Kaddamar da Kalkulashin Kiransu na Jirgin Yamma?

Yadda ake kalkulata Short Circuit Current?

Takardun Short Circuit Current

Short circuit current yana nufin alama mai girma da ke shiga cikin yanayin jirgin elektriki a lokacin da zaka so kuɗi, wanda ya fi karɓar da kayan aiki na muhimman mutanen jirgin.

A lokacin da zaka so kuɗi short circuit, alama mai girma ce ke shiga cikin yanayin, tare da circuit breaker (CB). Wannan alama, idan ba a saurara ta tun daga CB, ya fi karɓar da mutanen CB da kayan aiki na mechanical da thermal stress.

Idan abubuwan da ke gudanar da CB ba su da tsari mai yawa, za su iya haifi, wanda zai iya karɓar da insulation. Kuma contacts na CB sun haifi. Thermal stress a kan contacts yana cikin I2Rt, inda R ita ce resistance na contact, I ita ce rms value na short circuit current, da kuma t ita ce lokaci na shiga alama.

Bayan samun zaka so kuɗi, short circuit current ya ci gaba har zuwa lokacin da interrupting unit na CB ya kusa. Saboda haka, lokaci t ita ce breaking time na circuit breaker. Idan wannan lokaci ita ce mili second, ana sani cewa duka heat da aka fara a lokacin zaka so kuɗi ya ci gaba a kan conductor saboda ba a da lokaci don convention da radiation.

Zan iya tabbatar da temperature rise tare da formula:

Inda T ita ce temperature rise per second a degree centigrade. I ita ce current (rms symmetrical) a Ampere. A ita ce cross-sectional area na conductor. ε ita ce temperature coefficient of resistivity na conductor a 20 ^oC.

Aluminum ya ci gaba da strength a lokacin da yake 160°C, kuma ya fi kyau a bincika temperature rise a cikin wannan limit. Wannan talabinta tana ba da temperature rise da ake iya fara a lokacin short circuit, wanda ake iya kawo karfi tare da control breaking time na CB da kuma design dimensions na conductor daidai.

Short Circuit Force

Electromagnetic force da ke fara a kan biyu parallel electric current carrying conductors, yana nuna tare da formula:

Inda L ita ce length na biyu conductors a inch. S ita ce distance bayan biyu a inch. I ita ce current carried by each of the conductors.

An yi experiment da ya tabbatar cewa, electromagnetic short circuit force ya fi girma a lokacin da value na short circuit current I, ita ce 1.75 times initial rms value na symmetrical short circuit current wave.

Amma, a wasu haloyi, ana iya fara forces masu girma, kamar, misali, a lokacin da bars sun fi rigid ko resonance a lokacin da bars sun fi mechanical vibration. Experiments sun tabbatar cewa reactions produced in a non resonating structure by an alternating current at the instant of application or removal of the forces may exceed the reactions experienced while the current is flowing.

Saboda haka, ya fi kyau a bincika safety da kuma a fuskantar dukkan abubuwa, wanda ake buƙata maxima force which could be developed by the initial peak value of the asymmetrical short circuit current. Wannan force ita ce twice of that calculated from the above formula.

Formula ita ce useful for circular cross-sectional conductor. Amma, L ita ce finite length na portions na conductors run parallel to each other, amma formula ita ce suitable where the total length of each conductor is assumed as infinite.

A haloyin practical, total length na conductor ba ita ce infinite. Ana sani cewa, flux density near the ends of current carrying conductor ita ce different than its middle portion.

Saboda haka, idan a yi amfani da formula a kan short conductor, force calculated ita ce much higher than actual. Ana sani cewa, this error may be eliminated considerably if we use the term. It is stead of L/S in the above formula.

Formula, represented by equation (2), gives error free result when the ratio L/S is greater than 20. When 20 > L/S > 4, formula (3) is suitable for error free result.

If L/S < 4, formula (2) is suitable for error free result. The above formulas are only applicable for circular cross-sectional conductors. But for rectangular cross-sectional conductor, the formula needs to have some correction factor. Say this factor is K. Hence, the above formula ultimately becomes.

Although the effect of shape of cross-section of conductor reduces rapidly if spacing between the conductor increases the value of K is maximum for strip like conductor whose thickness is quite less than its width. K is negligible when shape of cross-section of conductor is perfectly square. K is unity for perfectly circular cross-sectional conductor. This holds true for both standard and remote control circuit breaker.