Caracteristica performantiarum et design structurae interruptorum vacui montatorum in columnas exteriores
A tempore ab anno 2009 usque ad annum 2010, State Grid erat in phase piloto planificationis retei intelligentis, intenta in elaborationem plani forti retei intelligentis, investigationem et developmentum technologiarum clavium, fabricationem apparatus, et executionem projectorum pilotarum in variis sectoribus. Tempus ab 2011 usque ad 2015 signavit phase constructionis plenae, in qua systema controlis operationis et servitii interactionis pro rete intelligente initio formabatur, et progressus magni in technologiis et apparatu clavibus adepti sunt, ducendo ad applicationem extensam eorum.
A 2016 usque ad 2020, intravit in stagium leadership et improvementis, cum rete unificatum et fortissimum intelligens perfecte constitutum est, et technologiae et apparatus ad niveles internationales advancedos pervenerunt. Tunc capacitas retei in optimisationem allocationis ressourcerum multum meliorabitur. Ad respondendum scopis developmentis retei intelligentis nationalis, interruptores vacui montati in pole exteriores, qui in principibus retibus electricis installantur, requiruntur ut microcomputer-based protectionem intelligentem altissimae sensitivitatis, id est valorem minimum operativum currentis primarii minimi, assequantur.
Itaque, praeterquam quod singulis trium phasium transformatores currentis separati ad protectionem differentialem equipantur, interruptores vacui montati in pole exteriores etiam transformatores currentis residuorum ad protectionem microcomputer necessitant, ut protectionem leakage accuratam microcomputer offerant. Transformatores currentis residuorum traditionales magni sunt in magnitudine, graves in pondere, et parvi in accurate.
Affecti per factores ut spatium installationis limitatum et circuiti conductus secundarii longi, vix possunt exigentias applicationis protectionis microcomputer pro interruptoribus vacuis montatis in pole exteriores satisfacere. Nunc omnes interruptores externi qui exigentias retei intelligentis nationalis potest assequi a societatibus foreign-funded producuntur, resultans in costibus altis. Ad adaptationem exigentiarum developmentis retei intelligentis nationalis, necessarium est ut interruptores externi qui necessitatibus retei intelligentis nationalis satisfaciant developentur.
Nunc, principalis difficultas technica quam solvere debemus est ut transformatores currentis residuorum ad protectionem microcomputer, qui cum his interruptoribus conjunctim uti possint, developantur, satisfaciendo exigentiis installationis in spatiis parvis, protectionis leakage microcomputer altissimae sensitivitatis, et operationis accuratae, et primo localisationem transformatores currentis residuorum ad protectionem microcomputer assequentes.
Applicationes et Exigentiae Performance transformatores currentis residuorum ad protectionem microcomputer
Transformator currentis residui (transformator currentis zero-sequenciae) est transformator currentis specialis designatus ad transformationem currentis residui (currentis zero-sequenciae). Utitur ad protectionem earthing unius phase in systematibus neutral-insulated. Trium conductorum phasealium simul per fenestram nucleo transformatoris transeunt, fungentes ut primario windingo transformatoris.
Quando systema normaliter operatur, summa phasoria currentium triphase est nulla, nec output ab lateris secundario transformatoris currentis residui. Quando fault earthing unius phase in linea certa occurrit, currentis primarius transformatoris currentis residui ad minimum currentem operativum relais vel protectionis microcomputer pervenit, activans dispositivum protectionis actum.
Alioquin, remanet inactivum. In transformatribus currentis residuorum traditionalibus, latus secundarium directe connectitur ad relais. Quoniam numerus rotationum in primario windingo transformatoris saepissime est 1, numerus rotationum in secundario windingo est parvus. Minimum currentis primarii operativi transformatrorum currentis residuorum traditionalium saepissime inter 2.4A et 10A, et rated currentis primarii transformatrorum currentis residuorum traditionalium generaliter selectus est in range 15A ad 300A. Ad satisfaciendum exigentiis accurate, area sectionalis nuclei transformatoris designatur esse magnum, resultans in magnitudine magna, pondere gravi, accurate parva, et onere secundario parvo.
Cum currentis fault minor sit quam 2.4A, currentis output a transformatore traditionali insufficiens est ad activandum relais, creans "dead zone." Itaque, ut transformator possit protectionem accuratam pro microcomputer intra latum range currentis operativi sine dead zone praebere, oportet ut transformator currentis residuorum specialis qui cum protectione microcomputer conjunctim uti possit designetur.
Restrictus per spatium installationis interruptoris, transformator currentis residuorum specialis qui cum protectione microcomputer conjunctim uti debet non solum parvus in magnitudine et levis in pondere esse debet, sed etiam high-precision output secundarium et onus secundarium magnum requiret. Generaliter, currentis primarius operativus transformatoris requiritur esse inter 0.2A et 10A. Si transformator potest linearity bonam et sensitivitatem sub conditione output oneris secundarii magni assecurare, posset exigentias protectionis microcomputer satisfacere et occurrentiam "dead zone" evitare.
Structura Design transformatores currentis residuorum ad protectionem microcomputer
Selectio Parametrorum Onus Rated Transformatoris
Interruptores vacui montati in pole exteriores generaliter externa installantur et longe a dispositivis automationis supporting distant. At onus a protectione microcomputer ipso requisitus est parvus. Cum designatur transformator currentis residuorum, onus rated principale considerat onus circuiti lead secundarii transformatoris. Quoniam dispositivum protectionis microcomputer usualiter longe a interruptore montato in pole externo distant, onus rated transformatoris generaliter selectus est magnum, maximus circa 200Ω (hoc onus potest determinari secundum situationem actual user).
Selectio Numeri Rotationum Windingorum Primarii et Secundarii, Formae Nuclei, et Materialis
Transformatores currentis residuorum ad protectionem microcomputer altissimam sensitivitatem requirunt et prompte et accurate responder debent. Sensitivitas referitur ad capacity secundarii windingi transformatoris ad responsionem ad currentem leakage, quae describi potest sic: sub quantitate certa currentis leakage, quanto maius fuerit electromotive force diversorum transformerum, tanto maior erit eorum sensitivitas.
Sensitivitas est relata ad numerum rotationum windingorum primarii et secundarii transformatoris. Quanto plus rotationum in secundario windingo, tanto maior sensitivitas. Transformator currentis residuorum directe installatur in tribus conductoribus primariis phasealibus, et filum primarium est linea protecta, cum numero rotationum primarii unum. Augmentare numerum rotationum primarii non practicum est.
Electromotive force secundarii windingi, U2=4.44f⋅N2⋅μ⋅I1⋅S, ubi:
I1representat rated currentem primariam.
S est area sectionalis ferri core.
muis permeabilitas magnetica.
f est frequencia.
N2 est numerus rotationum windingi secundarii.
Ut ex formula videre potest, propter limitationes positionis installationis transformatoris, dimensiones externae transformatoris non possunt esse magnae. Itaque, area sectionalis ferri core transformatoris est parva. Ut sensitivitatem transformatoris augmentet, necessarium est aut numerum rotationum windingi secundarii augmentare aut permeabilitatem magneticam ferri core transformatoris meliorare.
Rated currentis primarii interruptorum externorum est fere 630A vel minus. Dato parvo area sectionalis ferri core transformatoris, ut alta sensitivitas assequatur, experimentis, numerus rotationum windingi secundarii generaliter initio inter 1500 et 2000 rotationes ponitur. Numerus specificus rotationum potest determinari secundum onus secundarium et voltage output secundarium transformatoris a microcomputer requiritur.
Cum area sectionalis ferri core, numerus rotationum, et onus secundarium determinata sunt, parametri qui affectant induced electromotive force (id est, sensitivitas) secundarii transformatoris solum ad permeabilitatem magneticam ferri core pertinet. Itaque, determinatio materialis ferri core usi in transformatoris est maximi momenti. Linearity et residual characteristics transformatoris postea mentionati etiam stricte ad materialis ferri core pertinent.
Analyzing data in Table 1, both nanocrystalline alloy and Metglas have the highest magnetic permeability. However, Metglas has a relatively low saturation induction intensity and is also expensive in the market. Considering comprehensively, we preferentially select nanocrystalline alloy as the material.The sensitivity of the transformer is not only directly proportional to the magnetic permeability of the iron core but also has a direct relationship with the shape of the iron core and the length of the magnetic circuit.
Generally, apart from using high-permeability materials for the iron core to enhance the transformer's sensitivity, we also try to shorten the magnetic circuit of the iron core as much as possible to reduce magnetic leakage and ensure the utilization rate of the iron core. Under normal circumstances, a circular iron core has the shortest magnetic circuit. However, since the three-phase primary conductors of the outdoor pole-mounted circuit breaker are arranged side-by-side in a line, when space permits, the iron core should be designed as an ellipse based on the arrangement shape and spacing of the three-phase primary conductors of the circuit breaker. The shape of the transformer and its positional relationship with the primary conductor are shown in Figure 1.
The residual current transformer should be able to respond quickly to abnormal leakage states in the circuit and provide an actionable voltage signal to the microcomputer protection device. The transformer must have good linearity to truly reflect the operating status of the circuit. Linearity refers to the ratio of the change in the input current to the change in the output voltage of the transformer being a constant, as shown in Figure 2.
transformer is only related to the magnetic permeability of the iron core. Therefore, determining the material of the iron core used in the transformer is of crucial importance. The linearity and residual characteristics of the transformer mentioned later are also closely related to the material of the iron core.
In the circuit, the minimum primary operating current of the circuit breaker is generally required to be below 10A. Therefore, it is generally required that when the primary current of the transformer is below 10A, the better the ratio of the change in the input current to the change in the output voltage of the transformer is linear, the more it can meet the usage requirements. The linearity requirement of the transformer needs repeated testing.
Under the condition of a certain magnetic permeability of the iron core and secondary load, the voltage output of the transformer is ensured to change linearly by adjusting the cross-sectional area of the iron core or the number of secondary turns. However, in actual circuits, there are often other factors that affect the transformer from providing an accurate voltage signal to the microcomputer protection device.
When the transformer is installed, it needs to be sleeved on the three-phase conductors arranged side-by-side in a line. When the primary conductor passes the rated current, the residual current transformer will be interfered by the magnetic fields generated by the three-phase currents simultaneously, and the local magnetic flux density of the iron core will increase. If the local part of the iron core is oversaturated, the linearity of the transformer will deteriorate, seriously affecting the magnitude of the secondary output voltage. As a result, the microcomputer protection may malfunction or fail to operate.
During actual operation, after the residual current transformer is impacted by a large-scale ground-fault current, and after the protection action is completed and power supply is restored for continued operation, if the technical parameters of the transformer cannot return to the state before the impact, that is, there is residual magnetism in the iron core of the transformer, it will seriously affect the accurate action of the leakage protector next time.
When designing this residual current transformer, the following points should be noted:
The iron core is preferably made of nanocrystalline alloy with high magnetic permeability and low residual magnetism. This material has good overload characteristics and can easily return to the initial magnetic state under over-current impact. The residual voltage of the transformer can be controlled and detected not to be too large by simulating the passage of various ground-fault currents on the primary side. However, the residual voltage of the transformer generally increases with the increase of the rated primary current. But after the iron core reaches magnetic saturation, the residual voltage on the secondary side of the transformer will increase sharply.
When designing the transformer, in order to minimize the influence of the primary current on the residual voltage value of the residual current transformer, when choosing nanocrystalline alloy with high magnetic permeability and low residual magnetism to make the iron core, measures such as appropriately increasing the cross-sectional area of the iron core or reducing the internal resistance of the secondary winding can be taken jointly to reduce the residual voltage of the residual current transformer.
