Daga yadda ake amfani da hanyoyin da na gaba suka da dukkan H61 distribution transformers?

An da zaɓi masu kaɗanar da zafi don H61 distribution transformers?

Yana da kyau a fadada surge arrester a tsakiyar hanyar na gaba na H61 distribution transformer. Daga SDJ7–79 "Technical Code for Design of Overvoltage Protection of Electric Power Equipment," yana da kyau a magance surge arrester a tsakiyar hanyar na gaba na H61 distribution transformer. Tsakiya cikin surge arrester, tsakiyar hanyar na gaba ta kasa na tsakiya na gaba, da kuma karfin kirkiro na transformer suna iya haɗa da kusa da kusan haɗa. An yi magance wannan hukumar a DL/T620–1997 "Overvoltage Protection and Insulation Coordination for AC Electrical Installations," wanda Ministry of Electric Power ta baka.

Amma, bayanai da tarihin yadda ake amfani da su ne sun nuna cewa, hakan da surge arresters an yi a tsakiyar hanyar na gaba kawai, yaɗuwar transformer ya faruwa ne a kan zamantakewa. A wurare masu yawan samun rayuwa, tushen yan faruwa a shekarar ta shi ita ce 1%; a wurare masu yawan samun rayuwa mafi yawa, yaɗuwar yan faruwa ita ce 5%; da kuma a wurare masu yawan samun rayuwa mafi yawa da ke da 100 rana a shekarar, tushen yan faruwa ita ce 50%. Dalilin da yaɗuwar yan faruwa na biye shine so-called "forward and reverse transformation overvoltages" wanda suka fitowa a tsakiyar hanyar na gaba na distribution transformer. Yadda suka faruwa a nan suna da dalilai:

1. Reverse Transformation Overvoltage
Idan lightning surge ta ji a kan tsakiyar hanyar na gaba 3–10 kV, wanda yake buƙace surge arrester, yana buƙata mai zurfi da ke haɗa a kan tsakiya. Wannan tsayi na haɗa ta samu a kan tsakiyar hanyar na gaba ta kasa, wanda yake buƙata tsayinsa. Idan tsakiya ta kasa tana da ɗaliluwa, yana iya haɗa da kusa da wave impedance a kan tsakiya. Tushen tsayin tsakiyar hanyar na gaba ta kasa ta buƙata mai zurfi da ke haɗa a kan tsakiyar hanyar na gaba ta kasa. Mai zurfin dukkan al'ummun ta sama da tsayin da abin da suka haɗa, wanda yake buƙata zero-sequence magnetic flux da shi da mahimmanci.

 Wannan flux ta buƙata pulse voltage mai yawa a kan tsakiyar hanyar na gaba da kuka tsayin da ake haɗa da tsayin da ake haɗa da transformer. Dukkan al'ummun pulse voltages ta sama da tsayin da abin da suka haɗa. Saboda haka, saboda tsakiyar hanyar na gaba ana haɗa a kan star configuration tare da tsakiyar hanyar na gaba ta kasa, idan pulse voltages mai yawa ta samu, ba a gama da impulse current na tsakiyar hanyar na gaba a kan tsayin da ake haɗa da magnetizing effect. Saboda haka, dukkan impulse current na tsakiyar hanyar na gaba ta kasa ta yi waɗanda ake haɗa da magnetizing current, wanda yake buƙata zero-sequence flux da shi da mahimmanci da kuma pulse voltage mai yawa a kan tsakiyar hanyar na gaba. 

Saboda tsayin terminal na hanyar na gaba ta ciwo da residual voltage na surge arrester, wannan pulse voltage ta ciwo a kan tsakiyar, inda yake buƙata tsayin da shi da yawa a kan tsakiyar hanyar na gaba ta kasa. Saboda haka, insulation na tsakiyar hanyar na gaba ta kasa ta fi yawa a kan tsayin da shi da yawa. Da ɗaya, interlayer da interturn voltage gradients ta buƙata tsayin da shi da yawa, wanda yake buƙata insulation failure a wurare masu ɗaya. Wannan ɗan yawan overvoltage ta samu a kan tsakiyar hanyar na gaba da kuma ta buƙata a kan tsakiyar hanyar na gaba ta kasa—wanda ake kira "reverse transformation."

2.Forward Transformation Overvoltage
Forward transformation overvoltage ta samu idan lightning surge ta ji a kan tsakiyar hanyar na gaba ta kasa. Impulse current ta ji a kan tsakiyar hanyar na gaba ta kasa, wanda yake buƙata voltage a kan tsakiyar hanyar na gaba da kuka tsayin da ake haɗa, wanda yake buƙata tsayin da shi da yawa a kan tsakiyar hanyar na gaba ta kasa. Wannan ta buƙata interlayer da interturn voltage gradients. Wannan ɗan yawan overvoltage, wanda ake kira "forward transformation," ta samu a kan tsakiyar hanyar na gaba ta kasa da kuma ta buƙata overvoltage a kan tsakiyar hanyar na gaba. Bayanai sun nuna cewa, idan 10 kV surge ta ji a kan tsakiyar hanyar na gaba ta kasa da kuma grounding resistance ta 5 Ω, interlayer voltage gradient a kan tsakiyar hanyar na gaba ta iya buƙata full-wave impulse withstand strength ta interlayer insulation da kuma tsayin da shi da yawa, wanda yake buƙata insulation breakdown.

Saboda haka, ordinary valve-type ko metal oxide surge arresters suna da kyau a fadada tsakiyar hanyar na gaba ta kasa na H61 distribution transformer. A wannan protection scheme, grounding conductors na dukkan high- da kuma low-voltage arresters, neutral point na tsakiyar hanyar na gaba ta kasa, da kuma transformer’s metal casing suna iya haɗa da kusa da kusan haɗa (wanda ake kira "four-point bonding" ko "three-in-one grounding").

Bayanai da tarihin yadda ake amfani da su ne sun nuna cewa, hakan da surge arresters an yi a tsakiyar hanyar na gaba kawai, yaɗuwar transformer da suka fi sanon insulation, suna faruwa ne a kan zamantakewa saboda forward da reverse transformation overvoltages. Saboda haka, high-voltage-side arresters ba su iya buƙatar forward ko reverse transformation overvoltages. Interlayer voltage gradient a kan ɗan yawan overvoltages ta ciwo da number of turns da kuma winding distribution; insulation breakdown ta samu a kan ɗaya, ƙasar, ko ƙaramin tsakiyar—amman ƙaramin tsakiyar ta fi yawa. Installation na surge arresters a kan tsakiyar hanyar na gaba ta kasa ta iya buƙatar forward da reverse transformation overvoltages zuwa ɗan yawan da suke da kyau.

Wannan ɗan yawan protection shine separate grounding for high- da kuma low-voltage sides. A wannan configuration, high-voltage arrester ta haɗa da kusa, ba a gama da surge arrester a kan tsakiyar hanyar na gaba ta kasa, da kuma neutral point na tsakiyar hanyar na gaba ta kasa da kuma transformer casing ta haɗa da kusa da kusan haɗa kudan a kan high-voltage grounding system.

Wannan ɗan yawan ta amfani da earth’s attenuation effect on lightning waves don ci gaba reverse transformation overvoltage. A kan forward transformation overvoltage, bayanai sun nuna cewa, idan a ci gaba low-voltage grounding resistance daga 10 Ω zuwa 2.5 Ω, za a ci gaba high-voltage forward transformation overvoltage da kusan 40%. Idan a yi amfani da low-voltage grounding electrode da kusa, za a ci gaba forward transformation overvoltage da kusan.

Wani hanyar inganta wannan tushen inganci da kuma yawan gaba, amma yana nufin muhimmanci ga tsari na zuba da rafuwar gaba, wanda yake iya ba da darasi masu yadda a cikin fannin damar.

A kan wasu hanyoyin da aka bayyana, wasu hanyoyin da za su iya yi don inganta rayukansu na musamman sun haɗa da sadarwa mai kyau a ciki na gwamnati na transforma don inganta rayukan da ya faru a cikin ko karshen, ko kuma sanin shiga mai kyau na metal oxide surge arresters zuwa cikin transforma.