Chapter 3: 23MCQ (page 142)
Question:Does an openoperation, the kVA rating compared to that of the original three-phase bank is
(a) 2/3
(b) 58%
(c) 1
Therefore, the correct option is (b) 58 %.
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For a conceptual single-phase phase-shifting transformer, the primary voltage leads the secondary voltage by . A load connected to the secondary winding absorbs at an 0.8 power factor leading and at a voltage . Determine (a) the primary voltage, (b) primary and secondary currents, (c) load impedance referred to the primary winding, and (d) complex power supplied to the primary winding.
Reconsider Problem 3.64 with the change that now includes both a transformer of the same turns ratio as and a regulating transformer with a phase shift. On the base of the impedance of the two components of per unit. Determine the complex power in per unit transmitted to the load through each transformer. Comment on how the transformers share the real and reactive powers.
Figure 3.39 shows a oneline diagram of a system in which the three-phase generator is rated 300 MVA , 20kV with a sub transient reactance of 2.0 per unit and with its neutral grounded through a 0.4 V reactor. The transmission line is 64 km long with a series reactance of . The three-phase transformer is rated 350 MVA , 230/20kV with a leakage reactance of 0.1 per unit. Transformer is composed of three single-phase transformers,each rated 100 MVA , 127/13.2 kV with a leakage reactance of 0.1 per unit. Two 13.2kV motors and with a sub transient reactance of 0.2 per unit for each motor represent the load. has a rated input of 200 MVA with its neutral grounded through a 0.4 V current-limiting reactor. has a rated input of 100 MVA with its neutral not connected to ground. Neglect phase shifts associated with the transformers. Choose the generator rating as base in the generator circuit and draw the positive-sequence reactance diagram showing all reactance in per unit.
For the power system in Problem 3.41, the synchronous motor absorbs at 0.8 power factor leading with the bus 3 voltage at.Determine the bus 1 and bus 2 voltages in. Assume that generators 1and 2 deliver equal real powers and equal reactive powers. Also assume abalanced three-phase system with positive-sequence sources.
The equivalent circuit of two transformers and connected in parallel, With the same nominal voltage ratio and the same reactance of per unit on the same base, is shown in Figure 3.43. Transformer has a voltage magnitude Step-up toward the load of times that of (that is, the tap on the secondary winding ofis set to ). The load is represented by unit at a voltage per unit. Determine the complex power in per unit transmitted to the load througheach transformer. Comment on how the transformers share the real and reactive powers.
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