Superconducting cable electromagnetic compatibility evaluation method
阅读说明：本技术 超导电缆电磁兼容性评价方法 (Superconducting cable electromagnetic compatibility evaluation method ) 是由 焦婷 李红雷 魏本刚 赵丹丹 田昊洋 辛亮 王黎明 于 2021-08-19 设计创作，主要内容包括：超导电缆电磁兼容性评价方法,包括：根据超导电缆本体的单相结构尺寸、接头的单相超导带材绕制,建立超导电缆本体和接头的电磁场仿真模型；在正常工作和单相接地短路下,计算超导电缆本体及接头的电磁场仿真值；考虑三相电流的不平衡性,分别计算平衡部分电流和不平衡部分电流的磁通密度,以获得超导电缆不同运行工况下的电磁场理论值；以输变电设施电磁环境控制限值为依据,利超导电缆不同运行工况下的电磁场理论值,对超导电缆输电线路途径上敏感点的电磁兼容性进行评价。本发明仿真获得不同复杂环境下超导电缆周围电磁场的分布数据,作为超导电缆电磁兼容性的评价依据。(The superconducting cable electromagnetic compatibility evaluation method comprises the following steps: establishing an electromagnetic field simulation model of the superconducting cable body and the joint according to the single-phase structure size of the superconducting cable body and the single-phase superconducting strip winding of the joint; under normal work and single-phase grounding short circuit, calculating electromagnetic field simulation values of the superconducting cable body and the superconducting cable joint; considering the unbalance of the three-phase current, respectively calculating the magnetic flux density of the current of the balanced part and the current of the unbalanced part so as to obtain the electromagnetic field theoretical value of the superconducting cable under different operating conditions; and evaluating the electromagnetic compatibility of sensitive points on the transmission line path of the superconducting cable according to the electromagnetic environment control limit value of the power transmission and transformation facility and by utilizing the electromagnetic field theoretical value of the superconducting cable under different operating conditions. The method provided by the invention can be used for obtaining the distribution data of the electromagnetic field around the superconducting cable under different complex environments by simulation and taking the distribution data as the evaluation basis of the electromagnetic compatibility of the superconducting cable.)
1. A superconducting cable electromagnetic compatibility evaluation method is characterized in that,
the method comprises the following steps:
step 1, establishing an electromagnetic field simulation model of a three-phase superconducting cable body according to the single-phase structure size parameters of the superconducting cable body;
step 2, under the normal working condition and the single-phase grounding short circuit condition, utilizing an electromagnetic field simulation model of the three-phase superconducting cable body to simulate and calculate an electromagnetic field simulation value of the superconducting cable body;
step 3, establishing an electromagnetic field simulation model of the three-phase superconducting cable joint according to winding parameters of the single-phase superconducting strip of the superconducting cable joint;
step 4, under the normal working condition and the single-phase grounding short circuit condition, simulating and calculating an electromagnetic field simulation value of the superconducting cable joint by using an electromagnetic field simulation model of the three-phase superconducting cable joint;
step 5, considering the unbalance of the three-phase current, respectively calculating the magnetic flux density of the balanced part current and the magnetic flux density of the unbalanced part current by utilizing the electromagnetic field simulation value of the superconducting cable body and the electromagnetic field simulation value of the superconducting cable joint;
step 6, obtaining electromagnetic field theoretical values of the superconducting cable under different operating conditions by utilizing the magnetic flux density of the balanced part current and the magnetic flux density of the unbalanced part current;
and 7, evaluating the electromagnetic compatibility of sensitive points on the transmission line path of the superconducting cable by using the electromagnetic field theoretical values of the superconducting cable under different operating conditions on the basis of the electromagnetic environment control limit value of the power transmission and transformation facility.
2. The superconducting cable electromagnetic compatibility evaluation method of claim 1,
in step 1, the single-phase structure size parameters of the superconducting cable include: the outer diameter of the lining core, the number of layers and the outer diameter of the superconducting tape, the thickness and the outer diameter of the PPLP insulating layer, the number of layers and the outer diameter of the superconducting shielding layer and the outer diameter of the copper tape;
based on the characteristics of the cylindrical axisymmetric structure of the superconducting cable, the electromagnetic field simulation model of the three-phase superconducting cable is a two-dimensional simulation model.
3. The superconducting cable electromagnetic compatibility evaluation method of claim 1,
the step 2 comprises the following steps:
step 2.1, setting three-phase current parameters of the superconducting cable;
step 2.2, under the normal working condition, when the single-phase current reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable body;
step 2.3, under the normal working condition, when the single-phase current passes through zero, simulating and calculating an electromagnetic field simulation value of the superconducting cable body;
step 2.4, under the working condition of single-phase grounding short circuit, when the fault phase current reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable body;
step 2.5, under the working condition of single-phase grounding short circuit, when the fault phase current passes through zero, simulating and calculating an electromagnetic field simulation value of the superconducting cable body;
step 2.6, setting three-phase voltage parameters of the superconducting cable;
step 2.7, under the normal working condition, when the single-phase voltage reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable body;
step 2.8, under the normal working condition, when the single-phase voltage passes through zero, simulating and calculating an electromagnetic field simulation value of the superconducting cable body;
step 2.9, under the working condition of single-phase grounding short circuit, when the non-fault two-phase voltage reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable body;
and 2.10, under the working condition of single-phase grounding short circuit, when the fault phase voltage passes through zero, simulating and calculating the electromagnetic field simulation value of the superconducting cable body.
4. The superconducting cable electromagnetic compatibility evaluation method of claim 1,
in step 2.1, the three-phase current parameters of the superconducting cable include: the three-phase current parameters of the conducting layer and the three-phase current parameters of the shielding belt.
5. The superconducting cable electromagnetic compatibility evaluation method of claim 1,
in step 3, the winding parameters of the single-phase superconducting tape of the superconducting cable include: the winding radius, pitch, number, spiral angle and winding direction of each layer of strip of conducting layer, and the winding radius, pitch, number, spiral angle and winding direction of each layer of strip of shielding layer.
6. The superconducting cable electromagnetic compatibility evaluation method of claim 1,
step 4 comprises the following steps:
step 4.1, setting three-phase current parameters of the superconducting cable;
step 4.2, under the normal working condition, when the single-phase current reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable joint;
4.3, under the normal working condition, when the single-phase current passes through zero, simulating and calculating an electromagnetic field simulation value of the superconducting cable joint;
4.4, under the working condition of single-phase grounding short circuit, when the fault phase current reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable joint;
and 4.5, under the working condition of single-phase grounding short circuit, when the fault phase current passes through zero, simulating and calculating the electromagnetic field simulation value of the superconducting cable joint.
7. The superconducting cable electromagnetic compatibility evaluation method of claim 1,
the step 5 comprises the following steps:
step 5.1, obtaining the induction proportion alpha of the current of the balance part on the shielding layer of the superconducting cable according to the net current value of each phase;
and 5.2, calculating the magnetic flux density proportion beta of the balance part current according to the following relational expression by using the induction proportion of the balance part current:
β＝1-α
step 5.3, the magnetic flux density B of the balance part current is calculated by the following relational expressiont，b：
In the formula (I), the compound is shown in the specification,in order to simulate the electromagnetic field of the superconducting cable body,the electromagnetic field simulation value of the superconducting cable joint is obtained;
step 5.4, calculating the magnetic flux density B of the unbalanced part current according to the following relational expressiont，ub：
In the formula, mu0Is a vacuum magnetic permeability and satisfies mu0＝4π×10-7H/m，IuTo balance the current, r is the distance from the point calculated by the simulation number to the center of the superconducting cable.
8. The superconducting cable electromagnetic compatibility evaluation method of claim 7,
in step 6, the magnetic flux density B of the balance part current under different operation conditions is measuredt，bAnd the magnetic flux density B of the unbalanced partial currentt，ubAdding to obtain the electromagnetic field theoretical value B of the superconducting cable under different operating conditionst。
9. The superconducting cable electromagnetic compatibility evaluation method of claim 1,
the step 7 comprises the following steps:
step 7.1, determining the distance from the sensitive point on the superconducting cable transmission line path to the center of the superconducting cable
Step 7.2, according to the distanceObtaining the electromagnetic field analysis value of the sensitive point
Step 7.3, controlling the limit value B by the electromagnetic environment of the power transmission and transformation facility*As a reference, when the electromagnetic field of the sensitive point analyzes the valueNot greater than electromagnetic environment control limit B*If so, judging that the electromagnetic compatibility of the sensitive point meets the requirement of public exposure limit; otherwise, the electromagnetic compatibility of the sensitive point is judged not to meet the public exposure limit requirement.
10. The superconducting cable electromagnetic compatibility evaluation method of claim 1,
step 7.3 also includes:
controlling limit value B by electromagnetic environment of power transmission and transformation facilities*For reference, the electromagnetic field analysis value B of any point on the superconducting cable transmission line path can be ensuredr′Is not more than the electromagnetic environment control limit value B*The corresponding distance r' is used for determining the transmission channel width of the superconducting cable meeting the electromagnetic compatibility.
Technical Field
The invention relates to the technical field of superconducting cable electromagnetic compatibility, in particular to a superconducting cable electromagnetic compatibility evaluation method.
Background
The high-temperature superconducting cable system consists of four main parts, namely a cable body, a cable accessory, a refrigerating system and a detection and protection system. High temperature superconducting cables typically use liquid nitrogen (77K, i.e., -196 c) as the cooling medium and the insulating medium. The cable insulation structure is an indispensable component of a High Temperature Superconducting (HTS) cable, provides necessary guarantee for the safe operation of the HTS cable, and polypropylene laminated paper (PPLP) has good impregnation and high electrical strength, and is an excellent low temperature insulation material.
The electromagnetic compatibility of the superconducting cable is one of important items of environmental evaluation, and the method for evaluating the electromagnetic compatibility of the superconducting cable can judge whether the power frequency magnetic field intensity distribution rule of the three-phase cold insulation high-temperature superconducting cable and the distribution condition of the electromagnetic field around the superconducting cable under different complex environments meet the public exposure limit value requirement or not.
In the prior art, in view of the limitations of the current situations of construction and operation of a superconducting cable, research and development of technologies such as simulation calculation and actual measurement of an electromagnetic field around the superconducting cable are all in a starting state, and electromagnetic field data associated with a complex operation environment of the superconducting cable are relatively less, so how to accurately perform simulation calculation on the electromagnetic field of the superconducting cable and effectively combine actual measurement data under different operation conditions and operation environments to obtain electromagnetic field data capable of evaluating the electromagnetic compatibility of the superconducting cable is a research focus of the superconducting cable electromagnetic compatibility technology.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a superconducting cable electromagnetic compatibility evaluation method.
The invention adopts the following technical scheme.
The superconducting cable electromagnetic compatibility evaluation method comprises the following steps:
step 1, establishing an electromagnetic field simulation model of a three-phase superconducting cable body according to the single-phase structure size parameters of the superconducting cable body;
step 2, under the normal working condition and the single-phase grounding short circuit condition, utilizing an electromagnetic field simulation model of the three-phase superconducting cable body to simulate and calculate an electromagnetic field simulation value of the superconducting cable body;
step 3, establishing an electromagnetic field simulation model of the three-phase superconducting cable joint according to winding parameters of the single-phase superconducting strip of the superconducting cable joint;
step 4, under the normal working condition and the single-phase grounding short circuit condition, simulating and calculating an electromagnetic field simulation value of the superconducting cable joint by using an electromagnetic field simulation model of the three-phase superconducting cable joint;
step 5, considering the unbalance of the three-phase current, respectively calculating the magnetic flux density of the balanced part current and the magnetic flux density of the unbalanced part current by utilizing the electromagnetic field simulation value of the superconducting cable body and the electromagnetic field simulation value of the superconducting cable joint;
step 6, obtaining electromagnetic field theoretical values of the superconducting cable under different operating conditions by utilizing the magnetic flux density of the balanced part current and the magnetic flux density of the unbalanced part current;
and 7, evaluating the electromagnetic compatibility of sensitive points on the transmission line path of the superconducting cable by using the electromagnetic field theoretical values of the superconducting cable under different operating conditions on the basis of the electromagnetic environment control limit value of the power transmission and transformation facility.
Preferably, in step 1, the single-phase structure size parameters of the superconducting cable include: the outer diameter of the lining core, the number of layers and the outer diameter of the superconducting tape, the thickness and the outer diameter of the PPLP insulating layer, the number of layers and the outer diameter of the superconducting shielding layer and the outer diameter of the copper tape;
based on the characteristics of the cylindrical axisymmetric structure of the superconducting cable, the electromagnetic field simulation model of the three-phase superconducting cable is a two-dimensional simulation model.
Preferably, step 2 comprises:
step 2.1, setting three-phase current parameters of the superconducting cable;
step 2.2, under the normal working condition, when the single-phase current reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable body;
step 2.3, under the normal working condition, when the single-phase current passes through zero, simulating and calculating an electromagnetic field simulation value of the superconducting cable body;
step 2.4, under the working condition of single-phase grounding short circuit, when the fault phase current reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable body;
step 2.5, under the working condition of single-phase grounding short circuit, when the fault phase current passes through zero, simulating and calculating an electromagnetic field simulation value of the superconducting cable body;
step 2.6, setting three-phase voltage parameters of the superconducting cable;
step 2.7, under the normal working condition, when the single-phase voltage reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable body;
step 2.8, under the normal working condition, when the single-phase voltage passes through zero, simulating and calculating an electromagnetic field simulation value of the superconducting cable body;
step 2.9, under the working condition of single-phase grounding short circuit, when the non-fault two-phase voltage reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable body;
and 2.10, under the working condition of single-phase grounding short circuit, when the fault phase voltage passes through zero, simulating and calculating the electromagnetic field simulation value of the superconducting cable body.
Further, in step 2.1, the three-phase current parameters of the superconducting cable include: the three-phase current parameters of the conducting layer and the three-phase current parameters of the shielding belt.
Preferably, in step 3, the winding parameters of the single-phase superconducting tape of the superconducting cable include: the winding radius, pitch, number, spiral angle and winding direction of each layer of strip of conducting layer, and the winding radius, pitch, number, spiral angle and winding direction of each layer of strip of shielding layer.
Preferably, step 4 comprises:
step 4.1, setting three-phase current parameters of the superconducting cable;
step 4.2, under the normal working condition, when the single-phase current reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable joint;
4.3, under the normal working condition, when the single-phase current passes through zero, simulating and calculating an electromagnetic field simulation value of the superconducting cable joint;
4.4, under the working condition of single-phase grounding short circuit, when the fault phase current reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable joint;
and 4.5, under the working condition of single-phase grounding short circuit, when the fault phase current passes through zero, simulating and calculating the electromagnetic field simulation value of the superconducting cable joint.
Preferably, step 5 comprises:
step 5.1, obtaining the induction proportion alpha of the current of the balance part on the shielding layer of the superconducting cable according to the net current value of each phase;
and 5.2, calculating the magnetic flux density proportion beta of the balance part current according to the following relational expression by using the induction proportion of the balance part current:
β＝1-α
step 5.3, the magnetic flux density B of the balance part current is calculated by the following relational expressiont，b：
In the formula (I), the compound is shown in the specification,in order to simulate the electromagnetic field of the superconducting cable body,the electromagnetic field simulation value of the superconducting cable joint is obtained;
step 5.4, calculating the magnetic flux density B of the unbalanced part current according to the following relational expressiont，ub：
In the formula, mu0Is a vacuum magnetic permeability and satisfies mu0＝4π×10-7H/m，IuTo balance the current, r is the distance from the point calculated by the simulation number to the center of the superconducting cable.
Preferably, in step 6, the magnetic flux density B of the balance part current under different operation conditions is adjustedt，bAnd the magnetic flux density B of the unbalanced partial currentt，ubAdding to obtain the electromagnetic field theoretical value B of the superconducting cable under different operating conditionst。
Preferably, step 7 comprises:
step 7.1, determining the distance from the sensitive point on the superconducting cable transmission line path to the center of the superconducting cable
Step 7.2, according to the distanceObtaining the electromagnetic field analysis value of the sensitive point
Step 7.3, controlling the limit value B by the electromagnetic environment of the power transmission and transformation facility*As a reference, when the electromagnetic field of the sensitive point analyzes the valueNot greater than electromagnetic environment control limit B*If so, judging that the electromagnetic compatibility of the sensitive point meets the requirement of public exposure limit; otherwise, the electromagnetic compatibility of the sensitive point is judged not to meet the public exposure limit requirement.
Further, step 7.3 also includes:
controlling limit value B by electromagnetic environment of power transmission and transformation facilities*For reference, the electromagnetic field analysis value of any point on the superconducting cable transmission line path can be ensuredBr′Is not more than the electromagnetic environment control limit value B*The corresponding distance r' is used for determining the transmission channel width of the superconducting cable meeting the electromagnetic compatibility.
Compared with the prior art, the method for evaluating the electromagnetic compatibility of the superconducting cable has the advantages that the distribution rule of the power frequency magnetic field intensity of the three-phase cold insulation high-temperature superconducting cable and the distribution condition of the electromagnetic field around the superconducting cable in different complex environments are fully mastered by adopting the method for evaluating the electromagnetic compatibility of the superconducting cable, so that whether the power transmission line path of the superconducting cable meets the public exposure limit value requirement or not is judged.
The method provided by the invention can accurately obtain the influence of the electromagnetic radiation of the superconducting cable transmission line on the surrounding ecological and social environments, guides the protection design of the related circuit facilities along the line based on the simulation result and adopts corresponding measures to process, and ensures that the sensitive points of the surrounding environment are changed, and the monitoring values of the power frequency electric field intensity and the power frequency magnetic induction intensity are within the limits of the national evaluation standards.
When the method provided by the invention is applied to the environmental evaluation work of the superconducting cable engineering, the obtained data is accurate and reliable, and data support is provided for the evaluation of the project environmental protection feasibility and the operation and maintenance environment.
When the method provided by the invention is applied to superconducting cable equipment management and selection, the obtained data can guide equipment type selection, equipment grading and perfect inspection, and particularly, when the equipment type selection and the equipment grading are carried out, the comprehensive analysis is carried out by combining simulation data of an electromagnetic compatibility level so as to balance the influence degree on the safe operation of power equipment such as a superconducting cable and the like, and insulation and relay protection management are reasonably considered; meanwhile, the technical state of the equipment can be verified in a supporting manner, and the auxiliary effects of strengthening maintenance and eliminating hidden dangers are achieved, so that the equipment can run in a good state.
Drawings
Fig. 1 is a flow chart of a superconducting cable electromagnetic compatibility evaluation method of the present invention;
fig. 2 is an electromagnetic field simulation model diagram of the superconducting cable body established in the superconducting cable electromagnetic compatibility evaluation method of the present invention;
fig. 3 is a graph showing the magnetic field distribution from the sheath of the superconducting cable to a position 3m away from the center of the cable when the phase current of a reaches the peak value when t is 0.005s under normal working conditions according to an embodiment of the present invention;
fig. 4 is a graph showing a magnetic field distribution from the sheath of the superconducting cable to a position 3m away from the center of the cable when the phase a current passes through zero at a time t equal to 0.01s under normal working conditions according to an embodiment of the present invention;
fig. 5 is a graph illustrating a magnetic field distribution from the sheath of the superconducting cable to a position 3m away from the center of the cable when the phase current a reaches the peak value when t is 0.005s under the single-phase short-circuit fault condition in accordance with an embodiment of the present invention;
fig. 6 is a graph showing a magnetic field distribution from the sheath of the superconducting cable to a position 3m away from the center of the cable when the phase-a current passes through zero at a time t of 0.01s under the single-phase ground short-circuit fault condition in an embodiment of the present invention;
fig. 7 is an electromagnetic field simulation model diagram of a superconducting cable joint established in the superconducting cable electromagnetic compatibility evaluation method of the present invention;
FIG. 8 shows an electromagnetic field theoretical value B in an embodiment of the present inventiontAnd the measured value B of the electromagnetic fieldmA comparative graph of (a).
Detailed Description
The present application is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present application is not limited thereby.
As shown in fig. 1, the superconducting cable electromagnetic compatibility evaluation method includes:
step 1, establishing an electromagnetic field simulation model of the three-phase superconducting cable body according to the single-phase structure size parameters of the superconducting cable body, as shown in fig. 2, the three-phase superconducting cable 1 is positioned inside the electromagnetic field simulation model of the three-phase superconducting cable body at the vertex of an equilateral triangle, and the armor layer 2 is positioned outside the electromagnetic field simulation model of the three-phase superconducting cable body.
Specifically, in step 1, the single-phase structure size parameters of the superconducting cable include: the specific parameters of the outer diameter of the lining core, the number of layers and the outer diameter of the superconducting tape, the thickness and the outer diameter of the PPLP insulating layer, the number of layers and the outer diameter of the superconducting shielding layer and the outer diameter of the copper strip are detailed in Table 1.
Table 1 list of single-phase structure size parameters of high-temperature superconducting cable
Serial number
Material
Outer diameter (mm)
1
Lining core
22.5
2
Superconducting tape (2-layer superconducting)
24.4
3
PPLP insulation (5.5mm)
36.2
4
Superconducting shield (2-layer superconducting)
38.9
5
Copper strip
40.4
In the preferred embodiment, the three phases of the superconducting cable are contained in parallel in one insulated pipe and sheath, sharing the same cryogenic environment. The outer warp of the heat-insulating pipe and the outer warp of the sheath of the three-phase system cable are respectively 180mm and 186mm, so that compared with the traditional cable, considerable physical space is saved, and the three-phase system cable has higher power transmission efficiency per unit cross section.
Based on the characteristics of the cylindrical axisymmetric structure of the superconducting cable, the electromagnetic field simulation model of the three-phase superconducting cable is a two-dimensional simulation model.
In the preferred embodiment, the simulation of the power frequency magnetic field is researched by COMSOL Multiphysics software.
And 2, under the normal working condition and the single-phase grounding short circuit condition, simulating and calculating the electromagnetic field simulation value of the superconducting cable body by using the electromagnetic field simulation model of the three-phase superconducting cable body.
Specifically, step 2 comprises:
and 2.1, setting three-phase current parameters of the superconducting cable.
Further, in step 2.1, the three-phase current parameters of the superconducting cable include: the three-phase current parameters of the conducting layer and the three-phase current parameters of the shielding belt.
In the preferred embodiment, the excitation current function is set to 2200A for rated current according to the designed current-carrying capacity of the 35kV superconducting cableThe phase difference is 120 deg.. Setting three-phase current parameters (unit: ampere) of the superconducting layer as shown in formula (1):
the three-phase current parameter (unit: ampere) of the shielding belt is set as shown in the formula (2):
and 2.2, under the normal working condition, when the single-phase current reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable body.
In the preferred embodiment, under normal operation, when T is 0.005s, the a-phase current reaches a peak, and the magnetic field distribution curve from the superconducting cable sheath to a position 3m away from the cable center is as shown in fig. 3, and the magnetic flux density is about 38 μ T near the cable sheath, and then decays rapidly according to the inverse of the square of the distance. As can be seen from fig. 3, the magnetic flux density at the cable sheath position has been less than 100 μ T, and the magnetic flux density at the position 200mm from the cable sheath has decayed to 6 μ T. The magnetic flux density at about 0.7m decays to less than 1 μ T.
And 2.3, under the normal working condition, when the single-phase current passes through zero, simulating and calculating the electromagnetic field simulation value of the superconducting cable body.
In the preferred embodiment, under normal operation, when T is 0.01s, the a-phase current crosses zero, the magnetic field distribution curve from the superconducting cable sheath to the position 3m away from the cable center is as shown in fig. 4, and the magnetic flux density near the superconducting cable sheath is about 36 μ T, and then decays rapidly. As can be seen in fig. 4, the cable jacket flux density has decayed below 100 μ T; the magnetic flux density at a position 200mm away from the cable sheath is attenuated to 5.8 mu T; the magnetic flux density at about 0.7m was reduced to 1 μ T or less.
Step 2.4, under the working condition of single-phase grounding short circuit, when the fault phase current reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable body;
in the preferred embodiment, the current-carrying capacity when the phase a is grounded and short-circuited is designed, and the three-phase current parameter (unit: ampere) of the superconducting layer is as shown in formula (3):
the three-phase current parameter (unit: ampere) of the shielding belt is as shown in the formulas (5-26):
in the preferred embodiment, in the single-phase ground short-circuit condition, when T is 0.005s, the a-phase current reaches a peak, and the magnetic field distribution curve from the superconducting cable sheath to a position 3m away from the cable center is as shown in fig. 5, where the magnetic flux density is about 50 μ T near the cable sheath, and then decays rapidly according to the inverse of the square of the distance. As can be seen from fig. 5, the magnetic flux density at the cable sheath position has decayed to below 100 μ T, and the magnetic flux density at the position 200mm from the cable sheath has decayed to 7 μ T. The magnetic flux density at about 2m decays to less than 1 μ T.
And 2.5, under the working condition of single-phase grounding short circuit, when the fault phase current passes through zero, simulating and calculating the electromagnetic field simulation value of the superconducting cable body.
In the preferred embodiment, in the single-phase ground short-circuit condition, when T is 0.01s, the a-phase current crosses zero, the magnetic field distribution curve from the superconducting cable sheath to the position 3m away from the cable center is as shown in fig. 6, and the magnetic flux density near the superconducting cable sheath is about 36 μ T, and then decays rapidly. As can be seen from fig. 6, the magnetic flux density has decayed below 100 μ T at the cable jacket; the magnetic flux density at a position 200mm away from the cable sheath is attenuated to 6 mu T; the magnetic flux density at about 2m was reduced to 1 μ T or less.
And 2.6, setting three-phase voltage parameters of the superconducting cable.
In the preferred embodiment, when the 35kV superconducting cable is in the rated voltage working state, the excitation voltage function is set asThe phase difference is 120 deg.. The three-phase voltage parameter is shown as the formula (5) (unit: volt):
and 2.7, under the normal working condition, when the single-phase voltage reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable body.
In the preferred embodiment, under a normal working condition, when t is 0.005s, the a-phase voltage reaches a peak value, the power frequency electric field is well shielded, and the power frequency electric field outside the cable is close to zero.
And 2.8, under the normal working condition, when the single-phase voltage passes through zero, simulating and calculating the electromagnetic field simulation value of the superconducting cable body.
In the preferred embodiment, under a normal working condition, when t is 0.01s, the zero-crossing time of the a-phase voltage is the same as that when the a-phase voltage is at the voltage peak value, and at this time, the power frequency electric field outside the cable is close to zero.
And 2.9, under the working condition of single-phase grounding short circuit, when the non-fault two-phase voltage reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable body.
In the preferred embodiment, when the 35kV superconducting cable is in the working state of a phase a ground short circuit, the three-phase voltage parameter is as shown in formula (6) (unit: volt):
under the single-phase ground short circuit operating mode, when t is 0.005s, B, C looks voltage reaches the peak value, and the power frequency electric field has obtained fine shielding, and the power frequency electric field of cable outside is close to zero.
And 2.10, under the working condition of single-phase grounding short circuit, when the fault phase voltage passes through zero, simulating and calculating the electromagnetic field simulation value of the superconducting cable body.
Under the single-phase grounding short-circuit working condition, when t is 0.01s, the zero-crossing moment of the phase voltage A is the same as that when the phase B, C is at the voltage peak value under the working condition of the phase grounding short-circuit, and the power frequency electric field outside the cable is close to zero at the moment.
The electromagnetic field distribution simulation results of the superconducting cable running under different working conditions are shown in table 2.
TABLE 2 simulation results of electromagnetic field of superconducting cable under different working conditions
From table 2, under normal working conditions, the public exposure limit requirement can be met at the superconducting cable sheath; the requirement of the immunity limit value of I-type power frequency magnetic field sensitive equipment can be met at a position about 0.7m away from the superconducting cable; under the working condition of A-phase short circuit grounding, the public exposure limit requirement can be met at the superconducting cable sheath, and the immunity limit requirement of I-class power frequency magnetic field sensitive equipment can be met at a position about 2m away from the superconducting cable.
Both simulation and analysis show that the distribution rule of the electromagnetic field around the superconducting cable is consistent with that of a common cable according to the potential and electric field distribution around the superconducting cable, which is consistent with the theoretical analysis of the cable structure and the electromagnetic field distribution.
And 3, establishing an electromagnetic field simulation model of the three-phase superconducting cable joint according to the winding parameters of the single-phase superconducting strip of the superconducting cable joint, as shown in fig. 7.
Specifically, in step 3, the winding parameters of the single-phase superconducting tape of the superconducting cable include: the winding radius, pitch, number, spiral angle and winding direction of each layer of strip of conducting layer, and the winding radius, pitch, number, spiral angle and winding direction of each layer of strip of shielding layer.
After the winding radius of the superconducting tapes is determined, each layer of tape of the superconducting cable is spirally wound on the cable framework in a certain pitch and direction. The winding parameters of the single-phase superconducting tapes are shown in Table 3.
TABLE 3 winding parameters of single-phase superconducting tapes for superconducting cable joints
A three-phase superconducting cable joint model is established according to the actual size and the internal structure of a superconducting cable, and because the superconducting tapes are of a spiral structure, the joint part needs to be formed by welding each layer of tapes of two cables to form a current-carrying channel, so that a three-dimensional simulation model is established. And in modeling of the welding part, the welding thickness is considered to be 2mm, and the winding direction is consistent with that of the strip.
And 4, under the normal working condition and the single-phase grounding short circuit condition, simulating and calculating the electromagnetic field simulation value of the superconducting cable joint by using the electromagnetic field simulation model of the three-phase superconducting cable joint.
Specifically, step 4 includes:
and 4.1, setting three-phase current parameters of the superconducting cable.
In the preferred embodiment, the excitation current is set to 2200A for rated current, based on the designed current capacity of the 35kV superconducting cable. The current excitation function is consistent with the superconducting cable body.
And 4.2, under the normal working condition, when the single-phase current reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable joint.
In the preferred embodiment, under normal working condition, when T is 0.005s, the a-phase voltage reaches the peak value, the magnetic flux density is about 46 μ T near the cable sheath, then the a-phase voltage is rapidly attenuated according to the inverse of the square distance, the magnetic flux density at the cable sheath position is less than 100 μ T, and the magnetic flux density at the cable sheath position 200mm is attenuated to 10 μ T. The magnetic flux density at about 0.8m decays to less than 1 μ T.
And 4.3, under the normal working condition, when the single-phase current passes through zero, simulating and calculating the electromagnetic field simulation value of the superconducting cable joint.
In the preferred embodiment, under a normal working condition, when T is 0.01s, the a-phase current zero-crossing time is that the magnetic flux density near the superconducting cable sheath is about 43 μ T, and then the magnetic flux density is attenuated rapidly, so that the magnetic flux density of the cable sheath is already attenuated to be less than 100 μ T; the magnetic flux density at a position 200mm away from the cable sheath is attenuated to 8 mu T; the magnetic flux density at about 0.8m was reduced to 1 μ T or less.
And 4.4, under the working condition of single-phase grounding short circuit, when the fault phase current reaches the peak value, simulating and calculating the electromagnetic field simulation value of the superconducting cable joint.
In the preferred embodiment, the current-carrying capacity at the time of the phase-to-ground short circuit is designed according to the rated voltage of 35kV of the 35kV superconducting cable and the rated current of 2200A. The current excitation function is consistent with the superconducting cable body.
Under the condition of single-phase grounding short circuit, when T is 0.005s, the A-phase voltage reaches a peak value, the magnetic flux density is about 62.5 mu T close to the cable sheath, then the A-phase voltage is quickly attenuated according to the inverse of the square distance, the magnetic flux density at the cable sheath position is already attenuated to be less than 100 mu T, and the magnetic flux density at the position 200mm away from the cable sheath is already attenuated to be 12.5 mu T. The magnetic flux density at about 2m decays to less than 1 μ T.
And 4.5, under the working condition of single-phase grounding short circuit, when the fault phase current passes through zero, simulating and calculating the electromagnetic field simulation value of the superconducting cable joint.
In the preferred embodiment, under the condition of single-phase ground short circuit, when T is 0.01s, the flux density of the phase a current at the zero-crossing time is about 41 μ T near the superconducting cable sheath, and then the flux density is attenuated rapidly, and the flux density at the cable sheath is already attenuated to be less than 100 μ T; the magnetic flux density at a position 200mm away from the cable sheath is attenuated to 7 mu T; the magnetic flux density at about 2m was reduced to 1 μ T or less.
The results of the electromagnetic field distribution simulation of the superconducting cable joint part operating under different working conditions are shown in table 4.
TABLE 4 simulation results of electromagnetic field of superconducting cable joint under different working conditions
From the calculation result, under the normal working condition, the public exposure limit requirement can be met at the superconducting cable joint sheath; the requirement of the immunity limit value of I-type power frequency magnetic field sensitive equipment can be met at a position about 0.8m away from the superconducting cable joint; under the working condition of A-phase short circuit grounding, the public exposure limit requirement can be met at the sheath of the superconducting cable joint, and the immunity limit requirement of I-type power frequency magnetic field sensitive equipment can be met at a position about 2m away from the superconducting cable joint.
Both simulation and analysis show that the distribution rule of the electromagnetic field around the superconducting cable is consistent with that of a common cable.
And (5) integrating simulation results under various conditions to obtain the electromagnetic field data of the superconducting cable shown in the table 5.
TABLE 5 simulation results of electromagnetic fields of superconducting cables under different working conditions
For a power frequency electric field, due to the shielding effect of the cable armor layer and the liquid nitrogen pipe, no electric field influence is caused to the outside.
Under the comprehensive multiple working conditions, for the influence of electromagnetic field exposure, no matter under normal working conditions or under the condition of single-phase short circuit, the power frequency magnetic field of the superconducting cable can meet the public exposure limit requirement (far less than 100 mu T) at the superconducting cable sheath.
For the influence of electromagnetic field interference, even when the electromagnetic field is higher under the condition of short circuit, the power frequency magnetic field of the superconducting cable can meet the requirement (1 mu T) of the immunity limit value of I-type power frequency magnetic field sensitive equipment at a position 2m away from the cable sheath; under rated current, the power frequency magnetic field around the superconducting cable can meet the requirement (1 mu T) of the immunity limit value of I-type power frequency magnetic field sensitive equipment at a position 0.7m away from the cable sheath.
In the preferred embodiment of the invention, a power frequency electromagnetic field tester is used for measuring the electromagnetic field of the superconducting cable; the power frequency electromagnetic field tester adopts power frequency electric field and magnetic field integrated equipment, and provides a three-dimensional power frequency magnetic field accurate alignment measuring method and designs a corresponding measuring auxiliary device in order to quickly and accurately position measuring sensors in three directions of a power frequency magnetic field measuring instrument X, Y, Z to the same measuring point. The electromagnetic field measurements of the superconducting cables are detailed in table 6.
TABLE 6 superconducting cable sample segment ambient electromagnetic field measurements (Unit: μ T)
Distance r (cm)
26.7
56.3
76.3
96.3
116.3
136.3
156.3
176.3
196.3
216.3
Bm
99.2
40.5
29.0
22.1
17.9
14.8
12.7
11.4
10.6
9.9
In the embodiment of the invention, the electromagnetic field theoretical value BtAnd the measured value B of the electromagnetic fieldmThe comparison curve of (a) is shown in fig. 8.
And 5, considering the unbalance of the three-phase current, and respectively calculating the magnetic flux density of the balanced part current and the magnetic flux density of the unbalanced part current by using the electromagnetic field simulation value of the superconducting cable body and the electromagnetic field simulation value of the superconducting cable joint.
Specifically, step 5 comprises:
step 5.1, obtaining the induction proportion alpha of the current of the balance part on the shielding layer of the superconducting cable according to the net current value of each phase;
and 5.2, calculating the magnetic flux density proportion beta of the balance part current according to the following relational expression by using the induction proportion of the balance part current:
β＝1-α
step 5.3, the magnetic flux density B of the balance part current is calculated by the following relational expressiont,b：
In the formula (I), the compound is shown in the specification,in order to simulate the electromagnetic field of the superconducting cable body,the electromagnetic field simulation value of the superconducting cable joint is obtained;
in the preferred embodiment, the current values of the three-phase cables are 2201A, 2198A and 2250A, respectively. From the net current data, it can be concluded that the balanced portion of the three-phase current can induce about 93.5% of the current on the shield. The theoretical flux density of the balance section current should be multiplied by 6.5% of the simulated value of the electromagnetic field.
Step 5.4, calculating the magnetic flux density B of the unbalanced part current according to the following relational expressiont,ub：
In the formula, mu0Is a vacuum magnetic permeability and satisfies mu0＝4π×10-7H/m，IuTo balance the current, r is the distance from the point calculated by the simulation number to the center of the superconducting cable.
And 6, obtaining the electromagnetic field theoretical value of the superconducting cable under different operating conditions by using the magnetic flux density of the balanced part current and the magnetic flux density of the unbalanced part current.
In step 6, the magnetic flux density B of the balance part current under different operation conditions is measuredt,bAnd an unbalanced portionMagnetic flux density B of the partial currentt，ubAdding to obtain the electromagnetic field theoretical value B of the superconducting cable under different operating conditionst. See table 7 for details.
TABLE 7 theoretical calculation value (unit: μ T) of the peripheral electromagnetic field outside the superconducting cable sample section
Distance r (cm)
20
40
60
80
100
120
140
160
180
200
220
Bt，b
35.3
8.77
3.89
2.19
1.40
0.97
0.71
0.55
0.43
0.35
0.29
Bt，ub
50.0
25.0
16.7
12.5
10.0
8.33
7.14
6.25
5.56
5.0
4.54
Bt
85.3
33.8
20.6
14.7
11.4
9.30
7.85
6.80
5.99
5.34
4.83
As can be seen from Table 7, the power frequency magnetic field value is already below 100 μ T at a distance of 26cm from the center of the cable, and meets the public exposure limit requirement.
And 7, evaluating the electromagnetic compatibility of sensitive points on the transmission line path of the superconducting cable by using the electromagnetic field theoretical values of the superconducting cable under different operating conditions on the basis of the electromagnetic environment control limit value of the power transmission and transformation facility.
Specifically, step 7 includes:
step 7.1, determining the distance from the sensitive point on the superconducting cable transmission line path to the center of the superconducting cable
Step 7.2, according to the distanceObtaining the electromagnetic field analysis value of the sensitive point
Step 7.3, controlling the limit value B by the electromagnetic environment of the power transmission and transformation facility*As a reference, when the electromagnetic field of the sensitive point analyzes the valueNot greater than electromagnetic environment control limit B*If so, judging that the electromagnetic compatibility of the sensitive point meets the requirement of public exposure limit; otherwise, the electromagnetic compatibility of the sensitive point is judged not to meet the public exposure limit requirement.
Further, step 7.3 also includes:
controlling limit value B by electromagnetic environment of power transmission and transformation facilities*For reference, the electromagnetic field analysis value B of any point on the superconducting cable transmission line path can be ensuredr′Is not more than the electromagnetic environment control limit value B*The corresponding distance r' is used for determining the transmission channel width of the superconducting cable meeting the electromagnetic compatibility.
Compared with the prior art, the method for evaluating the electromagnetic compatibility of the superconducting cable has the advantages that the distribution rule of the power frequency magnetic field intensity of the three-phase cold insulation high-temperature superconducting cable and the distribution condition of the electromagnetic field around the superconducting cable in different complex environments are fully mastered by adopting the method for evaluating the electromagnetic compatibility of the superconducting cable, so that whether the power transmission line path of the superconducting cable meets the public exposure limit value requirement or not is judged.
The method provided by the invention can accurately obtain the influence of the electromagnetic radiation of the superconducting cable transmission line on the surrounding ecological and social environments, guides the protection design of the related circuit facilities along the line based on the simulation result and adopts corresponding measures to process, and ensures that the sensitive points of the surrounding environment are changed, and the monitoring values of the power frequency electric field intensity and the power frequency magnetic induction intensity are within the limits of the national evaluation standards.
When the method provided by the invention is applied to the environmental evaluation work of the superconducting cable engineering, the obtained data is accurate and reliable, and data support is provided for the evaluation of the project environmental protection feasibility and the operation and maintenance environment.
When the method provided by the invention is applied to superconducting cable equipment management and selection, the obtained data can guide equipment type selection, equipment grading and perfect inspection, and particularly, when the equipment type selection and the equipment grading are carried out, the comprehensive analysis is carried out by combining simulation data of an electromagnetic compatibility level so as to balance the influence degree on the safe operation of power equipment such as a superconducting cable and the like, and insulation and relay protection management are reasonably considered; meanwhile, the technical state of the equipment can be verified in a supporting manner, and the auxiliary effects of strengthening maintenance and eliminating hidden dangers are achieved, so that the equipment can run in a good state.
The present applicant has described and illustrated embodiments of the present invention in detail with reference to the accompanying drawings, but it should be understood by those skilled in the art that the above embodiments are merely preferred embodiments of the present invention, and the detailed description is only for the purpose of helping the reader to better understand the spirit of the present invention, and not for limiting the scope of the present invention, and on the contrary, any improvement or modification made based on the spirit of the present invention should fall within the scope of the present invention.