CN107478954B - A Calculation Method of Corona Loss in UHV System Based on Distributed Parameter Model - Google Patents

Abstract

The invention discloses a kind of methods for calculating ultra-high/extra-high voltage system corona loss based on Transmission Line Distributed Parameter model.The π shape Equivalent Circuit Parameter calculation formula of ultra-high/extra-high voltage long range transmission line of alternation current is first derived by the distributed parameter model of long range transmission line of alternation current, then by accurately considering that the voltage's distribiuting on long transmission line derives the annual corona loss formula in route unit length, and then the corona loss of system is acquired by corona loss power equation.The corona loss value that the method is found out is of great significance to the design, operation and economic analysis of ultra-high/extra-high voltage system closer to actual measured value.

Description

A Calculation Method of Corona Loss in UHV System Based on Distributed Parameter Model

technical field

The invention relates to a method for calculating corona loss of an ultra-ultra-high voltage system based on a distributed parameter model, and belongs to the technical field of power system line loss.

Background technique

In the modern power system, EHV/UHV transmission lines have become the main power grid in my country. For transmission lines with general voltage levels, lumped parameter equivalent circuits can be used. However, the transmission distance of EHV/UHV transmission lines is as long as hundreds of kilometers or even thousands of kilometers. When studying the transmission characteristics of this line, it is necessary to use a distributed parameter model. At this time, if the centralized parameter model is used again, there will be a large deviation .

Due to the high voltage level of EHV/UHV transmission lines, discharges are prone to occur on the surface of the lines, so the corona loss of EH/UHV transmission lines is a phenomenon that cannot be ignored but is very complicated. According to a large number of actual measurement studies, the corona loss of 500KV and above lines is very sensitive to the actual operating voltage of the line, and accounts for a considerable proportion of the total line loss. Therefore, the corona loss should not be ignored when calculating the total line loss of the system.

Contents of the invention

Objective: In order to overcome the deficiencies in the existing calculation methods, the present invention provides a method for calculating corona loss of ultra-high voltage systems based on distributed parameter models.

Technical solution: In order to solve the above-mentioned technical problems, the technical solution adopted in the present invention is:

A method for calculating corona loss of an ultra-high voltage system based on a distributed parameter model, specifically comprising the following steps:

S01: Based on the distributed parameter model of long-distance AC transmission lines, deduce the calculation formula of π-shaped equivalent circuit parameters of ultra-UHV long-distance AC transmission lines;

S02: Deduce the annual average corona loss formula per unit length of the line by accurately considering the voltage distribution on the long line of the UHV system;

S03: Carry out Newton-Raphson iteration based on the corona loss power equation, and then calculate the corona loss on each line and the corona loss of the system.

In step S01, the calculation formula of each parameter of the long line equivalent circuit is derived:

Based on the characteristic impedance of UHV transmission lines:

in: r, x and b are the resistance, reactance and susceptance per unit length of the transmission line, respectively;

Line propagation constant:

in: α and β are attenuation coefficient and phase shift coefficient respectively, and α=|γ|cosθ, β=|γ|sinθ;

Accurately account for the distributed parameter properties of transmission lines:

Where: l is the length of the transmission line;

Set u=αl, v=βl, using hyperbolic function

After derivation and simplification, let

Finally, the parameter calculation formula of the UHV transmission line π-shaped equivalent circuit can be obtained:

In step S02, the annual average corona loss formula on the line unit length is derived:

Under the long-line model of UHV transmission lines, when the voltage and current at the end of the line are known, the calculation formulas for voltage and current at any point along the line are:

in: Respectively represent the voltage and current at the length x from the end of the line; Respectively, the voltage and current at the end of the line;

Then the voltage expression of each point of the long line in the UHV system is:

in: is the voltage at the head end of the line; Z is the impedance of the line;

The calculation formula of corona loss per unit length on sunny day, snowy day and rainy day is:

Among them: P _f , P _s , P _r represent the corona loss (kw/km) on sunny days, snowy days and rainy days per unit length respectively; r _eq represents the equivalent radius of the split wire (cm); E _M is the maximum Field strength (kv/cm); E ₀ is the critical electric field strength (kv/cm) calculated with the Pigram formula;

The surface field strength of the middle phase is:

The surface field strength of the edge phase is:

Among them: n is the number of split wires; r' is the radius of the wire (cm); d is the split distance (cm); Dm is the geometric mean distance (cm); U is the actual operating voltage (kv);

K ₂ =1.03K ₁ /1.1;

The Pique formula is expressed as:

Among them: m ₁ is the surface roughness coefficient of the wire; m ₂ is the meteorological coefficient; δ is the relative density of the air;

If T _f is a good day in a year, T _s is a snowy day, and T _r is a rainy day, at the same time, t+1 points are evenly generated in the line, and the voltage of each point from the beginning to the end is U ₁ , U ₂ ,..., U _t+1 , then the corona loss of the line is the sum of the corona losses of t small line segments, the actual operating voltage of the small line segment is expressed as the average voltage of the head end and the end of the segment, and the two n and m lines in the line The annual mean value of corona loss per unit length of the small line segment between points is:

Among them, U _n and U _m are the voltages of two points n and m in the line respectively;

Then the annual average value of corona loss per unit length of the line is:

In step S03, the corona loss on each line and the corona loss of the system are obtained:

In order to simplify the calculation, the corona loss of the line is divided into two equal parts and suspended at both ends of the transmission line, which is considered as "active load". For an N-node system, the power equation of node i is derived as :

Will Y _ij ＝G _ij +jB _ij is substituted to get:

Among them: P _i is the injected active power of PQ and PV nodes; Q _i is the injected reactive power of PQ node; G _ij and B _ij are branch conductance and susceptance respectively; θ _ij is the voltage between nodes i and j Phase angle difference; l _ij is the length of line ij; U _i and U _j are the voltages of nodes i and j respectively;

The annual average corona loss value P _cij per unit length of each line in the system can be obtained after the iteration of the cow pull method, and then the corona loss P _cij l _ij on each line can be obtained, and finally the corona loss of the system can be obtained by accumulating.

Beneficial effects: The present invention provides a method for calculating the corona loss of ultra-high voltage systems based on distributed parameter models. This calculation method accurately considers the voltage of each point on the line, so the results are more accurate. And the analysis is of great significance.

Description of drawings

Fig. 1 is the eight-node system diagram of the calculation example of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

As shown in Figure 1, the eight-node system includes balance node 5, PV node 6, and the rest are PQ nodes; the system has a total of 5 lines, of which the length of L1, L2, L3, and L4 is 400km, and the length of L5 is 800km ; T _f = 7471h, T _s = 56h, T _r = 1233h, segment number t = 20, air relative density δ = 1, wire roughness coefficient m ₁ = 0.9, m ₂ = 1.0 in fine weather, m ₂ = in snowy weather 0.997, m ₂ =0.993 in rainy days, 500kv line model is 4*LGJ-300, wire radius r'=1.213cm, split distance d=45cm, three phases are arranged horizontally, and the distance between phases is 13m.

In step S01, obtain the value of each parameter of long line equivalent circuit:

R=9.88572Ω, X=109.126Ω, B=0.00321S for lines L1, L2, L3, and L4, and R=16.279Ω, X=199.285Ω, B=0.00673S for line L5.

In step S02, the annual average value of corona loss on the line unit length is obtained:

In step S03, the corona loss on each line and the corona loss of the system are obtained:

In order to simplify the calculation, the corona loss of the line is divided into two equal parts and suspended at both ends of the transmission line, which is considered as "active load". For an N-node system, the power equation of node i is derived as :

Will Y _ij ＝G _ij +jB _ij is substituted to get:

Among them: P _i is the injected active power of PQ and PV nodes; Q _i is the injected reactive power of PQ nodes; l _ij is the length of line ij.

The annual average corona loss value P _cij per unit length of each line in the system can be obtained after the iteration of the Niu pull method, and then the corona loss P _cij l _ij on each line can be obtained: the corona loss on lines L1 and L2 are both 3.55693 MW, the corona loss on lines L3 and L4 are both 3.90702MW, and the corona loss on line L5 is 7.94192MW; finally the corona loss of the system is 22.8698MW. The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications are also possible. It should be regarded as the protection scope of the present invention.

Claims (2)

1. a kind of super extra-high voltage system corona loss calculation method based on distributed parameter model, it is characterised in that: including as follows Step:

S01: the distributed parameter model based on long range transmission line of alternation current derives excess of export extra-high voltage long range transmission line of alternation current π shape Equivalent Circuit Parameter calculation formula；

S02: by accurately considering that the voltage's distribiuting on super extra-high voltage system long transmission line derives that the year in route unit length flat Equal corona loss formula；

S03: Newton-Raphson iteration is carried out based on corona loss power equation, and then finds out the corona loss on every route With the corona loss of system；

The step S01 includes:

Characteristic impedance based on super UHV transmission line:

Wherein:R, x and b be respectively transmission line of electricity resistance per unit length, Reactance and susceptance；

Line propagation constant:

Wherein:α, β are respectively attenuation coefficient and phase coefficient, and α=| γ | cos θ, β=| γ | sin θ；

The accurate characteristics of distributed parameters for considering transmission line of electricity:

Wherein: l is the length of transmission line of electricity；

U=α l, v=β l is enabled, hyperbolic functions are utilizedThrough derivation and Abbreviation enablesIt can must finally surpass UHV transmission line π shape The parameter calculation formula of equivalent circuit:

The step S02 includes:

Under the long wire model of super UHV transmission line, it is known that electricity when line end voltage, electric current, along route arbitrary point Pressure, electric current calculation formula:

Wherein:Respectively indicating away from line end length is voltage, the electric current at x；Respectively line end voltage, Electric current；

The then voltage expression of super extra-high voltage system middle or long line road every bit:

Wherein:For route head end voltage；Z is the impedance of route；B is the susceptance of route；

The first-class day of unit length, snowy day and the corona loss calculation formula of rainy day are as follows:

Wherein: P_f、P_s、P_rRespectively indicate the corona loss in the first-class day of unit length, snowy day and rainy day, unit kw/km；r_eqIt indicates Split conductor equivalent redius, unit cm；E_MFor conductive line surfaces maximum field strength, unit kv/cm；E₀Face for what is calculated with peek's formula Boundary's electric field strength, unit kv/cm；

The surface field strength of middle phase are as follows:

The surface field strength of side phase are as follows:

Wherein: n is split conductor radical；R ' is wire radius, unit cm；D is division spacing, unit cm；Dm is geometric mean distance, Unit cm；U is actual motion voltage, unit kv；

K₂=1.03K₁/1.1；

Peek's formula indicates are as follows:

Wherein: m₁For the conductive line surfaces coefficient of roughness；m₂For meteorological coefficient；δ is the relative density of air；

If setting in 1 year good day as T_f, snowy day T_s, rainy day T_r, while t+1 point is uniformly generated in the line, from head end Every voltage to end is followed successively by U₁、U₂、……、U_t+1, then the corona loss of route is the total of t small line segment corona loss With small line segment actual motion voltage is expressed as the average voltage of this section of head end and end, the small line segment list of n, m point-to-point transmission in route The annual mean of corona loss on bit length are as follows:

Wherein, U_n、U_mThe voltage of n, m two o'clock respectively in route；

The annual mean of corona loss so in route unit length are as follows:

2. a kind of super extra-high voltage system corona loss calculation method based on distributed parameter model according to claim 1, It is characterized by: the step S03 includes:

The corona loss of route is divided into the both ends that equal two parts are suspended on transmission line of electricity, " burden with power " is set as, pushes away Export is for a N node system, the power equation of node i are as follows:

It willY_ij=G_ij+jB_ijIt substitutes into, obtains:

Wherein: P_iFor the injection active power of PQ and PV node；Q_iFor the injection reactive power of PQ node；G_ij、B_ijRespectively prop up Road conductance and susceptance；θ_ijPhase difference of voltage between node i and j；l_ijFor the length of route i-j；U_i、U_jRespectively node i, The voltage of j；

Every route unit length annual corona loss value P of system is obtained after Newton-Raphson approach iteration_cij, and then acquire every Corona loss P on route_cijl_ij, the corona loss of system can be obtained by finally adding up.