[شهبازی]

در دو ترانسفورماتور با قدرتهای یکسان که یکی دارای ساختار زرهی و دیگری دارای ساختار هسته ای هستند به چه علت مدارهای توالی صفر آنها با یکدیگر تفاوت دارد ؟ این تفاوت در چه پارامتر های است؟

Topic

[Guest]

ترانسفورمر “شل” دارای مسیر برگشت آزاد فلوی مغناطیسی است ولی این مسیر برای ترانسفورمر “کور” هوا ، روغن و ورق بدنه ترانسفورمر که دارای رلوکتانس بالایی هستند مي باشد . در ترانسفورمر “شل” حتی به ازاء مقدار کمی بار نامتعادل یا بار تکفاز نقطه نیوترال شدیداً جابجاشده ولتاژ فاز بار شده را کوچک می کند و ولتاژ دو فاز دیگر را بزرگ می کند و همچنین باعث نوسان نقطه نیوترال می شود . در ترانسفورمر “کور ” این بار تکفاز تا حدی قابل تحمل است و نقطه نیوترال را خیلی زیاد جابجا نمی کند . هر چند باعث گرم شدن غیر عادی ترانسفورمر می شود ولی تا حد 10%توان نامی قابل تحمل است .

[Guest]

For a three-phase three-limb core, since fluxes in three limbs are in the same direction, they have to return through a path outside the core. In this case, tank acts as an equivalent delta winding, and the magnetizing zero-sequence reactance is the reactance between the tank and excited winding. Since the gap/area between the excited winding and tank is much larger than the gap/area between the windings, the magnetizing zero-sequence reactance is considerably higher than the positive-sequence leakage reactance. The tank influences the zero-sequence reactance in the following way. It provides a comparatively lower reluctance return path (as compared to air) to the zero-sequence flux, which has the effect of increasing the reactance; on the other hand the tank enclosing three phases acts as a short-circuited winding reducing the reactance. In a three-phase five-limb core, the zero-sequence flux has a return path through the end yokes and end limbs and hence the zero-sequence magnetizing reactance has the same value as the corresponding positive-sequence magnetizing reactance (quite a high value) unless the voltage applied is such that yokes and end limbs saturate. For an applied value of zero-sequence voltage, close to the rated voltage, yokes and end limbs will get completely saturated (area of yokes and end limbs are too less to carry the zero-sequence flux of all the three phases at the rated voltage) giving a lower value of magnetizing zero-sequence reactance close to that of a transformer with three-phase three-limb core. For single-phase three-limb cores, since the zero-sequence flux has a return path through end limbs, the zero-sequence magnetizing reactance is equal to the positive-sequence magnetizing reactance (~infinite value). Thus, for a three-phase bank of single-phase transformers, the zero-sequence reactance for any type connection is usually equal to the positive-sequence reactance

[Author]

Replies