CN103913652A - Steady-state iteration measuring method for current-carrying capacity of cable - Google Patents

Abstract

The invention discloses a steady-state iteration measuring method for the current-carrying capacity of a cable, which comprises the following steps: measuring the skin temperature of the cable and the environmental temperature of the cable; and obtaining initial cable environment thermal resistance according to the cable skin temperature and the cable environment temperature, and calculating the current-carrying capacity of the cable by using an iteration method. The steady-state iteration measurement method for the current-carrying capacity of the cable measures the skin temperature of the cable and the environmental temperature of the cable, and then calculates the current-carrying capacity of the cable by an iteration method according to the two measured temperatures, wherein the calculation of thermal resistance is involved in the calculation of the current-carrying capacity of the cable, the calculation of the thermal resistance comprises the internal thermal resistance of the cable and the environmental thermal resistance, the environmental thermal resistance is changed along with the change of the load of the cable, and the iteration method is used for taking the change of the environmental thermal resistance into account, so that the calculation error of the current-carrying.

Description

The stable state iteration assay method of current-carrying capacity of cable

Technical field

The present invention relates to a kind of assay method of current-carrying capacity of cable, especially a kind of stable state iteration assay method of current-carrying capacity of cable, belongs to power technology field.

Background technology

Current-carrying capacity of cable is an important parameter in cable line, and the accurate Calculation of current-carrying capacity of cable has important directive function for the design department of cable and the operation department of cable, significant to the safe operation of whole electric system.

At present, the method for determining current-carrying capacity is generally to calculate according to IEC60287, IEC60853 standard.The current-carrying capacity obtaining by IEC standard, nargin is excessive larger with the actual current-carrying capacity phase ratio error of cable, take IEC60287 standard as example, environment is reduced to single uniformly transfer heat medium by this standard, in fact cable is in operation to generate heat surrounding environment is changed, make error calculated very large, the current-carrying capacity obtaining is inaccurate.

Current-carrying capacity of cable relates to the calculating of thermal resistance while calculating, comprise cable internal thermal resistance and environment thermal resistance, and environment thermal resistance changes along with the variation of cable load, and environment thermal resistance is considered as a constant by current computing method, makes the error of calculation have certain error.

Summary of the invention

The object of the invention is the defect in order to solve above-mentioned prior art, a kind of stable state iteration assay method of accurate and effective current-carrying capacity of cable is provided.

Object of the present invention can be by taking following technical scheme to reach:

The stable state iteration assay method of current-carrying capacity of cable, is characterized in that described method comprises: measure cable skin temperature and wireline environment temperature; According to cable skin temperature and wireline environment temperature, obtain initial wireline environment thermal resistance, and utilize process of iteration to calculate the current-carrying capacity of cable.

As a kind of preferred version, described method concrete steps are as follows:

1) measure cable skin temperature T ₀with wireline environment temperature T _x, obtain cable conductor electric current initial value I and cable resistance initial value R simultaneously;

2) utilize step 1) the cable skin temperature T that obtains ₀, wireline environment temperature T _x, cable conductor electric current initial value I and cable resistance initial value R calculate initial wireline environment thermal resistance R _x, be the wireline environment thermal resistance of the 1st time, be shown below:

$R_x=\frac{T_0-T_x}{I^{2}R}$

3) set up cable Re road model, obtain thermal resistance and the temperature of each hierarchy according to IEC60287, IEC60853 standard;

4) utilize process of iteration to calculate current-carrying capacity of cable

4.1) adopt following formula to calculate current-carrying capacity of cable value:

In formula, I _max(k) be the current-carrying capacity of cable value of the k time; T ₁for cable conductor temperature, 90 degrees Celsius of values; T ₀(k) be the cable skin temperature of the k time; T _x(k) be the wireline environment temperature of the k time, T _x(k)=T _x; R ₉₀resistance during for 90 degrees Celsius, cable; R _x(k) be the wireline environment thermal resistance of the k time; R _nfor protective coverings of cable thermal resistance; R _heat=R ₁λ ₁+ R ₂(λ ₁+ λ ₂)+... R _n-1(λ ₁+ λ ₂+ ...+λ _n-1), R ₁, R ₂..., R _n-1represent that respectively the thermal resistance, conductor of cable internal shield are to the thermal resistance of the each distribution layer of epidermis, λ ₁, λ ₂..., λ _n-1represent respectively the ratio between quantity of heat production and the quantity of heat production of cable conductor of each layer of cable; Wherein, k>=1;

4.2) if k=1 directly performs step 4.3); If k>1, by step 4.1) the current-carrying capacity of cable value and the last current-carrying capacity of cable value comparison of calculating that obtain, obtain the relative error of current-carrying capacity, if relative error is greater than threshold value δ %, execution step 4.3); If relative error is less than or equal to threshold value δ %, the current-carrying value that this time calculated is as current-carrying capacity of cable;

4.3) by step 4.1) the current-carrying capacity of cable value that obtains calculates cable skin temperature value and wireline environment temperature next time, then adopts following formula to calculate wireline environment thermal resistance:

$R_x(k+1)=\frac{T_0(k+1)-T_x\left(k\right)}{I_{\max }{\left(k\right)}^2{R}_{90}}$

In formula, I _max(k) be the current-carrying capacity of cable value of the k time, T ₀(k+1) be the cable skin temperature of the k+1 time, T _x(k) be the wireline environment temperature of the k time, R ₉₀resistance during for 90 degrees Celsius, cable, R _x(k+1) be the wireline environment thermal resistance of the k+1 time; Wherein, k>=1;

4.4) return to step 4.1), by step 4.3) the cable skin temperature value that obtains and wireline environment thermal resistance substitution current-carrying capacity of cable value calculate formula and calculate.

As a kind of preferred version, step 4.2) described by step 4.1) the current-carrying capacity of cable value obtaining and the current-carrying capacity of cable value comparison of last calculating, the relative error that obtains current-carrying capacity is wherein, k>=2.

As a kind of preferred version, the value of described threshold value δ % is 5%.

As a kind of preferred version, described cable skin temperature and wireline environment temperature adopt respectively the first thermopair and the second thermopair to measure.

The present invention has following beneficial effect with respect to prior art:

The stable state iteration assay method of current-carrying capacity of cable of the present invention is by measuring cable skin temperature and wireline environment temperature, utilize process of iteration to calculate the current-carrying capacity of cable according to the temperature of these two measurements again, current-carrying capacity of cable relates to the calculating of thermal resistance while calculating, comprise cable internal thermal resistance and environment thermal resistance, environment thermal resistance changes along with the variation of cable load, use process of iteration that the variation of environment thermal resistance is taken into account, can make the error of calculation of current-carrying capacity of cable less.

Accompanying drawing explanation

Fig. 1 is the schematic flow sheet of the stable state iteration assay method of current-carrying capacity of cable of the present invention.

Fig. 2 is the cable point for measuring temperature schematic diagram of the stable state iteration assay method of current-carrying capacity of cable of the present invention.

Fig. 3 is the hot road of the cable model structure schematic diagram of the stable state iteration assay method of current-carrying capacity of cable of the present invention.

Embodiment

Embodiment 1:

As shown in Figure 1, the stable state iteration assay method of the current-carrying capacity of cable of the present embodiment comprises the following steps:

1) point for measuring temperature as shown in Figure 2, adopts the first thermopair and the second thermopair to measure respectively cable skin temperature T ₀with wireline environment temperature T _x, obtain cable conductor electric current initial value I and cable resistance initial value R simultaneously;

2) utilize step 1) the cable skin temperature T that obtains ₀, wireline environment temperature T _x, cable conductor electric current initial value I and cable resistance initial value R calculate initial wireline environment thermal resistance R _x, be the wireline environment thermal resistance of the 1st time, be shown below:

$R_x=\frac{T_0-T_x}{I^{2}R}---\left(1\right)$

3) set up cable Re road model, model structure schematic diagram is by carrying out layering shown in Fig. 3, in Fig. 2, and T ₁, T ₂..., T _n-1, T ₀, T _xrepresent that respectively the temperature, conductor of cable conductor are to temperature, the temperature of epidermis and the temperature of wireline environment of the each distribution layer of epidermis, R ₁, R ₂..., R _n-1, R _n, R _xrepresent that respectively the thermal resistance, conductor of cable internal shield are to the thermal resistance of thermal resistance, outer jacket thermal resistance and the wireline environment of the each distribution layer of epidermis, Q ₁, Q ₂..., Q _n-1, Q _nrepresent that respectively the quantity of heat production, conductor of cable conductor are to the quantity of heat production of the each distribution layer of epidermis and the quantity of heat production of outer jacket, wherein T ₁, T ₂..., T _n-1and R ₁, R ₂..., R _n-1, R _n, can obtain according to IEC60287, IEC60853 standard; According to the relation between thermal resistance, temperature and quantity of heat production, can be obtained by Fig. 2:

$\left\{\begin{array}{c}\frac{T_n-T_0}{R_n}=\frac{T_0-T_x}{R_x}\\ \frac{T_{n-1}-T_n}{R_{n-1}}=Q_1+Q_2+...+Q_{n-1}\\ \frac{T_{n-1}-T_{n-1}}{R_{n-1}}=Q_1+Q_2+...+Q_{n-1}\\ ...\\ \frac{T_1+T_2}{R_2}=Q_1\end{array}\right.---\left(2\right)$

Formula group (2) abbreviation is obtained

$\left\{\begin{array}{c}{T}_n-T_0=\frac{R_n(T_0-T_x)}{R_x}\\ T_{n-1}-T_n=R_{n-1}(Q_1+Q_2+...+Q_{n-1})\\ T_{n-2}-T_{n-1}=R_{n-2}(Q_1+Q_2+...+Q_{n-2})\\ ...\\ T_1-T_2=R_1{Q}_1\end{array}\right.---\left(3\right)$

N formula both sides in formula group (3) are added, obtain

$T_1-T_0=\frac{R_n(T_o-T_x)}{R_x}+R_1{Q}_1+R_2(Q_1+Q_2)+...R_{n-1}(Q_1+Q_2+...+Q_{n-1})---\left(4\right)$

Make the quantity of heat production of each layer and the ratio of conductor quantity of heat production be respectively λ ₁, λ ₂..., λ _n-1, above formula abbreviation is

$T_1=T_0+\frac{R_n(T_0-T_x)}{R_x}+Q_1[R_1{\mathrm{\λ}}_1+R_2({\mathrm{\λ}}_1+{\mathrm{\λ}}_2)+...R_{n-1}({\mathrm{\λ}}_1+{\mathrm{\λ}}_2+...+{\mathrm{\λ}}_{n-1})]---\left(5\right)$

Note R _heat=R ₁λ ₁+ R ₂(λ ₁+ λ ₂)+... R _n-1(λ ₁+ λ ₂+ ...+λ _n-1), be further reduced to

Will bring formula (6) into,

In formula, I _maxfor current-carrying capacity of cable value; T ₁for cable conductor temperature, 90 degrees Celsius of values; R ₉₀resistance during for 90 degrees Celsius, cable;

4) utilize process of iteration to calculate current-carrying capacity of cable

4.1) through type (7) conversion obtains following formula and calculates current-carrying capacity of cable value:

In formula, I _max(k) be the current-carrying capacity of cable value of the k time; T ₀(k) be the cable skin temperature of the k time; T _x(k) be the wireline environment temperature of the k time, T _x(k)=T _x; R _x(k) be the wireline environment thermal resistance of the k time; R _nfor protective coverings of cable thermal resistance; Wherein, k>=1;

4.2) if k=1 directly performs step 4.3); If k>1, by step 4.1) the current-carrying capacity of cable value and the last current-carrying capacity of cable value comparison of calculating that obtain, obtain the relative error of current-carrying capacity if relative error is greater than threshold value δ %, be expressed as execution step 4.3); If relative error is less than or equal to threshold value δ %, be expressed as the current-carrying value that this time calculated is as current-carrying capacity of cable; Wherein, the value of described threshold value δ % is 5%;

4.3) by step 4.1) obtain current-carrying capacity of cable value calculate cable skin temperature value next time, employing formula (8) is carried out inverse operation, as shown in the formula:

$T_0(k+1)=T_x\left(k\right)+I_{\max }^2\left(k\right)R_{90}{R}_x\left(k\right)---\left(9\right)$

Adopt again following formula to calculate wireline environment thermal resistance:

$R_x(k+1)=\frac{T_0(k+1)-T_x\left(k\right)}{I_{\max }{\left(k\right)}^2{R}_{90}}---\left(10\right)$

In formula, I _max(k) be the current-carrying capacity of cable value of the k time, T ₀(k+1) be the cable skin temperature of the k+1 time, the wireline environment temperature that Tx (k) is the k time, R ₉₀resistance during for 90 degrees Celsius, cable, R _x(k+1) be the wireline environment thermal resistance of the k+1 time; Wherein, k>=1.

4.4) return to step 4.1), by step 4.3) the cable skin temperature value and the wireline environment thermal resistance substitution formula (8) that obtain calculate.

In sum, the stable state iteration assay method of current-carrying capacity of cable of the present invention is by measuring cable skin temperature and wireline environment temperature, utilize process of iteration to calculate the current-carrying capacity of cable according to the temperature of these two measurements again, current-carrying capacity of cable relates to the calculating of thermal resistance while calculating, comprise cable internal thermal resistance and environment thermal resistance, environment thermal resistance changes along with the variation of cable load, uses process of iteration that the variation of environment thermal resistance is taken into account, can make the error of calculation of current-carrying capacity of cable less.

The above; it is only patent preferred embodiment of the present invention; but the protection domain of patent of the present invention is not limited to this; anyly be familiar with those skilled in the art in the disclosed scope of patent of the present invention; according to the present invention, the technical scheme of patent and inventive concept thereof are equal to replacement or are changed, and all belong to the protection domain of patent of the present invention.

Claims (5)

1. the stable state iteration assay method of current-carrying capacity of cable, is characterized in that described method comprises: measure cable skin temperature and wireline environment temperature; According to cable skin temperature and wireline environment temperature, obtain initial wireline environment thermal resistance, and utilize process of iteration to calculate the current-carrying capacity of cable.

2. the stable state iteration assay method of current-carrying capacity of cable according to claim 2, is characterized in that described method concrete steps are as follows:

1) measure cable skin temperature T ₀with wireline environment temperature T _x, obtain cable conductor electric current initial value I and cable resistance initial value R simultaneously;

2) utilize step 1) the cable skin temperature T that obtains ₀, wireline environment temperature T _x, cable conductor electric current initial value I and cable resistance initial value R calculate initial wireline environment thermal resistance R _x, be the wireline environment thermal resistance of the 1st time, be shown below:

$R_x=\frac{T_0-T_x}{I^{2}R}$

3) set up cable Re road model, obtain thermal resistance and the temperature of each hierarchy according to IEC60287, IEC60853 standard;

4) utilize process of iteration to calculate current-carrying capacity of cable

4.1) adopt following formula to calculate current-carrying capacity of cable value:

In formula, I _{pin x}(k) be the current-carrying capacity of cable value of the k time; T ₁for cable conductor temperature, 90 degrees Celsius of values; T ₀(k) be the cable skin temperature of the k time; T _x(k) be the wireline environment temperature of the k time, T _x(k)=T _x; R ₉₀resistance during for 90 degrees Celsius, cable; R _x(k) be the wireline environment thermal resistance of the k time; R _nfor protective coverings of cable thermal resistance; R _heat=R ₁λ ₁+ R ₂(λ ₁+ λ ₂)+... R _n-1(λ ₁+ λ ₂+ ...+λ _n-1), R ₁, R ₂..., R _n-1represent that respectively the thermal resistance, conductor of cable internal shield are to the thermal resistance of the each distribution layer of epidermis, λ ₁, λ ₂..., λ _n-1represent respectively the ratio between quantity of heat production and the quantity of heat production of cable conductor of each layer of cable; Wherein, k>=1;

4.2) if k=1 directly performs step 4.3); If k>1, by step 4.1) the current-carrying capacity of cable value and the last current-carrying capacity of cable value comparison of calculating that obtain, obtain the relative error of current-carrying capacity, if relative error is greater than threshold value δ %, execution step 4.3); If relative error is less than or equal to threshold value δ %, the current-carrying value that this time calculated is as current-carrying capacity of cable;

4.3) by step 4.1) the current-carrying capacity of cable value that obtains calculates cable skin temperature value and wireline environment temperature next time, then adopts following formula to calculate wireline environment thermal resistance:

$R_x(k+1)=\frac{T_0(k+1)-T_x\left(k\right)}{I_{\max }{\left(k\right)}^2{R}_{90}}$

In formula, I _max(k) be the current-carrying capacity of cable value of the k time, T ₀(k+1) be the cable skin temperature of the k+1 time, T _x(k) be the wireline environment temperature of the k time, R ₉₀resistance during for 90 degrees Celsius, cable, R _x(k+1) be the wireline environment thermal resistance of the k+1 time; Wherein, k>=1;

4.4) return to step 4.1), by step 4.3) the cable skin temperature value that obtains and wireline environment thermal resistance substitution current-carrying capacity of cable value calculate formula and calculate.

3. the stable state iteration assay method of current-carrying capacity of cable according to claim 2, it is characterized in that: step 4.2) described by step 4.1) the current-carrying capacity of cable value obtaining and the current-carrying capacity of cable value comparison of last calculating, the relative error that obtains current-carrying capacity is $\frac{|I_{\max }\left(k\right)-I_{\max (k-1)}|}{\left|I_{\max }(k-1)\right|};$ Wherein, k >=2.

4. according to the stable state iteration assay method of the current-carrying capacity of cable described in claim 2 or 3, it is characterized in that: the value of described threshold value δ % is 5%.

5. the stable state iteration assay method of current-carrying capacity of cable according to claim 1, is characterized in that: described cable skin temperature and wireline environment temperature adopt respectively the first thermopair and the second thermopair to measure.