protector does not exceed the designed maximum loss P max , the internal resistance characteristics of the resistor R g in the protection device are initially determined, which is called the first range of resistance characteristics.

[0099] Step S12 specifically includes the following steps:

[0100] S121. Under the power frequency overvoltage, regarding the capacitor and the equivalent capacitor as open circuits, the calculation formula for the voltage at both ends of the cable sheath protector is:

[0101] , Equation (5),

[0102] Then there is: , Equation (6);

[0103] where UaOV , U aOV.max and U csp.max are the power frequency overvoltage amplitude and the maximum power frequency overvoltage respectively that the cable sheath withstands, and U aOV.max is the overvoltage at both ends of the cable sheath protector corresponding to U

[0104] S122. The expression of the operating voltage constraint condition is:

[0105] , Equation (7),

[0106] where U csp.max is the overvoltage at both ends of the cable sheath protector corresponding to U aOV.max , and U act is the operating voltage of the cable sheath protector;

[0107] S123. Combining Equation (6) and Equation (7), the second range of the resistance characteristic is obtained:

[0108] , Equation (8).

[0109] Specifically, through the operating voltage constraint condition during power frequency overvoltage, the resistance characteristic of the resistor in the protection device is determined secondly. The specific content is as follows:

[0110] In this embodiment, when the cable sheath withstands power frequency overvoltage, similarly, the reactance of the capacitor C g is very large, and the cable sheath protector has not reached the action threshold. The capacitors C g and C csp are regarded as open circuits, and the voltage division of the cable sheath protector approximately depends on the ratio of the resistor R g and the equivalent resistor R csp .

[0111] After connecting the series protection device, in order to ensure that the cable sheath protector does not act and avoid its explosion, the operating voltage constraint condition that the cable sheath protector needs to meet is: under the maximum power frequency overvoltage U aOV.max , the overvoltage U csp.max at both ends of the corresponding cable sheath protector is less than the starting voltage U act . Thus, the internal resistance characteristic of the resistor R g in the protection device is determined secondly in combination with the voltage division calculation formula. This is called the second range of the resistance characteristic.

[0112] In step S13, the resistor Rg The resistance characteristic is as follows:

[0113] , Equation (9).

[0114] Step S14 specifically includes the following steps:

[0115] S131. Under lightning overvoltage, the resistor R in the step-down circuit of the protection device is regarded as a short circuit, and the equivalent resistor R in the cable sheath protector circuit is ignored. Then, the voltage calculation formula at both ends of the cable sheath protector is: g Regarding it as a short circuit, and the equivalent resistor R in the cable sheath protector circuit is ignored. Then, the voltage calculation formula at both ends of the cable sheath protector is: csp Ignoring it, the voltage calculation formula at both ends of the cable sheath protector is:

[0116] , Equation (10),

[0117] where, U l is the lightning overvoltage borne by the cable sheath;

[0118] Since the cable sheath protector can identify the fundamental frequency voltage more accurately when it operates, using the fundamental frequency component of the minimum lightning overvoltage to calculate the voltage division of the cable sheath protector, then Equation (10) becomes:

[0119] , Equation (11),

[0120] where, U l.min(1) is the fundamental frequency component of the minimum lightning overvoltage, and U csp.min is the voltage at both ends of the cable sheath protector corresponding to the cable sheath bearing the minimum lightning overvoltage;

[0121] S132. The action voltage correction constraint condition is:

[0122] , Equation (12),

[0123] where, 30 is a preset overlimit coefficient, which is used to ensure that the cable sheath protector operates quickly when the cable sheath bears the minimum lightning overvoltage;

[0124] S133. Combining Equation (11) and Equation (12), the capacitance characteristic is obtained:

[0125] , Equation (13).

[0126] Specifically, through the overlimit start constraint condition of the fundamental wave value of the minimum lightning overvoltage, that is, the action voltage correction constraint condition, making the protector operate normally under lightning overvoltage, the capacitance characteristic of the capacitor in the protection device is designed and determined. The specific content is as follows:

[0127] In this embodiment, when the cable sheath bears lightning overvoltage, due to the equivalent frequency of the lightning overvoltage being approximately 2.08×10 5Hz, much higher than the power frequency, the capacitance C g has a very small reactance and can be approximately equivalent to short - circuiting R g ; and when the cable sheath protector operates normally, the equivalent capacitance C csp conducts and discharges current, and the resistance R of the cable sheath protector csp can be ignored. The voltage division of the cable sheath protector under the lightning voltage at a high equivalent frequency is calculated according to formula (10), and its voltage division mainly depends on the capacitance C g and the reactance ratio of the 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 that U csp and U l are not much different.

[0128] The cable sheath protector starts according to the over - limit start constraint condition of the minimum lightning over - voltage U l.min . Because the cable sheath protector can identify the fundamental frequency voltage more accurately when it operates, the fundamental frequency component U l.min of the minimum lightning over - voltage U l.min（1） is obtained by using the fast Fourier transform FFT, and the voltage division formula of the protector calculated by using U l.min（1） is as shown in formula (11). In order to make the voltage protection reliability of the cable sheath protector higher, the 30 * U act value is used as the minimum threshold of the voltage division of the protector, and the limiting condition of the voltage division of the cable sheath protector is obtained as shown in formula (12), and finally the range selection formula of the capacitance is obtained as shown in formula (13).

[0129] After step S14, it further includes the steps of:

[0130] S15. Calculate the maximum value R g of the resistance R according to the preset resistance cost, and combine with the resistance characteristics in step S13 to obtain the final value range of the resistance characteristics; g.max

[0131] S16. Calculate the maximum value C g of the capacitance C according to the maximum harmless electric - field effect of the preset capacitance​g.max , combined with the capacitance characteristics in step S14, the final value range of the capacitance characteristics is obtained.

[0132] Specifically, the minimum values of the preset resistance characteristics and capacitance characteristics are determined through steps S11 - S13. In this embodiment, in order to balance cost and electric field effect, the maximum values of resistance and capacitance are additionally considered, so as to comprehensively obtain the value ranges of the preset resistance characteristics and capacitance characteristics, increasing rationality and practicality.

[0133] To further explain the method of the present invention, the following is elaborated through specific examples.

[0134] First, obtain various voltage parameters of the cable sheath protector under the operating state of the cable line, as well as other design parameters of the cable sheath protector: the power frequency induced voltage of the 110 kV cable sheath U a0 = 100 V, the maximum value of power frequency overvoltage U aOV.max = 6 * U a0 , the fundamental wave component of the minimum lightning overvoltage U l.min（1） = 10 kV, the maximum loss P 1 = 3 * 10 -4 W; other parameters of the cable sheath protector are taken as R csp = 15 MΩ, C csp = 0.72 nF, B csp = 0.226 μΩ, the operating voltage U act = 250 V; at high frequency f l = 2.08 * 10 5 Hz, the capacitance of the cable sheath protector decreases slightly, making B csp slightly increase. The increased voltage division of the cable sheath protector is beneficial to normal operation, so it does not affect the calculation of the appropriate range of parameters.

[0135] First step, through the loss constraint condition, preliminarily determine the internal resistance characteristics of the device. When the cable is operating normally, calculated according to formula (4) R g ≥ 7.36 MΩ.

[0136] Second step, through the power frequency overvoltage voltage division constraint condition, re - determine the internal resistance characteristics of the device. When the cable bears the maximum power frequency overvoltage, calculated according to formula (8) R g > 21 MΩ.

[0137] Step 3: Determine the internal capacitance characteristics of the device by the fundamental wave value over-limit starting constraint condition of the minimum lightning overvoltage. When the cable withstands the minimum lightning overvoltage, calculate according to formula (13) to get C g >0.52 pF.

[0138] Through comprehensive comparison, the resistance R g has a resistance characteristic of R g >21 MΩ, and the capacitance C g has a capacitance characteristic of C g >0.52 pF.

[0139] In this embodiment, finally, calculate the maximum value R g of the resistor R according to the preset resistor cost, and obtain the final value range of the resistor characteristic as: g.max 21 MΩ <

[0140] < R g < R g.max ;

[0141] Calculate the maximum value C g of the capacitor C according to the maximum harmless electric field effect of the preset capacitor, and obtain g.max the final value range of the capacitance characteristic as: 0.52 pF <

[0142] < R g < C g.max .

[0143] Embodiment 2

[0144] A device for reducing loss, explosion-proof and extending the service life of a cable sheath protector includes a protection device step-down circuit and a cable sheath protector circuit connected in series therewith. The protection device step-down circuit includes a resistor R g and a capacitor C g connected in parallel therewith. The resistor R g has a preset resistance characteristic, and the capacitor R g has a preset capacitance characteristic; the cable sheath protector circuit includes an equivalent resistor R csp and an equivalent capacitor C csp connected in parallel therewith.

[0145] According to the maximum loss constraint condition when the cable sheath withstands the power frequency induced voltage, calculate the first range of the resistance characteristic:

[0146] When the cable sheath withstands power frequency overvoltage and the cable sheath protector does not operate, the operating voltage constraint condition is obtained, and thus the second range of the resistance characteristic is calculated.

[0147] Combining the first range of the resistance characteristic and the second range of the resistance characteristic, the resistance R g of the resistance characteristic is analyzed.

[0148] When the cable sheath withstands lightning overvoltage and the cable sheath protector needs to operate normally, the operating voltage correction constraint condition is obtained, and thus the capacitance C g of the capacitance characteristic is calculated.

[0149] Specifically, the present invention provides a device for reducing loss, explosion-proof and extending the service life of a cable sheath protector. The device includes a protection device step-down circuit and a cable sheath protector circuit connected in series therewith. The protection device step-down circuit includes a resistor R g and a capacitor C g connected in parallel therewith, having preset resistance and capacitance characteristics. The device has a simple structure, good economy and strong practicability.

[0150] The above embodiments are preferred embodiments of the present invention and cannot limit the present invention. Any other changes or other equivalent replacement methods made without departing from the technical solution 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, construct a cable sheath protector circuit, the cable sheath protector circuit includes an equivalent resistor R csp And the equivalent capacitance C in parallel csp ; S3, connecting the step-down circuit of the protection device and the cable sheath protector circuit in series to automatically adjust the voltage at both ends of the cable sheath protector according to the preset resistance characteristics and capacitance characteristics; The voltage U at both ends of the cable sheath protector circuit 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; 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.

2. The method for reducing damage, preventing explosion and extending service life of a cable sheath protector according to claim 1, 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).

3. The method for reducing damage, preventing explosion and extending service life of a cable sheath protector according to claim 2, 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).

4. A method for reducing damage, preventing explosion and extending service life of a cable sheath protector according to claim 3, characterized in that: In step S13, the resistor R g The resistance characteristics are: , formula (9).

5. The method for reducing damage, preventing explosion and extending service life of a cable sheath protector according to claim 1, 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 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).

6. The method for reducing damage, preventing explosion and extending service life of a cable sheath protector according to claim 1, 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.

7. 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 Having a preset capacitance characteristic; the cable sheath protector circuit includes an equivalent resistor R csp And the equivalent capacitance C in parallel csp ; 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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