1 Introduction 2 Fundamentals 3 Power Transformers 4 Transmission Line Parameters 5 Transmission Lines: Steady-state Operation 6 Power Flows 7 Symmetrical Faults 8 Symmetrical Components 9 Unsymmetrical Faults 10 System Protection 11 Transient Stability 12 Power System Controls 13 Transmission Lines: Transient Operation 14 Power Distribution Chapter3: Power Transformers
Chapter Questions Section: Chapter Questions
Problem 3.1MCQ: The Ohms law for the magnetic circuit states that the net magnetomotive force (mmf) equals the... Problem 3.2MCQ: For an ideal transformer, the efficiency is (a) 0 (b) 100 (c) 50 Problem 3.3MCQ: For an ideal 2-winding transformer, the ampere-turns of the primary winding, N1I1 is equal to the... Problem 3.4MCQ: An ideal transformer has no real or reactive power loss. (a) True (b) False Problem 3.5MCQ: For an ideal 2-winding transformer, an impedance Z2 connected across winding 2 (secondary) is... Problem 3.6MCQ: Consider Figure 3.4. For an ideal phase-shifting transformer, the imda nce is unchanged when it is... Problem 3.7MCQ: Consider Figure 3.5. Match the following, those on the left to those on the right. (i) Im (a)... Problem 3.8MCQ: The units of admittance, conductance, and susceptance are siemens. (a) True (b) False Problem 3.9MCQ: Match the following: (i) Hysteresis loss (a) Can be redud by constructing the core with laminated... Problem 3.10MCQ: For large power transformers rated more than 500 kVA, the winding resistances, which are small... Problem 3.11MCQ: For a short-circuit test on a 2-winding transformer, with one winding shorted, can you apply the... Problem 3.12MCQ: The per-unit quantity is always dimensionless. (a) True (b) False Problem 3.13MCQ: Consider the adopted per-unit system for the transformers. Specify true or false for each of the... Problem 3.14MCQ: The ideal transformer windings are eliminated from the per-unit equivalent circuit of a transformer.... Problem 3.15MCQ: To convert a per-unit impedance from old to new base values, the equation to be used is... Problem 3.16MCQ: In developing per-unit circuits of systems such as the one shown in Figure 3.10. when moving across... Problem 3.17MCQ Problem 3.18MCQ Problem 3.19MCQ: With the American Standard notation, in either a Y-or-Y transformer, positive- sequen quantities on... Problem 3.20MCQ Problem 3.21MCQ: In order to avoid difficulties with third-harmonic exciting current, which three-phase transformer... Problem 3.22MCQ: Does an open connection permit balanced three-phase operation? - (a) Yes (b) No Problem 3.23MCQ: Does an open- operation, the kVA rating compared to that of the original thr-phase bank is (a) 2/3... Problem 3.24MCQ: It is stated that (i) balanced three-phase circuits can be solved in per unit on a per-phase basis... Problem 3.25MCQ: In developing per-unit equivalent circuits for three-phase transformers. under balanced three-phase... Problem 3.26MCQ: In per-unit equivalent circuits of practical three-phase transformers, under balanced thr-phase... Problem 3.27MCQ Problem 3.28MCQ Problem 3.29MCQ: For developing per-unit equivalent circuits of single-phase three-winding transformer, a common... Problem 3.30MCQ Problem 3.31MCQ Problem 3.32MCQ Problem 3.33MCQ: The direct electrical connection of the windings allows transient over voltages to pass through the... Problem 3.34MCQ: Consider Figure 3.25 of the text for a transformer with off-nominal turns ratio. (i) The per-unit... Problem 3.1P: (a) An ideal single-phase two-winding transformer with turns ratio at=N1/N2 is connected with a... Problem 3.2P: An ideal transformer with N1=1000andN2=250 is connected with an impedance Z22 across winding 2. If... Problem 3.3P: Consider an ideal transformer with N1=3000andN2=1000 turns. Let winding 1 be connected to a source... Problem 3.4P: A single-phase 100-kVA,2400/240-volt,60-Hz distribution transformer is used as a step-down... Problem 3.5P Problem 3.6P Problem 3.7P: Consider a source of voltage v(t)=102sin(2t)V, with an internal resistance of 1800. A transformer... Problem 3.8P Problem 3.9P Problem 3.10P: A single-phase step-down transformer is rated 13MVA,66kV/11.5kV. With the 11.5 kV winding... Problem 3.11P: For the transformer in Problem 3.10. The open-circuit test with 11.5 kV applied results in a power... Problem 3.12P Problem 3.13P: A single-phase 50-kVA,2400/240-volt,60-Hz distribution transformer has a 1-ohm equivalent leakage... Problem 3.14P: A single-phase 50-kVA,2400/240-volt,60-Hz distribution transformer is used as a step-down... Problem 3.15P: Rework Problem 3.14 if the transformer is delivering rated load at rated secondary voltage and at... Problem 3.16P: A single-phase, 50-kVA,2400/240-V,60-Hz distribution transformer has the following parameters:... Problem 3.17P: The transformer of Problem 3.16 is supplying a rated load of 50 kVA at a rated secondary voltage of... Problem 3.18P: Using the transformer ratings as base quantities, work Problem 3.13 in per-unit. Problem 3.19P: Using the transformer ratings as base quantities. work Problem 3.14 in per-unit. Problem 3.20P: Using base values of 20 kVA and 115 volts in zone 3, rework Example 3.4. Problem 3.21P Problem 3.22P: A balanced Y-connected voltage source with Eag=2770volts is applied to a balanced-Y load in parallel... Problem 3.23P: Figure 3.32 shows the oneline diagram of a three-phase power system. By selecting a common base of... Problem 3.24P: For Problem 3.18, the motor operates at full load, at 0.8 power factor leading, and at a terminal... Problem 3.25P: Consider a single-phase electric system shown in Figure 3.33. Transformers are rated as follows:... Problem 3.26P: A bank of three single-phase transformers, each rated 30MVA,38.1/3.81kV, are connected in Y- with a... Problem 3.27P: A three-phase transformer is rated 1000MVA,220Y/22kV. The Y-equivalent short-circuit impedance,... Problem 3.28P: For the system shown in Figure 3.34. draw an impedance diagram in per unit by choosing 100 kVA to be... Problem 3.29P: Consider three ideal single-phase transformers (with a voltage gain of ) put together as ... Problem 3.30P: Reconsider Problem 3.29. If Va,VbandVc are a negative-sequence set, how would the voltage and... Problem 3.31P Problem 3.32P: Determine the positive- and negative-sequence phase shifts for the three- phase transformers shown... Problem 3.33P: Consider the three single-phase two-winding transformers shown in Figure 3.37. The high-voltage... Problem 3.34P: Three single-phase, two-winding transformers, each rated 450MVA,20kV/288.7kV, with leakage reactance... Problem 3.35P: Consider a bank of this single-phase two-winding transformers whose high-voltage terminals are... Problem 3.36P: Three single-phase two-winding transformers, each rated 25MVA,34.5/13.8kV, are connected to form a... Problem 3.37P: Three single-phase two-winding transformers, each rated 25MVA,54.2/5.42kV, are connected to form a... Problem 3.38P: Consider a three-phase generator rated 300MVA,23kV, supplying a system load of 240 MA and 0.9 power... Problem 3.39P: The leakage reactance of a three-phase, 300-MVA,230Y/23-kV transformer is 0.06 per unit based on its... Problem 3.40P Problem 3.41P: Consider the single-line diagram of the power system shown in Figure 3.38. Equipment ratings are... Problem 3.42P: For the power system in Problem 3.41, the synchronous motor absorbs 1500 MW at 0.8 power factor... Problem 3.43P: Three single-phase transformers, each rated 10MVA,66.4/12.5kV,60Hz, with an equivalent series... Problem 3.44P: A 130-MVA,13.2-kV three-phase generator, which has a positive-sequence reactance of 1.5 per unit on... Problem 3.45P: Figure 3.39 shows a oneline diagram of a system in which the three-phase generator is rated 300 MVA,... Problem 3.46P: The motors M1andM2 of Problem 3.45 have inputs of 120 and 60 MW, respectively, at 13.2 kV, and both... Problem 3.47P: Consider the oneline diagram shown in Figure 3.40. The three-phase transformer bank is made up of... Problem 3.48P: With the same transformer banks as in Problem 3.47, Figure 3.41 shows the oneline diagram of a... Problem 3.49P: Consider the single-Line diagram of a power system shown in Figure 3.42 with equipment ratings... Problem 3.50P: A single-phase three-winding transformer has the following parameters: Z1=Z2=Z3=0+j0.05,Gc=0, and... Problem 3.51P: The ratings of a three-phase three-winding transformer are Primary(1): Y connected 66kV,15MVA... Problem 3.52P Problem 3.53P: The ratings of a three-phase, three-winding transformer are Primary: Y connected, 66kV,15MVA... Problem 3.54P: An infinite bus, which is a constant voltage source, is connected to the primary of the... Problem 3.55P: A single-phase l0-kVA,2300/230-volt,60-Hz two-winding distribution transformer is connected as an... Problem 3.56P: Three single-phase two-winding transformers, each rated 3kVA,220/110volts,60Hz, with a 0.10 per-unit... Problem 3.57P: A two-winding single-phase transformer rated 60kVA,240/1200V,60Hz, has an efficiency of 0.96 when... Problem 3.58P: A single-phase two-winding transformer rated 90MVA,80/120kV is to be connected as an autotransformer... Problem 3.59P Problem 3.60P: PowerWorid Simulator case Problem 3_60 duplicates Example 3.13 except that a resistance term of 0.06... Problem 3.62P: Rework Example 3.12 for a+10 tap, providing a 10 increase for the high-voltage winding. Problem 3.63P: A 23/230-kV step-up transformer feeds a three-phase transmission line, which in turn supplies a... Problem 3.64P: The per-unit equivalent circuit of two transformers Ta and Tb connected in parallel, with the same... Problem 3.65P: Reconsider Problem 3.64 with the change that now Tb includes both a transformer of the same turns... Problem ACSQ: What are the advantages of correctly specifying a transformer most Suita ble for its application? Problem BCSQ: Why is it important to reduce the moisture within a transformer to acceptable levels during... Problem CCSQ: What should be the focus of transformer preventive maintenance efforts? Problem 3.51P: The ratings of a three-phase three-winding transformer are Primary(1): Y connected 66kV,15MVA...
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Concept explainers
Three 1-phase Transformers connected in mesh supply 1000 A per line to a 3-phase, 3-wire system. (a) What is the current in each transformer? One unit develops a fault and is removed: (b) by how mjuch is the capacity of the set reduced for the same temperatura-rise? (c) Find the current in each of the remaining transformer if the line current corresponds to the rating in (b). Draw the vector diagram.
Transcribed Image Text: 6. Three 1-phase Transformers connected in mesh supply 1000 A per line to a 3-phase, 3-wire system. (a)
What is the current in each transformer? One unit develops a fault and is removed: (b) by how mjuch is
the capacity of the set reduced for the same temperatura-rise? (c) Find the current in each of the remaining
transformer if the line current corresponds to the rating in (b). Draw the vector diagram.
Quantities that have magnitude and direction but not position. Some examples of vectors are velocity, displacement, acceleration, and force. They are sometimes called Euclidean or spatial vectors.
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