阅读说明：本技术 一种具有半导电外护层结构的海缆登陆段接地方法 (Grounding method for submarine cable landing section with semi-conductive outer protective layer structure ) 是由 曹京荥 杨景刚 张量 刘建军 陈杰 陶风波 李陈莹 谭笑 胡丽斌 张伟 于 2021-08-27 设计创作，主要内容包括：本发明公开了一种具有半导电外护层结构的海缆登陆段接地方法,包括：将交叉互联段接地单元划分为N1个小段,每小段的最大长度为L1；将单段接地单元划分为N2个小段,每小段的最大长度为L1；计算每小段金属护套的电容电流和电磁感应电压；计算外护层的接地点电阻；运用叠加定理建立电压约束方程；联立以上步骤的方程,求解出L1、N1的最小值和N2的最小值；基于步骤5求解出的L1、N1的最小值和N2的最小值,对海底电缆登陆段进行划分,将交叉互联段接地单元的每小段外护层的中位点直接接地,将单段接地单元的每小段外护层的中位点直接接地,完成海底电缆登陆段接地。(The invention discloses a grounding method for a submarine cable landing section with a semi-conductive outer protective layer structure, which comprises the following steps: dividing the grounding unit of the cross interconnection section into N1 small sections, wherein the maximum length of each small section is L1; dividing the single-section grounding unit into N2 small sections, wherein the maximum length of each small section is L1; calculating the capacitance current and the electromagnetic induction voltage of each small section of metal sheath; calculating the grounding point resistance of the outer protective layer; establishing a voltage constraint equation by using a superposition theorem; solving the minimum values of L1 and N1 and the minimum value of N2 by combining the equations of the above steps; and (4) dividing the landing section of the submarine cable based on the minimum values of L1 and N1 and the minimum value of N2 obtained in the step 5, directly grounding the middle point of each small section of the outer protective layer of the grounding unit of the cross interconnection section, and directly grounding the middle point of each small section of the outer protective layer of the single-section grounding unit to finish grounding the landing section of the submarine cable.)

1. A grounding method for a landing section of a submarine cable with a semi-conductive outer protective layer structure is characterized in that: the method comprises the following steps:

step 1: dividing a grounding unit of a cross interconnection section of a submarine cable landing section into N1 small sections, wherein the maximum length of each small section is L1, and directly grounding a middle point of an outer protective layer of each small section of the grounding unit of the cross interconnection section; dividing a single-section grounding unit of a submarine cable landing section into N2 small sections, wherein the maximum length of each small section is L1, and directly grounding the middle point of the outer protective layer of each small section of the single-section grounding unit; wherein N1 is not less than [ L '/L1], [ L'/L1] is the minimum integer of L '/L1, and L' is the total length of the grounding unit of the cross interconnection section; n2 is ≧ L '/L1, [ L'/L1] is the smallest integer of L '/L1, L' is the total length of the single-segment grounding unit;

step 2: calculating the capacitance current and the electromagnetic induction voltage of each small section of metal sheath according to the ohm law and the electromagnetic induction law;

and step 3: calculating the grounding point resistance of the outer protective layer according to the relationship among the resistivity, the volume and the resistance;

and 4, step 4: establishing a voltage constraint equation by applying a superposition theorem that the sum of the magnetic field induced voltage and the electric field induced voltage does not exceed the minimum value of the allowed voltage of the outer protective layer of the submarine cable or the breakdown voltage borne by the minimum distance of the outer protective layer adjacent to the grounding point in the axial direction;

and 5: solving the minimum values of L1 and N1 and the minimum value of N2 by combining the equations of the above steps;

step 6: and (4) dividing the landing section of the submarine cable based on the minimum values of L1 and N1 and the minimum value of N2 obtained in the step 5, directly grounding the middle point of each small section of the outer protective layer of the grounding unit of the cross interconnection section, and directly grounding the middle point of each small section of the outer protective layer of the single-section grounding unit to finish grounding the landing section of the submarine cable.

2. The method of claim 1, wherein the method comprises: in the step 2, the capacitance current and the electromagnetic induction voltage of each small section of metal sheath are obtained according to the following formula;

IC＝2×PI×50×U₀×C₀×L1 (1)

UL＝M₀×I₀×L1 (2)

wherein, U₀For subsea cable phase voltages, I₀Rated current for submarine cable core, C₀For submarine cable unit length capacitance, M₀The submarine cable core and the metal sheath are mutually inductive.

3. The method of claim 1, wherein the method comprises: in step 3, calculating the grounding point resistance of the outer protective layer according to the following formula;

R₀＝ρ×h₀/S₀ (3)

where ρ is the volume resistivity of the outer sheath of the submarine cable, h₀Thickness of the outer jacket, S₀The contact area between the outer protective layer and the grounding point.

4. The method of claim 1, wherein the method comprises: in step 4, the voltage constraint equation is expressed as:

UL+IC×R₀≤U_S (4)

U_S＝MIN{M，F(z)} (5)

in the formula of U_SThe allowable voltage of the outer sheath of the submarine cable, M is a set induced voltage, F (z) is the minimum value of the breakdown voltage borne by the minimum distance between the outer sheath of the submarine cable and the grounding point in the axial direction, and z is the minimum value of the distance between the semi-conductive outer sheath of the submarine cable and the grounding body at each point along the axis.

5. The method of claim 4, wherein the method comprises: said F (z) is represented by:

F(z)＝3×z (6)。

Technical Field

The invention belongs to the technical field of power transmission and transformation equipment, and particularly relates to a grounding method for a submarine cable landing section with a semi-conductive outer protective layer structure.

Background

In order to solve the problem of overlarge alternating current induction circulation of long-distance submarine cable power transmission, the submarine cable for power transmission of projects such as offshore wind power and the like at present widely adopts an outer protective layer with a semi-conductive structure, so that a metal sheath of the submarine cable is connected with seawater through the conductive outer protective layer in a marine environment, and the purpose of reducing circulation is achieved. The submarine cable is from a landing end to a land station, the laying and operating environment is different from the marine environment, the grounding along the cable laying cannot be guaranteed, the conventional submarine cable landing section adopts a land cable laying mode and a grounding method in a tunnel, a bridge frame, a cable trench and the like, the cable is grounded at a cable joint or a terminal and the like, and the risk that the submarine cable conductive outer protective layer discharges with an adjacent grounding point or is electrically shocked to hurt people is not considered.

Disclosure of Invention

The purpose of the invention is as follows: the invention provides a submarine cable landing section grounding method with a semi-conductive outer protective layer structure, which can calculate the minimum grounding point distance of a semi-conductive outer protective layer of a submarine cable landing section with the semi-conductive outer protective layer structure, effectively reduce the induction voltage of the semi-conductive outer protective layer of the submarine cable landing section, avoid fire or personal electric shock accidents caused by ground discharge and ensure the operation safety of a submarine cable.

The technical scheme is as follows: a grounding method for a submarine cable landing section with a semi-conductive outer protection layer structure comprises the following steps:

step 1: dividing a grounding unit of a cross interconnection section of a submarine cable landing section into N1 small sections, wherein the maximum length of each small section is L1, and directly grounding a middle point of an outer protective layer of each small section of the grounding unit of the cross interconnection section; dividing a single-section grounding unit of a submarine cable landing section into N2 small sections, wherein the maximum length of each small section is L1, and directly grounding the middle point of the outer protective layer of each small section of the single-section grounding unit; wherein N1 is not less than [ L '/L1], [ L'/L1] is the minimum integer of L '/L1, and L' is the total length of the grounding unit of the cross interconnection section; n2 is not less than L/L1, L/L1 is the minimum integer of L/L1, L is the total length of the single-section grounding unit;

step 2: calculating the capacitance current and the electromagnetic induction voltage of each small section of metal sheath according to the ohm law and the electromagnetic induction law;

and step 3: calculating the grounding point resistance of the outer protective layer according to the relationship among the resistivity, the volume and the resistance;

and 4, step 4: establishing a voltage constraint equation by applying a superposition theorem that the sum of the magnetic field induced voltage and the electric field induced voltage does not exceed the minimum value of the allowed voltage of the outer protective layer of the submarine cable or the breakdown voltage borne by the minimum distance of the outer protective layer adjacent to the grounding point in the axial direction;

and 5: solving the minimum values of L1 and N1 and the minimum value of N2 by combining the equations of the above steps;

step 6: and (4) dividing the landing section of the submarine cable based on the minimum values of L1 and N1 and the minimum value of N2 obtained in the step 5, directly grounding the middle point of each small section of the outer protective layer of the grounding unit of the cross interconnection section, and directly grounding the middle point of each small section of the outer protective layer of the single-section grounding unit to finish grounding the landing section of the submarine cable.

Further, in step 2, the capacitance current and the electromagnetic induction voltage of each small section of metal sheath are obtained according to the following formula;

IC＝2×PI×50×U₀×C₀×L1 (1)

UL＝M₀×I₀×L1 (2)

wherein, U₀For subsea cable phase voltages, I₀Rated current for submarine cable core, C₀For submarine cable unit length capacitance, M₀The submarine cable core and the metal sheath are mutually inductive.

Further, in step 3, the grounding point resistance of the outer protective layer is calculated according to the following formula;

R₀＝ρ×h₀/S₀ (3)

where ρ is the volume resistivity of the outer sheath of the submarine cable, h₀Thickness of the outer jacket, S₀The contact area between the outer protective layer and the grounding point.

Further, in step 4, the voltage constraint equation is expressed as:

UL+IC×R₀≤U_S (4)

U_S＝MIN{M,F(z)} (5)

in the formula of U_SThe allowable voltage of the outer sheath of the submarine cable, M is a set induced voltage, F (z) is the minimum value of the breakdown voltage borne by the minimum distance between the outer sheath of the submarine cable and the grounding point in the axial direction, and z is the minimum value of the distance between the semi-conductive outer sheath of the submarine cable and the grounding body at each point along the axis.

Further, f (z) is represented by:

F(z)＝3×z (6)。

has the advantages that: the minimum grounding unit of the grounding system of the landing section of the submarine cable is set to be N small sections, the middle point of each small section of the outer protective layer is directly grounded, the ohm law, the electromagnetic induction law and the relation among resistivity, volume and resistance are applied to calculate the capacitance current, the magnetic induction voltage and the grounding point resistance of the outer protective layer of each section of the submarine cable, the contact failure and infinite resistance of the adjacent metal sheaths at the two sides of the landing section of the submarine cable are considered under the extreme state, the capacitance current flowing into the induced voltage of each contact point of the outer protective layer of the submarine cable and the electromagnetic induction voltage of the metal sheath are in the same direction, and a voltage constraint equation is established by applying the superposition theorem, so that the maximum L1 or the minimum N value of the landing section of the submarine cable is obtained by solving, the induced voltage of the semi-conductive outer protective layer of the landing section of the submarine cable can be effectively reduced, and the safety of operation and personnel is guaranteed.

Drawings

FIG. 1 is a schematic diagram of a minimum grounding unit of a cross-connection section and a single-section grounding section of a sea cable landing section;

FIG. 2 is a schematic diagram of minimum ground unit dividing N small segments and grounding the bit point in each small segment;

FIG. 3 is an equivalent circuit diagram of minimum grounding unit divided into N small segments and each small segment with its middle point connected with magnetic induction;

fig. 4 is an equivalent circuit diagram of the minimum grounding unit divided into N small segments and the bit grounding field induction in each small segment.

Detailed Description

As shown in fig. 1, the submarine cable landing section of the present invention is composed of a head and a tail single-section grounding unit and a plurality of cross-interconnection section grounding units, wherein the plurality of cross-interconnection section grounding units are arranged between the two single-section grounding units and are used for connecting the head and the tail single-section grounding units; and the submarine cable landing section with the semi-conductive outer protection layer structure is formed by wrapping a metal sheath outside a submarine cable, and the metal sheath is communicated with seawater through the conductive outer protection layer.

The submarine cable landing section is 3 km long and comprises a cross interconnection section grounding unit and a single-section grounding unit, wherein the length of the cross interconnection section grounding unit is 2.4km, and the single-section grounding unit is connected with the single-section grounding unitThe length of the ground unit is 0.6km, and the parameters of the line system are as follows: u shape₀＝128kV，I₀＝500A，C₀＝1.673×10^-4μF/m，M₀＝4.24×10^-4mH/m，ρ＝200Ω×mm，h₀＝5mm，S₀＝100mm²The grounding method for a landing zone of a submarine cable with a semiconductive outer sheath structure according to the present invention is further described with reference to fig. 1 to 4, where M is 50V and z is 6 mm.

Dividing the grounding unit of the cross interconnection section into N1 small sections, wherein the maximum length of each small section is L1; dividing the single-segment grounding unit into N2 small segments, wherein the maximum length of each small segment is L1; and directly grounding the middle point of each small section of the outer protection layer.

Calculating the capacitance current, the magnetic induction voltage and the contact resistance of each small section of cable metal sheath according to the following formula by using the ohm law and the electromagnetic induction law;

IC＝2×PI×50×U₀×C₀×L1 (1)

UL＝M₀×I₀×L1 (2)

wherein, U₀Is the submarine cable phase voltage, kV; i is₀Rated current for the core of the submarine cable, A; c₀The capacitance per unit length of the submarine cable is mu F/m; m₀The submarine cable core and the metal sheath are mutually inductive, and mH/m.

Calculating the grounding point resistance of the outer protective layer of the submarine cable by using the relationship among the resistivity, the volume and the resistance;

R₀＝ρ×h₀/S₀ (3)

in the formula, rho is the volume resistivity of the outer protective layer of the submarine cable, and is omega multiplied by mm; h is₀The thickness of the outer protective layer is mm; s₀Mm is the contact area between the outer protective layer and the grounding point²。

Considering that under an extreme state, the resistance is infinite due to poor contact between adjacent metal sheaths on two sides of a landing section of the submarine cable and a grounding device, and the capacitance current flowing induction voltage of each contact point of the outer protection layer of the submarine cable and the electromagnetic induction voltage of the metal sheath are in the same direction, and by applying the superposition theorem, the following voltage constraint equation is established by using the magnetic field induction voltage and the electric field induction voltage not to exceed the set voltage or the minimum breakdown voltage of the cable outer protection layer adjacent to the grounding point in the axial direction:

UL+IC×R₀≤U_S (4)

U_S＝MIN{M,F(z)} (5)

F(z)＝3×z (6)

L1≤50/{2×PI×50×U₀×C₀×(ρ×h0/S₀)+M₀×I₀} (7)

N1≥[24000/L1] (8)

N2≥[800/L1] (9)

in the formula of U_SAllowing a voltage, V, for the outer jacket of the submarine cable; m is a set induction voltage, V, such as 50V, 36V; f (z) is the minimum value of the breakdown voltage, V, borne by the minimum distance between the outer sheath of the cable and the grounding point in the axial direction; z is the minimum distance, mm, from the adjacent ground body of the semi-conductive outer sheath of the cable at each point along the axis.

Combining the equations of the above steps, calculating to obtain the section L1 ≧ 70.85m, N1 ≧ [2400/70.85] ═ 34, and N2 ≧ [600/70.85] ═ 9.

For the cross interconnection segment grounding unit, the cross interconnection segment grounding unit is divided into 34 small segments with the length of 70.85m, and the middle point of each small segment outer protective layer is directly grounded; for the single-segment grounding unit, the single-segment grounding unit is divided into 9 small segments with the length of 70.85m, and the middle point of the outer protection layer of each small segment is directly grounded.