Kawaradda Masana'antu da Kace-kacen Farkon Tansufa
Akawo daban-daban na transformers suna da transformers da biyu ko biyar yankin, auto transformer, regulating transformers, earthing transformers, rectifier transformers, kuma wasu. Transformers daban-daban suna bukatar hanyoyi daban-daban na hanyar zama na transformer batunan muhimmancinta, hanyoyi na yankin, earthing methods, kuma hukumomin yi, kamar haka.
Ita ce al'adun da ake amfani da shi wajen bayyana Buchholz relay protection zuwa duk transformers da suka ɗauke 0.5 MVA. Amma har zuwa transformers masu yawan daidai, an samun high voltage fuses kawai cewa main protective device. Don transformers masu yawan daidai da muhimmanci, an amfani da over current protection tare da restricted earth fault protection.
An buƙata da differential protection zuwa transformers da suka ɗauke 5 MVA.
Batunan al'amuran yau da kullum, tsarin abin da suka faruwar transformers, daraja na over load, hukumomin tap changing, da wasu abubuwa masu muhimmanci, an zaɓi hanyoyi daban-daban na hanyar zama na transformer.
Tsarin Abin Da Suka Faruwar Transformers
Idan electrical power transformer ita ce wuri mai karfi, amma abin da suka faruwar su suna da gaba da harkokin al'adun da suka faru.
A transformer ya faruwar da abin da suka faruwar transformers:
Over current batunan overloads da external short circuits,
Terminal faults,
Winding faults,
Incipient faults.
Duk abin da aka bayyana transformer faults suna faɗa mechanical da thermal stresses a cikin winding da connecting terminals na transformer. Thermal stresses suna haɗa su kaɗuwa wanda ya ƙara waɗannan insulation system na transformer. Deterioration of insulation suna haɗa su kaɗuwa winding faults. Yanzu inda cooling system na transformer ya faru, suna haɗa su kaɗuwa transformer. Saboda haka, hanyoyi daban-daban na hanyar zama na transformer suna bukatar da ma.
Short circuit current na electrical transformer ana iya ƙara saboda reactance, da amma don low reactance, zahiri na short circuit current zai iya zama mafi ƙari. Tsari na external short circuits wanda transformer zai iya ƙara ba tabbas a kan BSS 171:1936.
| Transformer % reactance | Permitted fault duration in seconds |
| 4 % | 2 |
| 5 % | 3 |
| 6 % | 4 |
| 7 % and over | 5 |
Abin da suka faruwar winding a transformer suna da earth faults ko inter-turns faults. Phase to phase winding faults a transformer ita ce ƙarin. Phase faults a electrical transformer zai iya faruwar saboda bushing flash over da abin da suka faruwar tap changer equipment. Idan abin da suka faruwar, transformer ya kamata zama ta ƙara a kan fault, kafin a faru major breakdown a cikin electrical power system.
Incipient faults suna da abin da suka faruwar a cikin, amma bai faruwar major faults ba. Abin da suka faruwar a wannan group suna da inter-lamination short circuit saboda insulation failure between core lamination, lowering the oil level saboda oil leakage, blockage of oil flow paths. Duk abin da suka faruwar suna haɗa su kaɗuwa. Saboda haka, hanyar zama na transformer scheme ita ce buƙata zuwa incipient transformer faults. Earth fault, very nearer to neutral point of transformer star winding zai iya ƙara a kan incipient fault.
Influence of winding connections and earthing on earth fault current magnitude.
Suna da abubuwan da suka faruwar earth fault current zuwa winding to earth faults:
A current exists for the current to flow into and out of the winding.
Ampere-turns balance is maintained between the windings.
Zahiri na winding earth fault current suna da position of the fault on the winding, method of winding connection and method of earthing. Star point of the windings may be earthed either solidly or via a resistor. On delta side of the transformer the system is earthed through an earthing transformer. Grounding or earthing transformer provides low impedance path to the zero sequence current and high impedance to the positive and negative sequence currents.
Star Winding with Neutral Resistance Earthed
In this case the neutral point of the transformer is earthed via a resistor and the value of impedance of it, is much higher than that of winding impedance of the transformer. That means the value of transformer winding impedance is negligible compared to impedance of earthing resistor. The value of earth current is, therefore, proportional to the position of the fault in the winding. As the fault current in the primary winding of the transformers is proportional to the ratio of the short circuited secondary turns to the total turns on the primary winding, the primary fault current will be proportional to the square of the percentage of winding short circuited. The variation of fault current both in the primary and secondary winding is shown below.
Star Winding with Neutral Solidly Earthed
In this case the earth fault current magnitude is limited solely by the winding impedance and the fault is no longer proportional to the position of the fault. The reason for this non linearity is unbalanced flux linkage.
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