CN105552889A - Method for judging current operation mode feasibility of power transmission line - Google Patents

Abstract

The invention discloses a method for judging the current operation mode feasibility of a power transmission line. The method comprises the following steps: building an environmental time-varying parameter discrete state space equation for an active power line loss of the power transmission line; estimating an environmental time-varying parameter by a kalman filtering method; with a present active power loss, a present current and the estimated environmental time-varying parameter of the power transmission line as initial known quantities, when a load of the power transmission line suddenly changes, giving a current operation mode of the power transmission line; estimating an active power loss track of the power transmission line through an active power loss difference equation according to initial values of known active power loss, carrying capacity and environmental time-varying parameter of the power transmission line, so as to obtain an active power loss sequence of the power transmission line, and comparing with the given maximum permissible active power loss of the power transmission line; if the active power loss is smaller than the given maximum permissible active power loss, judging the current operation mode of the power transmission line to be feasible; or else, judging the current operation mode of the power transmission line to be infeasible.

Description

A kind of method judging the electric current operational mode feasibility of transmission line

Technical field

The invention belongs to technical field of power systems, relate to a kind of method judging the electric current operational mode feasibility of transmission line.

Background technology

Transmission line static determinacy value (STR) is the maximum permission current-carrying of conductor determined under given illumination, heat loss through convection and heat loss through radiation condition, usually this value is determined under uptight environmental condition, thus, when actual motion, the true current capacity of its transmission line can not be given full play to.Dynamic Thermal definite value (DynamicThermalRating, DTR) be under basis measures the environmental conditions such as sunshine, wind speed and temperature in real time, determine the maximum permission current-carrying of transmission line, meeting under transmission pressure allowable temperature prerequisite, the transmission capacity of existing conventional line can be improved, contribute to the capability of overload in short-term under raising network load peak and N-1 accident, can postpone or build circuit less, also can reduce the investment of newly-built circuit, Social and economic benef@is remarkable.

The DTR launched around equation of heat balance principle realizes, and need obtain temperature of electric transmission line and environmental parameter.This parameter obtains by building corresponding hardware monitoring device; Also can by existing electric parameters measurement information, adopt method of estimation indirectly to obtain, the latter is referred to as soft DTR and realizes.The core technology of soft DTR is, adopts certain method of estimation to obtain the thermal tracking of temperature of electric transmission line in section continuous time, and then estimates the time-varying parameter of the heat balance differential equation.The method is when estimating temperature, first transmission line resistance is estimated, and then be translated into temperature parameter according to the coupled relation between resistance and temperature, in the process, no matter be that resistance is estimated, or estimation resistance is converted into temperature parameter, very easily affect by error in measurement, and the phenomenon having error to amplify.Thus, make Temperature estimate result be difficult to reach the requirement of common engineering application, have impact on the practical application of soft DTR.

In order to avoid carrying out the error brought when direct estimation and resistance are further converted to temperature of electric transmission line to transmission line resistance, further for the practical application of soft DTR technology provides rational solution, need badly and a kind ofly judge that the method for the electric current operational mode feasibility of transmission line is to judge the electric current operational mode feasibility that transmission line is given, and then obtain under the condition meeting transmission pressure allowable temperature, determine the maximum permission current-carrying of transmission line.

Summary of the invention

Object of the present invention, exactly for solving the problem, proposes a kind of method judging the electric current operational mode feasibility of transmission line.The method limits transmission line maximum temperature, under certain current-carrying condition can be converted into, and the maximum permissible value of transmission line loss; And then, when to environment time-varying uncertainty, transmission line electric current and active power loss can be directly utilized to carry out, avoid and the error brought when direct estimation and resistance are further converted to temperature of electric transmission line is carried out to transmission line resistance, finally determine the maximum permission current-carrying of transmission line under the condition meeting transmission pressure allowable temperature.

For achieving the above object, the present invention adopts following technical scheme:

Judge a method for the electric current operational mode feasibility of transmission line, comprising:

Step (1): according to transmission line resistance and the non-linear relation of temperature and the Equivalent Model of transmission line, set up the environment time-varying parameter separate manufacturing firms equation of transmission line active power line loss;

Step (2): according to the environment time-varying parameter separate manufacturing firms equation of step (1) and the transmission line electric current of transmission route survey and these historical datas of active power loss, adopts kalman filter method to estimate environment time-varying parameter;

Step (3): using the environment time-varying parameter of current time transmission line active power loss, current flow and estimation as initial known quantity, when the load carving transmission line changes suddenly, the electric current operational mode of given transmission line; Described electric current operational mode comprises transmission line and estimates maximum current-carrying, rises to running time when estimating maximum current-carrying by current flow, and transmission line operates in the duration of maximum current-carrying;

Step (4): the initial value of known transmission line active power loss, ampacity and environment time-varying parameter, according to active power loss difference equation, estimate the active power loss track of transmission line, and then obtain transmission line active power loss sequence, and compared with the maximum permission active power loss of given transmission line, if the former is less than the latter, then judge that the electric current operational mode of transmission line is feasible; Otherwise, judge that the electric current operational mode of transmission line is infeasible.

In described step (1), the Equivalent Model of transmission line is transmission line π type equivalent circuit.

In the environment time-varying parameter separate manufacturing firms equation of the middle transmission line active power line loss of described step (1), environment time-varying parameter has Markov characteristic.

In described step (1), the environment time-varying parameter separate manufacturing firms equation of transmission line active power line loss comprises environment time-varying parameter equation and transmission line active power line loss equation;

In environment time-varying parameter equation, the process noise of environment time-varying parameter and current time that the environment time-varying parameter of subsequent time equals current time folds sum;

In transmission line active power line loss equation, the transmission line active power line loss of subsequent time equals the transmission line active power line loss of current time and the measurement noises sum of current time.

Described process noise and measurement noise take equal Gaussian distributed.

The detailed process of environment time-varying parameter is to adopt kalman filter method to estimate in described step (2):

Step (2.1): the environment time-varying parameter of given transmission line and the initial value of evaluated error covariance, and as the current time value of transmission line;

Step (2.2): according to the current time value of transmission line, calculates the subsequent time value of transmission line environment time-varying parameter and evaluated error covariance respectively;

Step (2.3): according to the resistance of transmission line current time, electric current and active power loss, the gain matrix of computing electric power line active power line loss variable quantity, again in conjunction with transmission line electric current and these historical datas of active power loss of transmission route survey, the optimal estimation value of computing environment time-varying parameter subsequent time, and the evaluated error covariance matrix upgrading subsequent time.

When the load carving transmission line changes suddenly as the load of transmission line increases suddenly or reduces in described step (3).

The beneficial effect that the present invention reaches:

(1) the present invention proposes temperature of electric transmission line restriction to be converted into the restriction of maximum active power loss, based on transmission line electric current, active power loss, set up the state space equation following the trail of the change of transmission line active power loss, and according to historical data by kalman filter method estimating system state variable; When estimating that larger change will occur current-carrying, according to the current state of state space equation and system, predicting following transmission line active power change curve, and judging the possibility of the electric current operational mode of transmission line accordingly;

(2) the method for the present invention requires lower to metric data on the one hand, and only need transmission line electric current, two ends active power metric data, nearly all actual track harvester all can obtain these data; On the other hand, the method is avoided estimating transmission line resistance, thus eliminates the adverse effect measuring number error and bring estimation, solves the core technology difficult point in the soft Dynamic Thermal stabilization system of transmission line, for practical application provides rational solution.

Accompanying drawing explanation

Fig. 1 is transmission line π type equivalent circuit diagram of the present invention;

Fig. 2 is the method flow diagram of the electric current operational mode feasibility of judgement transmission line of the present invention;

Fig. 3 is the transmission line active power loss change curve of embodiments of the invention.

Embodiment

Below in conjunction with accompanying drawing and embodiment, the present invention will be further described:

The present invention adopts π type equivalent circuit to be described for the equivalent electric circuit of transmission line, and as shown in Figure 1, wherein, concentrated impedance is made up of resistance R and reactance X its equivalent circuit diagram, and admittance is Y=jB over the ground ₀, wherein B ₀represent susceptance over the ground; P ₁, P ₂be respectively the active power of transmission line branch road 1 and branch road 2; Q ₁, Q ₂be respectively the reactive power of transmission line branch road 1 and branch road 2.

As shown in Figure 2, the method for the electric current operational mode feasibility of judgement transmission line of the present invention, comprising:

Step (1): according to transmission line resistance and the non-linear relation of temperature and the Equivalent Model of transmission line, set up the environment time-varying parameter separate manufacturing firms equation of transmission line active power line loss;

Step (2): according to the environment time-varying parameter separate manufacturing firms equation of step (1) and the transmission line electric current of transmission route survey and these historical datas of active power loss, adopts kalman filter method to estimate environment time-varying parameter;

Step (3): using the environment time-varying parameter of current time transmission line active power loss, current flow and estimation as initial known quantity, when the load carving transmission line changes suddenly, the electric current operational mode of given transmission line; Described electric current operational mode comprises transmission line and estimates maximum current-carrying, rises to running time when estimating maximum current-carrying by current flow, and transmission line operates in the duration of maximum current-carrying;

Step (4): the initial value of known transmission line active power loss, ampacity and environment time-varying parameter, according to active power loss difference equation, estimate the active power loss track of transmission line, and then obtain transmission line active power loss sequence, and compared with the maximum permission active power loss of given transmission line, if the former is less than the latter, then judge that the electric current operational mode of transmission line is feasible; Otherwise, judge that the electric current operational mode of transmission line is infeasible.

Wherein, the theoretical foundation of the environment time-varying parameter separate manufacturing firms establishing equation of the transmission line active power line loss in step (1) is as follows:

Transmission line resistance and temperature relation as follows:

R＝R ₀(1+αΔT)＝R ₀[1+α(T _c-T ₀)](1)

Wherein, T _cfor transmission line actual temperature (DEG C); T ₀for factory settings reference temperature (DEG C); R ₀for the resistance (Ω) of corresponding reference temperature; α is the temperature varying coefficient (1/ DEG C) of corresponding transmission line material, for aluminium, is α=0.0036, for copper, and α=0.00382.

By formula (1), can obtain:

$T_c=\frac{R}{{\mathrm{\αR}}_0}-\frac{1}{\mathrm{\α}}+T_0---\left(2\right)$

In transmission line runs, in the short time, the heating that current-carrying causes can simplify and is expressed as the following differential equation in engineering:

$\frac{d(T_c-T_a)}{dt}={\mathrm{\θ}}_1(T_c-T_a)+{\mathrm{\θ}}_2{I}^2---\left(3\right)$

In formula, θ ₁, θ ₂be environment time-varying parameter, can think in the short time and remain unchanged, T _aatmospheric temperature residing for transmission line, with θ ₁, θ ₂similar, the change within the research period of this parameter is slow.

Formula (2) is substituted into formula (3) can obtain:

$\frac{1}{{\mathrm{\αR}}_0}\frac{dR}{dt}-\frac{{\mathrm{dT}}_a}{dt}={\mathrm{\θ}}_1(\frac{R}{{\mathrm{\αR}}_0}-\frac{1}{\mathrm{\α}}+T_0-T_a)+{\mathrm{\θ}}_2{I}^2---\left(4\right)$

In formula, I is the electric current flowing through transmission line.

Above formula can obtain through abbreviation

$\frac{dR}{dt}={\mathrm{\θ}}_1\[R-R_0+{\mathrm{\αR}}_0(T_0-T_a)\]+{\mathrm{\αR}}_0{\mathrm{\θ}}_2{I}^2+{\mathrm{\αR}}_0\frac{{\mathrm{dT}}_a}{dt}---\left(5\right)$

Comparison expression (3) and formula (5) known, both are equivalences completely at the heating differential equation that expression current-carrying causes, meaning, namely based on the DTR technology of transmission line current-carrying variations in temperature, can be converted into and realize according to transmission line resistance variations track.

Formula (5) is carried out difference, then adjacent moment resistance difference is:

$\begin{array}{c}{\mathrm{\ΔR}}_k={\mathrm{\ΔR}}_{k+1}-{\mathrm{\ΔR}}_k\\ ={\mathrm{\θ}}_1\[R_k-R_0+{\mathrm{\αR}}_0(T_0-T_a)\]\mathrm{\Δ}t+{\mathrm{\αR}}_0{\mathrm{\θ}}_2{I}_k^2\mathrm{\Δ}t+{\mathrm{\αR}}_0{\mathrm{\ΔT}}_a\end{array}---\left(6\right)$

In formula, Δ T _afor the difference of adjacent moment ambient temperature.

To transmission line, its active power loss can be expressed as:

P＝I ²R(7)

If adjacent moment resistance and electric current are respectively:

I _k+1＝I _k+ΔI _k

(8)

R _k+1＝R _k+ΔR _k

According to formula (7), the rate of change of adjacent moment line loss is:

$\begin{array}{c}\frac{{\mathrm{\ΔP}}_k}{\mathrm{\Δ}t}=\frac{P_{k+1}-P_k}{\mathrm{\Δ}t}\\ =I_k^2\frac{{\mathrm{\ΔR}}_k}{\mathrm{\Δ}t}+2I_k{R}_k\frac{{\mathrm{\ΔI}}_k}{\mathrm{\Δ}t}+2\frac{(2I_k{\mathrm{\ΔI}}_k{\mathrm{\ΔR}}_k+{\mathrm{\ΔI}}_k^2{R}_k+{\mathrm{\ΔI}}_k^2{\mathrm{\ΔR}}_k)}{\mathrm{\Δ}t}\\ =I_k^2\frac{{\mathrm{\ΔR}}_k}{\mathrm{\Δ}t}+2P_k\frac{{\mathrm{\ΔI}}_k}{I_k\mathrm{\Δ}t}+\frac{{\mathrm{\Δ\ϵ}}_0}{\mathrm{\Δ}t}\end{array}---\left(9\right)$

Wherein:

${\mathrm{\Δ\ϵ}}_0=2I_k{\mathrm{\ΔI}}_k{\mathrm{\ΔR}}_k+{\mathrm{\ΔI}}_k^2{R}_k+{\mathrm{\ΔI}}_k^2{\mathrm{\ΔR}}_k$

Known, under normal operation, adjacent quarter electric current, resistance variations is minimum, secondary higher order term Δ ε ₀≈ 0.

Formula (6) is substituted into (9):

$\begin{array}{c}\frac{{\mathrm{\ΔP}}_k}{\mathrm{\Δ}t}={\mathrm{\θ}}_1\[P_k-I_k^2{R}_0+{\mathrm{\αI}}_k^2{R}_0{T}_0\]+{\mathrm{\θ}}_2{\mathrm{\αR}}_0{I}_k^4+{\mathrm{\αR}}_0{I}_k^2\frac{{\mathrm{\ΔT}}_a}{\mathrm{\Δ}t}+2P_k\frac{{\mathrm{\ΔI}}_k}{I_k\mathrm{\Δ}t}+\frac{{\mathrm{\Δ\ϵ}}_2}{\mathrm{\Δ}t}\\ =2P_k\frac{{\mathrm{\ΔI}}_k}{I_k\mathrm{\Δ}t}+{\mathrm{\θ}}_1{P}_k+{\mathrm{\θ}}_2{\mathrm{\αR}}_0{I}_k^4+I_k^2{R}_0({\mathrm{\αT}}_0{\mathrm{\θ}}_1-{\mathrm{\θ}}_1+\mathrm{\α}\frac{{\mathrm{\ΔT}}_a}{\mathrm{\Δ}t})+\frac{{\mathrm{\Δ\ϵ}}_0}{\mathrm{\Δ}t}\\ =2P_k\frac{{\mathrm{\ΔI}}_k}{I_k\mathrm{\Δ}t}+{\mathrm{\θ}}_1{P}_k+{\mathrm{\θ}}_2{\mathrm{\αR}}_0{I}_k^4+{\mathrm{\θ}}_3\end{array}---\left(10\right)$

Wherein:

${\mathrm{\θ}}_3=I_k^2{R}_0({\mathrm{\αT}}_0{\mathrm{\θ}}_1-{\mathrm{\θ}}_1+\mathrm{\α}\frac{{\mathrm{\ΔT}}_a}{\mathrm{\Δ}t})+\frac{{\mathrm{\Δ\ϵ}}_0}{\mathrm{\Δ}t}---\left(11\right)$

Due to Δ ε ₀≈ 0, Δ T _a≈ 0, θ ₁slowly, above formula shows θ in change ₃also be a gradual change parameter.

So far, x=[θ can be made ₁θ ₂θ ₃] ^t, each element of state variable, as the parameter of slowly change continuously, has the feature of Markov process.State transition equation can be written as

x(k+1)＝x(k)+ω(k)(12)

In formula, ω (k) is discrete white Gaussian noise.

Order formula (9) can be write as following form

$y_k=\[\begin{array}{ccc}{P}_k& {\mathrm{\αR}}_0{I}_k^4& 1\end{array}\]\left[\begin{array}{c}{\mathrm{\θ}}_1\\ {\mathrm{\θ}}_2\\ {\mathrm{\θ}}_3\end{array}\right]---\left(13\right)$

Convolution (12), the environment time-varying parameter separate manufacturing firms equation obtaining transmission line active power line loss is

$\left\{\begin{array}{c}x(k+1)=x\left(k\right)+\mathrm{\ω}\left(k\right)\\ y\left(k\right)=H\left(k\right)x\left(k\right)+v\left(k\right)\end{array}\right.---\left(14\right)$

In formula, $H\left(k\right)=\[\begin{array}{ccc}{P}_k& {\mathrm{\αR}}_0{I}_k^4& 1\end{array}\];$ K is sampling instant 1,2,3 ...; ω, v are respectively process and measurement noise; P _kfor the active power loss (MW) of k moment transmission line; Δ P _kfor the difference of adjacent moment transmission line active power loss, Δ P _k=P _k+1-P _k; Δ t is sampling interval (S); I _kfor k moment transmission line current-carrying (kA); Δ I _kfor the difference of adjacent moment transmission line ampacity, Δ I _k=I _k+1-I _k; R ₀for transmission line lumped parameter resistance value (Ω) when reference temperature (such as 20 DEG C); α is the temperature varying coefficient (1/ DEG C) of corresponding transmission line material, for aluminium, is α=0.0036, for copper, and α=0.00382.

If process noise Gaussian distributed in formula (14), its covariance matrix is Q, and measurement noise v obeys the Gaussian Profile of (0, σ), suppose that measurement noise does not change in time and changes, then in step (2), the step of Kalman filtering is as follows:

(1) k=0, to the initial condition x of fixed system (0) and evaluated error covariance matrix initial value P (0), this battle array is 3 × 3 square formations;

(2) k=k+1, according to system k-1 moment status predication k moment state

x(k|k-1)＝x(k-1)

(3) estimation error covariance battle array P (k|k-1) is calculated:

P(k|k-1)＝P(k-1)+Q

(4) calculated gains matrix:

$K_g=\frac{P\left(k\right|k-1)H^T\left(k\right)}{H\left(k\right)P\left(k\right|k-1)H^T\left(k\right)+\mathrm{\σ}}$

(5) in conjunction with predicted value and measuring value, the optimal estimation value in computing mode variable k moment:

x(k)＝x(k|k-1)+K _g(k)[y(k)-H(k)x(k|k-1)]

(6) k moment evaluated error covariance matrix is upgraded:

P(k)＝[I-K _gH(k)]P(k|k-1)

In formula, $I=\left[\begin{array}{ccc}1& & \\ & 1& \\ & & 1\end{array}\right].$

In step (3), if the initial moment active power loss of transmission line is P ₀, transmission line initial current is I ₀; In the electric current operational mode of given transmission line, transmission line estimates that maximum current-carrying is I _max.

Be a kind of embodiment in the present invention as shown in Figure 2, select 220kV circuit in Heze Prefecture of Shandong Province to be example, this transmission line parameter r ₀=2.529 Ω, x ₀=15.464 Ω, b ₀=99.583 × 10 ^-6s, t running time risen to when estimating maximum current-carrying by current flow is 30min.

Known transmission line current-carrying I _maxand transmission line maximum resistance R under limiting temperature _max, according to the definition of transmission line active power loss, determine the maximum permission active power loss of transmission line:

$P_{\max }=I_{max}^2{R}_{\max }.$

According to calculating needs, get the SCADA measured data of one day in January, 2013 15:50 ~ 17:30, as shown in table 1, the sampling interval is 5 minutes.

Table 1 transmission line real-time measurement data

Adopt Kalman Filter Technology, state variable estimated result is in table 2.

Table 2 Kalman filtered results

Data display from table 2, each state variable change is slow, and each variate-value can be considered constant at short notice.

Get last moment estimated result x ₀=[0.007-0.47870.0005], P ₀=3.555MW, I ₀=0.75kA is as initial condition, and this transmission line model is LGJ-400, and by maximum permissible temperature 80 DEG C calculating, this transmission line maximum permissible current is 767A.Now transmission line actual current is close to its limiting value.

Assuming that following 30 minutes, this transmission line will bear larger load current, and electric current rose to I in 15 minutes ₀=0.85kA, runs 15 minutes subsequently near 0.85kA.According to relation between line loss, resistance temperature, this transmission line is maximum permission line loss P within this time period _max=6.67MW.

According to step (4), x ₀=[0.007-0.47870.0005], P ₀=3.555MWI ₀=0.75kA, as initial condition, calculates following 30 minutes transmission line active power loss change curves, as shown in Figure 3.

As shown in Figure 3, within half an hour transmission line active power loss along with the increase of electric current be rapid ascendant trend, in current stabilization after 0.85kA, active power loss fluctuates between 4.4 ~ 4.6MW, much smaller than transmission line maximum power loss value P when maximum permissible temperature 80 DEG C _max=6.67MW, although show to be greater than standard to allow current value, short-term operation at 0.85kA, for transmission line still in safe range.

State variable in the present invention all refers to environment time-varying parameter.

By reference to the accompanying drawings the specific embodiment of the present invention is described although above-mentioned; but not limiting the scope of the invention; one of ordinary skill in the art should be understood that; on the basis of technical scheme of the present invention, those skilled in the art do not need to pay various amendment or distortion that creative work can make still within protection scope of the present invention.

Claims (7)

1. judge a method for the electric current operational mode feasibility of transmission line, it is characterized in that, comprising:

Step (1): according to transmission line resistance and the non-linear relation of temperature and the Equivalent Model of transmission line, set up the environment time-varying parameter separate manufacturing firms equation of transmission line active power line loss;

Step (2): according to the environment time-varying parameter separate manufacturing firms equation of step (1) and the transmission line electric current of transmission route survey and these historical datas of active power loss, adopts kalman filter method to estimate environment time-varying parameter;

Step (3): using the environment time-varying parameter of current time transmission line active power loss, current flow and estimation as initial known quantity, when the load carving transmission line changes suddenly, the electric current operational mode of given transmission line; Described electric current operational mode comprises transmission line and estimates maximum current-carrying, rises to running time when estimating maximum current-carrying by current flow, and transmission line operates in the duration of maximum current-carrying;

Step (4): the initial value of known transmission line active power loss, ampacity and environment time-varying parameter, according to active power loss difference equation, estimate the active power loss track of transmission line, and then obtain transmission line active power loss sequence, and compared with the maximum permission active power loss of given transmission line, if the former is less than the latter, then judge that the electric current operational mode of transmission line is feasible; Otherwise, judge that the electric current operational mode of transmission line is infeasible.

2. a kind of method judging the electric current operational mode feasibility of transmission line as claimed in claim 1, is characterized in that, in described step (1), the Equivalent Model of transmission line is transmission line π type equivalent circuit.

3. a kind of method judging the electric current operational mode feasibility of transmission line as claimed in claim 1, it is characterized in that, in the environment time-varying parameter separate manufacturing firms equation of the middle transmission line active power line loss of described step (1), environment time-varying parameter has Markov characteristic.

4. a kind of method judging the electric current operational mode feasibility of transmission line as claimed in claim 1, it is characterized in that, in described step (1), the environment time-varying parameter separate manufacturing firms equation of transmission line active power line loss comprises environment time-varying parameter equation and transmission line active power line loss equation;

In environment time-varying parameter equation, the process noise of environment time-varying parameter and current time that the environment time-varying parameter of subsequent time equals current time folds sum;

In transmission line active power line loss equation, the transmission line active power line loss of subsequent time equals the transmission line active power line loss of current time and the measurement noises sum of current time.

5. a kind of method judging the electric current operational mode feasibility of transmission line as claimed in claim 4, it is characterized in that, described process noise and measurement noise take equal Gaussian distributed.

6. a kind of method judging the electric current operational mode feasibility of transmission line as claimed in claim 5, is characterized in that, the detailed process of environment time-varying parameter is to adopt kalman filter method to estimate in described step (2):

Step (2.1): the environment time-varying parameter of given transmission line and the initial value of evaluated error covariance, and as the current time value of transmission line;

Step (2.2): according to the current time value of transmission line, calculates the subsequent time value of transmission line environment time-varying parameter and evaluated error covariance respectively;

Step (2.3): according to the resistance of transmission line current time, electric current and active power loss, the gain matrix of computing electric power line active power line loss variable quantity, again in conjunction with transmission line electric current and these historical datas of active power loss of transmission route survey, the optimal estimation value of computing environment time-varying parameter subsequent time, and the evaluated error covariance matrix upgrading subsequent time.

7. a kind of method judging the electric current operational mode feasibility of transmission line as claimed in claim 1, is characterized in that, when the load carving transmission line changes suddenly as the load of transmission line increases suddenly or reduces in described step (3).