110年 - 110台灣聯合大學系統_碩士班招生考試_電機類:電力系統#104948

(一)、Describe the harmonic problems of a Y-Y connected three-phase transformer. (4%)

(二)、What is Y-Y with tertiary △ transformer? (4%)

(一)、(8%) 1. Find the efficiency at full load, cosθ=0.8.(4%)
2. Find the absolute maximum efficiency. (4%)

(二)、(8%)
1. Connect this conventional transformer as an auto-transformer with 2000/2200V (draw the circuit). (3%) 2. Find the VA rating of auto-transformer. (2.5%)
3. Find the efficiency at full load, cosθ=0.8.(2.5%)

(三)、 Three these single-phase transformers are connected as a delta-delta connected three- phase transformer bank, find its primary and secondary three-phase line-to-line voltages, and its three-phase VA rating. (6%)

三、(15%) 計算題Asingle phase full bridge inverter acts as the interface between the PV generation system and the grid voltage of 220 Vac (RMS), 60 Hz. A filter inductor of 2mH is on the AC side of the inverter to smooth the output current. The PV generation system can produce 5kW at its maximum. Assuming the inverter has no operational losses, what is the minimum DC bus voltage of the inverter that allows linear modulation under all conditions?

四、(15%) 計算題As shown in Fig.1, the source voltages are positive sequence sets and all impedances are equal to Z. Using an appropriate interconnection of sequence network, please find l^f(in terms of Z) and V'ag.

(一)、Find the admittance matrix. (5%)

(二)、 Illustrate how to find the power solution. (9%)

(三)、Determine the line from Bus 1 to Bus 2. (5%)

(四)、Find the complex power provided by SG2. (5%)

(ㅡ)、A temporary three-phase fault occurs at the sending end of the line at point F. When the fault is cleared, both lines are intact. Determine the critical clearing angle δ ₁. (7%)

(二)、 A three-phase fault occurs at the middle of one of the lines, the fault is cleared, and the fault line is isolated. Determine the critical clearing angleδ₂.(7%)

(三)、 Which one is larger between δ₁ andδ₂? (2%)

110年 - 110台灣聯合大學系統_碩士班招生考試_電機類:電力系統#104948

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