Plé ar Fhealláin Iarthar Trasnóir Deais na Tuaithe
1. Íntrodúchán
Mar gheall ar oibriú fada, ní féidir lucht na gréasáin réamhshocraithe éigeantais agus coimhlintí a sheachaint go cruinn. Is iad na cúrsaí éagsúla, mar shampla, forbrú ó thionscal amharcaíochta cosúil le dianadh nó loingseoireacht, agus forbrú ó mhóraíocht nádúrtha cosúil le gealtán, a chuironn orthu seo. I roinnt áiteanna tuaithe, níl an líne ísalvoltage ina stát maith, agus tar éis sin, forbronnann overloading agus short-circuit, rud a chuironn isteach ar an gcóras réamhsocraithe agus a dhéanann dó a bhrú as. Tá sé seo tar éis a bheith ina príomhfhorbairt a chuironn isteach ar an gcóras.
Chun a chosaint ar theiptheoirí réamhsocraithe ó bhrú as agus éileamh teicniúil a laghdú sa chóras gréasáin tuaithe, cuireann an t-alt seo síos agus anailísíonn sé roinnt de na príomhforbraíochtaí agus chúrsaí atá ag theiptheoirí réamhsocraithe, déanann sé cuardach ar bealaí chosanta, cuireann sé suas agus déileálann le haistriúcháin agus láncuidiú rialta ag theiptheoirí réamhsocraithe, agus tá sé in ann a chosaint go héifeachtach agus a chur as a chéile, ag cur isteach ar theiptheoirí réamhsocraithe a bhrú as, agus mar sin, ag feabhsú ar an gcumas soláthar gréasáin tuaithe.
Faoi láthair, is iad na theiptheoirí réamhsocraithe a úsáidtear sa chóras gréasáin tuaithe go príomha theiptheoirí réamhsocraithe sna huillinn. Is iad na theiptheoirí seo a chlasaítear go minic idir theiptheoirí laistigh agus theiptheoirí amuigh. Is iad na theiptheoirí laistigh ná na mídhaisleáin éagsúla a tharlaíonn laistigh den uillinneán theiptheora. Is iad na príomhchineál ná inter-phase short-circuits idir na windings, turn-to-turn short-circuits laistigh den windings, agus grounding faults nuair a bhíonn na windings nó lead-outs i dteagmháil leis an mbarr amuigh. Is iad na theiptheoirí amuigh ná na mídhaisleáin éagsúla a tharlaíonn ar insulating bushings amuigh den uillinneán theiptheora agus a lead-outs. Is iad na príomhchineál ná grounding mar gheall ar flashover nó briseadh insulating bushings, agus inter-phase short-circuits nó grounding de líne outlet ísl-voltage.
Ós rud é go bhfuil réimse mór teipeanna ag theiptheoirí réamhsocraithe, tá roinnt modhanna clasaíochta ar leith ann. Mar shampla, ó thaobh circuit loops, is iad na príomhchlasaíochtaí ná circuit faults, magnetic circuit faults, agus oil-circuit faults. Má chlasaítear i dtreo den struchtúr príomha theiptheora réamhsocraithe, is féidir leis a roinnt i winding faults, core faults, oil-quality faults, agus accessory faults. Go traidisiúnta, is iad na cineál teipeanna theiptheora réamhsocraithe a chlasaítear go ginearálta bunaithe ar áití éagsúla atá faoi chomhartha, cosúil le insulation faults, core faults, tap-changer faults, agus cetera. Ina measc, tá fault outlet short-circuit theiptheora réamhsocraithe ag faire is mó ar an theiptheora féin agus is airde an t-occurance rate faoi láthair. Chomh maith leis sin, tá teipeanna fuarthais theiptheora réamhsocraithe, agus cetera. D'fhéadfadh gach cineál teipeanna seo a léiriú mar thermal faults, electrical faults, nó both thermal and discharge faults ar an am céanna. Ach, ní léiríonn fault fuarthais theiptheora réamhsocraithe thermal ná electrical fault characteristics go gnách.
Mar sin, is deacair clasaíocht a dhéanamh ar theipeanna theiptheora réamhsocraithe laistigh de struchtúr ar leith. Seo an alt a úsáideann cineál teipeanna ginearálta agus coitianta theiptheora réamhsocraithe, cosúil le short-circuit faults, discharge faults, insulation faults, core faults, tap-changer faults, oil-gas leakage faults, external-force damage faults, agus fuse protection faults. Pléitear gach ceann ar leith i dtreo dá choincheap agus bealaí teicniúla comhtharlacha.
2. Anáil Theipeanna Theiptheora Réamhsocraithe
2.1 Short-Circuit Faults
2.1.1 Anáil Cúrsaí Teipeanna
Is é short-circuit faults theiptheora réamhsocraithe príomha outlet short-circuits theiptheora réamhsocraithe, agus short-circuits idir lead-outs laistigh nó windings go dtí an talamh, agus short-circuits idir phríomháin, a chuironn isteach.
Le linn oibriú normálach theiptheora réamhsocraithe, is é an dochar a chuironn isteach outlet short-circuit faults go príomha. De réir staitisticí, tá faults go díreach mar thoradh ar short-circuit fault current impacts on theiptheora réamhsocraithe sa chóras gréasáin tuaithe ag teorainn 40% de gach fault. Tá roinnt cásanna mar sin. Go háirithe, nuair a tharlaíonn outlet short-circuit theiptheora réamhsocraithe, is gá go ginearálta windings a athsholáthar. I gcásanna séasta, b'fhéidir go gá gach windings a athsholáthar, ag déanamh toradh go dúthrachtach agus a chur as a chéile. Mar sin, ba chóir a thabhairt faoi.
Tá na tionchar outlet short-circuits theiptheora réamhsocraithe go príomha i ndiaidh an dá ábhar:
Insulation Overheating Fault Caused by Short-Circuit Current
De bharr nach bhfuil an líne ísalvoltage i roinnt áiteanna tuaithe ag obair go maith, forbronnann overloading agus short-circuits go minic. Nuair a tharlaíonn short-circuit theiptheora réamhsocraithe go díoltasach, d'fhéadfadh a high- and low-voltage windings a tharlaíonn short-circuit currents a bhfuil roinnt scór níos mó ná an luach sonraithe. Tá sé seo ag cruthú go leor teasa, ag cur isteach ar theiptheora réamhsocraithe a dhéanamh go séasta agus an teocht coil a ardú go tapa, ag déanamh insulation aging. Nuair a bhfuil an cumas theiptheora réamhsocraithe a chosc ar short-circuit current neamhshonraithe agus a stabilité téarmaíoch níos lú, beidh an material insulation theiptheora réamhsocraithe go séasta agus a dhéanamh breakdown agus a chur as a chéile theiptheora réamhsocraithe.
Winding Deformation Fault Caused by Short-Circuit Electrodynamic Force
Nuair a tharlaíonn short-circuit theiptheora réamhsocraithe, má tá an short-circuit current beag agus an fuse blows correctly, beidh an winding deformation beag. Má tá an short-circuit current mór agus an fuse blows with a delay or fails to blow, gheobhaidh an secondary side short-circuit current 20 - 30 times higher than the rated current. Beidh an primary side theiptheora réamhsocraithe ag cruthú go leor current chun a chosc ar an demagnetizing effect of the secondary-side short-circuit current. Cruthóidh an go leor current go leor streachais meicníochta laistigh den coil, ag cur isteach ar an coil a chur faoi smacht, a shifreáil, nó a athrú, agus a dhéanamh insulation pads and plates a chur faoi smacht, agus a dhéanamh core clamping bolts a chur faoi smacht, agus a dhéanamh high-voltage coil a chur faoi smacht nó a chur as a chéile, agus in ainneoin a dhéanamh a failure theiptheora réamhsocraithe. Ag an am céanna, tá na windings ag fágáil go leor electromagnetic torque, agus a dhéanamh an material insulation a tharraingt, ag léiriú an wire body, ag déanamh inter-turn short-circuits. Do minor deformations, más gan a dhéanamh in a timely manner, such as restoring the position of the pads, tightening the pressure nails of the windings and the pull-plates and pull-rods of the yoke, and strengthening the clamping force of the lead-outs, the cumulative effect after multiple short-circuit impacts will also damage the distribution transformer.
2.1.2 Bealaí chun Short-Circuit Faults a Laghdú
Optimization of Selection Requirements. Nuair a roghnaíonn theiptheora réamhsocraithe, roghnaigh é a dtabhairfidh test short-circuit go sothuigthe. Ríomh go rialta an chumas theiptheora réamhsocraithe agus roghnaigh a short-circuit impedance rialta. Baine úsáid as S11-type theiptheora réamhsocraithe géar-dhíchumhacht agus scrios theiptheora réamhsocraithe géar-dhíchumhacht.
Optimization of Operating Conditions and Environment. Feabhsú an insulation level of power lines, go háirithe an insulation level of the low-voltage outlet lines of the theiptheora réamhsocraithe ar a slí. Ansin, cuir isteach ar an stánda safety corridor agus safety distance requirements of low-voltage lines chun laghdú ar tionchar agus éileamh nearby-area faults. Seo a chomhthéacs, cuir aird ar an instaláid agus maintenance quality of low-voltage dropper terminals (mar gheall ar an spáráil low-voltage terminals is mostly equivalent to a secondary short-circuit), preventing small animals from intruding, and improving the quality requirements for low-voltage fuses to prevent situations such as fuses not blowing.
Optimization of Operating Modes. Nuair a ríomhaíonn an operating mode, ríomhaíonn an short-circuit current agus a chosc ar a éileamh. Go háirithe, prevent the theiptheora réamhsocraithe from operating under overload. Try to calculate and adjust the electrical load of the theiptheora réamhsocraithe.
Improvement of Operation Management Level. First, prevent short-circuit impacts caused by misoperation. Strengthen the timely monitoring and maintenance of theiptheora réamhsocraithe, promptly detect the degree of deformation of theiptheora réamhsocraithe, and ensure their safe operation. At the same time, increase the inspection efforts on the power consumption of users in the theiptheora réamhsocraithe area to prevent overloading problems caused by user power theft.
2.2 Discharge Faults
Based on the energy density of the discharge, the discharge faults of theiptheora réamhsocraithe are commonly classified into partial discharge, spark discharge, and high-energy discharge. Discharge has two types of destructive effects on insulation: one is that the discharge particles directly bombard the insulation, causing local insulation damage and gradually expanding it until the insulation breaks down. The other is that the chemical action of active gases such as heat, ozone, and nitrogen oxides generated by the discharge corrodes the local insulation, increases the dielectric loss, and ultimately leads to thermal breakdown.
2.2.1 Partial Discharge Faults of Theiptheora Réamhsocraithe
Partial discharge refers to a non-through-type discharge phenomenon that occurs at the edges of air gaps, oil films, or conductors within the insulation structure under the action of voltage. At the beginning, partial discharge is a low-energy discharge. When this kind of discharge occurs inside a theiptheora réamhsocraithe, the situation is relatively complex. According to different insulation media, partial discharge can be divided into partial discharge in bubbles and partial discharge in oil. According to insulation locations, it includes partial discharge in cavities of solid insulation, at electrode tips, in oil-corner gaps, in oil gaps between oil and insulation paperboards, and along the surface of solid insulation in oil. The reasons for partial discharge are as follows:
When there are bubbles in the oil or cavities in the solid insulation material, due to the small dielectric constant of the gas, it bears a high electric field strength under alternating voltage, but its withstand voltage strength is lower than that of oil and paper insulation materials. Therefore, discharge is likely to occur first in the air gap.
Influence of external environmental conditions. For example, if the oil treatment is incomplete and bubbles precipitate from the oil, it will cause discharge.
Due to poor manufacturing quality. For example, discharge occurs at some parts with sharp corners. Bubbles, debris, and moisture are introduced, or due to external temperature-related factors such as paint nodules, they bear a relatively large electric field strength.
Discharge caused by poor contact between metal parts or conductors. Although the energy density of partial discharge is not large, if it develops further, it will form a vicious cycle of discharge, ultimately leading to the breakdown or damage of the equipment and causing serious burnout accidents.
2.2.2 Spark Discharge Faults of Theiptheora Réamhsocraithe
Generally, spark discharge does not quickly cause insulation breakdown. It is mainly reflected in abnormal oil chromatographic analysis, an increase in partial discharge quantity, or light gas. It is relatively easy to detect and handle, but sufficient attention should be paid to its development. There are mainly two reasons for spark discharge:
Spark Discharge Caused by Floating Potential. In high-voltage power equipment, a certain metal part, due to structural reasons or poor contact during transportation and operation, is disconnected and is located between the high-voltage and low-voltage electrodes, dividing the voltage according to its impedance. The potential to the ground generated on this metal part is called the floating potential. The electric field strength near an object with a floating potential is relatively concentrated, often gradually burning out the surrounding solid dielectric or carbonizing it.
It also causes the insulating oil to decompose a large amount of characteristic gases under the action of the floating potential, resulting in an abnormal result of the insulating oil chromatographic analysis. Floating discharge may occur in metal parts at high potential inside the theiptheora réamhsocraithe, such as the regulating winding, when the grading ball of the bushing and the no-load tap-changer shift fork have a floating potential. For parts at ground potential, such as the silicon steel sheet magnetic shielding and various metal bolts for fastening, if their connection to the ground is loose or detached, it will lead to floating-potential discharge. Poor contact at the end of the high-voltage bushing of the theiptheora réamhsocraithe can also form a floating potential and cause spark discharge.
Spark Discharge Caused by Impurities in Oil
The main cause of spark discharge faults in theiptheora réamhsocraithe is the influence of impurities in the oil. These impurities are composed of moisture, fibrous substances (mainly damp fibers), etc. The dielectric constant ε of water is approximately 40 times that of the theiptheora réamhsocraithe oil. In an electric field, the impurities are first polarized and attracted to the area with the strongest electric field intensity, namely near the electrodes, and are arranged in the direction of the electric field lines. Thus, an impurity "bridge" is formed near the electrodes.
The conductivity and dielectric constant of the "bridge" are both greater than those of the theiptheora réamhsocraithe oil. According to the principles of electromagnetic fields, the presence of the "bridge" distorts the electric field in the oil. Since the dielectric constant of the fibers is small, the electric field in the oil at the ends of the fibers is strengthened. Therefore, the discharge first occurs and develops in this part of the oil. The oil dissociates under a high-field-strength environment, decomposing into gases, which causes the bubbles to increase in size and the dissociation to strengthen. Subsequently, the process gradually develops, leading to spark discharge in the entire oil gap through the gas channel. So, spark discharge may occur at a relatively low voltage.
If the distance between the electrodes is not large and there are enough impurities, the "bridge" may connect the two electrodes. At this time, due to the relatively high conductivity of the "bridge", a large current flows along the "bridge" (the magnitude of the current depends on the capacity of the power supply), causing the "bridge" to heat up intensely. The moisture and the nearby oil in the "bridge" boil and vaporize, creating a gas channel - the "bubble bridge", and spark discharge occurs.
If the fibers are not damp, the conductivity of the "bridge" is very small, and its influence on the spark discharge voltage of the oil is also relatively small; conversely, the influence is greater. Therefore, the spark discharge of the theiptheora réamhsocraithe oil caused by impurities is related to the heating process of the "bridge". When an impulse voltage acts or the electric field is extremely non-uniform, it is not easy for the impurities to form a "bridge", and their effect is only limited to distorting the electric field. The spark discharge process mainly depends on the magnitude of the applied voltage.
2.2.3 Arc Discharge Faults of Theiptheora Réamhsocraithe
Arc discharge is a high-energy discharge, which is commonly seen as insulation breakdown between winding turns or layers. Other common faults include lead breakage, flashover to the ground, and arcing of tap-changers.
Influence of Arc Discharge. Due to the high energy density of arc discharge faults, gas is generated rapidly. It often impacts the dielectric in the form of electron avalanches, causing the insulating paper to perforate, char, or carbonize, deforming or melting and burning the metal materials. In severe cases, it may cause equipment damage or even explosions. Such accidents are generally difficult to predict in advance and have no obvious omens, often emerging in a sudden manner.
Gas Characteristics of Arc Discharge. After an arc discharge fault occurs, the theiptheora réamhsocraithe oil also carbonizes and turns black. The main components of the characteristic gases in the oil are H2 and C2H2, followed by C2H6 and CH4. When the discharge fault involves solid insulation, CO and CO2 will also be generated.In summary, the three forms of discharge have both differences and certain connections. The differences refer to the discharge energy level and gas composition, while the connection is that partial discharge is a precursor to the other two forms of discharge, and the latter two are inevitable results of the development of the former. Since the faults occurring inside theiptheora réamhsocraithe are often in a state of gradual development, and most of them are not single-type faults, but rather one type is accompanied by another type, or several types occur simultaneously. Therefore, more careful analysis and specific treatment are required.
2.3 Insulation Faults
Currently, the most widely used theiptheora réamhsocraithe in rural power grids are oil-immersed transformers. The insulation of a theiptheora réamhsocraithe refers to the insulation system composed of its insulation materials. It is a fundamental condition for the normal operation of the theiptheora réamhsocraithe, and the service life of the theiptheora réamhsocraithe is determined by the lifespan of the insulation materials (such as oil-paper or resin). Practical experience has proven that most of the damage and faults of theiptheora réamhsocraithe are caused by the damage of the insulation system.
Therefore, protecting the normal operation of the theiptheora réamhsocraithe and strengthening the reasonable maintenance of the insulation system can, to a large extent, ensure a relatively long service life for the theiptheora réamhsocraithe. Preventive and predictive maintenance are the keys to extending the service life of theiptheora réamhsocraithe and improving power supply reliability.
In oil-immersed theiptheora réamhsocraithe, the main insulation materials are insulating oil and solid insulation materials such as insulating paper, cardboard, and wooden blocks. The so-called aging of the theiptheora réamhsocraithe insulation means that these materials decompose under the influence of environmental factors, reducing or losing their insulation strength.
2.3.1 Solid Paper Insulation Faults
Solid insulation is one of the main components of the insulation of oil-immersed theiptheora réamhsocraithe, including insulating paper, insulating board, insulating pad, insulating coil, insulating binding tape, etc. Its main component is cellulose. After the insulating paper ages, its degree of polymerization and tensile strength gradually decrease, and water, CO, and CO2 are generated. In addition, furfural (furfuraldehyde) is also produced. Most of these aging products are harmful to electrical equipment. They can reduce the breakdown voltage and volume resistivity of the insulating paper, increase the dielectric loss, decrease the tensile strength, and even corrode the metal materials in the equipment.
2.3.2 Liquid Oil Insulation Faults
Reasons for the Deterioration of Theiptheora Réamhsocraithe Oil
Contamination means that moisture and impurities are mixed into the oil. These are not oxidation products of the oil. The insulation performance of contaminated oil deteriorates, the breakdown electric field strength decreases, and the dielectric loss angle increases.
Deterioration is the result of oil oxidation. This oxidation does not only refer to the oxidation of hydrocarbons in pure oil but also includes the acceleration of the oxidation process by impurities in the oil, especially copper, iron, and aluminum metal shavings.
Oxygen comes from the air inside the theiptheora réamhsocraithe. Even in a fully-sealed theiptheora réamhsocraithe, there is still about 0.25% of oxygen by volume. Oxygen has a relatively high solubility, so it occupies a relatively high proportion among the dissolved gases in the oil.
When the theiptheora réamhsocraithe oil oxidizes, moisture as a catalyst and heat as an accelerator cause the theiptheora réamhsocraithe oil to generate sludge. Its main impacts are as follows: under the action of the electric field, the sediment particles are large; the impurities concentrate in the area with the strongest electric field, forming a conductive "bridge" for the insulation of the theiptheora réamhsocraithe; the sediment is not uniform but forms separate slender strips, and it may be arranged in the direction of the electric field lines, which undoubtedly hinders heat dissipation, accelerates the aging of insulation materials, and leads to a decrease in insulation resistance and insulation level.
The Process of Theiptheora Réamhsocraithe Oil Deterioration
During the deterioration process of the oil, the main products in each stage are peroxides, acids, alcohols, ketones, and sludge.In the early deterioration stage, the peroxides generated in the oil react with the insulating fiber materials to form oxidized cellulose, which deteriorates the mechanical strength of the insulating fibers, causing embrittlement and insulation shrinkage. The generated acids are a kind of viscous fatty acid. Although its corrosiveness is not as strong as that of mineral acids, its growth rate and impact on organic insulation materials are significant.
In the later deterioration stage, sludge is generated. When acids erode copper, iron, insulating paint, and other materials, sludge is produced. It is a viscous, asphalt-like polymeric conductive substance that can moderately dissolve in the oil. Under the action of the electric field, it is generated very quickly and adheres to the insulation materials or the edges of the theiptheora réamhsocraithe tank, deposits in the oil pipes and radiator fins of the cooler, etc., increasing the operating temperature of the theiptheora réamhsocraithe and reducing its electrical withstand strength.
The oxidation process of the oil is composed of two main reaction conditions. One is that the acid value in the theiptheora réamhsocraithe oil is too high, making the oil acidic. The other is that the oxides dissolved in the oil are transformed into compounds insoluble in the oil, gradually deteriorating the quality of the theiptheora réamhsocraithe oil.
2.3.3 Winding Insulation Moisture Ingress
Winding insulation moisture ingress is mainly caused by poor-quality insulating oil or a decrease in the oil level. The main reasons are as follows:
