AU2021103063A4 - Cable terminal explosion protection system and method - Google Patents

Abstract

The present disclosure discloses a cable terminal explosion protection system and method, the system comprising a power transmission cable, a cable terminal, a switch cabinet and an explosion-protection branch circuit; the power transmission cable is connected with a photovoltaic power station and the cable terminal respectively; the switch cabinet includes a circuit breaker, the circuit breaker being connected with the cable terminal; the cable terminal includes an inlet wiring terminal connected with the power transmission cable, a first outlet wiring terminal connected with the circuit breaker and a second outlet wiring terminal connected with the explosion-protection branch circuit; when the cable terminal operates normally, the explosion protection branch circuit presents an open-circuited state. The present disclosure can avoid that the cable terminal explodes due to the fact that the photovoltaic power station is struck by lightning. 1/1 FIGURES 400 I r410 L 100 300- I510 320 310 330 540 1 500 LL 520 - - 530 200 100 200 300 400 500 10 FIG. 1 When the photovoltaic power station is struck by lightning, the S201 lightning voltage wave is generated in the power transmission cable, then the circuit breaker in the switch cabinet is disconnected, so that the lightning voltage wave generated by the lightning strike in the power transmission cable is transmitted to the ground terminal through the explosion-protection branch circuit It is judged whether the lightning voltage wave in the power S202 transmission cable 200 is eliminated or not. and if the lightning voltage wave in the power transmission cable has been eliminated. the explosion-protection branch circuit presents the open-circuited state: if the lightning voltage wave in the power transmission cable is not eliminated. the explosion-protection branch circuit shows the short circuited state. FIG. 2

Description

1/1 FIGURES

400 I r410 L

100 300- I510

320 310 330 540 1 500 LL 520 - - 530

200

100 200 300 400 500 10

FIG. 1

When the photovoltaic power station is struck by lightning, the S201 lightning voltage wave is generated in the power transmission cable, then the circuit breaker in the switch cabinet is disconnected, so that the lightning voltage wave generated by the lightning strike in the power transmission cable is transmitted to the ground terminal through the explosion-protection branch circuit

It is judged whether the lightning voltage wave in the power S202 transmission cable 200 is eliminated or not. and if the lightning voltage wave in the power transmission cable has been eliminated. the explosion-protection branch circuit presents the open-circuited state: if the lightning voltage wave in the power transmission cable is not eliminated.the explosion-protection branch circuit shows the short circuited state.

FIG. 2

CABLE TERMINAL EXPLOSION PROTECTION SYSTEM AND METHOD

Technical Field The present disclosure relates to the technical field of cable terminal explosion protection, in particular to a cable terminal explosion protection system and method.

Background Art In a power system of a photovoltaic power station, under normal circumstances, a power transmission cable works under a rated voltage, voltage deviation is very small, and a cable terminal entering a switch cabinet also works normally. But since a photovoltaic module works outdoors, there is a case that the photovoltaic module is struck by lightning, and in this case, there will be a lightning overvoltage wave in the system, the amplitude value being 300-400kV generally, and the lightning overvoltage wave is propagated along the power transmission cable in the form of a traveling wave for very short duration, about 50-100pts. Due to its relatively high amplitude value, huge energy can be brought in a short time, such that an electrical device can suffer from an insulation fault and a power outage.. In a power system with a cable as a power transmission line, a cable terminal is connected with a circuit breaker in a switch cabinet, and power transformation and distribution are performed by the switch cabinet and a power transforming and distributing device, so it is very important to guarantee an intact line of the cable terminal for the stable and reliable operation of the whole system. When the photovoltaic power station is attacked by lightning, the power transmission cable will propagate the lightning overvoltage wave, and when it is propagated to the cable terminal, a huge overcurrent is generated under the action of a high voltage to make the circuit breaker disconnected. At this time, since the voltage wave in the power transmission cable will be reflected and superposed, there is an ultra-high voltage twice as high as an incident wave, and a huge electrodynamic force and heat are generated, to result in an explosion of the cable terminal, thus damaging the power transmission cable and the switch cabinet.

Summary of the Invention The present disclosure provides a cable terminal explosion protection system and method, which aims to solve the technical problem that a cable terminal explodes due to the fact that a photovoltaic power station is struck by lightning in the prior art. The technical solution of the disclosure includes providing a cable terminal explosion protection system, comprising a power transmission cable, a cable terminal, a switch cabinet and an explosion-protection branch circuit; both ends of the power transmission cable are respectively connected with a photovoltaic power station and the cable terminal; the switch cabinet includes a circuit breaker, the circuit breaker being connected with the cable terminal; the cable terminal includes an inlet wiring terminal, a first outlet wiring terminal and a second outlet wiring terminal, the inlet wiring terminal being connected with the power transmission cable, the first outlet wiring terminal being connected with the circuit breaker, and the second outlet wiring terminal being connected with the explosion-protection branch circuit; when the cable terminal operates normally, the explosion-protection branch circuit presents an open-circuited state; when the photovoltaic power station is struck by lightning to make the circuit breaker disconnected, the explosion-protection branch circuit presents a short-circuited state, so that a lightning voltage wave generated by the lightning strike in the power transmission cable is transmitted to a ground terminal through the explosion-protection branch circuit. According to the present disclosure, the explosion-protection branch circuit includes an explosion-protection trace that connects the second outlet wiring terminal and the ground terminal, and a voltage-dependent valve plate and an adjustable resistor sequentially provided on the explosion-protection trace; the voltage-dependent valve plate is used for being turned off when the lightning voltage wave is not generated in the power transmission cable, and being turned on when the lightning voltage wave is generated in the power transmission cable; the adjustable resistor is used to make the resistance of the explosion-protection branch circuit match the line wave impedance of the power transmission cable when the voltage-dependent valve plate is turned on. According to the present disclosure, the explosion-protection branch circuit further includes a discharge gap provided on the explosion-protection trace, and the discharge gap is provided between the second outlet wiring terminal and the voltage-dependent valve plate, and the discharge gap is used for being turned off when the lightning voltage wave is not generated in the power transmission cable, and being turned on when the lightning voltage wave is generated in the power transmission cable. According to the present disclosure, the cable terminal explosion protection system further comprises detecting apparatus and controlling apparatus, the detecting apparatus is used to detect the voltage in the explosion-protection branch circuit, and to generate a voltage signal, the controlling apparatus is in a communication connection with the detecting apparatus, and is used to receive the voltage signal, and to judge whether the voltage signal is less than a threshold voltage or not; if the voltage signal is less than the threshold voltage, a close instruction is given to control the circuit breaker to be closed, and the explosion-protection branch circuit presents an open-circuited state; if the voltage signal is greater than or equal to the threshold voltage, the explosion-protection branch circuit presents a short-circuited state. According to the present disclosure, the line wave impedance Z of the power transmission cable is:

Z=-LO 1 2 c 'OPR In2h"

C0 s0R r

where P is the magnetic permeability of vacuum; r is relative magnetic permeability; 80

is a permittivity of vacuum or gas; er is a relative permittivity; he is a height between the power transmission cable and the ground; r is a radius of the power transmission cable. In the present disclosure, an explosion-protection branch circuit connected with a second outlet wiring terminal is provided, and when the photovoltaic power station is struck by lightning to make a circuit breaker disconnected, the explosion-protection branch circuit presents a short-circuited state, so that a lightning voltage wave generated by a lightning strike in a power transmission cable is transmitted to a ground terminal through the explosion-protection branch circuit, to avoid that the lightning voltage wave is reflected and superposed due to the fact that the lightning voltage wave causes disconnection of the circuit breaker, thereby avoiding that the cable terminal explodes, to guarantee the safety of the power transmission cable and a switch cabinet.

Brief Description of the Drawings In order to explain the technical solutions in the embodiments of the present disclosure more clearly, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present disclosure. For those skilled in the art, without creative work, other drawings can be obtained based on these drawings. FIG. 1 is a schematic structural diagram of an embodiment of a cable terminal explosion protection system provided by an embodiment of the present disclosure; FIG. 2 is a schematic flowchart of an embodiment of a cable terminal explosion protection method provided by an embodiment of the present disclosure.

Detailed Description of the Invention The technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative work shall fall within the protection scope of the present disclosure. In order to enable any person skilled in the art to implement and use the present disclosure, the following description is given. In the following description, the details are listed for the purpose of explanation. It should be understood that those of ordinary skill in the art can realize that the present disclosure can also be implemented without using these specific details. In other instances, well-known structures and processes will not be elaborated to avoid unnecessary details to obscure the description of the present disclosure. Therefore, the present disclosure is not intended to be limited to the illustrated embodiments, but is consistent with the widest scope that conforms to the principles and features disclosed in the present disclosure. An embodiment of the present disclosure provides a cable terminal explosion protection system and method, which will be described in detail below. FIG. 1 is a schematic structural diagram of an embodiment of a cable terminal explosion protection system provided by an embodiment of the present disclosure, as shown in FIG. 1. The cable terminal explosion protection system 10 being used to avoid that a cable terminal 300 explodes when a photovoltaic power station 100 is struck by lightning, and the cable terminal explosion protection system 10 comprising a power transmission cable 200, a cable terminal 300, a switch cabinet 400 and an explosion-protection branch circuit 500; Both ends of the power transmission cable 200 are connected with the photovoltaic power station 100 and the cable terminal 300 respectively; The switch cabinet 400 includes a circuit breaker 410, the circuit breaker 410 being connected with the cable terminal 300; The cable terminal 300 includes an inlet wiring terminal 310, a first outlet wiring terminal 320 and a second outlet wiring terminal 330, the inlet wiring terminal 310 being connected with the power transmission cable 200, the first outlet wiring terminal 320 being connected with the circuit breaker 410, and the second outlet wiring terminal 330 being connected with the explosion-protection branch circuit 500; When the cable terminal 300 operates normally, the explosion-protection branch circuit 500 presents an open-circuited state; when the photovoltaic power station 100 is struck by lightning to make the circuit breaker 410 disconnected, the explosion-protection branch circuit 500 presents a short-circuited state, so that a lightning voltage wave generated by a lightning strike in the power transmission cable 200 is transmitted to a ground terminal through the explosion-protection branch circuit 500. In the embodiment of the present disclosure, the explosion-protection branch circuit 500 connected between the second outlet wiring terminal 330 and the ground terminal is provided, and when the photovoltaic power station 100 is struck by lightning to make the circuit breaker 410 disconnected, the explosion-protection branch circuit 500 presents a short-circuited state, so that the lightning voltage wave generated by the lightning strike in the power transmission cable 200 is transmitted to the ground terminal through the explosion-protection branch circuit 500, to avoid that the lightning voltage wave is reflected and superposed due to the fact that the lightning voltage wave causes the disconnection of the circuit breaker 410, thereby avoiding that the cable terminal 300 explodes, to guarantee the safety of the power transmission cable 200 and the switch cabinet 400. Further, in some embodiments of the present disclosure, as shown in FIG. 1, the explosion-protection branch circuit 500 includes an explosion-protection trace 510 that connects the second outlet wiring terminal 330 and the ground terminal, and a voltage-dependent valve plate 520 and an adjustable resistor 530 that are sequentially arranged on the explosion-protection trace 510; The voltage-dependent valve plate 520 is used for being turned off when a lightning voltage wave is not generated in the power transmission cable 200, and being turned on when a lightning voltage wave is generated in the power transmission cable 200; The adjustable resistor 530 is used to make the resistance of the explosion-protection branch circuit 500 match the line wave impedance of the power transmission cable 200 when the voltage-dependent valve plate 520 is turned on. The specific work principle of the adjustable resistor 530 is: the adjustable resistor 530 can adjust its own resistance optionally, thereby realizing that the resistance of the explosion-protection branch circuit 500 matches the line wave impedance of the power transmission cable 200. Wherein, the line wave impedance Z of the power transmission cable 200 is:

Z= L 0 -=- 2inF-"

where P is the magnetic permeability of vacuum; 'r is relative magnetic permeability; 0

is a permittivity of vacuum or gas; e' is a relative permittivity; h, is a distance between the power transmission cable 200 and the ground; r is a radius of the power transmission cable 200. After the voltage-dependent valve plate 520 and the adjustable resistor 530 are provided, the explosion protection principle of the explosion-protection branch circuit 500 is: Suppose that a line 1 with line wave impedance of ZI and another line 2 with line wave impedance of Z2 are connected at a node A, and a traveling wave is propagated from the line 1 to the line 2; as far as the node A is concerned, a forward traveling wave of the line 1 is an incident wave projected on a point A; a forward traveling wave of the line 2 is a refracted wave that the incident wave refracted to Z2 through the node A; a reverse traveling wave of the line 1 is generated by the incident wave being reflected on the node A, so it can be called a reflected wave. There may also be a reverse traveling wave on the line 2, and it may be a reflected wave caused when the refracted wave arrives at a terminal of the line 2, or another overvoltage wave that invades from the terminal of the line 2, which is temporarily not considered here. Then a voltage refraction coefficient a and a voltage reflection coefficient P at the node A are respectively:

2Z2 ZI +Z2

fiZ2 -Z ZI +Z2

[0027] The relationship between the voltage refraction coefficient a and the voltage reflection

coefficient P is ,and as values of Zl and Z2 change, ranges of a and P satisfy:

rOa< 2 1 -1 ,§

When the terminal of the line 2 is short-circuited, which is equivalent to a case of Z2=00, a is equal to 2, and P is equal to 1. This result indicates that, the voltage incident wave will be totally reflected after arriving at an open-circuited terminal, and as a result, the voltage at the terminal of the line 1 rises to be twice the voltage incident wave. That is, when the lightning voltage wave is transmitted to the cable terminal 300, the circuit breaker 410 is disconnected to make the cable terminal 300 open circuited, and the voltage refraction coefficient a is equal to 1, that is, the lightning voltage wave can be totally reflected when being propagated to the cable terminal 200, and as a result, the voltage of the cable terminal 200 rises to be twice the voltage of the lightning voltage wave. Under the action of a huge voltage, the cable terminal 200 receives huge electrodynamic force and generates huge heat, and thereby, the cable terminal 200 will explode. When the lightning voltage wave is generated, the voltage-dependent valve plate 520 is turned on, to make the explosion-protection branch circuit 500 short circuited, and the impedance of the explosion-protection branch circuit matches that of the power transmission cable 200 by adjusting the adjustable resistor 530, namely that: Ziis equal to Z2, and then a is equal to 1, and P is equal to 0; this indicates that the voltage refracted wave is equal to the incident wave, while the voltage reflected wave is zero, there is no refraction or reflection, that is, the lightning voltage wave is not reflected at this time, and flows into the ground terminal along a path of the explosion-protection branch circuit 500. Furthermore, it is realized that no ultra-high voltage is generated at the cable terminal 200, thereby avoiding that the cable terminal 200 explodes. Further, in some embodiments of the present disclosure, the voltage-dependent valve plate 520 is further used for being turned off after the lightning voltage wave in the explosion-protection trace

510 is eliminated, so that the explosion-protection branch circuit 500 returns to present an open-circuited state. Through the above arrangement, it can be guaranteed that the photovoltaic power station 100 can rapidly resume normal operation after being struck by lightning, thus reducing the maintenance cost, and guaranteeing the safe and stable operation of the switch cabinet 400. In some embodiments of the present disclosure, the voltage-dependent valve plate 520 is a zinc oxide varistor. Further, the volt-ampere characteristic of the zinc oxide varistor is:

u = Ci"

where U is voltage, i is current, C is a material constant, and 1 is a nonlinear index. Wherein the nonlinear index is related to current density, the nonlinear index of the zinc oxide varistor is generally only 0.01-0.04, and even under a large impulse current (for example lOkA), the nonlinear index will not exceed 0.1. From the volt-ampere characteristic of the zinc oxide varistor, it can be seen that the work principle of the zinc oxide varistor is: under the action of a normal operation voltage (resistivity up to 1010-10 llQ-cm), a resistance value of the zinc oxide varistor is very big, and a passing leakage current is very small («lmA), while under the action of an overvoltage (for example: the lightning voltage wave), the resistance value will decrease sharply.

U8 Further, design parameters of the zinc oxide varistor include a rated operation voltage U , a

standard discharge current grade, an allowable maximum continuous operation voltage UMCON

an initial action voltage, a residual voltage UR, a protection level, a voltage ratio and an electric

load rate AVR, and each design parameter should be selected according to the following rules: 1. Selection of the rated operation voltage: when the voltage level of the protected power

transmission cable 200 is UN, the power frequency is 50Hz, and the rated operation voltage

UU of the zinc oxide varistor is 1.8 times the peak value of a rated phase voltage of the power transmission cable, namely:

,U, x F2

2. Selection of the standard discharge current grade: the standard discharge current grade should be selected according to the line wave impedance of the power transmission cable 200, and in some embodiments of the present disclosure, a standard discharge current 0kA grade can be selected as the discharge current grade.

3. Selection of the allowable maximum continuous operation voltage UMCON : the allowable

maximum continuous operation voltage UMCON refers to a maximum power frequency voltage

effective value that the zinc oxide varistor can operate continuously for a long time, and it should be equal to a highest operation phase voltage of the system, namely

UMCON U 3x

4. Selection of the initial action voltage: a voltage U 1nA when a ImA current passes is generally used as the initial action voltage. 5. Selection of the residual voltage: the residual voltage refers to a voltage peak between terminals of the zinc oxide varistor when a discharge current passes through the zinc oxide varistor, the residual voltage including three residual voltage values:

U A residual voltage R(I) under a lightning impulse current: the current waveform is 7-9/8-22ps, and the standard discharge current is 5kA, OkA, 20kA;

U A residual voltage R(s) under an operation impulse current: the current waveform is

-100/60-200ps, and the current peak value is 0.5kA, IkA, 2kA;

A residual voltage R(st) under a steep wave impulse current: the current wave front time is lps, and the peak value is the same as the standard (lightning impulse) current.

6. Selection of the protection level: the lightning protection level U'(') of the zinc oxide varistor

is the greater one of the following two values:

(1) The lightning impulse residual voltage UR(I)

(2) The steep wave shock residual voltage UR(st) divided by 1.15. Namely:

u,(/) - max UR() 1R1 1.15]

The operation protection level U'( ) of the zinc oxide varistor is equal to the operation impulse

U residual voltage R(s), namely

U') = UR(s)

7. Selection of the voltage ratio: the voltage ratio refers to a ratio of a residual voltage Uios to an initial action voltage UimA of the zinc oxide varistor under the action of a specified value of impulse current (for example 1OkA) with a waveform of 8/20ts. The smaller the voltage ratio is, the better the non-linearity is and the better the protective performance of the zinc oxide varistor is. In general: the voltage ratio is about 1.6-2.0. 8. Selection of the electric load rate: the electric load rate refers to a ratio of an amplitude value of the allowable maximum continuous operation voltage to the initial action voltage, namely:

AVR = UMCONx Un The electric load rate is a parameter indicating the voltage load degree of the zinc oxide varistor. The magnitude of the selected electric load rate has a great influence on the aging speed of the zinc oxide varistor, and generally, 45%- 7 5% is selected.

Further, in some embodiments of the present disclosure, the resistance value of the adjustable resistor 530 is 00-1000. It should be understood that: the resistance value range of the adjustable resistor 530 covers the range value of the line wave impedance of the power transmission cable 200, thus guaranteeing that the resistance value of the adjustable resistor 530 can be adjusted to be the same as the line wave impedance of the power transmission cable 200, to realize impedance matching. Further, in some embodiments of the present disclosure, as shown in FIG. 1, the explosion-protection branch circuit 500 further includes a discharge gap 540 provided on the explosion-protection trace 510, the discharge gap 540 being provided between the second outlet wiring terminal 330 and the voltage-dependent valve plate 520, and the discharge gap 540 being used for being turned off when the lightning voltage wave is not generated in the power transmission cable 200, and being turned on when the lightning voltage wave is generated in the power transmission cable 200. By providing the discharge gap 540, it can be guaranteed that no current passes through the voltage-dependent valve plate 520 when the explosion-protection branch circuit 500 presents an open-circuited state, so that the aging speed of the voltage-dependent valve plate 520 is delayed, and the service life of the voltage-dependent valve plate 520 is extended. It should be noted that: in some embodiments of the present disclosure, the discharge gap 540 is arranged vertically, and the gap value of the discharge gap 540 is 10pm. Further, in order to guarantee that the lightning voltage wave in the power transmission cable 200 is completely eliminated, to further improve the safety of the cable terminal 300, in some embodiments of the present disclosure, the cable terminal explosion protection system 10 further comprises detecting apparatus and controlling apparatus, the detecting apparatus being used to detect the voltage in the explosion-protection branch circuit 500, and to generate a voltage signal, and the controlling apparatus being in a communication connection with the detecting apparatus, and being used to receive the voltage signal, and to judge whether the voltage signal is less than a threshold voltage or not; if the voltage signal is less than the threshold voltage, a close instruction is given to control the circuit breaker 410 to be closed, and the explosion-protection branch circuit 500 presents an open-circuited state; if the voltage signal is greater than or equal to the threshold voltage, the explosion-protection branch circuit 500 presents a short-circuited state. Through the above arrangement, it can be guaranteed that the lightning voltage wave in the power transmission cable 200 is completely eliminated, thus enhancing the safety of the cable terminal 300. In some embodiments of the present disclosure, the threshold voltage is 0. In another aspect, an embodiment of the present disclosure further provides a cable terminal explosion protection method, which is applicable to the cable terminal explosion protection system 10 according to any one of the above embodiments, and as shown in FIG. 2, the cable terminal explosion protection method including: S201: When the photovoltaic power station 100 is struck by lightning, a lightning voltage wave is generated in the power transmission cable 200, which causes the circuit breaker 410 in the switch cabinet 400 to be disconnected, then the explosion-protection branch circuit 500 presents a short-circuited state, so that the lightning voltage wave generated by the lightning strike in the power transmission cable 200 is transmitted to the ground terminal through the explosion-protection branch circuit 500; S202: It is judged whether the lightning voltage wave in the power transmission cable 200 is eliminated or not, and if the lightning voltage wave in the power transmission cable 200 has been eliminated, the explosion-protection branch circuit 500 presents the open-circuited state; if the lightning voltage wave in the power transmission cable 200 is not eliminated, the explosion-protection branch circuit 500 presents the short-circuited state. Specifically, the explosion-protection branch circuit 500 includes an explosion-protection trace 510 that connects the cable terminal 300 and the ground terminal, and a voltage-dependent valve plate 520 and an adjustable resistor 530 that are sequentially arranged on the explosion-protection trace 510; Specifically in S201: when the photovoltaic power station 100 is struck by lightning, the lightning voltage wave is generated in the power transmission cable 200, and the circuit breaker 410 in the switch cabinet 400 is disconnected, the voltage-dependent valve plate 520 is turned on, and meanwhile the resistance value of the adjustable resistor 530 is adjusted, so that the impedance of the explosion-protection branch circuit 500 is equal to the line wave impedance of the power transmission cable 200, in order that the lightning voltage wave generated by the lightning strike in the power transmission cable 200 is transmitted to the ground terminal through the explosion-protection branch circuit 500; Specifically in S202: the voltage in the explosion-protection branch circuit 500 is detected by the detecting apparatus, and the voltage signal is generated, the controlling apparatus receives the voltage signal, and judges whether the voltage signal is less than the threshold voltage or not; if the voltage signal is less than the threshold voltage, the lightning voltage wave in the power transmission cable 200 has been eliminated, and the close instruction is given to control the circuit breaker 410 to be closed, so that the switch cabinet 400 works normally, and the voltage-dependent valve plate 520 is turned off at this time; if the voltage signal is greater than or equal to the threshold voltage, the lightning voltage wave in the power transmission cable 200 is not eliminated completely, and the voltage-dependent valve plate 520 remains on at this time, and the explosion-protection branch circuit 500 presents a short-circuited state, and the lightning voltage wave is continuously transmitted to the ground terminal through the explosion-protection branch circuit 500. In the embodiment of the present disclosure, the explosion-protection branch circuit 500 connected between the cable terminal 300 and the ground terminal is provided, and when the photovoltaic power station 100 is struck by lightning to make the circuit breaker 410 disconnected, the explosion-protection branch circuit 500 presents a short-circuited state, so that the lightning voltage wave generated by the lightning strike in the power transmission cable 200 is transmitted to the ground terminal through the explosion-protection branch circuit 500, to avoid that the lightning voltage wave is reflected and superposed due to the fact that the lightning voltage wave causes the circuit breaker 410 disconnected, thereby avoiding that the cable terminal 300 explodes, to guarantee the safety of the power transmission cable 200 and the switch cabinet 400. In addition, the explosion-protection branch circuit 500 is further used to return to the open-circuited state after the lightning voltage wave in the power transmission cable 200 is eliminated, thereby guaranteeing that the photovoltaic power station 100 can rapidly resume the normal operation after being struck by lightning, so that the maintenance cost is reduced, and the safe and stable operation of the switch cabinet 400 is guaranteed. A cable terminal explosion protection system and method provided by the embodiment of the present disclosure is introduced in detail above, specific examples are applied in the present disclosure to explain the principles and implementation modes of the present disclosure, and the description of the above embodiments is only used to help understand the method of the present invention and its core idea; meanwhile, for those skilled in the art, according to the idea of the present disclosure, there will be changes in the specific implementation modes and the scope of application, and in summary, the content of this specification should not be construed as a limitation of the present disclosure.

Claims (5)

1. A cable terminal explosion protection system, comprising a power transmission cable, a cable terminal, a switch cabinet and an explosion-protection branch circuit; both ends of the power transmission cable are respectively connected with a photovoltaic power station and the cable terminal; the switch cabinet includes a circuit breaker, the circuit breaker being connected with the cable terminal; the cable terminal includes an inlet wiring terminal, a first outlet wiring terminal and a second outlet wiring terminal, the inlet wiring terminal being connected with the power transmission cable, the first outlet wiring terminal being connected with the circuit breaker, and the second outlet wiring terminal being connected with the explosion-protection branch circuit; when the cable terminal operates normally, the explosion-protection branch circuit presents an open-circuited state; when the photovoltaic power station is struck by lightning to make the circuit breaker disconnected, the explosion-protection branch circuit presents a short-circuited state, so that a lightning voltage wave generated by the lightning strike in the power transmission cable is transmitted to a ground terminal through the explosion-protection branch circuit.

2. The cable terminal explosion protection system according to claim 1, wherein the explosion-protection branch circuit includes an explosion-protection trace that connects the second outlet wiring terminal and the ground terminal, and a voltage-dependent valve plate and an adjustable resistor sequentially provided on the explosion-protection trace; the voltage-dependent valve plate is used for being turned off when the lightning voltage wave is not generated in the power transmission cable, and being turned on when the lightning voltage wave is generated in the power transmission cable; the adjustable resistor is used to make the resistance of the explosion-protection branch circuit match the line wave impedance of the power transmission cable when the voltage-dependent valve plate is turned on.

3. The cable terminal explosion protection system according to claim 2, wherein the explosion-protection branch circuit further includes a discharge gap provided on the explosion-protection trace, and the discharge gap is provided between the second outlet wiring terminal and the voltage-dependent valve plate, and the discharge gap is used for being turned off when the lightning voltage wave is not generated in the power transmission cable, and being turned on when the lightning voltage wave is generated in the power transmission cable.

4. The cable terminal explosion protection system according to claim 1, wherein the cable terminal explosion protection system further comprises detecting apparatus and controlling apparatus, the detecting apparatus is used to detect the voltage in the explosion-protection branch circuit, and to generate a voltage signal, the controlling apparatus is in a communication connection with the detecting apparatus, and is used to receive the voltage signal, and to judge whether the voltage signal is less than a threshold voltage or not; if the voltage signal is less than the threshold voltage, a close instruction is given to control the circuit breaker to be closed, and the explosion-protection branch circuit presents an open-circuited state; if the voltage signal is greater than or equal to the threshold voltage, the explosion-protection branch circuit presents a short-circuited state.

5. The cable terminal explosion protection system according to claim 4, wherein the line wave impedance Z of the power transmission cable is:

Z=z LoL-- 1 FORIn i2h, HOAR

r 2 C0 2c 0R

where P is the magnetic permeability of vacuum; r is relative magnetic permeability; 80

is a permittivity of vacuum or gas; e' is a relative permittivity; h, is a height between the power transmission cable and the ground; r is a radius of the power transmission cable.