{"id":1705,"date":"2025-07-15T16:49:13","date_gmt":"2025-07-15T16:49:13","guid":{"rendered":"https:\/\/www.dioda.ro\/blog\/?p=1705"},"modified":"2025-07-21T07:37:56","modified_gmt":"2025-07-21T07:37:56","slug":"cum-alimentezi-un-motor-trifazat-de-la-o-retea-de-alimentare-monofazata","status":"publish","type":"post","link":"https:\/\/www.dioda.ro\/blog\/electronica\/scheme-electronice\/cum-alimentezi-un-motor-trifazat-de-la-o-retea-de-alimentare-monofazata\/","title":{"rendered":"Cum alimentezi un motor trifazat de la o retea de alimentare monofazat\u0103 ?"},"content":{"rendered":"\n<p>\u00a0<\/p>\n<p><iframe loading=\"lazy\" title=\"Motor trifazat alimentat la reteaua monofazata ?\" src=\"\/\/www.youtube.com\/embed\/5EzY2-7z2nI\" width=\"412\" height=\"732\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n\n\n\n<p class=\"first:mt-1.5\">In literatura internationala este denumita Schema Steinmetz . Aceasta \u00ee\u021bi permite s\u0103 porne\u0219ti \u0219i s\u0103 rulezi un motor asincron trifazat (p\u00e2n\u0103 la \u2248 2 kW) dintr-o re\u021bea monofazat\u0103 de 230 V, ad\u0103ug\u00e2nd un condensator care creeaz\u0103 o a treia \u201efaz\u0103 fictiv\u0103\u201d. Vei ob\u021bine aproximativ 80 % din puterea nominal\u0103 a motorului \u0219i un cuplu de pornire de 20\u201350 % din cel real, suficient pentru aplica\u021bii u\u0219oare \u2013 betoniere, ventilatoare, pompe de circula\u021bie etc.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">1. De ce ai nevoie de Schema Steinmetz?<\/h4>\n\n\n\n<figure class=\"wp-block-image size-full\"><a href=\"https:\/\/www.dioda.ro\/blog\/wp-content\/uploads\/2025\/07\/image-3.png\"><img loading=\"lazy\" decoding=\"async\" width=\"250\" height=\"147\" src=\"https:\/\/www.dioda.ro\/blog\/wp-content\/uploads\/2025\/07\/image-3.png\" alt=\"\" class=\"wp-image-1708\"\/><\/a><\/figure>\n\n\n\n\n\n<p class=\"first:mt-1.5\">Motoarele asincrone trifazate produc un c\u00e2mp rotitor perfect datorit\u0103 celor trei faze defazate la 120\u00b0. Dac\u0103 nu ai dec\u00e2t o priz\u0103 monofazat\u0103, motorul:<\/p>\n\n\n\n<ul class=\"wp-block-list list-disc\">\n<li>nu porne\u0219te singur;<\/li>\n\n\n\n<li>va vibra \u0219i poate lua curent excesiv.<\/li>\n<\/ul>\n\n\n\n<p class=\"first:mt-1.5\">Charles P. Steinmetz a propus \u00eenc\u0103 de la \u00eenceputul secolului XX o solu\u021bie simpl\u0103: ad\u0103ugarea unui condensator \u00eentre una dintre fazele alimentate \u0219i a treia born\u0103 a motorului pentru a genera o \u201efaz\u0103 de ajutor\u201d. Ob\u021bii un c\u00e2mp rotitor eliptic, suficient pentru pornire \u0219i func\u021bionare.<\/p>\n\n\n\n<p><img decoding=\"async\" src=\"https:\/\/www.dioda.ro\/blog\/wp-content\/uploads\/2025\/07\/250px-Steinmetzschema-1.svg.png\" alt=\"Dreieckschaltung\"\/><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">2. Principiul de func\u021bionare<\/h4>\n\n\n\n<ol class=\"wp-block-list list-decimal\">\n<li>Condensatorul <em>C<\/em> introduce o defazare &lt; 90\u00b0 \u00eentre curent \u0219i tensiune \u2192 creezi faza auxiliar\u0103.<\/li>\n\n\n\n<li>Statorul vede trei \u00eenf\u0103\u0219ur\u0103ri alimentate, dar amplitudinile nu mai sunt egale \u2192 moment motor oscilant.<\/li>\n\n\n\n<li>\u00cen gol, motorul atinge tura\u021bia normal\u0103; sub sarcin\u0103 ridicat\u0103 patineaz\u0103 \u0219i scade cuplul.<\/li>\n<\/ol>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">3. Cum alegi legarea motorului<\/h4>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Tensiune re\u021bea<\/th><th>Legare \u00eenf\u0103\u0219ur\u0103ri<\/th><th>Situa\u021bie practic\u0103<\/th><\/tr><\/thead><tbody><tr><td>230 V<\/td><td>triunghi (\u0394)<\/td><td>Cel mai frecvent \u00een Rom\u00e2nia; motorul poate fi trecut pe stea (Y) c\u00e2nd dispui de 400 V trifazat.<\/td><\/tr><tr><td>230 V<\/td><td>stea (Y)<\/td><td>Doar dac\u0103 bobinele motorului sunt pentru 133 V\/230 V \u2013 rar.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"first:mt-1.5\">Schimbarea sensului de rota\u021bie se face simplu: mut\u0103 condensatorul pe cealalt\u0103 faz\u0103 alimentat\u0103 sau \u00eencruci\u0219eaz\u0103 cele dou\u0103 fire de alimentare.<\/p>\n\n\n\n<p>&nbsp;<\/p>\n<p><img decoding=\"async\" src=\"https:\/\/www.dioda.ro\/blog\/wp-content\/uploads\/2025\/07\/250px-Steinmetzschema-Anlaufkondensator.svg.png\" alt=\"Dreieckschaltung mit Anlaufkondensator\"\/><\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">4. Dimensionarea condensatorului<\/h4>\n\n\n\n<p class=\"first:mt-1.5\">Regula practic\u0103 (fosta DIN 48501):<br \/>\u2022 ~ 70 \u00b5F per kW la 230 V.<\/p>\n\n\n\n<p class=\"first:mt-1.5\">Formul\u0103 general\u0103:<\/p>\n\n\n\n<p><span class=\"katex-display\"><span class=\"katex\"><span class=\"katex-mathml\">C=2P3\u2009\u03c9U2C = \\frac{2P}{\\sqrt{3}\\,\\omega U^{2}} <\/span><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"mord mathnormal\">C<\/span><span class=\"mrel\">=<\/span><\/span><span class=\"base\"><span class=\"mord\"><span class=\"mfrac\"><span class=\"vlist-t vlist-t2\"><span class=\"vlist-r\"><span class=\"vlist\"><span class=\"mord sqrt\"><span class=\"svg-align\">3<\/span><span class=\"vlist-s\">\u200b<\/span><\/span><span class=\"mord mathnormal\">\u03c9<\/span><span class=\"mord mathnormal\">U<\/span><span class=\"msupsub\"><span class=\"vlist-t\"><span class=\"sizing reset-size6 size3 mtight\"><span class=\"mord mtight\">2<\/span><\/span><\/span><\/span>2<span class=\"mord mathnormal\">P<\/span><\/span><span class=\"vlist-s\">\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/p>\n\n\n\n<p class=\"first:mt-1.5\">unde<br \/>\u2022 <em>P<\/em> \u2013 puterea nominal\u0103 a motorului (W)<br \/>\u2022 <em>U<\/em> \u2013 tensiunea de linie (V)<br \/>\u2022 <span class=\"katex\"><span class=\"katex-mathml\">\u03c9=2\u03c0f\\displaystyle \\omega = 2\\pi f<\/span><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"mord mathnormal\">\u03c9<\/span><span class=\"mrel\">=<\/span><\/span><span class=\"base\"><span class=\"mord\">2<\/span><span class=\"mord mathnormal\">\u03c0<\/span><span class=\"mord mathnormal\">f<\/span><\/span><\/span><\/span> , iar <em>f<\/em> = 50 Hz.<\/p>\n\n\n\n<p class=\"first:mt-1.5\">Exemplu \u2013 motor de 1,1 kW (\u0394 230 V):<\/p>\n\n\n\n<p><span class=\"katex-display\"><span class=\"katex\"><span class=\"katex-mathml\">C\u224870\u2009\u03bcF\/kW\u00d71,1&nbsp;kW\u224877\u2009\u03bcFC \\approx 70 \\,\\mu\\text{F\/kW} \\times 1{,}1 \\text{ kW} \\approx 77 \\,\\mu\\text{F} <\/span><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"mord mathnormal\">C<\/span><span class=\"mrel\">\u2248<\/span><\/span><span class=\"base\"><span class=\"mord\">70<\/span><span class=\"mord mathnormal\">\u03bc<\/span><span class=\"mord text\"><span class=\"mord\">F\/kW<\/span><\/span><span class=\"mbin\">\u00d7<\/span><\/span><span class=\"base\"><span class=\"mord\">1<\/span><span class=\"mord\"><span class=\"mpunct\">,<\/span><\/span><span class=\"mord\">1<\/span><span class=\"mord text\"><span class=\"mord\">&nbsp;kW<\/span><\/span><span class=\"mrel\">\u2248<\/span><\/span><span class=\"base\"><span class=\"mord\">77<\/span><span class=\"mord mathnormal\">\u03bc<\/span><span class=\"mord text\"><span class=\"mord\">F<\/span><\/span><\/span><\/span><\/span><\/span><\/p>\n\n\n\n<p class=\"first:mt-1.5\">Recomandat: condensator metal-polipropilen\u0103 400\u2013450 V AC, autoregenerant.<\/p>\n\n\n\n<p class=\"first:mt-1.5\">Pentru cuplu de pornire mai mare po\u021bi ad\u0103uga un <strong class=\"\">condensator de pornire<\/strong> (de 1,5\u20132 \u00d7 valoarea lui <em>C<\/em>) pe care \u00eel sco\u021bi din circuit cu un micro-\u00eentrerup\u0103tor centrifugal sau un temporizator dup\u0103 1\u20133 s.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><a href=\"https:\/\/www.dioda.ro\/blog\/wp-content\/uploads\/2025\/07\/image-2.png\"><img loading=\"lazy\" decoding=\"async\" width=\"733\" height=\"460\" src=\"https:\/\/www.dioda.ro\/blog\/wp-content\/uploads\/2025\/07\/image-2.png\" alt=\"\" class=\"wp-image-1707\" srcset=\"https:\/\/www.dioda.ro\/blog\/wp-content\/uploads\/2025\/07\/image-2.png 733w, https:\/\/www.dioda.ro\/blog\/wp-content\/uploads\/2025\/07\/image-2-300x188.png 300w\" sizes=\"auto, (max-width: 733px) 100vw, 733px\" \/><\/a><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p><img decoding=\"async\" src=\"https:\/\/www.dioda.ro\/blog\/wp-content\/uploads\/2025\/07\/250px-Steinmetzschema-2.svg.png\" alt=\"Sternschaltung\" \/><\/p>\n\n\n\n<h4 class=\"wp-block-heading\">5. Performan\u021be \u0219i limit\u0103ri<\/h4>\n\n\n\n<p class=\"first:mt-1.5\">\u2022 Cuplu de pornire <span class=\"katex\"><span class=\"katex-mathml\">MA\u22480,3\u2009MNM_A \\approx 0,3\\,M_N<\/span><span class=\"katex-html\" aria-hidden=\"true\"><span class=\"base\"><span class=\"mord\"><span class=\"mord mathnormal\">M<\/span><span class=\"msupsub\"><span class=\"vlist-t vlist-t2\"><span class=\"vlist-r\"><span class=\"vlist\"><span class=\"sizing reset-size6 size3 mtight\"><span class=\"mord mathnormal mtight\">A<\/span><\/span><\/span><span class=\"vlist-s\">\u200b<\/span><\/span><\/span><\/span><\/span><span class=\"mrel\">\u2248<\/span><\/span><span class=\"base\"><span class=\"mord\">0<\/span><span class=\"mpunct\">,<\/span><span class=\"mord\">3<\/span><span class=\"mord\"><span class=\"mord mathnormal\">M<\/span><span class=\"msupsub\"><span class=\"vlist-t vlist-t2\"><span class=\"vlist-r\"><span class=\"vlist\"><span class=\"sizing reset-size6 size3 mtight\"><span class=\"mord mathnormal mtight\">N<\/span><\/span><\/span><span class=\"vlist-s\">\u200b<\/span><\/span><\/span><\/span><\/span><\/span><\/span><\/span> (20\u201350 %).<br \/>\u2022 Putere util\u0103 \u2248 0,8 \u00b7 Pn.<br \/>\u2022 Curentul din ramura cu condensator difer\u0103 de cel\u0103lalt; motorul \u201ez\u00fcmbie\u201d la 100 Hz.<br \/>\u2022 Limit\u0103 practic\u0103: 1,5\u20132 kW \u2013 peste at\u00e2t costul \u0219i gabaritul condensatorului devin prohibitive, iar re\u021beaua e dezechilibrat\u0103.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">6. Avantaje vs. alternative<\/h4>\n\n\n\n<p class=\"first:mt-1.5\">Avantaje<br \/>\u2022 Cost minim (un condensator \u0219i un comutator).<br \/>\u2022 Folose\u0219ti motoare trifazate second-hand, robuste, la instala\u021bii f\u0103r\u0103 3 \u00d7 400 V.<br \/>\u2022 Inversarea sensului este trivial\u0103.<\/p>\n\n\n\n<p class=\"first:mt-1.5\">Limit\u0103ri<br \/>\u2022 Cuplu mic \u2013 aten\u021bie la \u00eenc\u0103rc\u0103ri grele (compresoare, pompe cu deplasare pozitiv\u0103).<br \/>\u2022 Dezechilibru de faz\u0103 \u00een re\u021bea la sarcin\u0103 mare.<br \/>\u2022 Nu ai reglaj de tura\u021bie.<\/p>\n\n\n\n<p class=\"first:mt-1.5\">Alternative moderne<br \/>\u2022 <strong class=\"\">Convertizor de frecven\u021b\u0103 monofazat \u2192 trifazat<\/strong>: cost mai mare, dar<br \/>\u2013 cuplu de 100 %,<br \/>\u2013 pornire lin\u0103,<br \/>\u2013 tura\u021bie variabil\u0103,<br \/>\u2013 protec\u021bii \u00eencorporate.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">7. Aplica\u021bii tipice<\/h4>\n\n\n\n<ol class=\"wp-block-list list-decimal\">\n<li>Betoniere de \u0219antier \u0219i malaxoare de furaje.<\/li>\n\n\n\n<li>Ventilatoare industriale \u0219i exhaustoare de praf.<\/li>\n\n\n\n<li>Pompe de circula\u021bie \u00een instala\u021bii vechi de \u00eenc\u0103lzire.<\/li>\n\n\n\n<li>Ma\u0219ini de sp\u0103lat industriale\/semiprofesionale de genera\u021bie mai veche.<\/li>\n<\/ol>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">8. Pa\u0219i practici de implementare<\/h4>\n\n\n\n<ol class=\"wp-block-list list-decimal\">\n<li>Identific\u0103 bornele motorului; monteaz\u0103 pun\u021bile pentru \u0394 230 V.<\/li>\n\n\n\n<li>Alege <em>C<\/em> conform regulii 70 \u00b5F \/ kW sau formulei.<\/li>\n\n\n\n<li>Monteaz\u0103 condensatorul \u00eentre borna liber\u0103 \u0219i una dintre fazele alimentate.<\/li>\n\n\n\n<li>Testeaz\u0103 pornirea; dac\u0103 motorul nu pleac\u0103:<br \/>\u2022 cre\u0219te temporar capacitatea de pornire,<br \/>\u2022 redu sarcina mecanic\u0103 (sl\u0103be\u0219te curelele, decupleaz\u0103 tamburul).<\/li>\n\n\n\n<li>Verific\u0103 \u00eenc\u0103lzirea condensatorului dup\u0103 10 min de func\u021bionare continu\u0103.<\/li>\n<\/ol>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\">9. Concluzie<\/h4>\n\n\n\n<p class=\"first:mt-1.5\">Schema Steinmetz este un \u201ehack\u201d electrotehnic elegant, vechi de peste un secol, care r\u0103m\u00e2ne util c\u00e2nd:<\/p>\n\n\n\n<ul class=\"wp-block-list list-disc\">\n<li>ai la dispozi\u021bie doar 230 V monofazat;<\/li>\n\n\n\n<li>vrei s\u0103 folose\u0219ti un motor trifazat economic \u0219i fiabil;<\/li>\n\n\n\n<li>sarcina este u\u0219oar\u0103, iar pornirile nu sunt foarte frecvente.<\/li>\n<\/ul>\n\n\n\n<p class=\"first:mt-1.5\">Pentru proiecte DIY sau echipamente industriale mici, aceast\u0103 solu\u021bie cost-eficient\u0103 poate fi tot ce-\u021bi trebuie. Dac\u0103, \u00eens\u0103, ai nevoie de cuplu maxim, pornire lin\u0103 \u0219i control de vitez\u0103, investe\u0219te \u00eentr-un convertizor de frecven\u021b\u0103.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p class=\"first:mt-1.5\">Articol adaptat \u0219i sintetizat pe baza materialului \u201eSteinmetzschaltung\u201d de pe Wikipedia (licen\u021b\u0103 CC-BY-SA 4.0).<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Cum alimentezi un motor trifazic la reteaua monofazata ?<\/p>\n","protected":false},"author":1,"featured_media":1716,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"Cum conectezi un motor trifazic la reteaua monofazata ? 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