Electromagnetic interference shielding performance calculate model for double layer shielded cable connector in EV

Abstract

Due to the high voltage and high current working characteristics of EV driving system, strong electromagnetic interference is formed in the working process, and the shielding effectiveness of the high-voltage connector assembly connecting each part of the driving system is directly related to the level of its electromagnetic interference emission. The high-voltage connector is usually made by triaxial method. However, due to the influence of sample coupling length and cutoff frequency, the triaxial method is prone to produce a region of more than 25 MHz, resulting in test failure. Therefore, modeling analysis of the shielding effectiveness of the connector assembly in the early stage is crucial for the final development of a connector assembly with good shielding effectiveness. In this paper, an analytical optimization model named Z _TD-Demoulin is proposed to calculate the transfer impedance value of the dynamic shielded wire (double-layer shielded) of the electric vehicle. The model takes into account the influence of the double-layer shielded cable (braided-belt and aluminum foil) on the DC resistance and small-hole inductance of the shielding layer, and analyzes the transfer impedance value which presents the shielding effectiveness of the connector assembly. Based on the double-layer shield optimization model, an optimization model of high-voltage connector assembly is established. This established model takes into account the influence of connector contact resistance and inductance value. Comparison between the triaxial coaxial method and the established model found that when K _connector = 6K _cable, the fitting effect of the model was the best and the transfer impedance value above 25 MHz could be predicted.

Keywords

Power cable transfer impedance triaxial method double layer shielding

1. Introduction

During the working process of electric vehicle drive system, strong electromagnetic interference results from the system characteristics of high voltage and high current. What’s more, the level of electromagnetic interference emission is directly related with the shielding effectiveness of HV (high-voltage) connector components. Poor shielding effectiveness of connector assembly often causes too high electromagnetic emission level [1], resulting in failure to pass the GB/standard test (150 kHz to 30 MHz).

Currently, HV connector tests usually adopt triaxial method. However, due to the in-fluence of sample coupling length and cutoff frequency, the test is prone to produce a region of more than 25 MHz, resulting in test failure. How to effectively evaluate and test the shielding effectiveness of connector assembly is a common concern of cable and connector suppliers and automobile manufacturers [2].

By far, there have been few studies on the shielding effectiveness simulation of connector assembly, and most of them are about the shielding effectiveness of braided cable, one of the single layer cables. For example, Vance [3], Tyni [4], Demoulin et al. [5] deduced the formula of the transfer impedance value of the single-layer braid cable model based on the electromagnetic field theory, which can effectively simulate the transfer impedance value of the corresponding parameter of the single-layer braid cable. YANG Peiming [6], Wang Xiaoling et al. [7] optimized the single-layer braided cable model on the basis of Demoulin model and verified the optimization model. Now, the HV power cables on electric cars are usually double shielding ones, but there seems to be little research on double layer shielding cable modeling. Therefore, this paper proposes an optimization models of double layer shielding, and based on it establishes a high voltage connector assembly mode which can predict the connector assembly transfer impedance value of more than 25 MHz.

Fig. 1.

Schematic diagram of transfer impedance definition.

2. Surface transfer impedance

Surface transfer impedance, a characteristic parameter, reflects the shielding performance of the power cable. The lower cable transfer impedance is, the better its shielding performance and the stronger electromagnetic immunity. It is defined as the induced voltage formed between the core wire and the shielding layer when the current flows through the shielding layer in the cable of unit length (as shown in Fig. 1), that is, the ratio of the axial voltage change rate on the braided layer to the axial current. The calculation formula of surface transfer impedance can be expressed as follows: $\begin{eqnarray}Z_{T}=\frac{1}{I_{0}}\frac{\partial V}{\partial z}.\end{eqnarray}$ (1)

Here I ₀ refers to the current flowing through the outer surface of the braid; ∂V∕∂z refers to the effective value of the voltage per unit length of the uniform transmission line composed of the core wire and the shielding layer; z stands for the axial direction of the cable; l in Fig. 1 is the cable length.

3. Analytical expression of transfer impedance

Since high-voltage power cables in electric vehicles are generally braided shielded ones as shown in Figs 2 and 3, the analytical model of transfer impedance can be established through the structural parameters of the cable braided layer and the theory of electromagnetic field theory. As for analytical model input parameters, seven parameters need to be included to describe the structure characteristics [8–10] of the cable braid: braid inside diameter D ₀, each braided wire diameter d, woven layer contains a lap weaving beam number C, wire weaving beam of a share of the number N, braid Angle 𝛼, braid the electrical conductivity of σ, braid the permeability of μ. The transfer impedance value of the shielded cable can be simulated after the 7 parameters are obtained, as shown in Fig. 3.

Fig. 2.

Schematic diagram of shielded cable structure.

Fig. 3.

Schematic diagrams of the structural parameters of the braid.

Demoulin proposed the analytic model of formula (2), taking into account the extra fluctuation effect. Extra fluctuation effect happens in the high frequency magnetic field under the code netting weaving beam between inside and outside layer and is caused by eddy current effect, so as to generate additional damping, resulting in high frequency range of transfer impedance value decreases, and the component can be caused by the tangential electric field on the shield of the vortex to describe, is proportional to the $\sqrt{{\omega}}$ . $\begin{eqnarray}Z_{T_{D_\mathit{Demoulin}}}=Z_{d}+j{\omega}(L_{h2}-L_{b1})+k\sqrt{{\omega}}e^{+j_{4}^{{\pi}}}.\end{eqnarray}$ (2)

Here: $\begin{eqnarray}\displaystyle Z_{d} & = & \displaystyle R_{0}\frac{(1+j)d}{\sin h[(1+j)d/{\delta}]}\end{eqnarray}$ (3) $\begin{eqnarray}\displaystyle R_{0} & = & \displaystyle \frac{4}{{\pi}d^{2}\mathit{NC}{\sigma}\cos {\alpha}}\end{eqnarray}$ (4) $\begin{eqnarray}\displaystyle {\delta} & = & \displaystyle \frac{1}{\sqrt{{\pi}f{\mu}{\sigma}}}\end{eqnarray}$ (5) $\begin{eqnarray}\displaystyle L_{h2} & = & \displaystyle \frac{2{\mu}C}{{\pi}\cos {\alpha}}\left[\frac{b}{{\pi}D_{M}}\right]^{2}\exp \left[\frac{-{\pi}d}{b}-2{\alpha}\right]\end{eqnarray}$ (6) $\begin{eqnarray}\displaystyle D_{M} & = & \displaystyle D_{0}+2d\end{eqnarray}$ (7) $\begin{eqnarray}\displaystyle L_{b1} & = & \displaystyle \frac{{\mu}h}{4{\pi}D_{M}}(1-\tan ^{2}{\alpha})\end{eqnarray}$ (8) $\begin{eqnarray}\displaystyle k & = & \displaystyle -\frac{1.16}{NCd}\cdot \arctan \frac{N}{3}\cdot \sin \left[\frac{{\pi}}{2}-2{\alpha}\right]\cdot \sqrt{\frac{{\mu}}{{\sigma}}}.\end{eqnarray}$ (9)

On this basis, considering the influence of aluminum foil on DC resistance and keyhole inductance, we propose an optimization model of double layer shielded cables. $\begin{eqnarray}Z_{T_{D\text{-}Demoulin}}=Z_{d}^{\prime }-j{\omega}L_{b1}+k\sqrt{{\omega}}e^{+j_{4}^{{\pi}}}.\end{eqnarray}$ (10)

Here: $\begin{eqnarray}\displaystyle Z_{d}^{\prime } & = & \displaystyle R^{\prime }\frac{(1+j)d}{\sin h[(1+j)d/{\delta}]}\end{eqnarray}$ (11) $\begin{eqnarray}\displaystyle R^{\prime } & = & \displaystyle \frac{4}{{\pi}d^{2}NC{\sigma}\cos {\alpha}}+R_{AL}.\end{eqnarray}$ (12)

For the aluminum foil additional DC resistance R _AL, the aluminum foil layer model can be established through Q3D software for numerical analysis and calculation to extract it. The cable thickness is set as 0.1 mm, the aluminum foil DC resistance in it can be computed to be 0.004 Ω/m.

Simulate and analyze the single-layer shielding model and the two-layer optimization model with the results shown in Fig. 4. Considering the influence of increasing DC resistance and eliminating the small-hole inductance, it can be seen that DC resistance is the main influence in the low frequency band, while inductance is the main influence in the high frequency band. From the perspective of the overall optimization model, the transfer impedance of the double-layer shielded cable at high frequency is obviously lower than that of the single-layer shielded cable.

Fig. 4.

Comparison of single-layer shielding model and double-layer optimization model.

4. Analytical model for high voltage shielded connector assembly

Schematic diagram of physical connector is shown in Fig. 5, A connector is divided into two main parts: part A (core conductor) and part B (shielding shell) [12,13]. In Fig. 6, A1 shows the connection of cable core and connector metal terminal: B1 is the connection of cable shielding layer and the metal shielding shell; A2 is the contact connection of two metal connectors which reverse at 90 degrees inside the connectors and B2 shows the point connection of shield shell metal and metal. In the connector, the electric field between Part A (core wire) and Part B (shield shell) will generate capacitance, which can be expressed as capacitor C _SC; The current flowing along the conductor will generate magnetic fields. In the circuit of A and B, conductor inductance and shielding inductance can be respectively equivalent to single inductive Lc and Ls in series, and there is mutual inductance M _SC between Lc and Ls. The connector shielding shell involves the existence of a contact resistance between the metal and the metal surface R _contact. Likewise, there is a contact resistance between the commutator connector at A2. The value of the contact resistance is closely related to the state of contact which is determined by the number of contact points and degree of compression on the structure. Usually, the more contact points, the greater the compression force, and the smaller the contact resistance. Similarly, in the case where the connection between metal and metal contact points is loose or there is a dielectric, there is a parasitic capacitor C _metalplate between metal surfaces. However, because under normal circumstances, compared with C _SC, the amplitude of C _metalplate is very low and can be ignored, only single-phase shielded cables and connectors are shown in Fig. 6.

Fig. 5.

Schematic diagram of physical connector.

Fig. 6.

Analysis of connector internal structure.

For its transfer impedance value of solution on the basis of the shield wire we need additional contact resistance R _contact and connector inductance value L _connector [14,15]. Since the extra capacitor will have little impact on the transfer impedance value, it is not considered. According to the above analysis, the low frequency band is determined by DC resistance, which indicates that after the addition of high-pressure connectors, extra resistance value, contact resistance R _contact is added. While the high frequency band is mainly determined by the inductance part, and L _connector is introduced as an additional inductance value.

To sum up, the analytic model of HV connection system assembly can be expressed as follows: $\begin{eqnarray}Z_{T_\mathit{Connector}}=\left[R^{\prime }\frac{(1+j)d}{\sin h\left[(1+j)d/{\delta}\right]}+K_{connector}\sqrt{{\omega}}e^{+j_{4}^{{\pi}}}-j{\omega}L_{B}\right]+j{\omega}L_{Connector}+R_{Connect},\end{eqnarray}$ (13) where, K _connector is the influence factor after the addition of connectors. At high frequency, the spinning current effect caused by the magnetic field between the braided bundles of the inner and outer layers of the woven mesh will generate additional attenuation, and the holes on the connector will also have an influence on this factor. R _contact contact resistance can be measured with low DC resistance measurement instrument. Usually, the inside contact resistance and additional L _connector inductance value of interlock type elbow connectors, which connect the shielding cables with specification of 35 mm² are 3 ∼ 5 mΩ, and 2.2 nH respectively.

5. Analysis of K _connector value

K _connector is described as the influence factor after the addition of connectors, K _cable is the empirical value to characterize the cable characteristic parameters. The simulation results obtained by simulating different K _connector values are compared with the test results to obtain the appropriate K _connector value, as shown in Fig. 7, and the data is shown in Table 1.

Fig. 7.

Impact of K _connector on transfer impedance values.

Table 1

The impact of the K _connector value the transfer impedance value

Frequency	Result	1*K _cable	5*K _cable	6*K _cable	10*K _cable	15*K _cable
	mΩ/m	mΩ/m	mΩ/m	mΩ/m	mΩ/m	mΩ/m
10 kHz	9.736	11.47	10.66	10.48	9.781	9.082
150 kHz	11.61	10.96	9.936	10.04	11.75	15.83
500 kHz	14.37	10.48	15.21	16.92	24.57	34.93
1 MHz	18.34	9.856	21.24	24.26	36.52	52.02
2 MHz	26.45	8.482	26.17	30.58	48.28	70.39
5 MHz	44.23	6.298	34.15	41.13	69.1	104.1
10 MHz	63.14	8.917	48.58	58.55	98.07	147.9
15 MHz	71.19	10.86	59.26	71.52	119.9	180.4

Error analysis was made on the above 1*K _cable, 5*K _cable, 6*K _cable, 10*K _cable and 15*K _cable respectively. Standard deviation is the most commonly used quantitative form to reflect the dispersion degree of a group of data, and it is an important indicator of accuracy. Standard deviation is defined as the square root of the arithmetic mean of the standard value of each unit and its mean deviation squared. It reflects the degree of dispersion among individuals within a group.

The calculation formula of sample standard deviation is as follows: $\begin{eqnarray}s=\sqrt{\frac{1}{n-1}}\mathop{\sum }_{i=1}^{n}(x_{i}-\bar{x})^{2}\end{eqnarray}$ (14) where, n is the number of observed samples, and $\bar{x}$ is the arithmetic mean of the samples, S reflects the dispersion degree of the whole sample variable. A low standard deviation indicates that the sample variable is close to the mean value and high ones shows that the sample variable is discrete from the mean value.

With reference to the ideas of the sample standard deviation, we will make standard deviation analysis of the corresponding frequency transfer impedance values and test values of 1*K _cable, 5*K _cable, 6*K _cable, 10*K _cable and 15*K _cable obtained from simulation, as shown in Table 2. Here, the simulation values are equivalent to sample test variables x _i, the measured values are equivalent to sample arithmetic average, observation sample n set as 8, which equals to the number of frequency points, $x_{i}-\bar{x}$ equivalent to the difference in value between simulation value and test value size, namely the error size.

Table 2

The standard deviations corresponding to different influence factors

K _connector	1*K _cable	5*K _cable	6*K _cable	10*K _cable	15*K _cable
Sample standard deviation	34.7071	8.1834	3.6334	27.0513	61.1806

It can be seen from the above results that when K _connector = 6*K _cable, the sample standard deviation is the minimum and the transfer impedance simulation value and test value of the connector assembly have good fitting effect, which can prove the correctness of the model.

6. Test and silulation estimate of high voltage shield connector assembly

A high voltage shield connector assembly consisting of high voltage shield cables and connectors, is an inseparable whole and plays a key role in the electromagnetic compatibility performance of the vehicle. The classic triaxial method is usually used for assembly testing. High voltage connection system assembly test data is as shown in Table 3. Table 4 shows the comparison between the triaxial method with one another, compared with A and C, the test dynamic range of B is higher, which is very important, because the actual test system is not a complete linear system and only has linear characteristics in part of the frequency band, so method B has better engineering application value. Meanwhile, method B is also simpler and more efficient than A and C. In this test, an expansion method of the triaxial B method was adopted. The coaxial tube was replaced with a larger box, so that high voltage connectors and shielded cables could be placed into it. This test referred Standard IEC62153-4-3 [16], IEC62153-4-15 [17], and principles of cable and individual connector tests. The data are as follows.

Table 3
High voltage connection system assembly test data

Frequency Transfer impedance value mΩ/m Frequency Transfer impedance value mΩ/m

10 KHz 9.736 10 MHz 63.14

150 KHz 11.61 15 MHz 71.19

500 KHz 14.37 20 MHz 63.26

1 MHz 18.34 25 MHz 47.67*

2 MHz 26.45 30 MHz 34.49*

5 MHz 44.23 35 MHz 24.83*

Frequency	Transfer impedance value mΩ/m	Frequency	Transfer impedance value mΩ/m
10 KHz	9.736	10 MHz	63.14
150 KHz	11.61	15 MHz	71.19
500 KHz	14.37	20 MHz	63.26
1 MHz	18.34	25 MHz	47.67*
2 MHz	26.45	30 MHz	34.49*
5 MHz	44.23	35 MHz	24.83*

Note: The test values marked with * are the values of the failure zone.

Table 4

Comparison of three coaxial methods A, B and C

Test method	Triaxial A	Triaxial B	Triaxial C
Advantages	It has a high cut-off frequency	It has a higher dynamic range	Be suitable for measuring very low transfer impedance values (less than 1 mΩ/m and lower)
Cut-off frequency f _cut * l	80 MHz * m	25 MHz * m	30 MHz * m
Disadvantages	The dynamic range is low	The cut-off frequency is low	The testing process is susceptible to outside influences
Characteristics	Require the Impedance matching adapter	Require the terminal resistor	Without Impedance matching adapter and terminal resistor

Fig. 8.

Physical layout of HV connection system assembly.

Fig. 9.

High pressure connection system Assembly test flow chart.

Test the high voltage connection system assembly based on IEC 62153-4-3. The shielding layer of the cable and the inner conductor constitute the inner circuit, the shielding layer of the cable and the coaxial test fixture constitute the outer circuit, meanwhile the inner circuit is terminated on a matched termination, the outer circuit is short-circuited on the near-end side on the cable shield. One end of the coaxial cable is connected with the load resistor R ₁ whose resistance value shall be equal to the impedance of the inner circuit, and the other end is connected with the signal generator. Network analyzer is a measuring equipment, the near end and the far end of the test tube are respectively connected to the network analyzer through the coupling device and matching resistance, and the measured data is transmitted to the computer. The physical figure is shown in Fig. 8 and the flow chart is shown in Fig. 9.

A block diagram of the test set-up method is shown in Fig. 10.

Fig. 10.

Schematic diagram of the test principle of triaxial B method. Description: 1—Network Analyzer or Receiver; 2—Cable insulation bushing; 3—Test sleeve; 4—terminal impedance R ₁ = Z ₁; 5—Signal generator; I ₁—The current in the inner circuit; 6—Cable Shield; 7—test core wire; 8—Test connector; Lc—Cable coupling length; Z ₁—The impedance of the inner circuit; U ₂—The voltage of the outer circuit.

The equation of transfer impedance value calculation of method Triaxial B is as follows. $\begin{eqnarray}Z_{t}=\frac{R_{1}+Z_{0}}{2\cdot L_{c}}\cdot 10^{-\left\{\frac{a_{meas}-a_{cal}}{20}\right\}}\end{eqnarray}$ (15) Where

a _meas =10log ₁₀(P ₁∕P ₂) is the attenuation loss of the measurement, while P ₁ is the power fed to the inner circuit, P ₂ is the power in the outer circuit;

a _cal is the compound loss during calibration;

Z ₀ is the impedance of the signal generator and receiver, its value usually equals to 50 Ω.

According to the simulation model of the high voltage connector assembly obtained in Section 3., the other two groups of samples were tested and verified. The test results and data are shown in Fig. 11 and Table 5.

Fig. 11.

Test curve of high voltage connection system assembly.

Table 5

Comparative analysis of sample test value and simulation values

Frequency	Sample 1	Sample 2	Sample 1	Sample 2	Sample 1	Sample 2
	Test value	Test value	Simulation values	Simulation values	Error rate	Error rate
	mΩ/m	mΩ/m	mΩ/m	mΩ/m	%	%
150 kHz	9.33	11.61	8.81	10.46	5.57	9.90
1 MHz	17.14	18.65	17.4	22.12	1.49	18.60
2 MHz	21.36	27.93	21.47	30.7	0.51	12.17
10 MHz	50.05	62.95	44.62	60.15	10.8	4.44
20 MHz	50.46	66.24	50.36	77.35	0.20	16.77

The connection system assembly was measured by three coaxial methods. According to the description in the Chapter 2. we learn that under the influence of the test equipment and sample length, when test frequency is more than 20 MHz, resonance happens, transfer impedance value fluctuates, test fails. And test results in high frequency are invalid. When the situation occurs, the measured values of the high frequency pare can be predicted by referring to the transfer impedance value calculated according to the simulation model as shown in Table 6.

Table 6

Connection system assembly high frequency transfer impedance prediction

Frequency MHz	Predictive value mΩ/m
20	82.18
25	11.61
30	100.2
35	108.1
40	115.3

7. Conclusion

(1) The transfer impedance value representing the shielding effectiveness of the shielded cable was analyzed, the transfer impedance values of single-layer shielded and the double-layer shielded cables were compared, the influence of the double-layer shield high voltage connection cables on the DC resistance and small-hole inductance was clarified and a double-layer shielded optimization model was presented.

(2) The structure of the high voltage connector is analyzed. The transfer impedance model of high voltage connector assembly is established by adding the contact resistance R _contact and the inductance value L _connector on the basis of the shielded cable.

(3) The shielding effectiveness of the high-voltage connector assembly was tested by triaxial method. Comparison of the test results of the model found that when K _connector = 6*K _cable, the sample standard deviation S value was the minimum, and the simulation value of transfer impedance of the connected system assembly had a good fitting effect with the tested value.

(4) Within 20 MHz, the error of the model can be basically guaranteed to be within 15%, and individual frequency points can be within 20%. This means the model has engineering application value for the shielding efficiency evaluation of the high voltage connector assembly. In addition, the transfer impedance of higher than 25 MHz of the high voltage connector assembly can be predicted.

Footnotes

Acknowledgements

This work was supported in part by Doctor Degree Scientific Research Foundation of Southwest University (No. SWU119001) and by the Scientific Research Foundation of Chongqing University of Technology (No. 2019ZD92).

References

Haiming

Yanyan

Guangyu

, Review on electrical performance and test methods of traction cables in electric vehicles, Auto Electric Parts (7) (2018), 10–13.

Marconi

Andrade

C.L.

, Evaluation of surface transfer impedance of coaxial cables, IEEE Latin America Transactions 18(3) (2020), 598–603.

Vance

E.F.

, Shielding effectiveness of braided-wire shields, IEEE Trans Electromagn Compat EMC-17(2) (1975), 71–77.

Tyni

, The transfer impedance of coaxial cables with braided conductors, in: Proc EMC Symp Wroclaw, Poland: Institute of Electrical and Electronics Engineers, 1976.

Demoulin

and Degauque

, Shielding effectiveness of braids with high optical coverage, in: Proceedings of the International Symposium on EMC, Institute of Electrical and Electronics Engineers, Zurich, 1981.

Yang

, Calculation and Measurement for Shield Cables in Power, North China Electric Power University, Hebei, 2006.

Wang

, Research on the Measurement and Simulation Method for Transfer Impedance of Shielded Coaxial Cables, Harbin Institute of Technology, Harbin, 2012.

Schippers

and Verpoorte

, Uncertainties in transfer impedance calculations, in: 2016 ESA Workshop on Aerospace EMC (Aerospace EMC), Institute of Electrical and Electronics Engineers, Spain, 2016.

Verpoorte

Schippers

and Rotgerink

J.H.G.J.L.

, Advanced models for the transfer impedance of metal braids in cable harnesses, in: 2018 IEEE International Symposium on Electromagnetic Compatibility and 2018 IEEE Asia-Pacific Symposium on Electromagnetic Compatibility (EMC/APEMC), Institute of Electrical and Electronics Engineers, Singapore, 2018.

10.

Frei

Mushtaq

Hermes

Current distribution in shielded cable-connector systems for power transmission in electric vehicles, in: 2018 IEEE International Symposium on Electromagnetic Compatibility and 2018 IEEE Asia-Pacific Symposium on Electromagnetic Compatibility (EMC/APEMC), Institute of Electrical and Electronics Engineers, Singapore, 2018.

11.

Weber

Guttowski

Hoene

EMI coupling from automotive traction systems, in: 2003 IEEE International Symposium on Electromagnetic Compatibility, Institute of Electrical and Electronics Engineers, Turkey, 2003.

12.

Mushtaq

and Frei

, Alternate methods for transfer impedance measurements of shielded HV-cables and HV-cable-connector systems for EV and HEV, International Journal of RF and Microwave Computer-Aided Engineering 26(4) (2016), 359–366.

13.

Mora

Rachidi

Pelissou

, An improved formula for the transfer impedance of two-layer braided cable shields, IEEE Transaction on Electromagnetic Compatibility 57(3) (2015), 607–610.

14.

Xiao

P.A.

and Zhang

, An analytical method for radiated electromagnetic and shielding effectiveness of braided coaxial cable, IEEE Transactions on Electromagnetic Compatibility 61(1) (2018), 1–7.

15.

Kim

and Jang

, Comparison of measurement results on the transfer impedance of a coaxial cable, in: 2017 Asia-Pacific International Symposium on Electromagnetic Compatibility (APEMC), Institute of Electrical and Electronics Engineers, Seoul, 2017.

16.

IEC 62153-4-3, Edition 2.0 2013-10. Metallic communication cable test methods-Part 4-3: Electromagnetic compatibility (EMC)-Surface transfer impedance-Triaxial method.

17.

IEC 62153-4-15:2015-12. Metallic communication cable test methods-Part 4-3: Electromagnetic compatibility (EMC)-Test method for measuring transfer impedance and screening attenuation-or coupling attenuation with triaxial cell.