The one-line diagram of a three-phase power system is shown in the above figure. The line impedances are in per- unit on a 100-MVA base, and the line admittances are neglected. !

The three-phase source line-to-neutral voltages are given by Ean=100,Ebh=10+240, and Ecn=10240volts. Is the source balanced? (a) Yes (b) No

Transkrmers phase with each bank with - adjuste 35. Three single-phase transformers, cach of 100 kVA rating, are conected in a closed-delta arrangement. If one of them is taken out, it would be possible to load the bank in such a manner that cach one is loaded to the extent of: A 86.6 kVA C. 57.7KVA B. 66.7 kVA D. 33.33 kVA when load is at unity power factor. 36. Average power factor at which V-V bank separate is A 86.6% C. 66.67% В. 73.3% D. None of these 37. Scott connections are used for: A. single-phase to three-phase transformation C. three-phase to two-phase transformation B. three-phase to single-phase transformation (D Any of the above 38. The current in low voltage winding of a 25 kVA, 6600/400 V, 50 Hz, 3-phase Y-A transformer, at full load is: A 36 A Č. 65,32 A B. 20.78 A D. 40.2 A 39. The current in high voltage winding of a 20 kVA, 2200/220 V, 50 Hz, 3-phase A-A transformer, at full load is: (A. 3.03 A C. jo.5 A B. 5.25 A D. None of above 40. The current in low voltage…

In a three-phase system the per-unit phase voltages are 100° , Vôn = 0.8Z180° Van 0.920° , Von = 0.92 - а What are the per-unit symmetrical components V0) and V)? Express in polar notation.

Q2) A 13.2-kV single-phase generator supplies power to a load through a transmission line. The load's impedance is Ztoad 500 236.87° ohm , and the transmission line's impedance is Zine = 60 253.1° ohm. To reduce transmission line losses to 0.0103 of its losses without using the transformers design and use two transformers T1 between the generator and the transmission line and T2 between the transmission line and the load.

The per unit impedance of a generator on a 60 MVA, 20 kV base is j0.09 p.u. The per unit impedance to a 100 MVA, 20 kV base will be (a.) j0.054 p.u. (c.) j 1.5 p.u. (b.) j0.54 p.u. (d.) j0.15 p.u.

Two single phase transformers with equal turns have impedance of (0.5+j0.3) ohms and (0.6+j10) ohms with respect to the secondary. If they operate in parallel, how  will they share a load of 100 kW at 0.8 p.f. lagging?

Draw three transformers for each of the different three-phase connections. That is, draw three transformers and then make the connection, eg star-star, then redraw three transformers and make another three-phase connection, and so on until all four combinations of three-phase connections are made.

2. The one-line diagram of a three-phase power system is as shown in the figure below. Impedances are marked in per unit on a 100-MVA, 400-kV base. The load at bus 2 is S2 = 15.93 MW-j33.4 Mvar, and at bus 3 is S3 = 77 MW +j14 Mvar. It is required to hold the voltage at bus 3 at 4006 0 kV. Working in per unit, determine the voltage at buses 2 and 1. V3 j0.5 pu V₂ S₂ j0.4 pu S3

3. The single-line diagram of a three-phase power system is as shown in Figure Al-3. Impedances are marked in per unit on a 100-MVA, 400-kV base. The load at bus 2 is S2 = 15.93 MW – j 33.4 Mvar, and at bus 3 is S3 = 77 MW +jl4 Mvar. It is required to hold the voltage at bus 3 at 40020° kV. Working in per unit, determine the voltage at buses 2 and 1. V2 V1 V3 j0.5 pu j0.4 pu S2 S3 Figure A1-3