1) Figure below shown the schematic diagram of 3-phase radial transmission system. The ratings and reactances of the various components are shown, along with the nominal transformer line voltages. A load of 50 MW at 0.8 p.f. lagging is taken from the 33-kV substation which is to be maintained at 30 kV. It is required to calculate the terminal voltage of the synchronous machine. The line and transformers may be represented by series reactances. The system is three-phase. 11 kV 132 kV 50MVA X = 10% Line j100 132 kV 33 kV 50 MVA X=12% 30kV 50MW 0-8p.f. lagging

1) Figure below shown the schematic diagram of 3-phase radial transmission system. The ratings and reactances of the various components are shown, along with the nominal transformer line voltages. A load of 50 MW at 0.8 p.f. lagging is taken from the 33-kV substation which is to be maintained at 30 kV. It is required to calculate the terminal voltage of the synchronous machine. The line and transformers may be represented by series reactances. The system is three-phase. 11 kV 132 kV 50MVA X = 10% Line j100 132 kV 33 kV 50 MVA X=12% 30kV 50MW 0-8p.f. lagging

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 3.48P: With the same transformer banks as in Problem 3.47, Figure 3.41 shows the oneline diagram of a...

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A single-phase power system consists of a 600-V 50-Hz generator supplying the circuit shown in Figure (1-a). Find the following: 1) What will the voltage at the load be? What will the transmission line losses be? 2) Suppose a 1:15 step-up transformer is placed at the generator end of the transmission line, and a 20:1 step-down transformer is placed at the load end of the line, as shown in Figure (1-b). What will the load voltage be now? What will the transmission line losses be now? V=600 20°V IG V=600 20°V T₁ 1:15 I line 0.22 22 j 0.30 Ω www Z line I₁ line Figure (1-a) 0.22 S2 Z line j 0.30 Ω Figure (1-b) V load + T2 20:1 load Z load I load 6+j8 Ω + Vload Z load 6+18 Ω
Three single-phase two-winding transformers, each rated 3kVA,220/110volts,60Hz, with a 0.10 per-unit leakage reactance, are connected as a three-phase extended autotransformer bank, as shown in Figure 3.36(c). The low-voltage winding has a 110 volt rating. (a) Draw the positive-sequence phasor diagram and show that the high-voltage winding has a 479.5 volt rating. (b) A three-phase load connected to the low-voltage terminals absorbs 6 kW at 110 volts and at 0.8 power factor lagging. Draw the per-unit impedance diagram and calculate the voltage and current at the high-voltage terminals. Assume positive-sequence operation.
Consider the oneline diagram shown in Figure 3.40. The three-phase transformer bank is made up of three identical single-phase transformers, each specified by X1=0.24 (on the low-voltage side), negligible resistance and magnetizing current, and turns ratio =N2/N1=10. The transformer bank is delivering 100 MW at 0.8 p.f. lagging to a substation bus whose voltage is 230 kV. (a) Determine the primary current magnitude, primary voltage (line-to-line) magnitude, and the three-phase complex power supplied by the generator. Choose the line-to-neutral voltage at the bus, Va as the reference Account for the phase shift, and assume positive-sequence operation. (b) Find the phase shift between the primary and secondary voltages.
With the same transformer banks as in Problem 3.47, Figure 3.41 shows the oneline diagram of a generator, a step-up transformer bank, a transmission line, a stepown transformer bank, and an impedan load. The generator terminal voltage is 15 kV (line-to-line). (a) Draw the per-phase equivalent circuit, aounting for phase shifts for positive-sequence operation. (b) By choosing the line-to-neutral generator terminal voltage as the reference, determine the magnitudes of the generator current, transmiss ion-line current, load current, and line-to-line load voltage. Also, find the three-phase complex power delivered to the load.
A synchronous generator is connected through a transformer and a transmission line to synchronous motor. The rated voltage and apparent power of the generator serve as the base quantities for this power system. On the system base, the per-unit sub transient reactance of the generator and the motor are 0.15 and 0.40 respectively, the series reactance of the transformer is 0.10, and the series reactance of the transmission line is 0.20. All resistances may be ignored. The generator is supplying rated apparent power and voltage at a power factor of 0.85 lagging when a three-phase synchronous fault occurs at the terminals of the motor. Find the per-unit sub transient current at the fault, in the generator, and in the motor.
A 3-phase synchronous generator is synchronizing with a bus bar. The transformer parameter are shown in the below table, what parameter should be required on generator side for accurate synchronization. Also discuss the role of synchronoscope in this operation. WAPDA Side Generator Side 50 Hz Frequency Terminal Voltage Phase Shift Phase Sequence 380 v 1200 R, Y, B
A generator is connected through a transformer to a synchronous motor as shown in the following figure. (All values in this problem are per unit.) Before the fault V,=0.9,1=1 with power factor 0.8 lagging. jX, P + jX ds jX" dm + E. E The reactances are Xd=0.15 , X,=0.1 , X âm=0.35. A symmetric fault occurs at P. Find the per-unit current magnitudes in the fault, the generator and the motor (a) using subtransient voltages. (b) using a Thevenin equivalent.
1.a. Separate voltage-regulating units provide voltage-ratio control under load byA. causing different impedance drops in each phase.B. combining voltages from different phases.C. having series transformers in phase with the line-to-neutral voltage.D. exciting transformers having their primaries delta-connected. 1.b. A reactor is sometimes used with an autotransformer toA. limit short-circuit current.B. increase the full-load current.C. provide increased internal impedance.D. decrease the voltage ratio.
2A. What is another term for "shunt"? a) in series b) in parallel c) compounded d) none of the above 2B. Which of the following is/are a basic type of DC generator connection? a) series b) shunt c) compound d) all of the above
Discussion : 1- What are the advantages and disadvantages of this test ? 2- Why it's imporctical carry out actual load test on large rating transformers ? 3- What will be the current in the primary windings? i) When secondaries are not loaded ? ii) When secondaries are loaded ?
17.a. For commercial tests on transformers, direct current may be used for theA. induced-voltage test.B. ratio test.C. temperature test.D. polarity kick back test.17.b. A core-form three-phase delta-delta transformer can provide some service with one phase damaged ifthe damaged phase isA. grounded.B. disconnected and short-circuited.C. open-circuited.D. short-circuited.
Ex: Consider a A/Y - Connected, 15-MVA, 33 / 11 -KV transformer with differential protection applied, For the current transformer notes ratios show in figure d.36. Calculate the relay currents on full load. Find the minimum relay Current setting to allow 125 percent overload. 33/11 Kv 300/5A 2000/5A faz m AAAA E C An tp ir m is