CN103630804B - Method for manufacturing local discharge model of conductive particles on insulating surface of intermediate head of cable - Google Patents

Abstract

The invention aims at providing a method for manufacturing a local discharge model of conductive particles on the insulating surface of an intermediate head of a cable. According to the method, a common XLPE (Cross Linked Polyethylene) cable is directly manufactured into a model in which conductive or semiconductive impurities are attached to the main insulating surface, and the problems exposed when the intermediate head of the cable is manufactured and installed can be really reflected. In order to solve the technical problems, through steps of peeling cables, binding, washing, connecting and the like, the local discharge model of the conductive particles on the insulating surface of the intermediate head of the 10kV cable can really reflect the representative typical defect property, characteristic and discharge mechanism, which are exposed during laying, installation and operation processes of a power cable line, realizes effective extraction of typical defect local discharge characteristic quantity and obtains pure local discharge signal spectrum characteristic. The method provides convenience for researchers to safely and repeatedly test, and data are more real and reliable.

Description

Method for making partial discharge model of conductive particles on insulating surface of cable intermediate joint

technical field

The invention relates to the field of power systems, in particular to a method for making a partial discharge model of conductive particles on the insulating surface of a cable intermediate joint.

Background technique

XLPE cables are widely used in transmission lines due to their excellent performance. When making cable intermediate joints, the insulation shield and metal sheath need to be stripped, which will cause electric field concentration. The key part of the insulation is the interface between the prefabricated joint and the XLPE cable insulation. Because the electrical insulation strength of the interface is related to various factors such as the cleanliness and smoothness of the insulating surface of the XLPE cable, the interface pressure, and the lubricant used for inserting the rubber insulation. If the outer semi-conductive layer remains during construction, or conductive and semi-conductive impurities are attached to the surface of the main insulation, a floating potential will be generated, which will cause partial discharge.

Partial discharge is the symptom and the main reason of XLPE cable insulation degradation. The partial discharge of the cable is closely related to its insulation condition, and the change of the partial discharge indicates that there may be defects in the cable insulation that may endanger the safe operation of the cable. At home and abroad, a lot of research has been done on the detection method of partial discharge mechanism of internal insulation defects of XLPE cables, and great progress has been made in the research and design of typical discharge models. However, due to the complex insulation structure of medium and high voltage cable accessories and other parts, there are many factors affecting the discharge, and there is no unified physical model for various types of insulation defects. However, if the faulty line is directly used as the experimental model, firstly, concurrent faults may affect the experimental results; secondly, the safety cannot be guaranteed. Experimental models with a safety factor are lacking in the prior art.

Contents of the invention

The object of the present invention is to need a kind of method for making the partial discharge model of the conductive particles on the insulating surface of the cable intermediate joint. The ordinary XLPE cable is directly made into a model in which conductive and semi-conductive impurities are attached to the main insulating surface, which can truly reflect the presence of the cable intermediate joint. Problems exposed during manufacturing, installation and operation.

In order to solve the above technical problems, the present invention is achieved through the following technical solutions:

The method for making the partial discharge model of conductive particles on the insulating surface of the cable intermediate joint first selects two sections of cables, and includes the following steps in turn:

Step 1: Stripping the cable: Scrub and clean the cable sheath at both ends of the cable with a length of at least 1 meter, strip the outer sheath of the cable at both ends, strip and cut the steel armor layer of the cable, and evenly scrape off the insulation inside the steel armor layer Shielding layer, and then peel off the outer semiconducting layer, main insulator layer and inner semiconducting layer wrapping the wire core from outside to inside, and finally expose the wire core, and polish the insulating surface until smooth;

Step 2: Wrapping: Wrap the semi-conductive tape back and forth in a half-fold manner, starting from 40mm above the copper shielding tape to 10mm on the main insulating layer;

Step 3: Cleaning: Clean the main insulation layer of the cable with a cleaning agent, and at the same time use sandpaper to polish off the outer semiconductor layer remaining on the main insulation;

Step 4: Connection: Put the cable from the longer end of the stripped length into the stress cone, install the copper connecting tube and crimp it, and the sequence of crimping is from the middle to the surrounding; after crimping, file the outer surface of the connecting tube flat Smooth, wipe clean with insulating cleaning paper; apply WACKER silicone grease from the junction of the outer semiconducting layer and the main insulating layer, and evenly spread it on the main insulating surface; sprinkle metal shavings of irregular shapes and sizes on the main insulating surface, The radius of a single metal chip is not more than 2mm, and the total area involved by the metal chip is not less than 400mm ² ; align the edge of the semi-conductive tape to position the main body of the joint, and pull out the core rope inside the stress cone counterclockwise to shrink and tighten the stress cone. Correct the axial position of the stress cone tube in time to avoid falling off of metal shavings, and the partial discharge model is completed.

Preferably, the cable body is an XLPE cable with a rated voltage of 10kV and a conductor cross section of ^240mm2 . The structure of XLPE cables with such specifications is clear and each structure is distinct, which is most suitable as a model building unit.

Preferably, the specific operation method of stripping and cutting the steel armor of the cable in the step 1 is: sawing the steel armor layer, the depth of the saw marks is 2/3 of the thickness of the steel armor, inserting a screwdriver into the saw marks to lift the wire core, and using pliers Clamp the saw marks, roll and tear the steel armor; use pliers to flatten the fracture of the steel armor. Because the steel armor is thick, it needs to be sawed with a saw, but if only a saw is used for sawing, it is easy to cause the core rope to be sawn off. And this way can prevent the inner layer of steel armor from being damaged and ensure the integrity of each layer.

Preferably, the lengths of the outer semiconductor layer, the main insulator layer and the inner semiconductor layer peeled off in the step 1 are reduced in equal length, and finally the exposed lengths of the outer semiconductor layer, the main insulator layer and the inner semiconductor layer are equal. Such equidistant exposure is conducive to tightening in the later stage. Since the thickness of each layer of the outer semiconductor layer, the main insulator layer and the inner semiconductor layer is not very thick, such a structure can ensure that when stretching the semi-conductive tape, a layer will not be exposed due to a short winding layer.

Preferably, the insulating shielding layer is a copper shielding tape.

Preferably, the placed metal shavings are copper shavings. In the actual application process, the study found that the most easily mixed impurities in the cable are the metal shavings falling from the copper shielding tape. Therefore, the use of copper shavings is the most representative.

Preferably, the placed metal filings are copper filings and iron filings arranged in a mass ratio of 3:1. Iron filings are worn out after long-term use in the wire core. The total amount is less than that of copper shavings. This mainly simulates the partial discharge model of conductive particles on the insulating surface of older cables.

Compared with the prior art, the partial discharge model of conductive particles on the insulating surface of the 10kV cable intermediate joint made by the present invention can truly reflect the nature, characteristics and discharge of representative typical defects exposed during the laying, installation and operation of power cables. The mechanism is used to realize the effective extraction of partial discharge characteristic quantities of typical defects, and obtain the spectral characteristics of pure partial discharge signals. It is convenient for researchers to safely repeat experiments, and the data is more authentic and reliable.

detailed description

The method for making the partial discharge model of conductive particles on the insulating surface of the cable intermediate joint first selects two sections of cables, and includes the following steps in turn:

Step 1: Stripping the cable: Scrub and clean the cable sheath at both ends of the cable with a length of at least 1 meter, strip the outer sheath of the cable at both ends, strip and cut the steel armor layer of the cable, and evenly scrape off the insulation inside the steel armor layer Shielding layer, and then peel off the outer semiconducting layer, main insulator layer and inner semiconducting layer wrapping the wire core from outside to inside, and finally expose the wire core, and polish the insulating surface until smooth;

Step 2: Wrapping: Wrap the semi-conductive tape back and forth in a half-fold manner, starting from 40mm above the copper shielding tape to 10mm on the main insulating layer;

Step 3: Cleaning: Clean the main insulation layer of the cable with a cleaning agent, and at the same time use sandpaper to polish off the outer semiconductor layer remaining on the main insulation;

Step 4: Connection: Put the cable into the stress cone from the longer end of the stripping and cutting length, install the copper connecting tube and crimp it, the force sequence of the crimping is from the middle to the surrounding; file the outer surface of the connecting tube after crimping Make it smooth and wipe it clean with insulating cleaning paper; use WACKER silicone grease to spread from the junction of the outer semiconductor layer and the main insulating layer, and evenly spread it on the main insulating surface; sprinkle metal shavings of irregular shapes and sizes on the main insulating surface , the radius of a single metal chip is not more than 2mm, and the total area involved by the metal chip is not less than 400mm ² ; align the edge of the semi-conductive tape to position the main body of the joint, and pull out the core rope inside the stress cone counterclockwise to shrink and tighten the stress cone. When shrinking, adjust the axis position of the stress cone tube in time to avoid metal shavings from falling off, and the partial discharge model is completed. The cable body is an XLPE cable with a rated voltage of 10kV and a conductor cross section of 240mm ² . The specific operation method for stripping and cutting the steel armor of the cable in step 1 is: sawing the steel armor layer, the depth of the saw marks is 2/3 of the thickness of the steel armor, inserting a screwdriver into the saw marks to lift the wire core, and clamping the saw with pliers If there is a gap in the mark, roll and tear the steel armor; use pliers to flatten the fracture of the steel armor. The lengths of the outer semiconductor layer, main insulator layer and inner semiconductor layer peeled off in step 1 are reduced in length, and finally the exposed lengths of the outer semiconductor layer, main insulator layer and inner semiconductor layer are equal. The insulating shielding layer is a copper shielding tape.

According to different periods of use, when the degree of use is relatively new, the metal shavings placed are copper shavings. When simulating a model with a long service life, copper filings and iron filings arranged in a mass ratio of 3:1 are used.

This actually breaks down a technical bias. Usually, when the insulating surface of the cable intermediate joint contains conductive particles, the first thing technicians think of is the copper shavings rubbed off from the copper shielding layer. However, long-term research and analysis have shown that when the service life reaches a certain level, the iron filings in the core may also wear through the inner shielding layer and adhere to the insulating surface. However, the two situations lead to different situations.

In the case of normal use, when the insulating surface of the cable intermediate joint contains conductive particles and other impurities, the electric field distortion of the impurities near the intermediate connecting pipe is the most severe, and partial discharge is prone to occur. Due to the proximity of the connecting pipe in the middle, the insulation distance between the two is smaller than that of other impurities and the connecting pipe. When the electric field is distorted and the field strength exceeds the breakdown strength of the insulating medium, it will cause insulation breakdown. When a breakdown occurs somewhere in the insulation layer, other good insulation will withstand a greater voltage, and the electric field will be further increased. Therefore, the breakdown will start from the connecting tube to the impurity near it, extend along the weak position of the insulation, further strengthen the partial discharge, and develop towards the stress cone, finally forming an arc discharge channel. However, such a research model is lacking in the prior art. If you take a faulty cable, you can't guarantee the safety during use, and you can't rule out other hidden dangers.

The above is only a specific embodiment of the present invention, but the technical characteristics of the present invention are not limited thereto, any changes or modifications made by those skilled in the art within the field of the present invention are covered by the patent scope of the present invention among.

Claims (5)

1. The method for making the partial discharge model of conductive particles on the insulating surface of the cable intermediate joint first selects two sections of cables, and is characterized in that: the following steps are sequentially included: Step 1: Stripping the cable: Scrub and clean the cable sheath at both ends of the cable with a length of at least 1 meter, strip the outer sheath of the cable at both ends, strip and cut the steel armor layer of the cable, and evenly scrape off the insulation inside the steel armor layer Shielding layer, and then peel off the outer semiconducting layer, main insulator layer and inner semiconducting layer wrapping the wire core from outside to inside, and finally expose the wire core, and polish the insulating surface until smooth; Step 2: Wrapping: Wrap the semi-conductive tape back and forth in a half-fold manner, starting from 40mm above the copper shielding tape to 10mm on the main insulating layer; Step 3: Cleaning: Clean the main insulation layer of the cable with a cleaning agent, and at the same time use sandpaper to polish off the outer semiconductor layer remaining on the main insulation; Step 4: Connection: Put the cable from the longer end of the stripped length into the stress cone, install the copper connecting tube and crimp it, and the sequence of crimping is from the middle to the surrounding; after crimping, file the outer surface of the connecting tube flat Smooth, wipe clean with insulating cleaning paper; apply WACKER silicone grease from the junction of the outer semiconducting layer and the main insulating layer, and evenly spread it on the main insulating surface; sprinkle metal shavings of irregular shapes and sizes on the main insulating surface, The radius of a single metal chip is not more than 2mm, and the total area involved by the metal chip is not less than 400mm ² ; align the edge of the semi-conductive tape to position the main body of the joint, and pull out the core rope inside the stress cone counterclockwise to shrink and tighten the stress cone. Correct the axial position of the stress cone tube in time to avoid falling off of metal shavings, and the partial discharge model is completed. 2. The method for making the partial discharge model of conductive particles on the insulating surface of the cable intermediate joint as claimed in claim 1, wherein the cable body is selected for use with a rated voltage of 10kV and an XLPE cable with a conductor cross ^- section of 240mm. 3. The method for making a partial discharge model of conductive particles on the insulating surface of cable intermediate joints as claimed in claim 1, wherein the specific operation method of stripping and cutting the steel armor of the cable in said step 1 is: sawing the steel armor layer, sawing marks The depth is 2/3 of the thickness of the steel armor. Use a screwdriver to insert the saw marks to lift the wire core, use pliers to clamp the saw mark gap, roll and tear the steel armor; use the pliers to flatten the steel armor fracture. 4. cable intermediate joint insulation surface conductive particle partial discharge model making method as claimed in claim 1, it is characterized in that, the outer semiconductive layer stripped in the described step 1, the main insulator layer and the inner semiconductive layer length equal difference reduce, Finally, the exposed lengths of the outer semiconducting layer, the main insulator layer and the inner semiconducting layer are equal. 5. The method for making a partial discharge model of conductive particles on the insulating surface of an intermediate cable joint according to claim 1, wherein the insulating shielding layer is a copper shielding tape.