Casus Analyse et Solutio Reparandi Distributorum Transformatorum

Causae Defectus Transformatorum Distributionis
Defectus Causati per Augmentum Caloris
Impactus in Materiales Metallicos
Cum transformator operatur, si amperage nimis magnus est, causans ut onus clientis superet capacitas nominata transformatoris, calor transformatoris augescet, quod in vicem materiales metallicos mollificat et vim mechanicam eorum significanter minuit. Exempli gratia, cuprum, si diu exponitur ad altam temperaturam supra 200 °C, vim mechanicam suam significanter debilitabit; si autem temperatura brevi tempore superat 300 °C, etiam cito diminuetur. Pro materialibus aluminii, longa tempora operativi debent esse sub 90 °C, et tempora brevia non superent 120 °C.
Impactus Contactus Pessimi
Contactus pessimus causa multarum defectuum apparationum distributionis est, et caliditas pars electrica contactus magnam habet in qualitatem contactus electrici. Si caliditas nimis magna est, superficies conductoris electrici violenter oxidabitur, et resistencia contactus significanter augmentabitur, causans ut calor conductoris et componentium eius crescat, et in casu gravissimo, contactus conglutinari possunt.
Impactus in Materiales Isolantes
Si caliditas ambientalis superat limites rationales, materiales isolantes organici fragiles fient, accelerantes processum senectutis, quod ad diminutionem significativam proprietatum isolantium ducit, et in casu gravissimo, fractura dielectrica evenire potest. Studia ostendunt, pro materialibus isolantibus classis A, intra limites tolerantiae caloris, pro incremento 8 - 10 °C, vita utiliter efficiens materialis dimidietur. Haec relatio inter calorem et vitam utiliter efficacem "effectus senectutis thermicae" vocatur, qui factor importantis est in fiducia materialium isolantium.
 Defectus Transformatorum Distributionis Causati per Contactum Pessimum
Defectus Causati per Oxidationem Stratorum Protectivorum
Ut perficiamus praestantiam partium conductivorum, saepe technologias modificationis superficiei ad tractandum partes contactus claves in usu ingeniorum ponimus. Exempli gratia, sicut in baculo conductivo transformatoris, stratum protectivum metalli pretiosi (sicut aurum, argentum, vel alligatum stannum-basiatum) per electroplating formatur in superficie operativa. Hoc stratum ligamentum metallurgicum vices et proprietates physicas et chemicas interfascialis contactus significanter meliorat.

Notandum est, in operatione mechanica in maintenance instrumentorum vel sub onere caloris longo tempore, stratum posset partim abscidi vel pati oxidationem et corrosionem, ita causans problema sicut incrementum anomalum resistencie contactus et decrementum capacitatis portandi currentem. Data experimentalia demonstrant, cum spesialiter amissio crassitudinis strati superet 30%, stabilitas conductivitatis electricae interfascialis exhibebit tendentiam decrementi exponentialis.
Corrosio Chemica Causata per Connexionem Directam Cupri et Aluminii
In systemate connexionis electricae, contactus directus inter dissimilia metalla cupri et aluminii significantem differentiam potentialem formabit, et valor huius potentialis potest attingere 0.6 - 0.7 V. Haec differentia potentialis galvanicam graves corrosiones provocabit. In usu ingeniorum, propter non conformitatem ad regulas constructionis vel electionem materialis improbam, frequenter contingit connexionem directam inter conductores cupri et aluminii sine tractamento transitionis.

Post hoc modum connexionis energizatum, stratum filmatis oxydatis paulatim formabitur in interfasciali contactus, resultans in incrementum non lineare resistencie contactus. Sub caliditate nominata operativa, vita utiliter efficiens talium iuncturarum solito non superat 2000 horas, et tandem, defectus ob deteriorationem superficiei contactus evenient.
Calor Gravis in Partibus Electricis Contactus Causatus per Contactum Pessimum
In installatione actuali transformatorum distributionis, saepe boxa mensurae anti-furtiva configuratur in parte basso-voltali. Propter spatium internum boxae restrictum et artes constructionis non standard, problemata sicut contortio filorum vel crimping mechanicus laxus terminalium saepe accidunt. Hi contactus pessimi ad incrementum anomalum resistencie contactus ducunt, causantes calorem excessivum sub actione currentis oneris, et postea, deficiens ablationis baculi conductivi basso-voltalis.

Gravius, continuus incrementus caloris in fine bobinae basso-voltalis processum senectutis thermicae materialis isolantis accelerabit, creando pericula occultata partialis discharges. Simul, caliditas excessiva causabit oleum transformatoris reagere pyrolysis, diminuens eius fortitudinem isolantis et efficaciam refrigerandi. Data experimentalia demonstrant, cum caliditas olei continuo superat 85 °C, tensio rupturei eius diminuetur circa 15% - 20% per annum. Hic multiplex effectus deteriorativus valde probabile est causare accidentia rupturei isolantis quando occurrit super-tensio fulguralis vel commutationis, ultime ducens ad defectum transformatoris.
Defectus Transformatorum Distributionis Causati per Humiditatem
Incrementum humiditatis relative ambientalis duplum impactum in systemate isolante apparationum distributionis habet. Primo, fortitudo dielectrica aeris humidi significanter diminuitur, et tensio rupturei eius negativiter cum humiditate corrigitur; secundo, adsorptio moleculorum aquae in superficie materialium isolantium canales conductivos formabit, resultans in decrementum resistivitatis superficialis. Gravius, cum humiditas diffunditur in interiorem media isolantis solidi vel dissolvitur in oleo transformatoris, tunc acutum incrementum dielectrici detrimenti eveniet.

Cum contentus aquae in oleo transformatoris attingit circa 100 μL/L, tensio rupturei frequentiae potentielle eius decidet ad circa 12.5% valoris initialis. Haec deterioratio praestantiae isolantis significanter incrementum currentis effluvii instrumenti augebit. In ambiente humido, partialis discharge etiam sub tensio operativa nominata contingere potest. Data statistica ostendunt, in ambiente cuius humiditas relativa superat 85%, ratio defectuum transformatorum distributionis augebitur 3 - 5 vice comparatione cum in sicco, praevalenter manifestans ut ruptura isolantis et accidentia flashover superficiales.

Defectus Transformatorum Distributionis Causati per Installationem Impropriam Pararrayos
In systemate electrico, fidelitas performance dispositivorum protectionis supervoltage directe affectat securitatem operationis transformatorum. Ut principalia elementa protectionis, qualitas installationis, operatio et maintenance, et testes preventivi arrestorum metallo-oxidicorum (MOA) sunt claves ad firmandam effectivitatem eorum. Tamen, propter artes constructionis non standard, imperfectam implementationem procedurarum detectionis, et defectum literaturae professionalis personarum operativarum et maintenance, effectus protectionis realis dispositivorum saepe multum diminuitur, quod causa importantis est accidentium rupturei isolantis transformatorum distributionis.

Ex perspectiva operationis practica, dispositiva protectionis variis stressibus ambientalibus affectabuntur in longo servitio. Factores sicut cyclus caloris, vibrationes mechanicarum, et media corrosiva fortassis ad degradantionem performance connexionis systematis earthing deducant. Quando systema percussu fulminis afficitur, circuitus earthing deficiens non poterit dispergere energiam supervoltage tempestive, resultans in rupturem thermicam ipsius dispositivi protectionis. Statistica ostendunt, inter casus defectuum dispositivorum, explosiones causatae earthing malo plus quam 60% occupant, et processus emissionis energiarum saepe arc discharge violentum comitantur.
Quaedam Methodi Diagnostici pro Defectibus Transformatorum Distributionis
Diagnosis per Iudicium Intuitivum
Diagnosis defectuum transformatorum distributionis initio per characteres externos iudicari potest. Observationes includunt: integritatem casae (fissuras, deformationes), statum mechanicum (fixationes laxas), performance sigillantis (vestigia effluxus), conditionem superficiei (gradum sordis, phenomenis corrosionis), et signa abnormalia (mutationes coloris, vestigia discharges, generationem fumi), etc. Hi characteres externi relationes specificas cum defectibus internis habent.

Cum oleum transformatoris colore brunneo obscuro ostendit et odores combusti habet, cum incremento caloris anomalo et operatione componentium protectionis alto-voltalium, hoc solito indicat anormalitates in systemate magnetico, possibiliter rupturam isolantis inter laminas silicioferas vel defectus multi-puncti earthing ferri magnetici.

Si amperage operativus anomaliter augeatur, calor olei significanter augeatur, parametri trium phasium sint asymmetra, cum operatione dispositivorum protectionis basso-voltalium, fumo in conservatore olei, et fluctuationibus tensio secundaria, tum determinari potest ut defectus short-circuit inter spiras causatus a defectu isolantis inter conductores spira. Cum parameter electricus unius phasis totaliter desinat (tensio et amperage sint 0), haec feature solito correspondet defectui apertus spira vel fusioni conductoris connectivi.

Phenomenon ejectus olei ex conservatorio olei est signum importantis defectus interni gravis transformatoris. Cum ratio generatio gas defectus superet capacitatem dispositivi depressio-pressure, pressio positiva formabitur intra tank olei. Initio, manifestatur per effluxus in punctis sigillationis infirmis. Cum pressio continuo augeatur, ejection olei denique in superficie juncturae corporis tanki evenire potest. Huiusmodi defectus plerumque causatur inter-phase ruptura isolantis spira, solito cum fusione componentium protectionis alto-voltalium. Ex statisticis actionum relay gas, circa 75% defectuum graviorum per hanc progressionem evoluturum erunt.
Diagnosis per Mutationes Caloris
In operatione transformatorum distributionis, conductores portantes currentem inevitabiliter perdas caloris generabunt propter effectum Joule, quod est phenomenon physicum normale. Tamen, cum instrumentum habeat defectus electricos (sicut degradatio isolantis, contactus pessimum) vel defectus mechanicos (sicut deformatio spira, defectus systematis refrigerationis), status thermodynamici eius turbabitur, manifestans ut caliditas operativa superet valor designatus. Secundum theoria senectutis thermicae, pro incremento 6 - 8 °C, ratio senectutis materialium isolantium duplicabitur, ita significanter affectans vitam utiliter efficiens instrumenti.

Pro incrementis caloris anomalibus causatis per defectus internos, solito apparentes anomaliae in systemate circuitus olei sunt. Cum caliditas puncti critici attingit, oleum transformatoris reagere pyrolysis incipiet, generans magnam quantitatem gas, causans dispositivum depressio-pressure operari, resultans in effluxus olei vel ejection olei. In usu ingeniorum, methodus simplex uti potest ad initio iudicandum status caloris instrumenti: si superficies casae transformatoris tangi potest manu plus quam 10 secundis, caliditas eius solito non superat 60 °C. Hoc valor empiricus uti potest ad celerem assessmentem in situ.
Diagnosis per Mutationes Odoris
Momento quo operculum conservatorii olei aperitur, peculiaris et acer odor combusti sentiri potest. Hoc indicat quod spira intus transformatoris est combusta, saepe cum fusione duorum vel trium fusibulorum cadentium phase.

Diagnosis per Mutationes Soni
In operatione transformatoris, effectus magnetostrictionis generatus per magnetization ferriti core periodicas vibrationes mechanicas triggerabit. Haec vibrationes et eorum characteristicae sonorum sunt indicatores importantis de normali operatione instrumenti. Technologia diagnosis sonorum permittit monitorare efficaciter status operativum transformatoris. Specificiter, characteristicae frequentiales signalis sonori, mutationes nivellae pressionis soni, et characteristicae spectrum vibrationis revelare possunt defectus potentialis instrumenti.

Cum usus methodi detectionis sonorum, baculus conductivus (sicut baculus insulans) uti potest medium propagationis undarum sonorum. Unum extremum baculi in contactu cum casae exterioris instrumenti ponitur, alterum vero proximum auditivum organum ad auscultandum. Cum signala sonorum abnormia detecta sunt, celeriter measurae maintenance preventivae implementari debent ad preveniendum exacerbationem defectus. Sequentes sunt correspondentia inter characteristica sonorum typica et genera defectus:

• Sonitus "click" intermittentes: Hoc solito indicat laminationes ferriti core esse laxas vel fixationes non habere sufficientem torque. Nivellae pressionis soni generaliter in ambitu 60 ad 70 decibels cadunt.
  Sonitus "cracking" altae frequentiae: Accompanying partial discharge phenomena, the sound signals exhibit a "cracking" characteristic. In severe cases, the sound pressure level can exceed 85 decibels, and visible discharge marks are often present.

• Sonitus "explosivi" subitani: Hoc maxime accidit quando isolamentum conductorum laeditur vel occurrunt discharges ad terram. Mutatio subitana nivellae pressionis soni superat 20 decibels.

• Sonitus "rumbling" bassae frequentiae: Communiter associantur cum defectibus earthing lateris basso-voltalis, frequentia signalum sonorum concentratur in ambitu 100 ad 400 hertz.

• Sonitus "whistling" acuti: Hoc indicat quod instrumentum est in stato over-excitation, et frequens principalis signalum soni generaliter inter 1 et 2 kilohertz cadit.

• Sonitus "bubbling" continuous: Accompanying abnormal increases in the oil temperature, the sound signals display a continuous "gurgling" characteristic, usually indicating the deterioration of the oil insulation performance.

Diagnosis per Instrumenta
Owing to the constraints of equipment technology, power supply stations mostly use a multimeter to measure whether the resistance of the winding conductors is conducting to determine whether there are broken wires or turn-to-turn short circuits inside the transformer; an insulation resistance tester is used to measure the insulation resistance of each winding of the transformer to the ground, so as to determine whether the main insulation is broken down. When the insulation between the winding and the ground or between phases is broken down, its insulation impedance value will approach 0 Ω.

When testing the insulation performance of the winding, the insulation parameters of the following three circuits need to be measured respectively: the insulation resistance between the primary winding, the secondary winding, and the casing; the insulation resistance between the secondary winding, the primary winding, and the casing; and the insulation resistance between the primary winding and the secondary winding. It should be noted that the reference ground potential point in the test is the metal casing structure of the transformer. The reference values of the insulation resistance of oil-immersed transformers are shown in Table 1.

Technologias Diagnosis pro Defectibus Transformatorum Distributionis
Technologias diagnosis pro defectibus transformatorum distributionis sunt medios cruciales ad securitatem operationis instrumenti assecurandam. Per technologias diagnosis avancatas, defectus potentialis tempestive detegi possunt, et measurae effectivae capi possunt ad expansionem defectus preveniendam. Sequentes introducuntur quaedam communiter usitatae technologias diagnosis pro defectibus transformatorum distributionis.
Test DC Resistance Winding
Test DC resistance winding est unus ex methodis basicis pro detectando statu sanitatis winding transformatoris. Per mensuram DC resistance winding, possumus determinare utrum sint problemata sicut broken wires, poor contact, vel turn-to-turn short circuits in winding. Exempli gratia, in inspectione routine transformatoris in quodam loco, detecta est DC resistance abnormalis winding alto-voltalis. Inspectio ulterior revelavit turn-to-turn short circuit in winding. Temporalis substitutio winding vitavit occurrence defectus gravioris. Test DC resistance winding habet advantagia operationis simplicis et resultatorum intuitivarum, et est methodus detectionis indispensabilis in maintenance quotidiana transformatorum.
Analyse Gas Dissolutus (DGA)
Analyse gas dissolutus (DGA) est means technicus importantis pro diagnosing defectus internos transformatorum. Per analysim componentium et contentorum gas dissolutus in oleo transformatoris, possumus determinare utrum sint defectus sicut overheating et discharge internos transformatoris. Usu methodi tri-ratio IEC60599, discharge-type defects accurate identificari possunt. Exempli gratia, alta concentra detecta est acetyleni (C2H2) et hydrogeni (H2) in oleo quodam transformatoris. Analysim tri-ratio determinavit id esse defectum type discharge. Maintenance temporalis vitavit damnum instrumenti. DGA habet advantagia sensibilitatis altae et diagnosis accuratae, et est means importantis pro monitoring conditionis transformatorum.
Detectio Partial Discharge
Detectio partial discharge est methodus importantis pro evaluando conditionem insulationis transformatorum. Partial discharge usualiter accidit in locis insulationis debilibus, et longa temporis discharge ducet ad gradual deterioration of insulation materials, ultimately causing serious faults. Per detectio partial discharge, insulation defects can be detected in a timely manner, and preventive measures can be taken. For example, during partial discharge detection of a certain transformer, a discharge phenomenon was found in the high-voltage bushing. After replacing the bushing, the discharge phenomenon disappeared, effectively extending the service life of the equipment. Partial discharge detection has the advantages of non-destructiveness and high sensitivity, and it is an important means for monitoring the insulation of transformers.
Combined Vibration and Acoustic Detection
Combined vibration and acoustic detection is to determine whether there are mechanical faults inside the equipment by analyzing the vibration and sound signals during the operation of the transformer. For example, for a faulty transformer, the vibration amplitude exceeded the standard by 3 dB in the 125 Hz frequency band. Inspection revealed that the iron core clamp was loose. After timely tightening, the vibration returned to normal. Combined vibration and acoustic detection has the advantages of real-time monitoring and accurate diagnosis, and it is an important means for diagnosing mechanical faults of transformers.
Infrared Thermography Detection
Infrared thermography detection is to determine whether there are overheating faults in the equipment by detecting the temperature distribution on the surface of the transformer. For example, during infrared thermography detection of a certain transformer, an abnormal temperature was found at the connection of the high-voltage bushing. Inspection revealed that the connection bolts were loose. After timely tightening, the temperature returned to normal. Infrared thermography detection has the advantages of non-contact and rapid diagnosis, and it is an important means for diagnosing overheating faults of transformers.
Fault Elimination Methods and Examples for Distribution Transformers
Line Tripping Caused by Turn-to-Turn Short-Circuit in Transformer
Fault Phenomenon
An over-current trip occurred on a 10 kV line in a certain substation. After reducing part of the load, over-current still occurred during the trial re-closing.
Fault Cause Analysis
After the on-site maintenance personnel arrived at the fault area, they first used a megohmmeter to test the insulation performance of the power supply line, and the measured insulation value to the ground was about 2 MΩ. Subsequently, a monitoring instrument was connected to the open-delta terminal of the secondary side of the 10 kV voltage transformer. During the temporary energization test, the voltage reading was observed to be about 40 V. Combining the on-site investigation results, no new electrical equipment was connected to this line before the fault occurred.

Based on this, the possibility of over-current protection action caused by overload was excluded. According to the analysis of normal operating parameters, this line should neither trigger over-current protection nor have a single-phase grounding anomaly. Through systematic detection and comprehensive judgment, it was initially determined that the root cause of the fault might be the turn-to-turn insulation breakdown in the internal winding of a certain distribution transformer. After analysis, it was possible that there was a turn-to-turn short-circuit fault in a certain distribution transformer of this line. Therefore, the line was transferred from operation to maintenance, and the line inspection was notified.

Further inspection revealed that there was a turn-to-turn short-circuit in phase A of the high-voltage side of a 250 kV·A distribution transformer of a customer on this line, which was the real cause of the trip. The following analyzes the over-current and false grounding situations caused by the turn-to-turn short-circuit of this distribution transformer. Because of the turn-to-turn short-circuit inside the distribution transformer, the simplified equivalent circuit is shown in Figure 1.

Let ZA, ZB, and ZC be the impedances of phases A, B, and C of the distribution transformer respectively. UO is the neutral point potential. When the three-phase load is balanced, UO = 0; when the three-phase load is unbalanced, UO≠0, resulting in neutral point displacement. When there is a phase-to-phase short circuit in phase A of the distribution transformer, the value of impedance ZA will decrease, and the value of IA will increase. When the sum of IA and the currents of phase A of other distribution transformers on this line is greater than the over-current operating value Idz of the relay protection, an over-current trip will occur. When there is a turn-to-turn short circuit in a certain transformer on phase A of the line, the impedance ZA of phase A of this transformer will decrease, and the voltage on the open delta side of the TV will rise. When this voltage exceeds the setting value of the relay, the central signal in the control room will send out a 10 kV grounding signal.

Accidents Caused by the Contact between the Low-Voltage Wire of the Transformer and its Shell
Fault Phenomenon
A 10 kV/400 V, 100 kV・A transformer in a certain unit supplies power to the load through two circuits on the low-voltage side. Since there is no power consumption load in one of the feeder circuits on the low-voltage side, it is decided to remove this line. After the wire removal work is completed, the power supply is restored. When the high-voltage drop-out fuses of phase A and phase C are closed, there is no abnormal phenomenon. However, when the drop-out fuse of phase B is closed, a huge arc suddenly occurs about 15 cm above the upper cover of the transformer, and then the transformer oil is ejected.
Fault Cause Analysis
After the accident occurs, a comprehensive understanding of the wire removal work is carried out, and a core lifting inspection of the transformer is conducted. During the inspection, it is found that the lead wire on the low-voltage side of phase B directly touches the shell, and there is a hole with a diameter of 1 cm at the contact point. The cause of the accident is that during the wire removal on the low-voltage side, the construction personnel accidentally rotate the screw of the low-voltage terminal of the transformer without noticing, resulting in the lead wire of phase B touching the shell of the transformer. Both the neutral point and the shell of this transformer are directly grounded, so the contact point between the lead wire of phase B and the shell becomes a grounding short-circuit point.
Treatment Countermeasures
First, the hole in the transformer body is repaired by welding. Then, the screw of the low-voltage lead wire connection is tightened. After that, the transformer oil is filtered, and the oil level is replenished to the safe level. After passing the test, the power supply is restored. In order to prevent such accidents, during the connection and disconnection of the transformer, the rotation of the connection screw should be avoided as much as possible. Once the screw rotates, strict treatment must be carried out. Only after confirming that there is no error can the transformer be put into use.