JPH0145187B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND AND OBJECTS OF THE INVENTION The present invention relates to a method for manufacturing molded connections for crosslinked polyethylene insulated cables (hereinafter referred to as CV cables).

The crosslinking process of the CV cable molded connection part is carried out under heating with a mold and pressure using high-temperature air. The heating conditions necessary for the insulator at the connection part to reach a predetermined degree of crosslinking and the pressurizing conditions for preventing foaming, cracking, etc. from occurring in the insulator are determined empirically in advance through several experiments. The temperature and gas pressure are then controlled in accordance with these conditions. However, individual processes almost never exactly match the target control conditions, and therefore it is not clear whether the predetermined performance has been achieved. In general, taking these into consideration, heating is often excessive and takes a long time, and this is a cause of variations in the performance of the resulting joints.

Furthermore, during on-site work, heating is interrupted if there is a problem such as a power outage during the crosslinking process, but once the temperature drops, the heating temperature and time required for reheating and crosslinking are unclear, and it is the same as in normal conditions. If the conditions are given and repeated, even if the target value in terms of degree of crosslinking can be obtained, partial deterioration may occur due to overheating, making it impossible to obtain the desired performance.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a molded connection part for a CV cable, which eliminates the drawbacks of the above-mentioned conventional techniques and allows a connection part with stable performance to be manufactured in a short time.

[Summary of the invention]

According to the present invention, the external temperature of the insulator of the mold connection part and the cable itself during the crosslinking process is actually measured, and the temperature of the conductor and insulator during the process, the degree of crosslinking, and the internal stress are calculated respectively, and these are determined as specified. The above objective is achieved by controlling heating and pressurization so that the value is within the range of .

In the mold crosslinking process, in order to shorten the process time as much as possible, the crosslinking reaction should be promoted by heating at high temperatures, and in order to generate a stable crosslinking reaction, it is necessary to suppress the overheating deterioration reaction at a relatively low temperature. .
All of these phenomena are related to reactants (crosslinking agents and enzymes) and time, and the temperature cannot be absolutely limited, but if the reactants and process times are within the range of the reactants and process times that are normally carried out in the mold crosslinking process. It is known from experience that the upper limit is 250°C.

In the case of bridging the connections of high-voltage cables, heat is generated from the internal conductor by external heater heating or electromagnetic induction heating, but either type of heating heats a block with thermal resistance and heat capacity. The temperature inside the insulator cannot be directly determined because it would damage the insulator. Furthermore, the progress of the crosslinking reaction in the molded insulator is determined by the temperature and heating time of that part. Conventionally, a connection was formed by heating using a predetermined heating method and maintaining the temperature outside the insulator at a certain value for a certain period of time, and measuring its performance or the degree of crosslinking of each part.
After confirming that the temperature is within the target range, the heating temperature and heating time are determined based on that.

However, regarding the upper limit temperature, when conductor heat generation by induction heating is used together, the outside of the insulator does not necessarily reach the maximum temperature, and the inside may reach the maximum temperature. In addition, the cable parts on both sides that are heated at the same time do not originally require heating, and if they are heated to the same temperature as the mold bridge part, they will be thermally deformed and the electrical performance of the connection part will be extremely degraded. Therefore, the upper limit temperature for the cable section must be set.

In order to truly obtain a connection with good performance, it is necessary to know the temperature at any point in and around the mold bridge, and to control the heating so that the temperature is within the allowable value for that part. There is. From now on,
If it is within this allowable value, it is possible to shorten the process time by performing rapid heating.

Regarding the lower limit temperature, in relation to time, unless the degree of crosslinking reaches a predetermined value or higher at all points of the molded crosslinked insulator part, the performance of the connection part will not be stable.
Therefore, during heating, the progress of the crosslinking reaction can be determined from chemical reaction kinetics from the temperature and time changes of any part of the mold insulator, and if the heating is continued until a predetermined value is reached, the formation of each connection part will reduce the environment, etc. Products with a predetermined degree of crosslinking can be produced even if the heating conditions change somewhat due to the influence. On the other hand, if the minimum point reaches a predetermined degree of crosslinking, the heating process can be immediately shifted to the cooling process, thereby making it possible to prevent unnecessary heating.

On the other hand, with regard to pressurization, it has been conventional practice to heat the molded insulator part and the cable part adjacent thereto with a fluid from the outside so as not to cause extreme expansion and foaming during the crosslinking reaction. After the crosslinking step is completed, it is desirable to cool the product as quickly as possible from the viewpoint of work efficiency. However, when rapidly cooled, the insulator portion also rapidly shrinks in an unbalanced manner, resulting in a large tensile force being generated inside the insulator. If this exceeds the strength of the material at that temperature, tearing will occur. That is, large bubbles and cracks are generated, resulting in a significant decrease in insulation performance. In addition, since cooling is generally performed from the outside, the temperature drops faster on the outside, causing it to harden and form a shell.
Therefore, pressure from the outside is not transmitted to the inside, and the internal tensile force increases.

To avoid this, it is necessary to control the pressure or temperature so that the difference between the stress due to thermal contraction and the stress due to external pressure is reduced by a certain margin in the tensile strength of the material at that temperature. . Furthermore, with this method, there is no need to lower the temperature unnecessarily slowly, and it becomes possible to lower the temperature and cool the device within a short period of time within a range that maintains performance. Furthermore, when the temperature reaches a certain level and then reaches a point where the internal stress is on the safe side, it is possible to begin the work of removing the pressurizing device, etc., making it possible to shorten the work time.

The present invention has been realized by considering various factors as described above, and examples thereof will be shown below to further facilitate understanding.

〔Example〕

FIG. 1 is a diagram showing a system for implementing the method of the present invention, and FIG. 2 is a diagram showing a thermal equivalent circuit in FIG. 1.

Connection part 1 arranged in mold 3 in FIG.
The temperature of the surface of the insulator and the surface of the cable 2 is actually measured by the temperature measurement sensor 6, and the temperature is input into the computer 4. Furthermore, the amount of heat generated from a plurality of external heaters (not shown) or induction heating devices (not shown) is also input to the computer 4. The computer 4 calculates the conductor temperature, calculates the degree of crosslinking of the insulator or the internal stress of the insulator,
The control device 5 returns to control of heating and pressurization.
The principle of these calculations by the computer 4 is as follows.

In Figure 2, which shows the thermal equivalent circuit of the connection part 1 and the cable part 2, the momentary surface temperature T _1(i)
By actually measuring the temperature T _2(i) , T _3(i), etc. of each part, it is possible to calculate with extremely high accuracy. However, the second
21, 22, 23, 24, 25, 26, 27 in the diagram
represent insulator surface temperature, insulator temperature, conductor temperature, conductor heat capacity, insulator thermal resistance, conductor thermal resistance, and insulator heat capacity, respectively. If the lowest temperature (usually near the conductor sleeve) of the insulators in the connecting portion 1 is T, then the crosslinking degree x of the insulator can be expressed by the following equation.

x=a(1-e ^-f(T)

Claims (1)

[Scope of Claims] 1. In manufacturing a molded connection part of a cross-linked polyethylene insulated cable, a polyethylene of the same type as the insulator of the above-mentioned cable is added with a cross-linking agent, etc., and processed into a tape or sheet shape, and then wound. Alternatively, in the step of extrusion molding with an extruder and then heating with a mold etc. to cause a crosslinking reaction, the temperature of the outside of the insulating layer such as the surface of the insulator to be molded and/or the outer surface of the above cable, and heating of each part The temperature inside the insulator to be molded, the inside of the cable, and the inside of the insulating layer such as the conductor is determined by theoretical estimation from the amount of heat generated, and the temperature of each part is below the respective allowable value, and the estimated temperature inside the insulator to be molded is determined. 1. A method for manufacturing a molded connection part for a crosslinked polyethylene insulated cable, characterized in that the amount of heating is controlled so that the degree of crosslinking of the molded part, calculated from the elapse of time, is equal to or higher than a target value. 2 The temperature inside the insulating layer is theoretically estimated from the temperature measured and the amount of heat generated in each part, and the internal stress is calculated from the temperature and temperature change of each part in the cooling process after crosslinking, and the calculated internal stress is A molded connection part for a crosslinked polyethylene insulated cable according to claim 1, characterized in that the heating part and the pressing part are controlled and cooled so that the stress at that temperature is below the allowable stress of the material forming the part. manufacturing method.