The three phase power and line-line ratings of the below electric power system is given below: V. Vm G G: 50 MVA 22 KV X= 4% T: 50 MVA 22/40 KV X= 496 M: 43.2 MVA 36 KV X= 4% By choosing 100 MVA and 22 KV on the generator side as base values. the new per unit impedance of the generator is and the new perunit impedance of the motor is None of these 8.333% Impedan 11.43% 7,5% 10.238% erunit on a100MVA. 100 KV base. The load at bus 2 1s S2= 16MW - 32 MVAR, and the load at bus 3 is 5OMVA at 0.8 pf lagging. it is required to hold the voltage a

The three phase power and line-line ratings of the below electric power system is given below: V. Vm G G: 50 MVA 22 KV X= 4% T: 50 MVA 22/40 KV X= 496 M: 43.2 MVA 36 KV X= 4% By choosing 100 MVA and 22 KV on the generator side as base values. the new per unit impedance of the generator is and the new perunit impedance of the motor is None of these 8.333% Impedan 11.43% 7,5% 10.238% erunit on a100MVA. 100 KV base. The load at bus 2 1s S2= 16MW - 32 MVAR, and the load at bus 3 is 5OMVA at 0.8 pf lagging. it is required to hold the voltage a

Power System Analysis and Design (MindTap Course List)

6th Edition

ISBN:9781305632134

Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Chapter3: Power Transformers

Section: Chapter Questions

Problem 3.36P: Three single-phase two-winding transformers, each rated 25MVA,34.5/13.8kV, are connected to form a...

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Three single-phase two-winding transformers, each rated 25MVA,34.5/13.8kV, are connected to form a three-phase bank. Balanced positive-suence voltages are applied to the high-voltage terminals, and a balanced, resistive Y load connected to the low-voltage terminals absorbs 75 MW at 13.8 kV. If one of the single-phase transformers is removed (resulting in an open connection) and the balanced load is simultaneously reduced to 43.3 MW (57.7 of the original value), determine (a) the load voltages Va,Vb, and Vc; (b) load currents Ia,Ib, and Ic; and (c) the MVA supplied by each of the remaining two transformers. Are balanced voltages still applied to the load? Is the open transformer overloaded?
In order to avoid difficulties with third-harmonic exciting current, which three-phase transformer connection is seldom used for step-up transformers between a generator and a transmission line in power systems. (a) Y- (b) -Y (c) Y-Y
A 30 MVA, 11 kV generator has a reactance of 0.10p.u.on its own base. Determine the per-unit reactance when referred to base kVA of 50,000 kVA and base kV of 33 kV.
In the system shown in Figure 1, the transformers are connected star-star with both star points grounded and the generator is connected in star with its star points grounded. The per unit impedances of each element on a 40 MVA base are given in Table 1 and the voltage levels are given in Table 2. Z [p.u.] 0 2 tööt Generator 0.01 +j0.08 p.u. L Figure 1: A section of the distribution system Transformer T1 Line V BASE [KV] 0.04 + j 0.03 + j 0.15000000000000002 0.06000000000000000 Generator Table 1: Sequence impedances (p.u. on 40 MVA base) 3 T2 181. Line 3 10 Table 2: Voltage bases (kV) Load 1 Transformer T2 Load Current A load current of 11.316 kA is flowing with a lagging power factor of 90 %. Convert this to a current vector in per-unit. IL = 0.04 + j 0.06000000000000000
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…
Connect three single-phase transformers in Y-Y, with subtractive polarity, so that the line-to-line voltages on the primary are 30 degrees delayed to their respective line-to-line voltages on the secondary. It should show each step that is needed to make this connection (example: the phasor diagram) and should show the final connection of the three transformers including the polarity markings. Assume phase A on the primary is terminal "H1".
The p.u. impedance value of an alternator corresponding to base values of 13.2 kV and 30 MVA is 0.2 p.u. Then the p.u. impedance value of an alternator for the new base values of 13.8 kV and 50 MVA is......
The one-line diagram of a three-phase system is shown in Figure 1. By selecting a common based of 90 MVA and 32.75 kV on the generator bus, all impedances including the load impedance in per-unit are as follows: XG (new) = j0.1421 p.u XT1 (new) = j0.1219 p.u XT2 (new) = j0.1219 p.u ZOH = 0.0016 +j 0.0083 p.u Хм пеw) 3D j0.247 р.u ZLoad = 2.2759+ j1.2306 p.u T1 T2 90 MVA Motor 90 MVA 55 MVA 33/275 kV 275/11kV 10.95 kV XT=12% Xr3=12% Xx=15% Generator 95 MVA M 32.75 kV Xg=15% 2 x OH Line 138 km R = 0.01 ohm/km X = 0.05 ohm/km Load 35 MVA 10.95 kV 0.88 pf lagging Figure 1 Note: Region 1 = Generator bus Region 2 = Transmission Lines busses Region 3 = Load Bus If the motor operates at full load 0.88 power factor lagging at a terminal voltage 10.95 kV, determine the voltage at the generator bus bar.
The reactance of a generator is given as 0.25 per-unit based on the generator’s of 18 kV, 500 MVA. Find its per-unit reactance on a base of 20 kV, 100 MVA. a. 0.0505 b. 0.0605 c. 0.0405 d. 0.0606
explain why Transformers are necessary in all stages of power distribution systems. Three-phase voltages may be stepped up or down by three-phase transformers
Three single-phase transformers, each rated 10 MVA , 66.4/12.5 kV, 60 Hz , with an equivalent series reactance of 0.1 per unit divided equally between primary and secondary, are connected in a three-phase bank. The high-voltage windings are Y-connected and their terminals are directly connected to a 115-kV three-phase bus. The secondary terminals are all shorted together. Find the currents entering the high-voltage terminals and leaving the low-voltage terminals if the low-voltage windings are (a) Y-connected and (b) Δ- connected.
3 X 0.1 1 2 XL = 0.2 to Eato oto O X = 0.1 X = 0.1 Above is the one-line diagram of a simple power system. Each generator is represented by an emf behind the subtransient reactance. All impedances are expressed in per unit on a common base. All resistances and shunt capacitance are neglected. The generators are operating on no load at their rated voltage with their emfs in phase. A symmetrical fault occurs at bus 1 through a fault impedance Z, =j0.08 per unit. a) Using Thevenin's Theorem, determine the impedance to the point of fault and the fault current in per unit. (2 Marks) b) Find the bus voltages and line currents during the fault. (2 Marks)