Composite insulator mechanical properties research
Composite insulator is light weight , high ability of anti-pollution and high anti-man damage etc,they are welcomed by the users increasingly.
The insulators become the main force of insulation industry in the urban-village network reconstruction project. The two basic requirements of
insulations are external insulation performance and stable mechanical properties ,and they are same important , so studying stable mechanical properties is important part which developing the insulating market. The outer insulating is rubber, whose mechanical load is mainly provided by the
fiber glass pulling rod, at the same time involves the fitting and pull rod
Connections. This is the safe operation key to analyse the insulation mechanical property.
1. end fitting connection structure and utilization of the rods.
Composite insulator mainly depends on one way fiber glass pulling rods(called rods)to bear mechanical load. The most outstanding performance
Of the FRP polling rods high strength tension and specific strength . Fiber glass in the pulling rods consequent arranged along the direction of axial load,Make it has high axial tensile strength,generally reach to 250KN,because the density of the pulling rod is 2.0 g/cm3,So the specific strength (tensile strength and the ratio of the weight) for 5 ~ 6 times of high quality carbon structural steel,pull rod of the characteristics of high strength, high specific strength, composite insulator is high strength, light weight, stem diameter, thin base.
Although composite insulator rely on fiber glass pulling rods to bear the mechanical load,however, the strength of rods is not equal to the strength of the insulator,this is because rods transfer load by end of insulator on the attachment,Connected with the tower and conductor of the transmission line，The end connection must be the largest concentration of mechanical stress，different connection structure can also lead to different degree of stress concentration,thus the mechanical strength of composite insulator in fact more than mechanical strength depends on the rods,But its connection of mechanical strength,the mechanical strength is different,the-refore using the strength of rod is different.
Composite insulator according to the connection structure at home and abroad,There are two types:wedge type and crimping type , current type pressure as the main form,type pressure to produce a high degree of automation,Small overall dimensions,well-formed,Both in fitting processing and cooperate with pressure is relatively simple,clearness.Our company adopts this kind of connection structure for 4 years,see from the experiment results and running after checking,Connection effect is very good.Type pressure to connect with the area of rod and dimensional accuracy,
When the rod pressure to detect the damage degree
the wedge type connection structure has the branch of wedge inside and outside the wedge,are using the self-locking principle,Wedge joint due to running effect is bad,In selectiving examination found that the mechanical load significantly decreased in the operation of the phenomenon.Which was abandoned by domestic electricity sector and manufacturers,wedge on the open end of the hardware is taking a positive wedge assembly process,At the same time control pressure of the wedge displacement and the force that press a wedge to avoid the connection area under pretensioning load displacement,Achieve a better end seal,And the wedge type belongs to the lock type structure,In the long run,Once had a larger impact load or serious accident situation such as at low temperature,When core rod to produce tiny slip,Since the locking structure can ensure that the mandrel clamping again.Hundreds of thousands of composite insulator only use this structure in China,It is better to run.But the process destroys the rod,At the same time human influence, high production costs, complex process,Only a few manufacturers use
2.The so-called creep of mechanical strength is which Of compound insulator is when applying a below its short-term failure load of mechanical strain, composite insulator, apparently, does not disconnect immediately,Although the tension has been constant does not increase, but the composite insulator is broken. The higher mechanical loadis , the shorter time the insulator maintain ,the lower mechanical imposed load is, the longer time the insulator maintain. For example, under the collapse load of 100%,composite insulator will break in the 1min .Under the collapse load of 60%,composite insulator can maintain at least 96h before the breaking,Under the collapse load of 40%,The, composite insulator can be maintained about 50 years,This mechanical strength with the extension of load time and drop phenomenon is the creep phenomenon
Composite insulator is the creep phenomenon of mechanical strength, due to undertake the mechanical load of mandrel composite structure.Adopted in the mandrel non-alkali fiberglass dia 5 ~ 20 mm, the glass fiber volume was 50% ~ 70% or even higher.Thus in dia18 mm rod has millions of glass fiber, and the millions of glass fiber is impossible to break at the same time.First, because in the connection structure of composite insulator,there is a stress concentration problems inevitably ,The various points inside the mandrel by mechanical stress are different,Some fiber bend some fiber straightnt, Within the core rod the state of the millions of glass fiber is different ,Some fiber bend some fiber straight even rod is uniform tensile load on the macro,The stress of the fiber also is not necessarily the same,Besides the millions of root fracture strength of glass fiber itself does not exactly the same,Even if the same strain,these fibers will not be pulled at the same time,Based on the above analysis,We can see that places a on the composite insulator under mechanical load of the short-term damage strength,Insulator is not immediately fracture,But the inside of the mandrel some fiber due to more than its own strength load has been broken,These broken fiber had had to bear the load transfer to the surrounding fiber, thus increased the average stress of surrounding fibers,If around the fiber can afford if these additional load around the fiber can afford these additional load,The internal process of the mandrel is stopped,If the fiber around bear these additional load,The rod fiber will continue to break,Need to take a broader range of fiber show the broken fiber increase gradually,whole strength of the core rod decrease creep phenomenon.
glass fiber pull rod creep phenomenon is not terrible，Because under the mechanical load of load is below a certain few or no fiber breakage ，Creep process stops，And the design process has left enough margin，destruction of the rod strength is very high,In the operation of the insulator daily mechanical load and low,General enough to cause a mandrel creep damage.
3.The influence of different connection forms of composite insulator mechanical load
From the current study can be found,composite insulator mechanical load control key,Is a control in metal accessories with rod ,Ahead of us have been analysis of connection form.Outer wedge connection and pressure welding type using the same principle,Is a prestress to the rod,To generate static friction force between them realize mechanical load transfer,But outside of the wedge wedge under huge pressure with the with the inner cavity of the strong molecular motion,Because it is the same kind of material,As a continuation of the time,Both as a whole,because of the mandrel and hardware have different expansion coefficient,do not agree on the expansion coefficient,Once appear, slip,mechanical load could be further reduced,At the same time cause end sheath fault sealing area,Seal damage caused by water again,Created conditions for hydrolysis of rod,Lead to further damage of rods,The last cause insulator rupture in the connection area.
The wedge connection structure using self-locking principle,the downside is the production of mandrel before saw a seam,It also reduces the mechanical strength of the core rod itself,In the middle of the saw seam into a wedge,
has a lot of stress on the rod,In the kerf when its symmetry is not easy to control,Asymmetric core rod stress is not uniform, easier to damage,Due to adopt self-locking structure,So don’t usually appear core-pulling phenomenon,
But asymmetric half mandrel rupture easily,fitting processing requirement is highg,The assembly manual process and more strict.
Pressure welding type is a common recognition at home and abroad is very popular form of connection,The principle of which is uniform hardware fitting pressure,Make the fitting produces plastic deformation,A prestress to the rod,To generate static friction force between the rod and the fitting,this process operation high mechanization degree,fitting is small and beautiful, lower production cost, has been widely applied.
4.Composite insulator of brittle fracture of rods
Glass belongs to typical brittle materials,Thus lead glass fiber pull rod in vertical fracture with tension stress direction and fracture morphology of smooth level off.Glass fiber led stick this class fiber reinforced composite material’s normal fracture morphology,And at the same time companion has a lot of fiber and matrix resin separation of stratification, rough break,Just like broken bamboo or sugar cane,Cross section perpendicular to the mandrel axial force direction,But mainly in a completely unexpected happen,so-called surprise,one aspect refers to brittle fracture load is far lower than the normal fracture load,Such as in the normal damage load less than 30% of the brittle fracture may occur.on the other hand,Time has unpredictability of brittle fracture,According to the experience of the operation,Brittle fracture irregular time can be found,Long can run for several years,Short of fracture is only a few months.
Based on the above two points,for the brittle fracture of the composite insulator,researchers from production to the broad masses of electricity users around the world attaches great importance to brittle fracture problem,According to the years of study,that is caused by stress corrosion,in acidic solution and under the function of mechanical load,Acid corrosion acid performance is not good glass fiber,Make the fiber produces tiny crack,Cause fiber crack expanding,Stress corrosion crack front further,So that the mandrel under low load the fracture,Cause fiber crack expanding,Stress corrosion crack front further,So that the mandrel under low load the fracture,As for acid solution is generally considered as a result of the composite insulator sheath or end seal failure,
Water into the lead to the outside world,Water under the action of a strong electric field,Or in a local weak discharge
seen from the above analysis,For improvement of the stress corrosion resistance of the composite insulator has two kinds.One is to improve the performance of composite insulator sheath and end seal,completely prevent the intrusion of moisture.Another way is to improve the composite insulator with glass fiber pull rod stress corrosion resistance,It is best to use ECR.
Insulator rupture will cause ground wire， seriousness of the brittle fracture is self-evident。But the probability of brittle fracture is extremely low，In the domestic operation of only a few millions in composite insulator rupture，Thus composite insulator can be trustworthy products，Especially the manufacturers in the adoption of the rod, sheed on the production and the end seal are improved greatly,As long as the production and use of collaboration agreement,Must be controlled for brittle fracture accident
From the above analysis we can draw advanced experience in running mode of connection,Strict production process control,Do a good job in the protection of rod,Using acid rod,On the mechanical properties of the composite insulator will be reliable.
Organic Composite Insulator should Notice key Issuses in the Process of Production
The outer insulation coating process of the organic composite insulator experienced following steps :dry umbrella dish -extruded sheath umbrella -flat machining – complete injection . The development of the composite insulator rod also experienced the several steps as below:E-glass rod -high temperature resistant -high temperature and acid resistant -transparent , high impact strength,acid resistant. The purpose of these changes are to fit the composite insulator production process,to surpass the international advanced level than the development of composite insulator domestic.
The most respected and concerned in the development of the organic composite insulator in the structure type of the whole injection and crimping . The ministerial standard for more than 220kv organic composite suspension insulator recommends using acid-resistant mandrel. The great resistance to high temperature of the rod services for the whole process of injection. Crimping structure requires strong impact strength during crimping. The structure of fitting and rod are firm and not pulled off. Experienced show that to crimp firmly,rod with good impact strength
1. When the insulator had been injected ,and taken down from the mould and examine, the insulator are torn which should be caused hard pry after separating the up-down mould , and don’t crack in the process of injection and mould. Prying cause the breaking of rods and tearing of silicone rubber shed.
⑴The one of reasons is mould ,and sticky mold is related to the following factors.
a.Mould material and smoothness are not good ,or gluing a model is related to the following several factors.
b.Inappropriate silicon raw material and hardness of rubber .(hardness should be adjusted in summer and winter)
c.Inappropriate time and pressure ,overheat mold, or overcure.
⑵Another reason is that rods are not heat-resistant. According to determination , in general , the internal temperature of a composite insulator mould is about 155℃ and its external temperature is about 170℃.
2. Measures to prevent insulator fracture when levering up.
2.1 Firstly, using good mould with good metal materials, technical content , and good smoothness. Using good release agents.
2.2 Second, stable quality of raw material in silicon rubber ingredients. Operation personnels must understand that the proportion changing of raw materials is always related to temperature , pressure and time in the whole process of production. Of course it includes the influence of the temperature of external environment ,and the hardness degree of rubbet.
2.3 Do not be eager to lever it up after opening mould no matter if it is sticked to the upper mould or the lower mould (of course no droping down ). You ‘d better stay 35minutes or blow it for a while with fans, air conditioning ,and cool the middle of insulator. The strength of such rods will increase greatly with the drop of temperature , and the risk of fracture will be lowered.
2.4 For 110kv composite insulator generally you lever it up with the angle between FRP rod and mould not being more than 30degrees. At present the insulator hardware have been pressed into the mandrel through injection and moulding , and the insulator will drop off easily with its own weight and your gentle touch. Otherwise you have find the reason.
2.5 Insulator manufactures must take equipment situation, personnel
Quality and raw material into consideration in from ulating and practising hour norm and piece-rate system , seeking the accordance of quality and benefit on the basis ensuring each finished product is qualified.
The Breaking Analysis of Rods in the Test of Crimping and Tension
Feature: if there is breaking part in the inner of socket and ball ,tensile strength is very low.
1.1 Crimping strength is big . That exceed compressive strength of the rods ,thus lead to damage.
1.2 If the crimping part is out of place. Briquetting should be located in the middle of connected region.
1.3 the machining accuracy of fitting is bad:a eccentricity b cylindrical is not enough c inner hole has a degree of pin.
1.4 the material of same batch fitting (esp the socket) is not uneven,
1.5 The rods can’t grid well, to bring about end taper or Cylindricity is not enough.
1.6 crimping machine is lack of stability, six or eight jaws is not the same step.
1.7 elasticity modulus of the rods is too high .(high heat resistance, rods brittle)
1.8 When assemble the socket and ball , they are not in the same straight line,
3. solving ideas:
3.1 Choose the products of manufactures .good quality,in order to solve the problem of fitting.to examine there are changes in the same batch of fitting ,the size of the inner hole and diameter tolerance of the rods other parameters according to the standard acceptance,
3.2 Use advanced equipment,technology,to guarantee quality of grid rods.
3.3 control the tolerance clearance during assembly
3.4Choose the right crimping parameter.when the fittings and rods of different batches and manufactures arrive the factory.Firstly, do the confirmed tests of the crimping parameters. If destroy 5-8pieces to make sure the best crimping parameters. Large -ton products should be crimped with section.
3.5 To make sure the stability of crimping machine .notice the exchange of the hydraulic oil,and cool the devices after working for few hours in the summer.