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

(b)  Find the Taylor series expansion of f(z) about the point z = 0; that is, find the coefficients such that in a certain neighborhood of x = 0.

(c)  Continuing from part (b), what is the region of convergence?

(d)  Let C denote the path along the y axis from -∞ to oo. Calculate f(z)dz; i.e., evaluate the following integral:

(一)、Describe the harmonic problems of a Y-Y connected three-phase 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 lf(in terms of Z) and V'ag.

(一)、Find the admittance matrix. (5%)