CN103245429A - Method for measuring skin temperature of three-core cable - Google Patents

Abstract

The invention discloses a method for measuring the skin temperature of a three-core cable, which comprises the following steps: S1 laying a copper ring on the cross-section skin of the three-core cable; S2 laying a temperature-measuring thermocouple on any point of the copper ring to measure the temperature As the temperature of the skin of the three-core cable. The copper ring laid by the present invention can realize the uniform temperature effect of the skin temperature of the loose core cable, can reduce the measurement error caused by the improper selection of the temperature measurement point, can accurately measure the skin temperature of the three-core cable under steady state or transient state, and the measurement process is simple , the measurement result is more accurate.

Description

A Method of Measuring the Skin Temperature of Three-core Cable

technical field

The invention relates to the temperature measurement technology of the cable skin, in particular to a method for measuring the temperature of the three-core cable skin.

Background technique

The measurement accuracy of the conductor temperature of the power cable is the basis for determining the ampacity of the cable line, but there are still technical difficulties in directly measuring the conductor temperature of the cable, especially for the three-core cable. At present, to determine the ampacity of three-core cables, the means of optical fiber temperature measurement is used to accurately measure the outer surface temperature of the power cable line, and then the conductor temperature is determined according to the method provided by the IEC standard to obtain the conductor temperature through the cable outer surface temperature, and then the cable ampacity is determined. .

Nowadays, almost all studies on the calculation of the conductor temperature and the determination of the current carrying capacity of the three-core cable in a steady state are based on the premise that the three-core cable skin is an isothermal surface, ignoring the uneven temperature distribution of the three-core conductor heat sources on the skin. However, in fact, the skin temperature of the three-core cable is not evenly distributed as that of the single-core cable, especially when the high current operation or the laying of multiple cable pipes or cable trenches, the temperature difference of the skin at different points is greater. Therefore, the above-mentioned optical fiber temperature measurement has defects for three-core cables: the temperature-measuring optical fiber is laid at any position on the surface of the cable, but in fact the thermal resistance of the three-core cable in all directions is different, so that the temperature of each point on the surface of the three-core cable is not the same. The reliability of the data measured by optical fiber is limited.

At present, there is no method at home and abroad to solve the large error of the temperature measurement point caused by the uneven temperature distribution of the three-core cable skin. Take one point as the representative temperature measurement point, and then calculate the core temperature according to the IEC standard according to the skin temperature value.

Contents of the invention

In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the object of the present invention is to provide a method for measuring the skin temperature of a three-core cable. The measurement process of the present invention is more direct and the measurement result is more accurate.

The object of the present invention is achieved through the following technical solutions:

A method for measuring the skin temperature of a three-core cable, comprising the steps of:

S1 Lay copper rings on the cross-section skin of the three-core cable;

S2 evenly lay thermocouples on the copper ring;

S3 After the three-core cable runs stably, record the temperature measured by the thermocouple, and calculate its average value, and the average value is the skin temperature of the three-core cable.

There are 3-6 thermocouples.

The thickness of the copper ring is more than or equal to 2mm, and the width is more than or equal to 1cm.

The above-mentioned three-core cable is a three-core cable in a transient state or a steady state.

The above-mentioned three-core cables are three-core cables under any laying method.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) The present invention uses a copper ring to measure temperature. Since the thermal conductivity of copper is very large, the heat dissipation of the cable itself after laying the copper ring has little effect, and it only has a uniform temperature effect on the surface temperature of the cable, which can well reduce the temperature caused by the three-core Errors caused by improper selection of measurement points for uneven cable skin temperature;

(2) After the copper ring is added in the present invention, the temperature of the outermost layer of the three-core cable is equalized, which is more in line with the premise of calculating the conductor temperature according to the IEC standard, and does not conflict with the calculation principle of calculating the core temperature from the skin temperature, and has little influence;

(3) The present invention is especially suitable for three-core cables laid in multiple rows of pipes and cable trenches. Since the three-core cables laid in multiple rows of pipes and cable trenches are in an environment with an external heat source, the skin temperature is more uneven. Ring temperature measurement can well avoid errors caused by improper selection of measurement points;

(4) The temperature measurement method provided by the present invention is direct and reasonable, and its temperature uniformity effect has passed the verification of the experiment. The accuracy of its temperature measurement makes it more reasonable to evaluate the ampacity of the three-core cable, and the dispatching department can more intuitively pass its The temperature measurement data can judge the actual carrying capacity of the cable, and guide the relevant scheduling work in a timely and reasonable manner.

Description of drawings

Figure 1 is a cross-sectional structure diagram of a device for measuring the skin temperature of a three-core cable.

Fig. 2 is a side schematic diagram of a device for measuring the skin temperature of a three-core cable,

Fig. 3 is when the copper ring thickness is 0.5mm in the specific embodiment of the present invention, three-core cable feeds the temperature variation diagram of six temperature measuring points of 200A electric current skin instantaneously from transient state to steady state,

Fig. 4 is when copper ring thickness is 2mm in the specific embodiment of the present invention, and three-core cable passes into 200A electric current epidermis six temperature-measuring points instantaneously from transient state to the temperature change figure of steady state,

Fig. 5 is a graph showing the temperature change from transient state to steady state at six temperature measuring points on the skin of the three-core cable instantaneously passing 200A current when there is no copper ring in the specific embodiment of the present invention.

Detailed ways

The present invention will be described in further detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example

As shown in Figure 1 and Figure 2, a method for measuring the skin temperature of a three-core cable comprises the following steps:

S1 Select any cross-section of the three-core cable, and lay a copper ring 1 with a width of 1 cm and a thickness of 2 mm close to the skin of the cross-section;

S2 evenly lays the thermocouple 2 on the copper ring 1;

S3 allows the three-core cable to run stably at a certain current, and calculates the average value of the temperature measured by the thermocouple 2 after the steady state, and the average value is the temperature of the skin of the three-core cable.

The above-mentioned three-core cable is a three-core cable in a transient state or a steady state.

The above-mentioned three-core cables are three-core cables under any laying method.

The uniform temperature effect of the copper ring of the above method is verified as follows:

In an environment without an external heat source, set three sections of a three-core cable, lay six thermocouples directly on the surface of the first section as temperature measuring points, and lay copper rings and six thermocouples on the skin of the second and third sections. A thermocouple is laid as shown in Figure 1 and Figure 2, but the second section uses a copper ring with a thickness of 0.5mm, and the third section uses a copper ring with a thickness of 2mm, and the width of the copper ring is 1cm.

The other end of each thermocouple is connected to a thermometer, and the temperature data of six temperature measurement points are measured when the three-core cable is supplied with a current of 200A from the moment it reaches a steady state, and the temperature data of the three cross-sectional skins from the transient state to the steady state are obtained. The test data are shown in Figure 3-5.

Comparing the curves of the six temperature measuring points in Fig. 3, Fig. 4 and Fig. 5, the maximum temperature difference of the six temperature measuring points in the transient state and reaching the steady state are shown in Table 1 respectively.

Table 1 Comparison of the maximum temperature difference of the three-section skin temperature measurement points

It can be seen from Figures 3, 4, 5 and Table 1 that the temperature measurement of the skin with copper rings does not affect the change law of the temperature of the three-core cable skin, but only makes the cable skin tend to be isothermal and has an effect on the temperature of the cable surface. And whether the three-core cable is in a transient state or a steady state, as the thickness of the copper ring increases, the temperature uniformity effect is more obvious.

The above verification process shows that the method for measuring the skin temperature of the three-core cable of the present invention has accurate measurement results, simple and direct testing process, obvious temperature equalization effect of the copper ring, and can well reduce measurement errors.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the embodiment, and any other changes, modifications, substitutions and combinations made without departing from the spirit and principle of the present invention , simplification, all should be equivalent replacement methods, and are all included in the protection scope of the present invention.

Claims (3)

1. a method for measuring three-core cable skin temperature, is characterized in that, comprises the steps: S1 Lay copper rings on the cross-section skin of the three-core cable; S2 evenly lay thermocouples on the copper ring; S3 After the three-core cable runs stably, record the temperature measured by the thermocouple, and calculate its average value, and the average value is the skin temperature of the three-core cable. 2. a kind of method for measuring three-core cable skin temperature according to claim 1, is characterized in that, described thermocouple is 3-6. 3. A method for measuring the skin temperature of a three-core cable according to claim 1, wherein the copper ring has a thickness ≥ 2mm and a width ≥ 1cm.

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