CN102426885A - Method for degassing flexible direct current transmission cable - Google Patents

Abstract

The present invention discloses a method for degassing a flexible direct current transmission cable, comprising the following steps: step 1: winding the cable core evenly on a cable drum to form a plurality of layers of core loops; step 2: placing the cable drum in a closed container; step 3: placing a heating device and a temperature measuring device in the closed container; step 4: turning on the heating device and the temperature measuring device to heat the air in the closed container; step 5: turning off the heating device and the temperature measuring device and taking out the cable core; step 6: selecting a section of the cable core for residual pressure detection, if the detection is unqualified, returning to step 2, if the detection is qualified, the cable degassing is completed. The present invention can effectively reduce the concentration of decomposition byproducts in the insulating material, improve the electrical properties of the insulating material, and inhibit the accumulation of space charge in the insulating material.

Description

A method for degassing flexible direct current transmission cables

technical field

The invention relates to a method for degassing a cable, in particular to a method for degassing a flexible DC transmission cable.

Background technique

Since the cross-linked polyethylene insulating material used in flexible direct current transmission cables is cross-linked with organic peroxides, all cables cross-linked with organic peroxides will always have some decomposition by-products in the structure. These by-products mainly include: Methane, Acetophenone, Cumyl Alcohol and Water.

Usually AC cables are considered to remove methane through degassing to avoid safety problems during welding or installation due to its flammability, and to avoid attachment problems caused by gas pressure during use. In the degassing process of flexible direct current transmission cables, not only the removal of methane must be considered, but also the influence of heteropolar substances such as acetophenone, cumyl alcohol and water on the dielectric properties, thermal conductivity and electric field breakdown strength of materials should be considered. At the same time, the heteropolar by-products of cross-linked polyethylene insulation materials will generate charge accumulation under the action of DC electric field, which will affect the distribution of space charges in the insulating layer, thereby affecting the performance of DC cables.

Contents of the invention

The purpose of the present invention is to provide a method for degassing flexible direct current transmission cables, which can reduce the concentration of decomposition by-products in insulating materials, improve the electrical properties of insulating materials, and inhibit the accumulation of space charges in insulating materials.

In order to achieve the above object, the present invention is achieved through the following technical solutions:

A method for degassing a flexible direct current transmission cable, comprising the steps of:

Step 1: Wind the cable core evenly on the cable reel to form several layers of core coils;

Step 2: Put the cable reel into an airtight container;

Step 3: Put heating device and temperature measuring device in the airtight container;

Step 4: Turn on the heating device and the temperature measuring device to heat the air in the airtight container;

Step 5: Turn off the heating device and temperature measuring device, and take out the cable core;

Step 6: Select one section of the cable core to carry out the residual voltage test; if the test is unqualified, return to the above step 2; if the test is qualified, the cable degassing is completed.

In said step 1, the number of layers of the coil core is no more than 8 layers.

The heating device adopts an electric radiator.

In said step 4, the time for heating the air in the airtight container is not less than 48 hours.

In step 4, the air temperature in the airtight container after heating ranges from 50°C to 80°C.

The residual pressure detection in the described step 6 also includes the following steps:

Step 6.1: slice along the axial direction of the cable core, and cut out several pieces;

Step 6.2: put the several slices into the airtight tank;

Step 6.3: installing a pressure measuring device on the airtight tank;

Step 6.4: vacuumize the airtight jar and seal it, and put the airtight jar into an oven;

Step 6.5: heating the sealed tank with an oven;

Step 6.6: Take out the airtight tank, wait for it to cool down to room temperature, read the reading of the pressure measuring device, and judge whether it is qualified. If not, return to step 2 to continue degassing; if it is qualified, the degassing is completed.

In the step 6.5, the temperature range of the oven heating the airtight tank is 100°C to 130°C.

Compared with the prior art, a method for degassing a flexible direct current transmission cable of the present invention has the following advantages:

Because the present invention adopts the heating device to heat the air in the airtight container, the heating of the cable is realized through heat radiation, which can ensure that the temperature of the outer surface of the cable is not lower than the internal temperature of the insulation, thereby effectively removing methane and benzene in the cable. By-products such as ethyl ketone, cumyl alcohol and water improve the electrical properties of cable insulation materials and inhibit the accumulation of space charges in cable insulation materials.

Since the present invention uses the residual voltage detection method to detect the degassed cable, the degassing effect of the cable can be confirmed, the quality of the cable can be enhanced, the safety of the cable can be improved, and an effective guarantee can be provided for the safe use of the flexible DC cable in the transmission line , which is of great significance to national energy security and economic development.

Description of drawings

Fig. 1 is a flow chart of a method for degassing a flexible direct current transmission cable of the present invention;

Fig. 2 is a flow chart of residual voltage detection in a method for degassing a flexible direct current transmission cable of the present invention;

Fig. 3 is a schematic diagram of the state in which the cable core is wound on a cable reel in a method for degassing a flexible direct current transmission cable according to the present invention;

Fig. 4 is a space charge distribution diagram of different samples under different electric field strengths in a method for degassing a flexible direct current transmission cable of the present invention;

Fig. 5 is the space charge distribution figure of different samples under different short-circuit time in the method for the degassing of a kind of flexible direct current transmission cable of the present invention;

Fig. 6 is a schematic diagram of a device for detecting residual voltage in a method for degassing a flexible direct current transmission cable according to the present invention.

Detailed ways

The present invention will be further elaborated below by describing a preferred specific embodiment in detail in conjunction with the accompanying drawings.

As shown in Figure 1, a method for degassing a flexible direct current transmission cable, the cable is degassed according to the following steps:

Step 1: Wind the cable core 1 evenly on the cable reel 2 (as shown in Figure 3) to form several layers of core coils. According to the different thickness specifications of the cable insulation layer, generally no more than 8 layers. In the present embodiment, select the cable whose insulating layer thickness is 4.0mm, and then the coil number of core is 8 layers, not only can guarantee the quantity of the cable core 1 of sufficient degassing as much as possible, improve production efficiency; Ensure that each layer of core coil can be effectively heated and degassed effectively;

Step 2: Put the cable reel 2 into an airtight container;

Step 3: Put a heating device and a temperature measuring device in the airtight container. In this embodiment, the heating device adopts an electric heat sink, because the acetophenone, cumyl alcohol and water in the cable have relatively high boiling points, and a good degassing effect cannot be achieved under natural conditions, so the degassing process should be done at It is carried out under heating conditions, and the heating process cannot use the conductor heating method. In the case of conductor heating, the escape of by-products will be limited because the temperature of the outer surface of the cable is lower than the internal temperature of the insulation. Therefore, external heating can only be used, and it is necessary to ensure that the ambient temperature of the entire cable is uniform during the degassing process, and heating with a heating plate can ensure uniform heating and uniform ambient temperature. The temperature measuring device is selected from a thermocouple thermometer, which can ensure accurate temperature measurement to ensure that the temperature is within a suitable range;

Step 4: Turn on the heating device and the temperature measuring device, heat the air in the airtight container for several hours and maintain it within a certain temperature range. According to the thickness of different cable insulation layers, the time is generally not less than 48 hours. In this embodiment, a cable with an insulation layer thickness of 4.0 mm is selected. Because the insulation layer thickness is small, the preferred heating time is 48 hours, which can not only effectively degas, but also ensure production efficiency. If the thickness of the cable insulation layer is greater than 4.0mm, the corresponding heating time needs to be increased; and the temperature range is 50°C~80°C. If the temperature is too low, it will affect the effect of degassing. If the temperature is too high, it will cause the cable insulation layer to be soft, causing the cable to be squeezed and deformed. The degassing temperature should decrease with the increase of the weight of the cable itself, so as to achieve the best degassing effect while ensuring that the cable is not damaged;

Step 5: Turn off the heating device and the temperature measuring device, and take out the cable core 1;

Step 6: Select a section of cable core 1 for residual voltage detection, as shown in Figure 2 and Figure 6, the steps are as follows:

Step 6.1: slice along the axial direction of the cable core, and cut out several pieces;

Step 6.2: put the several slices into the airtight tank 3;

Step 6.3: installing a pressure measuring device 4 on the airtight tank 3;

Step 6.4: vacuumize the airtight tank 3 and seal it, then put the airtight tank 3 into an oven;

Step 6.5: Heat the airtight tank 3 in an oven for several hours, and control the temperature at 100°C~130°C;

Step 6.6: Take out the airtight tank 3 from the oven, wait until it cools to room temperature, read the reading of the pressure measuring device 4, compare the air pressure with the specified air pressure reading, if it is greater than the specified value, it is judged as unqualified, and return to step 2 to continue Degassing until the test is qualified; if it is less than the specified value, it is qualified and the degassing is completed.

As shown in Fig. 4 and Fig. 5, in the actual use of the method of the present invention, under different short-circuit time and different electric field strengths, by real-time monitoring two kinds of different formulation cross-linked polyethylene insulating materials A and B, space charge distribution changes with time. The change of degassing time increases, and it is found that the increase of degassing time can effectively reduce the electric field distortion of heteropolar charges, which shows that with the increase of degassing time, the residual amount of cross-linked by-products in the insulation gradually decreases. Through real-time monitoring The data provided a basis for determining the degassing process time.

In summary, a method for degassing flexible direct current transmission cables according to the present invention can reduce the concentration of decomposition by-products in insulating materials, improve the electrical properties of insulating materials, and inhibit the accumulation of space charges in insulating materials, which has significant economic benefits. and social significance.

Although the content of the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as limiting the present invention. Various modifications and alterations to the present invention will become apparent to those skilled in the art upon reading the above disclosure. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (7)

1. the method for a flexible DC power transmission cable degassing is characterized in that, comprises following steps:

Step 1: cable core (1) is wound on the cable hank (2) equably, forms several layers core circle;

Step 2: described cable hank (2) is put into closed container;

Step 3: in described closed container, put into heater and temperature measuring equipment;

Step 4: open described heater and temperature measuring equipment, the air in the closed container is heated;

Step 5: close described heater and temperature measuring equipment, take out described cable core (1);

Step 6: select wherein one section of described cable core (1) to carry out residual voltage and detect; If detection is defective, then get back to described step 2; If it is qualified to detect, then the cable degassing is accomplished.

2. the method for the flexible DC power transmission cable degassing according to claim 1 is characterized in that in the described step 1, the number of plies of core circle is not more than 8 layers.

3. the method for the flexible DC power transmission cable degassing according to claim 1 is characterized in that described heater adopts electric fin.

4. the method for the flexible DC power transmission cable degassing according to claim 1 is characterized in that, in the described step 4, the time of the air in the heating closed container was not less than 48 hours.

5. the method for the flexible DC power transmission cable degassing according to claim 1 is characterized in that, in the described step 4, the air themperature scope in the closed container of heating back is 50 ℃ ~ 80 ℃.

6. the method for the flexible DC power transmission cable degassing according to claim 1 is characterized in that, the residual voltage in the described step 6 detects and also comprises following steps:

Step 6.1:, cut out some along axially cutting into slices of cable core (1);

Step 6.2: vapor tight tank (3) is put in described some sections;

Step 6.3: go up installing pressure tester (4) at described vapor tight tank (3);

Step 6.4: described vapor tight tank (3) is evacuated and seals, again this vapor tight tank (3) is put into baking oven;

Step 6.5: heat described vapor tight tank (3) with baking oven;

Step 6.6: take out vapor tight tank (3), the room temperature that arrives to be cooled reads the reading of pressure tester (4), and whether judge qualified, if defective, then return step 2 and continues the degassing; If qualified, then the degassing is accomplished.

7. the method for the flexible DC power transmission cable degassing according to claim 6 is characterized in that, in the described step 6.5, the temperature range of baking oven heating vapor tight tank (3) is 100 ℃ ~ 130 ℃.

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