Yuqori kuchlanishli to'g'ridan-to'g'ri oqim - High-voltage direct current - Wikipedia

Uzoq masofali HVDC liniyalari gidroelektr Kanadadan Nelson daryosi bunga konverter stantsiyasi bu erda u janubda foydalanish uchun AC ga aylantiriladi Manitoba panjara

A yuqori voltli, doimiy oqim (HVDC) elektr energiyasini uzatish tizim (shuningdek, a super magistral yoki an elektr magistral)[1][2][3] foydalanadi to'g'ridan-to'g'ri oqim (DC) elektr energiyasini ommaviy ravishda uzatish uchun, odatdagidan farqli o'laroq o'zgaruvchan tok (AC) tizimlari.[4]

HVDC ulanishlarining aksariyati 100 kV dan 800 kV gacha bo'lgan kuchlanishlardan foydalanadi. Xitoyda 1100 kV kuchlanishli aloqa 2019 yilda 12 GVt quvvat bilan 3300 km masofada qurib bitkazildi. [5][6] Ushbu o'lchov bilan qit'alararo ulanishlar mumkin bo'lib, bu tebranishlar bilan kurashishga yordam beradi shamol kuchi va fotoelektrlar.

HVDC elektr energiyasini uzatish imkonini beradi sinxronlashtirilmagan AC uzatish tizimlari. HVDC aloqasi orqali quvvat oqimi manba va yuk o'rtasidagi o'zgarishlar burchagidan mustaqil ravishda boshqarilishi mumkinligi sababli, quvvatning tez o'zgarishi tufayli tarmoqni buzilishlarga qarshi barqarorlashtirishi mumkin. HVDC shuningdek, turli xil chastotalarda ishlaydigan tarmoq tizimlari o'rtasida quvvatni uzatishga imkon beradi, masalan, 50 Hz va 60 Hz. Bu mos kelmaydigan tarmoqlar o'rtasida quvvat almashinuvini ta'minlash orqali har bir tarmoqning barqarorligi va tejamkorligini yaxshilaydi.

HVDC uzatishning zamonaviy shakli 1930 yillarda keng rivojlangan texnologiyadan foydalanadi Shvetsiya (ASEA ) va Germaniya. Dastlabki tijorat inshootlari bittasiga kiritilgan Sovet Ittifoqi 1951 yilda Moskva va Kashira va 100 kV, 20 MVt quvvatga ega tizim Gotland va 1954 yilda Shvetsiya materikida.[7] 2019 yilgi Xitoy loyihasidan oldin dunyodagi eng uzun HVDC aloqasi bu edi Rio-Madeyra ulanish Braziliya, har biri 3150 MVt bo'lgan birlashtiruvchi ± 600 kV ikkita bipoladan iborat Portu Velho holatida Rondoniya uchun San-Paulu maydon. DC chizig'ining uzunligi 2375 km (1476 mil).[8]

  Mavjud havolalar
  Qurilish ishlari olib borilmoqda
  Taklif qilingan
Ushbu HVDC liniyalarining ko'pi elektr energiyasini qayta tiklanadigan gidroenergiya va shamol kabi manbalardan uzatadi. Ismlar uchun, shuningdek, ga qarang izohli versiya.

Yuqori kuchlanishli uzatish

Yuqori kuchlanish uchun ishlatiladi elektr energiyasi yo'qolgan energiyani kamaytirish uchun uzatish qarshilik simlarning. O'tkazilgan ma'lum miqdordagi quvvat uchun kuchlanishni ikki baravar oshirish oqimning atigi yarmida bir xil quvvatni beradi. Simlardagi issiqlik sifatida yo'qolgan quvvat oqim kvadratiga to'g'ri proportsional bo'lgani uchun, kuchlanishni ikki baravar oshirish chiziqdagi yo'qotishlarni 4 baravar kamaytiradi, uzatishda yo'qolgan quvvatni ham o'tkazgich hajmini oshirish orqali kamaytirish mumkin, kattaroq o'tkazgichlar og'irroq va qimmatroq.

Yorug'lik yoki dvigatellar uchun yuqori voltajdan osonlikcha foydalanish mumkin emas, shuning uchun oxirgi foydalanish uskunalari uchun uzatish darajasidagi kuchlanishlarni kamaytirish kerak. Transformatorlar kuchlanish darajasini o'zgartirish uchun ishlatiladi o'zgaruvchan tok (AC) uzatish davrlari. Transformatorlar voltaj o'zgarishini amaliy holga keltirdilar va o'zgaruvchan tok generatorlari doimiy oqimdan ko'ra samaraliroq edi. Ushbu afzalliklar 20-asrning boshlarida o'zgaruvchan tok tizimlari tomonidan erta past kuchlanishli shahar uzatish tizimlarini almashtirishga olib keldi.[9]

Rivojlanish bilan o'zgaruvchan va doimiy shahar o'rtasida quvvatni amaliy konvertatsiya qilish mumkin bo'ldi quvvat elektroniği kabi qurilmalar simob-boshq valflari va 1970-yillardan boshlab yarimo'tkazgich qurilmalari tiristorlar, o'rnatilgan eshikli komutatorli tiristorlar (IGCTs), MOS tomonidan boshqariladigan tiristorlar (MCT) va izolyatsiya qilingan eshikli bipolyar tranzistorlar (IGBT).[10]

Tarix

Elektromexanik (Thury) tizimlar

Thury HVDC uzatish tizimining sxematik diagrammasi
1971 yilda HVDC: bu 150 kV simob-boshq valfi o'zgaruvchan tok gidroenergetika dan uzoq shaharlarga uzatish uchun kuchlanish Manitoba Hydro generatorlar.
Pylons Boltiq kabeli Shvetsiyadagi HVDC

Birinchi uzoq masofaga elektr energiyasini uzatish 1882 yilda to'g'ridan-to'g'ri oqim yordamida namoyish etildi Miesbach-Myunxen elektr uzatish, lekin faqat 1,5 kVt uzatildi.[11] Shveytsariyalik muhandis tomonidan HVDC uzatishning dastlabki usuli ishlab chiqilgan Rene Thury[12] va uning usuli 1889 yilda amalda qo'llanilgan Italiya tomonidan Akvadotto De Ferrari-Galliera kompaniya. Ushbu tizim ketma-ket ulangan holda ishlatilgan motor generatori kuchlanishni oshirish uchun to'plamlar. Har bir to'plam izolyatsiya qilingan elektr topraklama va a dan izolyatsiya qilingan vallar tomonidan boshqariladi asosiy harakat. Elektr uzatish liniyasi "doimiy oqim" rejimida ishlagan, har bir mashina bo'ylab 5000 voltgacha, ba'zi mashinalarda esa ikki baravar bo'lgan komutatorlar har bir kommutatorda kuchlanishni kamaytirish uchun. Ushbu tizim 630 kVt quvvatni doimiy ravishda 14 kV kuchlanish bilan 120 km masofaga uzatdi.[13][14] The Mutyers – Lion tizim 8,600 kVt gidroelektr energiyasini 200 km masofaga, shu jumladan 10 km er osti kabelini uzatdi. Ushbu tizimda musbat va manfiy qutblar orasidagi umumiy quvvati 150 kV bo'lgan ikkita komutatorli sakkizta ketma-ket ulangan generatorlar ishlatilgan va 1906 yildan 1936 yilgacha ishlagan. O'n besh Thury tizimlari 1913 yilga qadar ishlay boshlagan.[15] 100 kV kuchlanishli doimiy ishlaydigan boshqa Thury tizimlari 1930-yillarda ishlagan, ammo aylanadigan mashinalar yuqori texnik xizmat ko'rsatishni talab qilgan va katta energiya yo'qotishlarga duch kelgan. Turli xil elektromexanik qurilmalar 20-asrning birinchi yarmida kichik tijorat muvaffaqiyatlari bilan sinovdan o'tkazildi.[16]

To'g'ridan to'g'ri oqimni yuqori uzatish voltajidan pastroq foydalanish voltajiga o'tkazishga urinish usullaridan biri bu ketma-ket ulangan zaryadlash edi batareyalar, keyin tarqatish yuklariga xizmat qilish uchun batareyalarni parallel ravishda qayta ulang.[17] 20-asrning boshlarida kamida ikkita tijorat inshooti sinab ko'rilgan bo'lsa-da, batareyalar quvvati cheklanganligi, ketma-ket va parallel ulanishlarni almashtirishdagi qiyinchiliklar va batareyaning zaryadlash / zaryadsizlanishiga xos energiya samaradorligi tufayli texnik odatda foydali bo'lmadi. tsikl (Zamonaviy batareyani saqlash quvvat stantsiyasi energiyani o'zgaruvchan tokdan to'g'ridan-to'g'ri oqim shakllariga mos keladigan kuchlanishlarda o'zgartirish uchun transformatorlar va invertorlarni o'z ichiga oladi.)

Simob kamonli klapanlar

Birinchi marta 1914 yilda taklif qilingan,[18] tarmoq boshqariladi simob-boshq valfi 1920 yildan 1940 yilgacha elektr energiyasini etkazib berish imkoniyati paydo bo'ldi. 1932 yildan boshlab, General Electric sinovdan o'tgan simob-bug 'klapanlari va 12 kV doimiy elektr uzatish liniyasi, shuningdek, 40 Gts avlodni 60 Gts yuklarni ishlashga aylantirishga xizmat qildi. Mechanicville, Nyu-York. 1941 yilda shahar uchun 60 MVt, ± 200 kV, 115 km ko'milgan kabel aloqasi ishlab chiqilgan Berlin simob boshq vanalaridan foydalangan holda (Elbe-loyihasi ), ammo qulashi tufayli Germaniya hukumati 1945 yilda loyiha hech qachon tugallanmagan.[19] Loyiha uchun nominal asos, urush paytida, ko'milgan kabel bombardimon ob'ekti sifatida unchalik sezilmasligi edi. Uskunalar Sovet Ittifoqi va u erda Moskva-Kashira HVDC tizimi sifatida foydalanishga topshirildi.[20] Moskva-Kashira tizimi va 1954 yilgacha bo'lgan aloqa Uno Lamm guruhi da ASEA Shvetsiya materik va Gotland oroli o'rtasida HVDC yuqtirishning zamonaviy davri boshlandi.[11]

Simob kamonli valflari oqimni nolga etkazish va shu bilan valfi o'chirish uchun tashqi zanjirni talab qiladi. HVDC dasturlarida AC quvvat tizimining o'zi vositalarni ta'minlaydi kommutatsiya konvertorda boshqa valfga oqim. Binobarin, simob kamonli valflari bilan qurilgan konvertorlar chiziqli komutlangan konvertorlar (LCC) deb nomlanadi. LCClar ulangan o'zgaruvchan tok tizimlarida aylanadigan sinxron mashinalarni talab qiladi, bu esa passiv yukga elektr energiyasini etkazib berishni imkonsiz qiladi.

Simob kamonli klapanlar 1972 yilgacha tuzilgan tizimlarda keng tarqalgan edi, oxirgi HVDC simob kamon tizimi ( Nelson daryosi Bipol 1 tizimi yilda Manitoba, Kanada) 1972 yildan 1977 yilgacha bosqichma-bosqich foydalanishga topshirildi.[21] O'shandan beri barcha simob boshq tizimlari o'chirildi yoki qattiq holatdagi qurilmalardan foydalanishga aylantirildi. Simob boshq vanalarini ishlatgan so'nggi HVDC tizimi bu edi Orollararo HVDC aloqasi shimoliy va janubiy orollar o'rtasida Yangi Zelandiya, ularni ikkita qutbdan birida ishlatgan. Simob yoyi klapanlari 2012 yil 1 avgustda tiristor konvertorlarini almashtirishni ishga tushirish arafasida bekor qilindi.

Tiristor klapanlari

1977 yildan beri yangi HVDC tizimlari faqat ishlatilgan qattiq holatdagi qurilmalar, aksariyat hollarda tiristorlar. Simob boshq valflari singari, tiristorlar ularni yoqish va o'chirish uchun HVDC dasturlarida tashqi o'zgaruvchan tok zanjiriga ulanishni talab qiladi. Tiristorlardan foydalangan HVDC HVDC Line-Commutated Converter (LCC) deb ham ataladi.

HVDC uchun tiristor klapanlarini ishlab chiqish 1960 yillarning oxirlarida boshlangan. Tiristorga asoslangan birinchi to'liq HVDC sxemasi bu edi Eel daryosi tomonidan qurilgan Kanadadagi sxema General Electric va 1972 yilda xizmatga kirdi.

1979 yil 15 martda 1920 MVt quvvatga ega tiristor o'rtasida to'g'ridan-to'g'ri oqim aloqasi mavjud Kabora Bassa va Yoxannesburg (1,410 km) energiya bilan ta'minlandi. Konversion uskunalar 1974 yilda qurilgan Allgemeine Elektricitäts-Gesellschaft AG (AEG) va Jigarrang, Boveri va Cie (BBC) va Simens loyihaning sheriklari bo'lgan. Xizmatning bir necha yillik uzilishlari a Mozambikdagi fuqarolar urushi.[22] ± 533 kV kuchlanishli kuchlanish o'sha paytda dunyodagi eng yuqori ko'rsatkich edi.[11]

Kondensator bilan almashtirilgan konvertorlar (CCC)

Chiziqli komutatorli konvertorlar HVDC tizimlari uchun ba'zi cheklovlarga ega. Buning sababi, o'zgaruvchan tok zanjirining tiristor oqimini o'chirishi va o'chirishni (o'chirish vaqti) ta'sir qilish uchun qisqa muddatli "teskari" kuchlanish zarurligini keltirib chiqaradi. Ushbu cheklovlarni hal qilishga urinish bu kondensator bilan almashtirilgan konvertor (CCC) kam sonli HVDC tizimlarida ishlatilgan. CCC an'anaviy HVDC tizimidan farq qiladi, chunki u seriyali kondansatörler konvertor transformatorining birlamchi yoki ikkilamchi tomonida o'zgaruvchan tok liniyasi ulanishlariga kiritilgan. Seriyali kondensatorlar qisman ofsetni qoplaydi o'zgaruvchan indüktans konvertorning shikastlanishi va nosozlik oqimlarini kamaytirishga yordam beradi. Bu ham kichikroq bo'lishiga imkon beradi yo'q bo'lish burchagi konvertor / invertor bilan ishlatilishi kerak, bu ehtiyojni kamaytiradi reaktiv quvvat qo'llab-quvvatlash.

Biroq, o'chish (o'chirish) vaqtini to'liq bartaraf etadigan kuchlanish manbai konvertorlari (VSC) paydo bo'lishi sababli CCC faqat bo'sh joy dastur bo'lib qoldi.

Quvvat manbai konvertorlari (VSC)

Keng tarqalgan bo'lib ishlatiladi motorli drayvlar 1980-yillardan boshlab HVDC-da kuchlanish manbai konvertorlari 1997 yilda eksperimental ravishda paydo bo'la boshladi Hellsjön – Grängesberg Shvetsiyadagi loyiha. 2011 yil oxiriga kelib ushbu texnologiya HVDC bozorining muhim qismini egallab oldi.

Yuqori darajadagi rivojlanish izolyatsiya qilingan eshikli bipolyar tranzistorlar (IGBT), eshikni o'chirish tiristorlari (GTO) va o'rnatilgan eshikli komutatorli tiristorlar (IGCTs), kichikroq HVDC tizimlarini tejamkor qildi. Ishlab chiqaruvchi ABB guruhi ushbu kontseptsiyani chaqiradi HVDC nuri, esa Simens shunga o'xshash tushunchani chaqiradi HVDC PLUS (Power Link universal tizimi) va Alstom ushbu texnologiya asosida o'z mahsulotlarini chaqiring HVDC MaxSine. Ular HVDC-dan foydalanishni bir necha o'nlab megavattgacha bo'lgan bloklarga va bir necha o'n kilometrlik havo liniyalariga qadar kengaytirdilar. VSC texnologiyasining bir nechta turli xil variantlari mavjud: 2012 yilgacha qurilgan ko'pgina qurilmalar impuls kengligi modulyatsiyasi samarali ravishda ultra yuqori voltli dvigatel qo'zg'atuvchisi. Hozirgi qurilmalar, jumladan HVDC PLUS va HVDC MaxSine, konvertorning variantlari Modulli ko'p darajali konvertor (MMC).

Ko'p darajali konvertorlarning afzalliklari ular imkon beradi harmonik qisqartirilishi yoki umuman yo'q qilinishi kerak bo'lgan filtrlash uskunalari. Taqqoslash uchun, odatdagi chiziqli almashinadigan konverter stantsiyalarning o'zgaruvchan tok garmonik filtrlari konvertor stantsiyasi maydonining deyarli yarmini qamrab oladi.

Vaqt o'tishi bilan, kuchlanish manbalarini konvertor tizimlari, ehtimol, barcha o'rnatilgan oddiy tiristorlarga asoslangan tizimlarni, shu jumladan, eng yuqori shahar elektr uzatish dasturlarini almashtiradi.[10]

AC bilan taqqoslash

Afzalliklari

Uzoq masofaga, nuqtadan nuqtaga HVDC uzatish sxemasi odatda investitsiya xarajatlarining umumiy qiymatiga va o'zgaruvchan o'zgaruvchan tok uzatish sxemasidan kamroq yo'qotishlarga ega. Terminal stantsiyalaridagi HVDC konversion uskunalari qimmatga tushadi, ammo uzoq masofalarga doimiy uzatish liniyasining umumiy xarajatlari bir xil masofadagi o'zgaruvchan tok liniyasidan past bo'ladi. HVDC birligi masofaga o'zgaruvchan tok chizig'iga qaraganda kamroq o'tkazgich talab qiladi, chunki qo'llab-quvvatlashga hojat yo'q uch bosqich va yo'q teri ta'siri.

Voltaj darajasiga va qurilish detallariga qarab, HVDC uzatish yo'qotishlari 1000 km ga 3% dan kam, ya'ni bir xil kuchlanish darajalarida o'zgaruvchan tok liniyalariga qaraganda 30-40% kam.[23][tekshirib bo'lmadi ][yaxshiroq manba kerak ] Buning sababi shundaki, to'g'ridan-to'g'ri oqim faqat faol quvvatni uzatadi va shu bilan ikkalasini ham o'tkazadigan o'zgaruvchan tokdan kamroq yo'qotishlarni keltirib chiqaradi faol va reaktiv quvvat.

HVDC uzatilishi boshqa texnik imtiyozlar uchun ham tanlanishi mumkin. HVDC quvvatni alohida AC tarmoqlari o'rtasida o'tkazishi mumkin. Alohida o'zgaruvchan tok tizimlari orasidagi HVDC quvvat oqimi vaqtincha har qanday tarmoqni qo'llab-quvvatlash uchun avtomatik ravishda boshqarilishi mumkin, ammo katta xavf tug'dirmaydi quvvat tizimining qulashi bitta tarmoqda ikkinchisida qulashga olib keladi. HVDC tizimning boshqaruvchanligini yaxshilaydi, hech bo'lmaganda bitta HVDC havolasi o'zgaruvchan tok tarmog'iga o'rnatiladi - tartibga solinmagan muhitda, boshqarish qobiliyati xususan energiya savdosini boshqarish zarur bo'lganda foydalidir.

HVDC uzatishning umumiy iqtisodiy va texnik foydalari uni asosiy foydalanuvchilardan uzoqda joylashgan elektr manbalarini ulash uchun mos tanlov qilishi mumkin.

HVDC uzatish texnologiyasining afzalliklari mavjud bo'lgan maxsus dasturlarga quyidagilar kiradi:

  • Dengiz osti kabeli uzatish sxemalari (masalan, 580 km.) NorNed Norvegiya va Gollandiya,[24] Italiyaning 420 km SAPEI orasidagi simi Sardiniya va materik,[25] 290 km Basslink Avstraliya materik va o'rtasida Tasmaniya,[26] va 250 km Boltiq kabeli o'rtasida Shvetsiya va Germaniya[27]).
  • Uzoq masofadan elektr energiyasini uzatish uchun oraliq "kranlarsiz", odatda uzoqdan ishlab chiqaruvchi zavodni asosiy tarmoqqa ulash uchun, masalan, Nelson daryosi shahar uzatish tizimi yilda Kanada.
  • Mavjud quvvatni oshirish elektr tarmog'i qo'shimcha simlarni o'rnatish qiyin yoki qimmat bo'lgan holatlarda.
  • Sinxronizatsiya qilinmagan o'zgaruvchan tok tarmoqlari o'rtasida elektr energiyasini uzatish va barqarorlashtirish, shu bilan birga, turli xil chastotalarda o'zgaruvchan tokni ishlatadigan mamlakatlar o'rtasida quvvatni uzatish qobiliyati. Bunday uzatish har qanday yo'nalishda sodir bo'lishi mumkinligi sababli, bu ikkala tarmoqning barqarorligini favqulodda vaziyatlarda va nosozliklarda bir-birlariga chizishlariga imkon berish orqali oshiradi.
  • Nosozlik darajasini oshirmasdan, asosan o'zgaruvchan tok tarmog'ini barqarorlashtirish (istiqbolli qisqa tutashuv oqimi ).
  • Shamol kabi qayta tiklanadigan manbalarni asosiy uzatish tarmog'iga qo'shilishi. Shimoliy Amerika va Evropada quruqlikdagi shamollarni integratsiya qilish loyihalari uchun HVDC havo liniyalari va dengizdagi loyihalar uchun HVDC kabellari texnik va iqtisodiy sabablarga ko'ra taklif qilingan. Ko'p kuchlanishli manbali konvertorlar (VSC) bo'lgan doimiy tarmoqlar dengizdagi shamol energiyasini to'plash va uni quruqlikda joylashgan yuk markazlariga etkazish uchun texnik echimlardan biridir.[28]

Kabel tizimlari

Uzoq dengiz osti yoki er osti yuqori voltli kabellar yuqori elektrga ega sig'im havo uzatish liniyalari bilan taqqoslaganda, chunki kabel ichidagi elektr o'tkazgichlari nisbatan yupqa izolyatsiya qatlami bilan o'ralgan ( dielektrik ) va metall niqobi ostida. Geometriya uzun koaksialdir kondansatör. Umumiy sig'im kabelning uzunligi bilan ortadi. Ushbu sig'im a parallel elektron yuk bilan. Kabelni uzatish uchun o'zgaruvchan tok ishlatilgan joyda, ushbu simi sig'imini zaryad qilish uchun kabelda qo'shimcha oqim oqishi kerak. Ushbu qo'shimcha oqim oqimi kabelning o'tkazgichlarida issiqlik tarqalishi va uning haroratini ko'tarish orqali qo'shimcha energiya yo'qotishlarini keltirib chiqaradi. Natijada qo'shimcha energiya yo'qotishlari ham yuzaga keladi dielektrik kabel izolyatsiyasidagi yo'qotishlar.

Ammo, agar to'g'ridan-to'g'ri oqim ishlatilsa, simi sig'imi faqat simi birinchi marta quvvatlanganda yoki kuchlanish darajasi o'zgarganda zaryadlanadi; qo'shimcha oqim talab qilinmaydi. Etarli uzunlikdagi o'zgaruvchan tok kabeli uchun elektr o'tkazgichning butun oqim o'tkazuvchanlik qobiliyati faqat zaryadlovchi oqimni etkazib berish uchun kerak bo'ladi. Ushbu simi sig'im AC quvvat kabellarining uzunligi va elektr o'tkazuvchanligini cheklaydi.[29] Doimiy quvvatli kabellar faqat harorat ko'tarilishi va bilan cheklanadi Ohm qonuni. Ba'zi bir qochqin oqimi bo'lsa ham orqali dielektrik izolyator, bu kabelning nominal oqimi bilan taqqoslaganda kichikdir.

Havo liniyalari tizimlari

Uzoq muddatli er osti yoki dengiz osti kabellarining o'zgaruvchan tok uzatish dasturlaridagi sig'im effekti o'zgaruvchan tokning havo liniyalariga ham tegishli, garchi bu juda kam bo'lsa. Shunga qaramay, uzoq muddatli o'zgaruvchan elektr uzatish liniyasi uchun faqat chiziq sig'imini zaryad qilish uchun oqadigan oqim sezilarli bo'lishi mumkin va bu chiziqning masofadan oxirigacha yukni foydali oqimga etkazish qobiliyatini pasaytiradi. O'zgaruvchan tok liniyalarining foydali oqim o'tkazuvchanligini pasaytiradigan yana bir omil bu teri ta'siri, bu esa o'tkazgichning tasavvurlar maydoni bo'yicha oqimning bir xil bo'lmagan taqsimlanishiga olib keladi. To'g'ridan to'g'ri oqim bilan ishlaydigan elektr uzatish o'tkazgichlari hech qanday cheklovlardan aziyat chekmaydi. Shuning uchun, xuddi shu Supero'tkazuvchilar yo'qotishlari (yoki isitish effekti) uchun, ma'lum bir o'tkazgich HVDC bilan ishlashda o'zgaruvchan tokdan ko'ra ko'proq quvvatni ko'tarishi mumkin.

Va nihoyat, atrof-muhit sharoitlariga va HVDC bilan ishlaydigan havo uzatish izolyatsiyasining ishlashiga qarab, ma'lum bir uzatish liniyasining doimiy HVDC voltaji bilan ishlashi mumkin, bu uning o'zi ishlab chiqarilgan va o'zgaruvchan tokning eng yuqori voltaji bilan bir xil bo'ladi. izolyatsiya. AC tizimida etkazib beriladigan quvvat o'rtacha kvadrat (RMS) o'zgaruvchan voltaj, lekin RMS eng yuqori voltajning atigi 71% ni tashkil qiladi. Shuning uchun, agar HVDC liniyasi doimiy ravishda o'zgaruvchan tok kuchiga teng bo'lgan HVDC kuchlanishi bilan ishlay olsa, u holda ma'lum bir oqim uchun (bu erda HVDC oqimi o'zgaruvchan tok liniyasidagi RMS oqimi bilan bir xil bo'ladi), HVDC bilan ishlashda quvvatni uzatish qobiliyati AC bilan ishlashdan taxminan 40% yuqori.

Asenkron ulanishlar

HVDC sinxronizatsiya qilinmagan o'zgaruvchan tok tarqatish tizimlari o'rtasida elektr energiyasini uzatishga imkon berganligi sababli, bu tizimning barqarorligini oshirishga yordam beradi kaskadli nosozliklar kengroq elektr uzatish tarmog'ining boshqasidan boshqasiga tarqalishidan. O'zgaruvchan tok tarmog'ining qismlarini sinxronizatsiya qilinishiga va ajralib chiqishiga olib keladigan yukning o'zgarishi, xuddi shu kabi doimiy oqimga ta'sir qilmaydi va shahar zanjiri orqali quvvat oqimi o'zgaruvchan tok tarmog'ini barqaror qiladi. Shahar aloqasi orqali quvvat oqimining kattaligi va yo'nalishi to'g'ridan-to'g'ri boshqarilishi mumkin va o'zgaruvchan tokning har ikki uchida joylashgan AC tarmoqlarini qo'llab-quvvatlash uchun kerak bo'lganda o'zgartirilishi mumkin. Bu ko'plab energiya tizimlari operatorlarining barqarorligi uchun faqatgina HVDC texnologiyasidan kengroq foydalanishni o'ylashga majbur qildi.

Kamchiliklari

HVDC ning kamchiliklari konvertatsiya qilish, almashtirish, boshqarish, foydalanish va texnik xizmat ko'rsatishdir.

HVDC unchalik ishonchli emas va pastroq mavjudlik o'zgaruvchan tok (AC) tizimlariga qaraganda, asosan qo'shimcha konversion uskunalar tufayli. Yagona kutupli tizimlar taxminan 98,5% ni tashkil qiladi, ishlamay qolgan vaqtlarning uchdan bir qismi nosozliklar sababli rejadan tashqari. Xatolarga bardoshli bipolli tizimlar ulanish imkoniyatlarining 50 foizini yuqori darajada ta'minlaydi, ammo to'liq quvvatga ega bo'lish taxminan 97% dan 98% gacha.[30]

Kerakli konvertor stantsiyalari qimmat va haddan tashqari yuk hajmi cheklangan. Kichikroq uzatish masofalarida konvertor stantsiyalaridagi yo'qotishlar bir xil masofadagi o'zgaruvchan tok uzatish liniyasidan kattaroq bo'lishi mumkin.[31] Konvertorlarning narxi liniyani qurish narxining pasayishi va chiziqning past darajadagi yo'qotilishi bilan qoplanmasligi mumkin.

HVDC sxemasidan foydalanish ko'plab zaxira qismlarni saqlashni talab qiladi, ko'pincha faqat bitta tizim uchun, chunki HVDC tizimlari o'zgaruvchan tok tizimlariga qaraganda kamroq standartlangan va texnologiya tez o'zgarib turadi.

O'zgaruvchan tok tizimlaridan farqli o'laroq, ko'p terminalli tizimlarni amalga oshirish murakkab (ayniqsa, chiziqli komutatorli konvertorlar bilan), mavjud sxemalarni ko'p terminalli tizimlarga kengaytirmoqda. Ko'p terminalli doimiy tizimdagi quvvat oqimini boshqarish barcha terminallar o'rtasida yaxshi aloqani talab qiladi; quvvat oqimi o'zgaruvchan tok uzatish liniyasining o'ziga xos empedansi va fazali burchak xususiyatlariga ishonish o'rniga konvertorni boshqarish tizimi tomonidan faol ravishda tartibga solinishi kerak.[32] Ko'p terminalli tizimlar kamdan-kam uchraydi. 2012 yilga kelib faqat ikkitasi xizmat qiladi: Hydro Québec - Nyu-England translyatsiyasi Radisson, Sendi Pond va Nikolet o'rtasida[33] va Sardiniya - materik Italiya 1989 yilda orolni quvvat bilan ta'minlash uchun o'zgartirilgan havola Korsika.[34]

Yuqori kuchlanishli doimiy o'chirgich

HVDC elektron to'xtatuvchidir tufayli qurish qiyin boshq: o'zgaruvchan tok ostida voltaj invertsiyalari va shu bilan nol voltni kesib o'tadi, soniyada o'nlab marta. O'zgaruvchan tok yoyi ushbu nol o'tish nuqtalaridan birida "o'z-o'zidan o'chadi", chunki potentsiallar farqi bo'lmagan joyda yoy bo'lishi mumkin emas. Shahar hech qachon nol voltni kesib o'tmaydi va hech qachon o'z-o'zini o'chirmaydi, shuning uchun kamon masofasi va davomiyligi doimiy ravishda o'zgaruvchan tok kuchiga nisbatan ancha katta. Bu shuni anglatadiki, oqimni nolga etkazish va kamonni o'chirish uchun avtomatizatorga biron bir mexanizm kiritilishi kerak, aks holda yoyish va kontaktlarning zanglashiga olib o'tish ishonchli o'tish uchun juda yaxshi bo'lar edi.

2012 yil noyabr oyida ABB dunyodagi birinchi ultrafast HVDC elektron to'xtatuvchisi ishlab chiqarilganligini e'lon qildi.[35][36] Mexanik o'chirish to'xtatuvchilari HVDC tarmoqlarida foydalanish uchun juda sekin, garchi ular boshqa dasturlarda yillar davomida ishlatilgan bo'lsa ham. Aksincha, yarimo'tkazgich to'xtatuvchilari etarlicha tez, ammo normal ishlashda energiya sarflash va issiqlik hosil qilishda yuqori qarshilikka ega. ABB to'xtatuvchisi yarim o'tkazgich va mexanik to'sarlarni birlashtirib, "gibrid to'xtatuvchini" ishlab chiqaradi, bu esa tanaffusning tezligi va normal ishlashida qarshilik darajasi past.

Gibrid to'sar odatdagi yarimo'tkazgich to'xtatuvchiga ("asosiy to'sar") asoslangan bo'lib, xarakterli tez tanaffus vaqti, to'liq kuchlanish va tokning bardoshliligi, shuningdek, o'tkazishda xarakterli qarshilikka ega. Ushbu asosiy to'sar "yuk kommutatori" bilan parallel ravishda joylashtirilgan: tezkor mexanik kalit ("o'ta tez ajratuvchi") bilan ketma-ket kichik yarimo'tkazgichli to'sar ("yukni almashtirish kommutatori"). Garchi yuk kommutatorining hech bir elementi chiziqning to'liq kuchlanishini buzolmasa-da, yuk kommutatori asosiy ish to'xtatuvchisidan pastroq rezistiv yo'qotishlar bilan normal ish oqimini xavfsiz ravishda ko'tarishi mumkin. Nihoyat, chiziqni to'liq uzish uchun sekin mexanik kalit mavjud. Chiziq quvvatlanganda uni ochib bo'lmaydi, lekin oqim oqmasdan va issiqlik hosil bo'lmasdan chiziqni to'liq uzib qo'yadi. Oddiy ishlashda barcha kalitlar yopiq (yoqilgan) va oqimning katta qismi yuqori qarshilik asosiy to'sar o'rniga past qarshilik yuk kommutatoridan o'tadi.

O'chirishni talab qilishda birinchi navbatda yuk kommutatorini ajratish kerak: past kuchlanishli yarimo'tkazgichli to'sar ochiladi va bu deyarli barcha oqimlarni asosiy to'xtatuvchidan o'tkazadi. Asosiy to'sar hali ham ishlaydi, shuning uchun yuk kommutatori chiziqning butun kuchlanishini ko'rmaydi, faqat yuqori voltli asosiy to'sarning mukammal o'tkazgich bo'lmasligi sababli kuchlanish pasayishi. Yukni almashtirish kommutatori ochiq bo'lgani uchun, ultra tezkor ajratgich yuqori tok ta'siriga tushmaydi va kamon yordamida shikastlanmasdan ochilishi mumkin. Mexanik kalit ochilib, yuk komutatori endi to'liq uzilib qoldi: yarimo'tkazgichli kalitda issiqlik hosil bo'lmaydi va hatto to'liq chiziqli kuchlanish ham u orqali o'tolmaydi. Hozirgi vaqtda barcha oqim asosiy to'xtatuvchidan o'tmoqda.

Endi asosiy to'sar ochilib, oqimni buzadi. Bu oqimni nolga yaqin tushiradi, lekin asosiy to'sar va yuk kommutatoridagi kuchlanishni deyarli butun chiziq kuchlanishiga oshiradi. Agar yukni almashtirish kommutatori ilgari mexanik ravishda uzilmagan bo'lsa, bu kuchlanish unga zarar etkazishi mumkin edi. Asosiy to'sar yarimo'tkazgichli to'sar bo'lgani uchun, u deyarli barcha oqimlarni kesib tashlaydi, ammo hammasini emas, shuning uchun oxirgi izolyatsiyani bajarish uchun sekin mexanik kalit chiziqni uzib qo'yadi. Deyarli barcha oqimlarni asosiy to'sar to'sib qo'yganligi sababli, uni buzilmasdan ochish mumkin.[36]

Xarajatlar

Odatda, HVDC tizimlarining provayderlari, masalan Alstom, Simens va ABB, muayyan loyihalarning xarajatlari haqida ma'lumot bermang. Bu provayder va mijoz o'rtasida tijorat masalasi sifatida ko'rib chiqilishi mumkin.

Xarajatlar loyihaning o'ziga xos xususiyatlariga qarab (masalan, quvvat darajasi, elektr uzatish uzunligi, havo yo'llari va kabel yo'nalishi, er narxlari va har ikkala terminalda talab qilinadigan o'zgaruvchan tok tarmog'ini yaxshilash kabi) farq qiladi. DC uchun aniq texnik ustunlik bo'lmagan holatlarda doimiy o'zgaruvchan tokni uzatish xarajatlarini va taqqoslashni taqqoslash talab qilinishi mumkin, va faqat iqtisodiy asoslar tanlovni boshqaradi.

Biroq, ba'zi amaliyotchilar ba'zi ma'lumotlarni taqdim etdilar:

8 GVt quvvatga ega 40 km Ingliz kanali Quyida 2000 MVt quvvatga ega bo'lgan 500 kV quvvatli bipolyar an'anaviy HVDC aloqasi uchun dastlabki uskunalarning taxminiy xarajatlari keltirilgan (yo'lni tark etish, qirg'oqni mustahkamlash ishlari, rozilik berish, muhandislik, sug'urta va hk).

  • Konverter stantsiyalar ~ £ 110M (~ € 120M yoki $ 173.7M)
  • Dengiz osti kabeli + o'rnatish ~ £ 1M / km (~ € 1.2M yoki ~ $ 1.6M / km)

Shunday qilib, orasidagi 8 GVt quvvatga ega Britaniya va Frantsiya to'rtta havolada o'rnatilgan ishlar uchun 750 million funtdan ozgina mablag 'qolgan. Kerakli qo'shimcha quruqlikdagi ishlarga qarab, boshqa ishlar uchun yana 200-300 million funt qo'shing.[37]

Ispaniya va Frantsiya o'rtasida 2000 MVt, 64 km uzunlikdagi liniya uchun 2010 yil aprelda e'lon 700 million evroga baholanmoqda. Bunga Pireney orqali o'tadigan tunnel narxi kiradi.[38]

Konversiya jarayoni

Konverter

Asosiy maqola: HVDC konvertori

An qalbida HVDC konvertor stantsiyasi, AC va doimiy konversiyani amalga oshiradigan uskunalar konvertor. Deyarli barcha HVDC konvertorlari tabiiy ravishda o'zgaruvchan tokdan DC ga (tuzatish ) va DC dan AC ga (inversiya ), garchi ko'plab HVDC tizimlarida tizim umuman olganda faqat bitta yo'nalishda quvvat oqimi uchun optimallashtirilgan. Konverterning o'zi qanday yaratilganligidan qat'i nazar, o'zgaruvchan tokdan doimiy oqimgacha ishlaydigan stansiya (ma'lum bir vaqtda) rektifikator va doimiy oqimdan o'zgaruvchan tokgacha quvvat oqimi bilan ishlaydigan stantsiya inverter.

Dastlabki HVDC tizimlarida elektromexanik konversiya ishlatilgan (Thury tizimi), ammo 1940-yillardan beri qurilgan barcha HVDC tizimlarida elektron (statik) konvertorlar ishlatilgan. HVDC uchun elektron konvertorlar ikkita asosiy toifaga bo'linadi:

  • Chiziq bilan almashtirilgan konvertorlar (LCC)
  • Quvvat manbai bo'lgan konvertorlar yoki oqim manbali konvertorlar.

Chiziq bilan almashtirilgan konvertorlar

Bugungi kunda ishlaydigan HVDC tizimlarining aksariyati yo'naltirilgan konvertorlarga asoslangan.

Asosiy LCC konfiguratsiyasi uch fazadan foydalanadi ko'prikni to'g'irlovchi yoki olti impulsli ko'prik, oltita elektron kalitni o'z ichiga olgan bo'lib, ularning har biri uchta fazadan birini ikkita shahar relslaridan biriga ulaydi. To'liq kommutatsiya elementi odatda a deb nomlanadi vana, qurilishidan qat'i nazar. Biroq, o'zgarishlar o'zgarishi bilan faqat har 60 °, sezilarli darajada harmonik buzilish ushbu tartib ishlatilganda doimiy va o'zgaruvchan tok terminallarida ishlab chiqariladi.

O'n ikki pulsli ko'prikni to'g'irlovchi

Ushbu tartibni takomillashtirishda a-da 12 ta vanadan foydalaniladi o'n ikki pulsli ko'prik. O'zgarishdan oldin o'zgaruvchan tok ikkita alohida uch fazali manbalarga bo'linadi. So'ngra ta'minot to'plamlaridan biri yulduz (vye) ikkilamchi, ikkinchisi delta ikkilamchi bo'lishi uchun tuzilgan bo'lib, uchta fazaning ikkala to'plami o'rtasida 30 ° faza farqini o'rnatadi. Uch fazaning har ikkala to'plamining har ikkisini doimiy shahar relslariga ulaydigan o'n ikkita valf bilan har 30 ° da o'zgarishlar o'zgarishi sodir bo'ladi va harmonikalar sezilarli darajada kamayadi. Shu sababli, o'n ikki pulsli tizim 1970 yildan beri qurilgan ko'pgina HVDC konvertor tizimlarida standart bo'lib qoldi.

Komutli konvertorlarning konvertorlari bilan konvertor faqat bitta erkinlik darajasiga ega otish burchagi, bu valfdagi voltajning ijobiy bo'lishini (bu vaqtda valf diodlardan yasalgan bo'lsa) o'tkazishni boshlashi va tiristorlar orasidagi vaqt kechikishini anglatadi. Konvertorning doimiy chiqish quvvati doimiy ravishda otish burchagi oshganligi sababli kamroq ijobiy bo'ladi: 90 ° gacha bo'lgan otish burchaklari rektifikatsiyaga to'g'ri keladi va musbat doimiy kuchlanishlarga olib keladi, 90 ° dan yuqori bo'lgan burchaklar teskari tomonga to'g'ri keladi va salbiy shahar kuchlanishiga olib keladi . Kuyish burchagi uchun amaliy yuqori chegara taxminan 150-160 ° ni tashkil qiladi, chunki bu holda valf etarli bo'lmaydi aylanish vaqti.

Dastlabki LCC tizimlari ishlatilgan simob-boshq valflari qo'pol, ammo yuqori texnik xizmat ko'rsatishni talab qiladigan. Shu sababli, HVDC sxemasi olti impulsli rejimda qisqa muddat davomida xizmat ko'rsatish uchun har bir oltita impulsli ko'prik bo'ylab aylanma o'tish moslamalari bilan ko'plab simob-kamonli HVDC tizimlari qurilgan. Oxirgi simob boshq tizimi 2012 yilda yopilgan edi.

The tiristor Vana birinchi marta 1972 yilda HVDC tizimlarida ishlatilgan. Tiristor qattiq holatdir yarimo'tkazgich ga o'xshash qurilma diyot, lekin o'zgaruvchan tokning aylanishi paytida qurilmani ma'lum bir daqiqada yoqish uchun ishlatiladigan qo'shimcha boshqaruv terminali bilan. Ba'zi hollarda 800 kVgacha bo'lgan HVDC tizimlaridagi kuchlanishlar bu ko'rsatkichlardan ancha yuqori bo'lganligi sababli buzilish kuchlanishi ishlatiladigan tiristorlardan HVDC tiristor klapanlari ko'p sonli tiristorlar ketma-ket ishlatilgan holda qurilgan. Baholash kabi qo'shimcha passiv komponentlar kondansatörler va rezistorlar valfdagi kuchlanish tiristorlar o'rtasida teng ravishda taqsimlanishini ta'minlash uchun har bir tiristor bilan parallel ravishda ulanishi kerak. Tiristor va uning tasniflash davrlari va boshqa yordamchi uskunalari a nomi bilan tanilgan tiristor darajasi.

Qutb 2 uchun tiristorli valf stakalari HVDC orollararo ning shimoliy va janubiy orollari o'rtasida Yangi Zelandiya. Pastki qismdagi odam klapanlarning kattaligiga shkala beradi.

Har bir tiristor valfi odatda o'nlab yoki yuzlab tiristor sathlarini o'z ichiga oladi, ularning har biri erga nisbatan boshqa (yuqori) potentsialda ishlaydi. Shuning uchun tiristorlarni yoqish uchun buyruq ma'lumotlarini simli aloqa yordamida oddiygina yuborib bo'lmaydi - uni ajratish kerak. Izolyatsiya usuli magnit bo'lishi mumkin, lekin odatda optikdir. Ikkita optik usul qo'llaniladi: bilvosita va to'g'ridan-to'g'ri optik tetiklash. Bilvosita optik tetiklash usulida past kuchlanishli elektronika optik tolalar bo'ylab yorug'lik impulslarini yuboradi yuqori tomon har bir tiristordagi kuchlanishdan quvvat oladigan boshqaruv elektroniği. Muqobil to'g'ridan-to'g'ri optik tetiklash usuli yuqori tomonli elektronikaning aksariyat qismlariga mos keladi, buning o'rniga boshqarish elektronikasidan yorug'lik impulslari yordamida o'tish engil tirgakli tiristorlar (LTTs), garchi valfni himoya qilish uchun hali ham kichik o'lchash elektroniği qurilmasi talab qilinishi mumkin.

Chiziq bilan almashtirilgan konvertorda doimiy oqim (odatda) yo'nalishni o'zgartira olmaydi; u katta indüktans orqali oqadi va deyarli doimiy deb hisoblanishi mumkin. O'zgaruvchan tok tomonida, konvertor tok manbai sifatida o'zini tutadi va o'zgaruvchan tok tarmog'iga tarmoq chastotasi va harmonik oqimlarni kiritadi. Shu sababli, HVDC uchun chiziqli almashtirilgan konvertor ham joriy manbali inverter.

Kuchlanish manbalaridan konvertorlar

Tiristorlarni faqat boshqarish harakati bilan yoqish mumkin (o'chirilmaydi), boshqaruv tizimi faqat bitta erkinlik darajasiga ega - tiristorni qachon yoqish kerak. Bu ba'zi holatlarda muhim cheklovdir.

Kabi ba'zi bir yarimo'tkazgichli qurilmalar bilan izolyatsiyalangan eshikli bipolyar tranzistor (IGBT), ikkala yoqish va o'chirishni boshqarish mumkin, bu ikkinchi darajadagi erkinlikni beradi. Natijada, ular tayyorlash uchun ishlatilishi mumkin o'z-o'zini o'zgartiradigan konvertorlar. Bunday konvertorlarda doimiy voltajning polarligi aniqlanadi va katta sig'im bilan tekislangan doimiy kuchlanish doimiy deb hisoblanishi mumkin. Shu sababli, IGBTlardan foydalanadigan HVDC konvertori odatda a deb nomlanadi kuchlanishli konvertor. Qo'shimcha boshqarish qobiliyati juda ko'p afzalliklarga ega, xususan, IGBT-larni bir tsiklda ko'p marta yoqish va o'chirish, harmonik ko'rsatkichlarni yaxshilash uchun. O'z-o'zini o'zgartirgan holda, konvertor endi ishlash uchun o'zgaruvchan tok tizimidagi sinxron mashinalarga ishonmaydi. Shuning uchun kuchlanish manbalari konvertori faqat passiv yuklardan iborat o'zgaruvchan tok tarmog'iga quvvat etkazishi mumkin, bu esa LCC HVDC bilan imkonsizdir.

Volt manbali konvertorlarga asoslangan HVDC tizimlari odatda oltita impulsli ulanishdan foydalanadi, chunki konvertor taqqoslanadigan LCC ga qaraganda kamroq harmonik buzilish hosil qiladi va o'n ikki zarbali ulanish kerak emas.

2012 yilgacha qurilgan VSC HVDC tizimlarining aksariyati ikki darajali konvertor, bu oltita impulsli ko'prik deb qaralishi mumkin, bu erda tiristorlar teskari parallel diodli IGBTlar bilan almashtirildi va shaharni tekislash reaktorlari doimiylashtiruvchi kondansatkichlar bilan almashtirildi. Bunday konvertorlar o'zlarining nomlarini har bir fazaning o'zgaruvchan tokning chiqishidagi ijobiy va salbiy shahar terminallarining elektr potentsialiga mos keladigan ikkita kuchlanish darajasidan oladi. Puls kengligi modulyatsiyasi (PWM) odatda konvertorning harmonik buzilishini yaxshilash uchun ishlatiladi.

Ba'zi HVDC tizimlari qurilgan uchta darajadagi konvertorlar, lekin bugungi kunda aksariyat yangi VSC HVDC tizimlari ba'zi bir shakllar bilan qurilmoqda ko'p darajali konvertor, odatda Modulli ko'p darajali konvertor (MMC), unda har bir valf bir nechta mustaqil konvertor submodullaridan iborat bo'lib, ularning har biri o'z saqlash kondansatkichini o'z ichiga oladi. Har bir submoduldagi IGBT'lar kondensatorni chetlab o'tishadi yoki uni sxemaga ulab, valfga juda past darajadagi harmonik buzilish bilan pog'onali kuchlanishni sintez qilishga imkon beradi.

Konverter transformatorlari

Bir fazali, uch o'rashli konvertorli transformator. Devor bo'ylab prokladkali uzun valfli burmalar vana zali, chap tomonda ko'rsatilgan. Chiziqli burama burg'ulash loyihalari vertikal ravishda yuqoridan o'ngga

Har bir konvertorning o'zgaruvchan tok tomonida transformatorlar banki, ko'pincha uchta fizik jihatdan ajratilgan bitta fazali transformatorlar stantsiyani o'zgaruvchan tok manbaidan ajratib, mahalliy tuproqni ta'minlashi va doimiy doimiy voltajni ta'minlashi kerak. Ushbu transformatorlarning chiqishi keyinchalik konvertorga ulanadi.

LCC HVDC sxemalari uchun konvertor transformatorlari ular orqali o'tadigan harmonik oqimlarning yuqori darajasi va ikkilamchi o'rash izolyatsiyasi doimiy doimiy voltajga ega bo'lganligi sababli izolyatsiyalash inshootining konstruktsiyasiga ta'sir qiladiganligi sababli juda ixtisoslashgan (vana tomoni yanada qattiq izolyatsiyani talab qiladi) tank ichida. LCC tizimlarida transformatorlar, shuningdek, harmonik bekor qilish uchun zarur bo'lgan 30 ° o'zgarishlar o'zgarishini ta'minlashi kerak.

VSC HVDC tizimlari uchun konvertor transformatorlari odatda LCC HVDC tizimlariga qaraganda sodda va odatiy dizaynga ega.

Reaktiv quvvat

HVDC tizimlarining chiziqli almashinadigan konvertorlardan foydalanadigan muhim kamchiligi shundaki, konvertorlar tabiiy ravishda iste'mol qiladilar reaktiv quvvat. The AC current flowing into the converter from the AC system lags behind the AC voltage so that, irrespective of the direction of active power flow, the converter always absorbs reactive power, behaving in the same way as a shunt reactor. The reactive power absorbed is at least 0.5 Mvar/MW under ideal conditions and can be higher than this when the converter is operating at higher than usual firing or extinction angle, or reduced DC voltage.

Da HVDC konvertor stantsiyalari connected directly to elektr stantsiyalari some of the reactive power may be provided by the generators themselves, in most cases the reactive power consumed by the converter must be provided by banks of shunt kondansatörler connected at the AC terminals of the converter. The shunt capacitors are usually connected directly to the grid voltage but in some cases may be connected to a lower voltage via a tertiary winding on the converter transformer.

Since the reactive power consumed depends on the active power being transmitted, the shunt capacitors usually need to be subdivided into a number of switchable banks (typically four per converter) in order to prevent a surplus of reactive power being generated at low transmitted power.

The shunt capacitors are almost always provided with tuning reactors and, where necessary, damping resistors so that they can perform a dual role as harmonik filtrlar.

Voltage-source converters, on the other hand, can either produce or consume reactive power on demand, with the result that usually no separate shunt capacitors are needed (other than those required purely for filtering).

Harmonics and filtering

Hammasi elektr elektron converters generate some degree of harmonic distortion on the AC and DC systems to which they are connected, and HVDC converters are no exception.

With the recently developed Modular Multilevel Converter (MMC), levels of harmonic distortion may be practically negligible, but with line-commutated converters and simpler types of voltage-source converters, considerable harmonic distortion may be produced on both the AC and DC sides of the converter. As a result, harmonic filters are nearly always required at the AC terminals of such converters, and in HVDC transmission schemes using overhead lines, may also be required on the DC side.

Filters for line-commutated converters

The basic building-block of a line-commutated HVDC converter is the olti impulsli ko'prik. This arrangement produces very high levels of harmonic distortion by acting as a current source injecting harmonic currents of order 6n±1 into the AC system and generating harmonic voltages of order 6n superimposed on the DC voltage.

It is very costly to provide harmonic filters capable of suppressing such harmonics, so a variant known as the o'n ikki pulsli ko'prik (consisting of two six-pulse bridges in series with a 30° phase shift between them) is nearly always used. With the twelve-pulse arrangement, harmonics are still produced but only at orders 12n±1 on the AC side and 12n on the DC side. The task of suppressing such harmonics is still challenging, but manageable.

Line-commutated converters for HVDC are usually provided with combinations of harmonic filters designed to deal with the 11th and 13th harmonics on the AC side, and 12th harmonic on the DC side. Sometimes, high-pass filters may be provided to deal with 23rd, 25th, 35th, 37th... on the AC side and 24th, 36th... on the DC side. Sometimes, the AC filters may also need to provide damping at lower-order, noncharacteristic harmonics such as 3rd or 5th harmonics.

The task of designing AC harmonic filters for HVDC converter stations is complex and computationally intensive, since in addition to ensuring that the converter does not produce an unacceptable level of voltage distortion on the AC system, it must be ensured that the harmonic filters do not resonate with some component elsewhere in the AC system. A detailed knowledge of the harmonic impedance of the AC system, at a wide range of frequencies, is needed in order to design the AC filters.[39]

DC filters are required only for HVDC transmission systems involving overhead lines. Voltage distortion is not a problem in its own right, since consumers do not connect directly to the DC terminals of the system, so the main design criterion for the DC filters is to ensure that the harmonic currents flowing in the DC lines do not induce interference in nearby open-wire telefon liniyalari.[40] With the rise in digital mobile telekommunikatsiya systems, which are much less susceptible to interference, DC filters are becoming less important for HVDC systems.

Filters for voltage-sourced converters

Some types of voltage-sourced converters may produce such low levels of harmonic distortion that no filters are required at all. However, converter types such as the two-level converter, used with impuls kengligi modulyatsiyasi (PWM), still require some filtering, albeit less than on line-commutated converter systems.

With such converters, the harmonic spectrum is generally shifted to higher frequencies than with line-commutated converters. This usually allows the filter equipment to be smaller. The dominant harmonic frequencies are yon tasmalar of the PWM frequency and multiples thereof. In HVDC applications, the PWM frequency is typically around 1 to 2 kHz.

Konfiguratsiyalar

Monopol

Erni qaytarish bilan monopol tizimining blok diagrammasi

In a monopole configuration one of the terminals of the rectifier is connected to earth ground. The other terminal, at high voltage relative to ground, is connected to a transmission line. The earthed terminal may be connected to the corresponding connection at the inverting station by means of a second conductor.

If no metallic return conductor is installed, current flows in the earth (or water) between two electrodes. This arrangement is a type of bitta simli tuproqni qaytarish tizim.

The electrodes are usually located some tens of kilometers from the stations and are connected to the stations via a medium-voltage elektrod liniyasi. The design of the electrodes themselves depends on whether they are located on land, on the shore or at sea. For the monopolar configuration with earth return, the earth current flow is unidirectional, which means that the design of one of the electrodes (the katod ) can be relatively simple, although the design of anod electrode is quite complex.

For long-distance transmission, earth return can be considerably cheaper than alternatives using a dedicated neutral conductor, but it can lead to problems such as:

  • Electrochemical corrosion of long buried metal objects such as quvurlar
  • Underwater earth-return electrodes in seawater may produce xlor or otherwise affect water chemistry.
  • An unbalanced current path may result in a net magnetic field, which can affect magnetic navigatsion kompaslar for ships passing over an underwater cable.

These effects can be eliminated with installation of a metallic return conductor between the two ends of the monopolar transmission line. Since one terminal of the converters is connected to earth, the return conductor need not be insulated for the full transmission voltage which makes it less costly than the high-voltage conductor. The decision of whether or not to use a metallic return conductor is based upon economic, technical and environmental factors.[41]

Modern monopolar systems for pure overhead lines carry typically 1.5 GW.[42] If underground or underwater cables are used, the typical value is 600 MW.

Most monopolar systems are designed for future bipolar expansion. Transmission line towers may be designed to carry two conductors, even if only one is used initially for the monopole transmission system. The second conductor is either unused, used as elektrod liniyasi or connected in parallel with the other (as in case of Boltiq kabeli ).

Nosimmetrik monopol

An alternative is to use two high-voltage conductors, operating at about half of the DC voltage, with only a single converter at each end. In this arrangement, known as the symmetrical monopole, the converters are earthed only via a high impedance and there is no earth current. The symmetrical monopole arrangement is uncommon with line-commutated converters (the NorNed interconnection being a rare example) but is very common with Voltage Sourced Converters when cables are used.

Ikki qutbli

Ikki qutbli tizimning blok diagrammasi, u ham erga qaytishga ega

In bipolar transmission a pair of conductors is used, each at a high potential with respect to ground, in opposite polarity. Since these conductors must be insulated for the full voltage, transmission line cost is higher than a monopole with a return conductor. However, there are a number of advantages to bipolar transmission which can make it an attractive option.

  • Under normal load, negligible earth-current flows, as in the case of monopolar transmission with a metallic earth-return. This reduces earth return loss and environmental effects.
  • When a fault develops in a line, with earth return electrodes installed at each end of the line, approximately half the rated power can continue to flow using the earth as a return path, operating in monopolar mode.
  • Since for a given total power rating each conductor of a bipolar line carries only half the current of monopolar lines, the cost of the second conductor is reduced compared to a monopolar line of the same rating.
  • In very adverse terrain, the second conductor may be carried on an independent set of transmission towers, so that some power may continue to be transmitted even if one line is damaged.

A bipolar system may also be installed with a metallic earth return conductor.

Bipolar systems may carry as much as 4 GW at voltages of ±660 kV with a single converter per pole, as on the Ningdong–Shandong project in China. With a power rating of 2,000 MW per twelve-pulse converter, the converters for that project were (as of 2010) the most powerful HVDC converters ever built.[43] Even higher powers can be achieved by connecting two or more twelve-pulse converters in series in each pole, as is used in the ±800 kV Syanjiaba – Shanxay project in China, which uses two twelve-pulse converter bridges in each pole, each rated at 400 kV DC and 1,600 MW.

Submarine cable installations initially commissioned as a monopole may be upgraded with additional cables and operated as a bipole.

A block diagram of a bipolar HVDC transmission system, between two stations designated A and B. AC – represents an alternating current network CON – represents a converter valve, either rektifikator yoki inverter, TR represents a power transformator, DCTL is the direct-current transmission line conductor, DCL is a direct-current filter induktor, BS represents a bypass switch, and PM represent quvvat omilini tuzatish and harmonic filter networks required at both ends of the link. The DC transmission line may be very short in a back-to-back link, or extend hundreds of miles (km) overhead, underground or underwater. One conductor of the DC line may be replaced by connections to tuproq.

A bipolar scheme can be implemented so that the polarity of one or both poles can be changed. This allows the operation as two parallel monopoles. If one conductor fails, transmission can still continue at reduced capacity. Losses may increase if ground electrodes and lines are not designed for the extra current in this mode. To reduce losses in this case, intermediate switching stations may be installed, at which line segments can be switched off or parallelized. Bu amalga oshirildi Inga-Shaba HVDC.

Orqama orqa

A back-to-back station (or B2B for short) is a plant in which both converters are in the same area, usually in the same building. The length of the direct current line is kept as short as possible. HVDC back-to-back stations are used for

The DC voltage in the intermediate circuit can be selected freely at HVDC back-to-back stations because of the short conductor length. The DC voltage is usually selected to be as low as possible, in order to build a small valve hall and to reduce the number of thyristors connected in series in each valve. For this reason, at HVDC back-to-back stations, valves with the highest available current rating (in some cases, up to 4,500 A) are used.

Multi-terminal systems

The most common configuration of an HVDC link consists of two converter stations connected by an elektr uzatish liniyasi or undersea cable.

Multi-terminal HVDC links, connecting more than two points, are rare. The configuration of multiple terminals can be series, parallel, or hybrid (a mixture of series and parallel). Parallel configuration tends to be used for large capacity stations, and series for lower capacity stations. An example is the 2,000 MW Kvebek - Yangi Angliya transmissiyasi system opened in 1992, which is currently the largest multi-terminal HVDC system in the world.[44]

Multi-terminal systems are difficult to realize using line commutated converters because reversals of power are effected by reversing the polarity of DC voltage, which affects all converters connected to the system. With Voltage Sourced Converters, power reversal is achieved instead by reversing the direction of current, making parallel-connected multi-terminals systems much easier to control. For this reason, multi-terminal systems are expected to become much more common in the near future.

China is expanding its grid to keep up with increased power demand, while addressing environmental targets. China Southern Power Grid started a three terminals VSC HVDC pilot project in 2011. The project has designed ratings of ±160 kV/200 MW-100 MW-50 MW and will be used to bring wind power generated on Nanao island into the mainland Guangdong power grid through 32 km of combination of HVDC land cables, sea cables and overhead lines. This project was put into operation on December 19, 2013.[45]

In India, the multi-terminal Shimoliy-Sharqiy Agra project is planned for commissioning in 2015-2017. It is rated 6,000 MW, and it transmits power on a ±800 kV bipolar line from two converter stations, at Bisvanat Chariali va Alipurduar, in the east to a converter at Agra, a distance of 1,728 km.[46]

Boshqa tadbirlar

Cross-Skagerrak consisted since 1993 of 3 poles, from which 2 were switched in parallel and the third used an opposite polarity with a higher transmission voltage. This configuration ended in 2014 when poles 1 and 2 again were rebuilt to work in bipole and pole 3 (LCC) works in bipole with a new pole 4 (VSC). This is the first HVDC transmission where LCC and VSC poles cooperate in a bipole.

A similar arrangement was the HVDC orollararo yilda Yangi Zelandiya after a capacity upgrade in 1992, in which the two original converters (using mercury-arc valves) were parallel-switched feeding the same pole and a new third (thyristor) converter installed with opposite polarity and higher operation voltage. This configuration ended in 2012 when the two old converters were replaced with a single, new, thyristor converter.

A scheme patented in 2004[47] is intended for conversion of existing AC transmission lines to HVDC. Two of the three circuit conductors are operated as a bipole. The third conductor is used as a parallel monopole, equipped with reversing valves (or parallel valves connected in reverse polarity). This allows heavier currents to be carried by the bipole conductors, and full use of the installed third conductor for energy transmission. High currents can be circulated through the line conductors even when load demand is low, for removal of ice. 2012 yildan boshlab, no tripole conversions are in operation, although a transmission line in Hindiston has been converted to bipole HVDC (HVDC Sileru-Barsoor ).

Korona tushishi

Korona tushishi is the creation of ionlari a suyuqlik (kabi havo ) by the presence of a strong elektr maydoni. Elektronlar are torn from neutral air, and either the positive ions or the electrons are attracted to the conductor, while the charged particles drift. This effect can cause considerable power loss, create audible and radio-frequency interference, generate toxic compounds such as oxides of nitrogen and ozone, and bring forth arcing.

Both AC and DC transmission lines can generate coronas, in the former case in the form of oscillating particles, in the latter a constant wind. Tufayli kosmik zaryad formed around the conductors, an HVDC system may have about half the loss per unit length of a high voltage AC system carrying the same amount of power. With monopolar transmission the choice of polarity of the energized conductor leads to a degree of control over the corona discharge. In particular, the polarity of the ions emitted can be controlled, which may have an environmental impact on ozone creation. Salbiy koronalar generate considerably more ozone than positive coronas, and generate it further shamol of the power line, creating the potential for health effects. A dan foydalanish ijobiy voltage will reduce the ozone impacts of monopole HVDC power lines.

Ilovalar

Umumiy nuqtai

The controllability of a current-flow through HVDC rectifiers and inverters, their application in connecting unsynchronized networks, and their applications in efficient submarine cables mean that HVDC interconnections are often used at national or regional boundaries for the exchange of power (in North America, HVDC connections divide much of Canada and the United States into several electrical regions that cross national borders, although the purpose of these connections is still to connect unsynchronized AC grids to each other). Offshore windfarms also require undersea cables, and their turbinalar are unsynchronized. In very long-distance connections between two locations, such as power transmission from a large hydroelectric power plant at a remote site to an urban area, HVDC transmission systems may appropriately be used; several schemes of these kind have been built. For interconnections to Sibir, Kanada, Hindiston, va Skandinaviya North, the decreased line-costs of HVDC also make it applicable, see HVDC loyihalari ro'yxati. Other applications are noted throughout this article.

AC network interconnections

AC transmission lines can interconnect only synchronized AC networks with the same frequency with limits on the allowable phase difference between the two ends of the line. Many areas that wish to share power have unsynchronized networks. The power grids of the Buyuk Britaniya, Northern Europe and continental Europe are not united into a single synchronized network. Yaponiya has 50 Hz and 60 Hz networks. Continental North America, while operating at 60 Hz throughout, is divided into regions which are unsynchronized: Sharq, G'arb, Texas, Kvebek va Alyaska. Braziliya va Paragvay, which share the enormous Itaipu to'g'oni hydroelectric plant, operate on 60 Hz and 50 Hz respectively. However, HVDC systems make it possible to interconnect unsynchronized AC networks, and also add the possibility of controlling AC voltage and reactive power flow.

A generator connected to a long AC transmission line may become unstable and fall out of synchronization with a distant AC power system. An HVDC transmission link may make it economically feasible to use remote generation sites. Shamol ishlab chiqaradigan fermer xo'jaliklari located off-shore may use HVDC systems to collect power from multiple unsynchronized generators for transmission to the shore by an underwater cable.[48]

In general, however, an HVDC power line will interconnect two AC regions of the power-distribution grid. Machinery to convert between AC and DC power adds a considerable cost in power transmission. The conversion from AC to DC is known as tuzatish, and from DC to AC as inversiya. Above a certain break-even distance (about 50 km for submarine cables, and perhaps 600–800 km for overhead cables), the lower cost of the HVDC electrical conductors outweighs the cost of the electronics.

The conversion electronics also present an opportunity to effectively manage the power grid by means of controlling the magnitude and direction of power flow. An additional advantage of the existence of HVDC links, therefore, is potential increased stability in the transmission grid.

Renewable electricity superhighways

Two HVDC lines cross near Ving, Shimoliy Dakota.

A number of studies have highlighted the potential benefits of very wide area super grids based on HVDC since they can mitigate the effects of intermittency by averaging and smoothing the outputs of large numbers of geographically dispersed wind farms or solar farms.[49] Czisch's study concludes that a grid covering the fringes of Europe could bring 100% renewable power (70% wind, 30% biomass) at close to today's prices. There has been debate over the technical feasibility of this proposal[50] and the political risks involved in energy transmission across a large number of international borders.[51]

The construction of such green power superhighways is advocated in a oq qog'oz tomonidan chiqarilgan Amerika shamol energiyasi assotsiatsiyasi va Quyosh energiyasi sanoati assotsiatsiyasi 2009 yilda.[52] Clean Line Energy Partners is developing four HVDC lines in the U.S. for long distance electric power transmission.[53]

In January 2009, the European Commission proposed €300 million to subsidize the development of HVDC links between Ireland, Britain, the Netherlands, Germany, Denmark, and Sweden, as part of a wider €1.2 billion package supporting links to offshore wind farms and cross-border interconnectors throughout Europe. Meanwhile, the recently founded O'rta er dengizi ittifoqi has embraced a Mediterranean Solar Plan to import large amounts of concentrated solar power into Europe from North Africa and the Middle East.[54]

Advancements in UHVDC

UHVDC (ultrahigh-voltage direct-current) is shaping up to be the latest technological front in high voltage DC transmission technology. UHVDC is defined as DC voltage transmission of above 800 kV (HVDC is generally just 100 to 800 kV).

One of the problems with current UHVDC supergrids is that – although less than AC transmission or DC transmission at lower voltages – they still suffer from power loss as the length is extended. A typical loss for 800 kV lines is 2.6% over 800 km.[55] Increasing the transmission voltage on such lines reduces the power loss, but until recently, the o'zaro bog'lovchilar required to bridge the segments were prohibitively expensive. However, with advances in manufacturing, it is becoming more and more feasible to build UHVDC lines.

2010 yilda, ABB guruhi built the world's first 800 kV UHVDC in China. The Zhundong–Wannan UHVDC line with 1100 kV, 3400 km length and 12 GW capacity was completed in 2018. As of 2020, at least thirteen UHVDC transmission lines in China yakunlandi.

While the majority of recent UHVDC technology deployment is in China, it has also been deployed in South America as well as other parts of Asia. In India, a 1830 km, 800 kV, 6 GW line between Raigarx va Pugalur is expected to be completed in 2019.[56] In Brazil, the Xingu-Estreito line over 2076 km with 800 kV and 4 GW was completed in 2017. As of 2020, no UHVDC line (≥ 800 kV) exists in Europe or North America.

Shuningdek qarang

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Tashqi havolalar