Yadda Yake Wuya Mai Tsakiyar Gaba Ta Farko A Cikin Sisomin Rike ɗaya uku da Hanyar Zane Ƙwanƙwa

A cikin na'urar da shi zuwa waɗannan birnin karamin kirkiro, ana gudanar da a nan da ake yi a kan abin da suka fi sani cewa wannan zai iya haifar da adadin neutral line current ya kunshi mafi yawa idan abubuwan da ake amfani da su a kan tsohon fagen suna tsari. Amma, yawancin wasu abubuwa suna haifar da wannan takaitaccen bayanin.

Misali, a kan light boxes da ake amfani da su a kan wuri masu kirkiro, ake amfani da fluorescent lighting da electronic ballasts. Abubuwan da ake amfani da su a kan tsohon fagen suna tsari, kamar yadda aka nuna cewa adadin current ta hanyar fagen shine kusan 90A, amma adadin neutral line current ya faru zuwa 160A.

Farkon haka, abin da ake amfani da su a kan neutral line current shine mafi yawa ya zama babban mutum a yanzu. Me kuma mafi kyau, ba a san da ke karantawa ce, musamman idan abubuwan da ake amfani da su a kan tsohon fagen suna tsari, kuma ya samu 150% daga adadin phase line current? Wannan shine mafi yawan current da ake amfani da su a kan rectifier circuit.

Idan waveforms na current ta hanyar fagen shine sine waves, kuma suka fito 120° da suka samu amfani, ya kamata cewa result of their vector superposition on the neutral line is zero. Wannan shine mafi yawan abin da ake amfani da su a kan hankalin da ake amfani da su a kan tsohon fagen.

Amma, idan currents ta hanyar fagen shine pulsed da suka fito 120°, result of their superposition on the neutral line is as shown in Figure 2. Ya kamata cewa pulsed currents ta hanyar neutral line are staggered and cannot cancel each other out. Counting the number of pulsed currents on the neutral line, there are three in one cycle, so the current on the neutral line is the sum of the currents of each phase line. According to the calculation method of effective current value, the current on the neutral line is 1.7 times that of the phase line current.

Saboda hakan, saboda abin da ake amfani da su a kan electrical loads a yanzu suna rectifier circuit loads, kuma idan abubuwan da ake amfani da su a kan tsohon fagen suna tsari, ya kamata cewa neutral current mafi yawa zai iya haifar da adadin. Mafi yawan neutral current shine mafi yawan dalilai, kamar haka: kima, cross-sectional area na neutral shine mafi yawa da phase line, don haka overcurrent yana haifar da overheating; kimiya, bai a ni protective devices a kan neutral, saboda haka bai a iya disconnect kamar yadda ake yi a kan phase lines, wanda ya haifar da mafi yawan fire risk.

• For three-phase sinusoidal symmetric AC, with balanced loads, phase current vectors (equal magnitude, 120° phase difference) sum to zero, so zero-sequence current is zero.

• With unbalanced loads, unequal current vectors (phase differences not all 120°) give a non-zero sum; the zero-sequence current (unbalanced current) is smaller than any phase current.

• If three-phase loads have non-linear components (e.g., diodes), causing DC and 3rd/6th - order harmonics, zero-sequence current (arithmetic sum of these) may exceed phase current. For example, in a three-phase half-wave rectifier, any phase current is 1/3 of the load current (the zero-sequence current).

• In a three-phase bridge rectifier, current flows in both AC half-cycles (symmetric, balanced across phases), so no DC or 3rd - order harmonics; the three-phase current sum is zero (zero-sequence current = 0).

• In a single-phase bridge rectifier, current flows in both AC half-cycles (symmetric), so no DC or 3rd - order harmonics in the single-phase current.

• If all three-phase loads are single-phase bridge rectifiers, even with imbalance, the three-phase current sum is non-zero (zero-sequence current exists), but the neutral current won’t exceed the phase current.