CN105243198A - Method for designing anti-nuclear electromagnetic pulse power supply line filter - Google Patents

Abstract

The present invention relates to a method for designing an anti-nuclear electromagnetic pulse power supply line filter. The method comprises: determining a mathematical model of nuclear electromagnetic pulse interference, and calculating a maximum coupling magnitude of an interference source on a power supply line according to the mathematical model; according to the maximum coupling magnitude, determining a protection index; then selecting a filter circuit, and determining a required filter element of the filter circuit; and by repeatedly debugging filter insertion loss, determining the required filter element of the filter circuit, until meeting a requirement. In the selection of the filter circuit, the design for the power supply line filter is divided into two parts: a transient suppression part and a steady-state suppression part. The transient suppression part mainly suppresses a nuclear electromagnetic pulse with large pulse amplitude and short rise time, and is completed by a transient suppression device. The steady-state part mainly suppresses ordinary electromagnetic interference with small amplitude and long rise time, entering into a power grid, and can be implemented by a conventional power supply filter device.

Description

A kind of power line filter method for designing of anti-nuclear electromagnetic pulse

Technical field

The invention belongs to technical field of filter design, propose a kind of power line filter method for designing of anti-nuclear electromagnetic pulse especially.

Background technology

Along with the development of electronic industry, electronic equipment miscellaneous is applied to more and more to be produced with life.The quantity of electronic equipment and the continuous increase of density, make its mutually between interference problem become very outstanding, electromagnetic environment simultaneously residing for electronic equipment is more and more severe, such as ultra broadband, the High-Power Microwave even strong electromagnetic pulse such as nuclear blast all will disturb the normal work of electronic equipment, even cause breaking-up to electronic equipment.The present invention considers to resist the filter design problem under extreme strong electromagnetic pulse interference and small-sized nuclear blast condition.

Nuclear blast produce strong-electromagnetic field can be divided in early days (E1), mid-term (E2) and late period (E3) three part.Wherein, when the field of early origin accounts for, be about 1 μ s, by hole coupling in the wireless device of intermediate frequency, very high frequency(VHF) and some hyper band.In some standards abroad, nuclear electromagnetic pulse comprises E ₁(short pulse), E ₂(middle pulse), E ₃(long pulse) three parts, in the standard of China, the test waveform of nuclear electromagnetic pulse only refers to E ₁part.This part waveform characteristics amplitude is large, rising edge is steep, frequency spectrum is wide, the most serious on the impact of equipment, therefore, when considering nuclear electromagnetic pulse to the affecting of system or equipment, mainly refer to short pulse, be commonly referred to as upper low pressure trough (HEMP).

Nuclear electromagnetic pulse HEMP is coupled into electronic equipment internal by Qianmen (antenna), back door (cable, hole seam), and working normally to electronic equipment has an impact, therefore needs to suppress its interference.

HEMP causes severe jamming by power lead to electronic apparatus system, traditional power-supply filter can suppress low frequency, by a small margin electromagnetic interference (EMI) that power lead produces, but because the rise time of nuclear electromagnetic pulse is short, amplitude is large, conventional power source filter response speed is fast not, cannot complete the suppression to HEMP.

Summary of the invention

The object of this invention is to provide and a kind ofly both can suppress traditional small size electromagnetic interference (EMI) of low frequency, again can to high frequency significantly HEMP disturb the power line filter method for designing of the anti-nuclear electromagnetic pulse suppressed.

The object of the present invention is achieved like this, and a kind of power line filter method for designing of anti-nuclear electromagnetic pulse, is characterized in that: at least comprise the steps:

(1) nuclear electromagnetic pulse interference is simulated using double-exponential function as model, and the field intensity expression formula of its t electromagnetic pulse interference is as follows:

E(t)＝E ₀·k·(e ^-αt-e ^-βt)(1)

In formula, amplitude of field strength E ₀=5 × 10 ⁴v/m, scale-up factor k=1.3, factor alpha=4 × 10 ⁷/ s, factor beta=6 × 10 ⁸/ s;

(2) the maximum coupling magnitude of interference source on power cable is calculated according to step (1);

Nuclear electromagnetic pulse gets transmission line model to long conductor coupling, and namely utilize Agrawal mathematical model, its second order differential equation is:

$\left\{\begin{array}{c}\frac{d^{2}V}{dz}-{\mathrm{\γ}}^{2}V=\frac{{\mathrm{dE}}_z}{dz}\\ \frac{dI}{dz}-{\mathrm{\γ}}^{2}I=-{\mathrm{YE}}_z\end{array}\right.---\left(2\right)$

Wherein, V is scattering voltage, E _zfor arriving the electromagnetic pulse field intensity of cable, this field intensity expression formula can be expressed by formula (1) for standard nuclear electromagnetic pulse, and z is the coordinate along cable direction, E _zbe the function about coordinate z, I is the electric current along transmission line direction, γ ²=ZY, Z, Y are respectively transmission line unit length impedance over the ground and admittance;

The second order differential equation that what formula (2) was corresponding is about couple current on line, its form of separating comprises general solution and particular solution two parts;

General solution is

I(z)＝K ₁e ^-γz+K ₂e ^γz(3)

Particular solution is

$I^{*}\left(z\right)=\frac{1}{2Z_0}{{\∫}_{z_1}^z{E}_z{e}^{\mathrm{\γ}v}dv\·e}^{-\mathrm{\γ}z}+\frac{1}{2Z_0}{\∫}_z^{z_2}{E}_z{e}^{-\mathrm{\γ}v}dv\·e^{\mathrm{\γ}z}---\left(4\right)$

Make function $P\left(z\right)=\frac{1}{2Z_0}{\∫}_{z_1}^z{e}^{\mathrm{\γ}\mathrm{\υ}}{E}_{z}d\mathrm{\υ},$ Function $Q\left(z\right)=\frac{1}{2Z_0}{\∫}_z^{z_2}{e}^{-\mathrm{\γ}\mathrm{\υ}}{E}_{z}d\mathrm{\υ},$ The couple current obtained on line is

I _z(ω)＝[K ₁+P(z)]e ^-γz+[K ₂+Q(z)]e ^γz(5)

Wherein

$K_1={\mathrm{\Γ}}_1{e}^{{\mathrm{\γz}}_1}\frac{{\mathrm{\Γ}}_{2}P\left(z_2\right)e^{-{\mathrm{\γz}}_2}-Q\left(z_1\right)e^{{\mathrm{\γz}}_2}}{e^{\mathrm{\γ}(z_2-z_1)}-{\mathrm{\Γ}}_1{\mathrm{\Γ}}_2{e}^{-\mathrm{\γ}(z_2-z_1)}}---\left(6\right)$

$K_2={\mathrm{\Γ}}_2{e}^{{\mathrm{\γz}}_2}\frac{{\mathrm{\Γ}}_{1}P\left(z_1\right)e^{-{\mathrm{\γz}}_1}-Q\left(z_2\right)e^{{\mathrm{\γz}}_1}}{e^{\mathrm{\γ}(z_2-z_1)}-{\mathrm{\Γ}}_1{\mathrm{\Γ}}_2{e}^{-\mathrm{\γ}(z_2-z_1)}}---\left(7\right)$

Γ ₁, Γ ₂the reflection coefficient of terminal,

${\mathrm{\Γ}}_1=\frac{Z_1-Z_0}{Z_1+Z_0}---\left(8\right)$

${\mathrm{\Γ}}_2=\frac{Z_2-Z_0}{Z_2+Z_0}---\left(9\right)$

In formula, Z ₁for source termination impedance, Z ₂for load end impedance, Z ₀for the characteristic impedance of transmission line;

For single wire cable, the inductance L of its unit length ₀, electric capacity C ₀be calculated as follows:

$L_0=\frac{{\mathrm{\μ}}_0}{2\mathrm{\π}}ln\frac{2h}{a}---\left(10\right)$

$C_0=\frac{2{\mathrm{\π\ϵ}}_0}{ln(2h/a)}---\left(11\right)$

Wherein, h is cable distance floor level, and a is Cable radius, μ ₀for permeability of vacuum, ε ₀for permittivity of vacuum,

Thus, the characteristic impedance Z of transmission line ₀calculating formula be:

$Z_0=\sqrt{\frac{L_0}{C_0}};---\left(12\right)$

(3) according to the result of step (2), determine to protect index;

(4) Choose filtering circuit, determines filter element needed for filtering circuit;

(5) whether filter insertion loss meets design objective; Meet design objective, can circuit output be carried out; Otherwise, return step (4) and redefine filter element needed for filtering circuit; Until meet the demands.

The TVS pipe that the described filtering circuit described in step (4) comprises two 5KP36CA is protected as one-level, two 5KP36CA are connected in series in output terminal, be connected in series a connecting to neutral current potential, two 22nF electric capacity are connected in series, connecting to neutral current potential between two 22nF electric capacity electric connection points at output terminal, two the 22nF electric capacity two ends be connected in series be connected in series two TVS pipe and be connected in parallel, also be included in two voltage dependent resistor (VDR)s that input end has serial connection, two voltage dependent resistor (VDR)s be connected in series a connecting to neutral current potential, 1 μ F electric capacity is had with input end, 1 μ F electric capacity is in parallel with two the voltage dependent resistor (VDR) two ends be connected in series, between a 1 μ F electric capacity and two 22nF electric capacity, comprise a pair 5mH in positive loop and a pair 5mH in 30 μ H inductance and negative loop and 30 μ H inductance, wherein 1 μ F electric capacity is used for filtering low frequency differential mode electromagnetic interference (EMI), two couples of 5mH and 30 μ H inductance are used for filtering low frequency common electromagnetic interference (EMI), two 22nF electric capacity are used for filtering high frequency differential mode and common mode electromagnetic interference (EMI).

In described step (3), protection index is: inflow-rate of water turbine is 1000A, and the response time is ns level, and insertion loss is greater than 30dB.

Advantage of the present invention is: the present invention passes through the mathematical model of definite kernel electromagnetic pulse interference, according to the maximum coupling magnitude of calculated with mathematical model interference source on power cable; Determine to protect index according to maximum coupling magnitude; Then Choose filtering circuit, determines filter element needed for filtering circuit; Repeatedly debugged by filter insertion loss, determine filter element needed for filtering circuit; Until meet the demands.Selecting in filtering circuit, the design of power line filter is divided into two parts: transient state suppresses part and stable state to suppress part.Transient state suppresses the main nuclear electromagnetic pulse that suppressor pulse amplitude is large, the rise time is short of part, relies on transient suppression device to complete; Steady-state portion mainly suppresses that the amplitude entering electrical network is little, rise time ordinary electromagnetic interference slowly, realizes by conventional power source filtering device.

Accompanying drawing explanation

Fig. 1 nuclear electromagnetic pulse time domain beamformer;

Fig. 2 nuclear electromagnetic pulse frequency-domain waveform figure;

Nuclear electromagnetic pulse incident direction figure when Fig. 3 coupling amount is maximum;

Fig. 4 Agrawal precircuit describes figure;

Fig. 5 nuclear electromagnetic pulse filter circuit figure;

Fig. 6 wave filter Common Mode insertion loss analogous diagram;

Fig. 7 wave filter Differential Mode insertion loss analogous diagram.

Embodiment

A power line filter method for designing for anti-nuclear electromagnetic pulse, is designed to example by with the power line filter of the anti-nuclear electromagnetic pulse of a 24VDC/2A, provides concrete design process.

(1) characteristic of nuclear electromagnetic pulse interference is analyzed.

Nuclear electromagnetic pulse characteristic is simulated using double-exponential function as model, and its field intensity expression formula is as follows:

E(t)＝E ₀·k·(e ^-αt-e ^-βt)(1)

In formula, E ₀=5 × 10 ⁴v/m, k=1.3, α=4 × 10 ⁷/ s, β=6 × 10 ⁸/ s;

From the time domain waveform (Fig. 1) of nuclear electromagnetic pulse, HEMP has the rise time 2.3ns be exceedingly fast, and amplitude is 50kV/m; From frequency-domain waveform (Fig. 2), its frequency spectrum, from 100Hz to 200MHz, can cover wider frequency band, cause interference to various electronic.

(2) the maximum coupling magnitude of simulation calculation interference source on power cable.

Nuclear electromagnetic pulse gets transmission line model for the coupling of the long conductor such as electric wire, cable, utilize Agrawal mathematical model, Agrawal mathematical model is a kind of model for solving field wire coupling proposed by people such as Agrawal, is regard the coupled problem of external electromagnetic field to transmission line as an electromagnetic scattering process.Be considered as plane wave from above the ground incident electromagnetic pulse in this model, Electric and magnetic fields all can be analyzed to and is parallel to cable and perpendicular to this both direction of cable.For electric field, be parallel to the field intensity E of cable _//cable can be coupled to; For magnetic field, perpendicular to the field intensity H of cable _⊥the loop formed with ground produces magnetic flux, makes line produces induction current.

Consider situation when interference and coupling amount is maximum, the incident direction of electromagnetic pulse as shown in Figure 3.In Agrawal equation, external electromagnetic field can produce spread voltage source to represent by the incident electric field component along wire tangential direction to the coupling of transmission line on the transmission line.

Agrawal model is a kind of transmission line model, and circuit represents with distribution parameter in the model.But different from traditional transmission line model, will by the equivalence of extraneous strong electromagnetic pulse source on cable in the transmission line model of field wire coupling, therefore length be dz one section of cable on distribution parameter as shown in Figure 4.

Second order differential equation in Fig. 4 is:

$\left\{\begin{array}{c}\frac{d^{2}V}{dz}-{\mathrm{\γ}}^{2}V=\frac{{\mathrm{dE}}_z}{dz}\\ \frac{dI}{dz}-{\mathrm{\γ}}^{2}I=-{\mathrm{YE}}_z\end{array}\right.---\left(2\right)$

Wherein, V is scattering voltage, E _zfor arriving the field intensity of cable, z is along cable direction coordinate, and I is along transmission line choke, γ ²=ZY, Z, Y are respectively transmission line unit length impedance over the ground and admittance.

It is of concern that couple current on line in engineering, namely about the second order differential equation of electric current, its form of separating comprises general solution and particular solution two parts.

General solution is

I(z)＝K ₁e ^-γz+K ₂e ^γz(3)

Particular solution is

$I^{*}\left(z\right)=\frac{1}{2Z_0}{{\∫}_{z_1}^z{E}_z{e}^{\mathrm{\γ}v}dv\·e}^{-\mathrm{\γ}z}+\frac{1}{2Z_0}{\∫}_z^{z_2}{E}_z{e}^{-\mathrm{\γ}v}dv\·e^{\mathrm{\γ}z}---\left(4\right)$

Order $P\left(z\right)=\frac{1}{2Z_0}{\∫}_{z_1}^z{e}^{\mathrm{\γ}\mathrm{\υ}}{E}_{z}d\mathrm{\υ},Q\left(z\right)=\frac{1}{2Z_0}{\∫}_z^{z_2}{e}^{-\mathrm{\γ}\mathrm{\υ}}{E}_{z}d\mathrm{\υ},$ Obtaining electric current on line is

$I_z\left(\mathrm{\ω}\right)=\[K_1+P\left(z\right)\]e^{-\mathrm{\γ}z}+\[K_2+Q\left(z\right)\]e^{\mathrm{\γ}z}---\left(5\right)$

Wherein

$K_1={\mathrm{\Γ}}_1{e}^{{\mathrm{\γz}}_1}\frac{{\mathrm{\Γ}}_{2}P\left(z_2\right)e^{-{\mathrm{\γz}}_2}-Q\left(z_1\right)e^{{\mathrm{\γz}}_2}}{e^{\mathrm{\γ}(z_2-z_1)}-{\mathrm{\Γ}}_1{\mathrm{\Γ}}_2{e}^{-\mathrm{\γ}(z_2-z_1)}}---\left(6\right)$

$K_2={\mathrm{\Γ}}_2{e}^{{\mathrm{\γz}}_2}\frac{{\mathrm{\Γ}}_{1}P\left(z_1\right)e^{-{\mathrm{\γz}}_1}-Q\left(z_2\right)e^{{\mathrm{\γz}}_1}}{e^{\mathrm{\γ}(z_2-z_1)}-{\mathrm{\Γ}}_1{\mathrm{\Γ}}_2{e}^{-\mathrm{\γ}(z_2-z_1)}}---\left(7\right)$

Γ ₁, Γ ₂the reflection coefficient of terminal,

${\mathrm{\Γ}}_1=\frac{Z_1-Z_0}{Z_1+Z_0}---\left(8\right)$

${\mathrm{\Γ}}_2=\frac{Z_2-Z_0}{Z_2+Z_0}---\left(9\right)$

In formula, Z ₁for source termination impedance, Z ₂for load end impedance, Z ₀for the characteristic impedance of transmission line.

The solution procedure of analysis is above all based on frequency domain, the parameter that we are concerned about is the parameters such as current peak, rising edge, halfwidth, these parameters are all the results obtained under time domain, therefore, as long as carry out inversefouriertransform to the result of calculation of frequency field, just can the result of calculation in acquisition time territory.D in formula differentiates, and p is function and the letter that is not particularly illustrated, because be general implication, therefore just do not provide and specifically illustrates.

For single wire cable, the inductance L of its unit length ₀, electric capacity C ₀be calculated as follows:

$L_0=\frac{{\mathrm{\μ}}_0}{2\mathrm{\π}}ln\frac{2h}{a}---\left(10\right)$

$C_0=\frac{2{\mathrm{\π\ϵ}}_0}{ln(2h/a)}---\left(11\right)$

Wherein, h is cable distance floor level, and a is Cable radius, μ ₀for permeability of vacuum, ε ₀for permittivity of vacuum,

Characteristic impedance calculating formula is:

$Z_0=\sqrt{\frac{L_0}{C_0}}---\left(12\right)$

For above-mentioned solution procedure, Matlab is utilized to write corresponding solver, when carrying out initial parameter input in Matlab program, outbalance be determine sample frequency and sampling number, the determination of sample frequency need meet sampling thheorem, in order to improve computing velocity, directly adopt Fast Fourier Transform (FFT) (FFT) in program, sampling number is taken as the power side of 2.

In the process solved, the parameters such as length of cable, height off the ground, Cable radius, ground conductivity, relative dielectric constant all have impact for the current/voltage result on cable.

By writing Matlab simulated program, each parameter is analyzed the impact of current/voltage on line, research finds: Cable radius, ground conductivity, relative dielectric constant are less for the impact of the current/voltage on line, and topmost influence factor is length of cable and height off the ground.

(3) required protection Design index is determined.

The rise time being subject to couple current waveform when nuclear electromagnetic disturbs according to power lead is about 10ns, and peak value is less than 500A; Its protection index is: inflow-rate of water turbine is 1000A, and the response time is ns level, and insertion loss is greater than 30dB; According to above-mentioned parameter, carry out the test of MIL-188-125 according to testing standard, the protection index according to testing standard and simulation result determination power-supply filter is: inflow-rate of water turbine is 1000A, and the response time is ns level, and insertion loss is greater than 30dB;

(4) select suitable filtering circuit and determine required filter element.

Fig. 5 gives filter circuit figure, and select the TVS pipe of two 5KP36CA to protect as one-level in filtering circuit, two 5KP36CA are connected in series in output terminal, are connected in series a connecting to neutral current potential; When the high energy impact events of moment is stood at TVS pipe two ends; at a terrific speed the resistance value between two ends can be become Low ESR from high impedance; thus absorb the big current of moment; the most at last its both end voltage be clamped at one numerically predetermined, to protect circuit component below by the impact of high voltage transient spike.Two 22nF electric capacity are connected in series, connecting to neutral current potential between two 22nF electric capacity electric connection points at output terminal; Two the 22nF electric capacity two ends be connected in series and two TVS pipe be connected in series are connected in parallel.

Consider in circuit design have certain nargin, select voltage dependent resistor (VDR) to protect as secondary.As shown in Figure 5, have two voltage dependent resistor (VDR)s of serial connection at input end, two voltage dependent resistor (VDR)s be connected in series a connecting to neutral current potential.Voltage dependent resistor (VDR) is when resting state, for shielded electronic package, there is very high impedance (number megohm) and the circuit characteristic of former design can not be changed, but when moment surge voltage appearance (when exceeding the disruptive voltage of voltage dependent resistor (VDR)), the impedance of this voltage dependent resistor (VDR) is understood step-down (only having several ohm) and causes former line short; Therefore electronic product or assembly are protected.

Steady-state circuit, according to normal power supplies anti-emi filter, namely designs by the method for designing of electromagnetic interface filter: corresponding electron device is a 1 μ F electric capacity and two 22nF electric capacity in Fig. 5, and two couples of 5mH and 30 μ H inductance.Wherein 1 μ F electric capacity is used for filtering low frequency differential mode electromagnetic interference (EMI), and two couples of 5mH and 30 μ H inductance are used for filtering low frequency common electromagnetic interference (EMI), and two 22nF electric capacity are used for filtering high frequency differential mode and common mode electromagnetic interference (EMI).

(5) whether emulated filter insertion loss meets design objective.

The insertion loss of wave filter is divided into common and different mode two kinds of forms, and its Filtering Simulation result respectively as shown in Figure 6 and Figure 7.Visible, designed anti-nuclear electromagnetic pulse power line filter, its Common Mode insertion loss can reach 70dB, and Differential Mode insertion loss is close to 30dB.Meet design objective.

(6) meet design objective, can circuit output be carried out; Otherwise, return to the design that (4) carry out filtering circuit, until meet the demands.

In the present invention, the design of anti-nuclear electromagnetic pulse power line filter is divided into two parts: transient state suppresses part and stable state to suppress part.Transient state suppresses the main nuclear electromagnetic pulse that suppressor pulse amplitude is large, the rise time is short of part, relies on transient suppression device to complete; Steady-state portion mainly suppresses that the amplitude entering electrical network is little, rise time ordinary electromagnetic interference slowly, realizes by conventional power source filtering device.

1. transient state suppresses the method for designing of part

Conventional transient suppression device mainly contains gas-discharge tube (GDT), voltage dependent resistor (VDR) (MOV) and Transient Suppression Diode (TVS).Such device and protected circuit in parallel, release to ground with the macro-energy of the mode of bypass by moment.

The inside of gas-discharge tube is filled with certain inert gas, and during without surge voltage, its impedance is very large, cannot conducting.Once surge voltage invades, the gas in pipe ionizes, and creates free electron and positive ion, and now discharge tube just can conducting.Voltage drop in pipe thereupon, equipment both end voltage just can reduce, and provides leadage circuit like this to surge voltage, most transient energy is transferred, thus proterctive equipment is from the damage of overvoltage surge.

Voltage dependent resistor (VDR) is also called metal oxide varistor, is a kind of voltage-sensitive device, is use maximum peak restrained elements in current electronic product.It is a kind of nonlinear element, and when being in the prebreakdown district of low-voltage, its volt-ampere characteristic, by extraneous heat shock transmitter current effect control, shows as the high resistant resistance of current saturation, i.e. the resistance value of voltage dependent resistor (VDR); Once after voltage exceeded certain certain value, its volt-ampere characteristic enters breakdown region, and the conductive mechanism of heat shock transmitter current does not play a major role, what play a decisive role for it is tunnelling current conductive mechanism, and resistance value sharply can diminish along with the increase of voltage.

Transient Suppression Diode is a kind of Clamp transient suppression device.When the high energy impact events of moment is stood at its two ends; at a terrific speed the resistance value between two ends can be become Low ESR from high impedance; thus absorb the big current of moment; the most at last its both end voltage be clamped at one numerically predetermined, to protect circuit component below by the impact of high voltage transient spike.

The characteristic of three kinds of devices is as shown in table 1, and from the response time, the response time of TVS pipe is the shortest, and its response time is less than the rise time of nuclear electromagnetic pulse, therefore can be used in the protection of nuclear electromagnetic pulse.Usually TVS pipe is protected as one-level; The power capacity of voltage dependent resistor (VDR) is comparatively large, can be used for secondary protection.

When choosing transient suppression device, will on the basis of transient suppression device characteristic, in conjunction with the current amplitude that the line that emulation obtains is coupled and rising edge, determine two principles of suppression device demand fulfillment: the response time of device is less than the rise time of electric current/voltage waveform on line; The through-current capacity of device is greater than the maximal value of couple current on line.For power lead, substantially do not need to consider that the junction capacity size of device is on the impact of signal transmission on line, therefore just can determine selected required transient suppression device according to these two principles, complete the design of transient portion thereof.

Transient protective device property commonly used by table 1

Claims (3)

1. a power line filter method for designing for anti-nuclear electromagnetic pulse, is characterized in that: at least comprise the steps:

(1) nuclear electromagnetic pulse interference is simulated using double-exponential function as model, and its field intensity expression formula is as follows:

E(t)＝E ₀·k·(e ^-αt-e ^-βt)(1)

In formula, E ₀=5 × 10 ⁴v/m, k=1.3, α=4 × 10 ⁷/ s, β=6 × 10 ⁸/ s;

(2) the maximum coupling magnitude of interference source on power cable is calculated according to step (1);

Nuclear electromagnetic pulse gets transmission line model to long conductor coupling, and namely utilize Agrawal mathematical model, its second order differential equation is:

$\left\{\begin{array}{c}\frac{d^{2}V}{dz}-{\mathrm{\γ}}^{2}V=\frac{{\mathrm{dE}}_z}{dz}\\ \frac{dI}{dz}-{\mathrm{\γ}}^{2}I=-{\mathrm{YE}}_z\end{array}\right.---\left(2\right)$

Wherein, V is scattering voltage, E _zfor arriving the field intensity of cable, z is along cable direction coordinate, and I is along transmission line choke, γ ²=ZY, Z, Y are respectively transmission line unit length impedance over the ground and admittance;

The second order differential equation of couple current on line, its form of separating comprises general solution and particular solution two parts;

General solution is

I(z)＝K ₁e ^-γz+K ₂e ^γz(3)

Particular solution is

$I^{*}\left(z\right)=\frac{1}{2Z_0}{\∫}_{z_1}^z{E}_z{e}^{\mathrm{\γ}v}dv\·e^{-\mathrm{\γ}z}+\frac{1}{2Z_0}{\∫}_z^{z_2}{E}_z{e}^{-\mathrm{\γ}v}dv\·e^{\mathrm{\γ}z}---\left(4\right)$

Order $P\left(z\right)=\frac{1}{2Z_0}{\∫}_{z_1}^z{e}^{\mathrm{\γ}\mathrm{\υ}}{E}_{z}d\mathrm{\υ},Q\left(z\right)=\frac{1}{2Z_0}{\∫}_z^{z_2}{e}^{-\mathrm{\γ}\mathrm{\υ}}{E}_{z}d\mathrm{\υ},$ Obtaining electric current on line is

$I_z\left(\mathrm{\ω}\right)=\[K_1+P\left(z\right)\]e^{-\mathrm{\γ}z}+\[K_2+Q\left(z\right)\]e^{\mathrm{\γ}z}---\left(5\right)$

Wherein

$K_1={\mathrm{\Γ}}_1{e}^{{\mathrm{\γz}}_1}\frac{{\mathrm{\Γ}}_{2}P\left(z_2\right)e^{-{\mathrm{\γz}}_2}-Q\left(z_1\right)e^{{\mathrm{\γz}}_2}}{e^{\mathrm{\γ}(z_2-z_1)}-{\mathrm{\Γ}}_1{\mathrm{\Γ}}_2{e}^{-\mathrm{\γ}(z_2-z_1)}}---\left(6\right)$

$K_2={\mathrm{\Γ}}_2{e}^{{\mathrm{\γz}}_2}\frac{{\mathrm{\Γ}}_{1}P\left(z_1\right)e^{-{\mathrm{\γz}}_1}-Q\left(z_2\right)e^{{\mathrm{\γz}}_1}}{e^{\mathrm{\γ}(z_2-z_1)}-{\mathrm{\Γ}}_1{\mathrm{\Γ}}_2{e}^{-\mathrm{\γ}(z_2-z_1)}}---\left(7\right)$

Γ ₁, Γ ₂the reflection coefficient of terminal,

${\mathrm{\Γ}}_1=\frac{Z_1-Z_0}{Z_1+Z_0}---\left(8\right)$

${\mathrm{\Γ}}_2=\frac{Z_2-Z_0}{Z_2+Z_0}---\left(9\right)$

In formula, Z ₁for source termination impedance, Z ₂for load end impedance, Z ₀for the characteristic impedance of transmission line;

For single wire cable, inductance, the capacitance calculation of its unit length are as follows:

$L_0=\frac{{\mathrm{\μ}}_0}{2\mathrm{\π}}ln\frac{2h}{a}---\left(10\right)$

$C_0=\frac{2{\mathrm{\π\ϵ}}_0}{ln(2h/a)}---\left(11\right)$

Wherein, h is cable distance floor level, and a is Cable radius, μ ₀for permeability of vacuum, ε ₀for permittivity of vacuum,

Characteristic impedance Z ₀calculating formula is:

$Z_0=\sqrt{\frac{L_0}{C_0}};---\left(12\right)$

(3) according to the result of step (2), determine to protect index;

(4) Choose filtering circuit, determines filter element needed for filtering circuit;

(5) whether filter insertion loss meets design objective; Meet design objective, can circuit output be carried out; Otherwise, return step (4) and redefine filter element needed for filtering circuit; Until meet the demands.

2. the power line filter method for designing of a kind of anti-nuclear electromagnetic pulse according to claim 1, it is characterized in that: the TVS pipe that the described filtering circuit described in step (4) comprises two 5KP36CA is protected as one-level, two 5KP36CA are connected in series in output terminal, be connected in series a connecting to neutral current potential, two 22nF electric capacity are connected in series, connecting to neutral current potential between two 22nF electric capacity electric connection points at output terminal, two the 22nF electric capacity two ends be connected in series and two TVS pipe be connected in series are connected in parallel, also be included in two voltage dependent resistor (VDR)s that input end has serial connection, two voltage dependent resistor (VDR)s be connected in series a connecting to neutral current potential, 1 μ F electric capacity is had with input end, 1 μ F electric capacity is in parallel with two the voltage dependent resistor (VDR) two ends be connected in series, between a 1 μ F electric capacity and two 22nF electric capacity, comprise a pair 5mH in positive loop and a pair 5mH in 30 μ H inductance and negative loop and 30 μ H inductance, wherein 1 μ F electric capacity is used for filtering low frequency differential mode electromagnetic interference (EMI), two couples of 5mH and 30 μ H inductance are used for filtering low frequency common electromagnetic interference (EMI), two 22nF electric capacity are used for filtering high frequency differential mode and common mode electromagnetic interference (EMI).

3. the power line filter method for designing of a kind of anti-nuclear electromagnetic pulse according to claim 1, is characterized in that: in described step (3), and protection index is: inflow-rate of water turbine is 1000A, and the response time is ns level, and insertion loss is greater than 30dB.