(a) With neat diagram explain auto transformer and write any two advantages.( (b) A transformer takes a current of 0.7A, when its primary is connected to a 220V, 50HZ supply, the secondary being open circuited. If the power absorbed is 70Owatts, determine () the core loss current(lc) (i) the power factor on no-load and () the magnetizing current(im). core loss current (Ic) power factor Magnetizing current (Im)

(a) With neat diagram explain auto transformer and write any two advantages.( (b) A transformer takes a current of 0.7A, when its primary is connected to a 220V, 50HZ supply, the secondary being open circuited. If the power absorbed is 70Owatts, determine () the core loss current(lc) (i) the power factor on no-load and () the magnetizing current(im). core loss current (Ic) power factor Magnetizing current (Im)

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 3.58P: A single-phase two-winding transformer rated 90MVA,80/120kV is to be connected as an autotransformer...

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A single-phase 50-kVA,2400/240-volt,60-Hz distribution transformer is used as a step-down transformer at the load end of a 2400-volt feeder whose series impedance is (1.0+j2.0) ohm. The equivalent series impedance of the transformer is (1.0+j2.5) ohms referred to the high-voltage (primary) side. The transformer is delivering rated load at a 0.8 power factor lagging and at a rated secondary voltage. Neglecting the transformer exciting current, determine (a) the voltage at the transformer primary terminals, (b) the voltage at the sending end of the feeder, and (c) the real and reactive power delivered to the sending end of the feeder.
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.
Consider the adopted per-unit system for the transformers. Specify true or false for each of the following statements: (a) For the entire power system of concern, the value of Sbase is not the same. (b) The ratio of the voltage bases on either side of a transformer is selected to be the same as the ratio of the transformer voltage ratings. (c) Per-unit impedance remains unchanged when referred from one side of a transformer to the other.
Consider a bank of this single-phase two-winding transformers whose high-voltage terminals are connected to a three-phase, 13.8-kV feeder. The low-voltage terminals are connected to a three-phase substation load rated 2.0 MVA and 2.5 kV. Determine the required voltage, current, and MVA ratings of both windings of each transformer, when the high-voltage/low- voltage windings are connected (a) Y-, (b) -Y, (c) Y-Y, and (d) -.
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 three-phase transformer is rated 1000MVA,220Y/22kV. The Y-equivalent short-circuit impedance, considered equal to the leakage reactance, measured on the low-voltage side is 0.1. Compute the per-unit reactance of the transformer. In a system in which the base on the high-voltage side of the transformer is 100MVA,230kV what value of the per-unit reactance should be used to represent this transformer?
A 130-MVA,13.2-kV three-phase generator, which has a positive-sequence reactance of 1.5 per unit on the generator base, is connected to a 135-MVA,13.2/115Y-kV step-up transformer with a series impedance of (0.005+10.1) per unit on its own base. (a) Calculate the per-unit generator reactance on the transformer base. (b) The load at the transformer terminals is 15 MW at unity power factor and at 115 kV Choosing the transformer high-side voltage as the reference phasor, draw a phasor diagram for this condition. (C) For the condition of part (b), find the transformer low-side voltage and the generator internal voltage behind its reactance. Also compute the generator output power and power factor.
A single-phase 100-kVA,2400/240-volt,60-Hz distribution transformer is used as a step-down transformer. The load, which is connected to the 240-volt secondary winding, absorbs 60 kVA at 0.8 power factor lagging and is at 230 volts. Assuming an ideal transformer, calculate the following: (a) primary voltage, (b) load impedance, (c) load impedance referred to the primary, and (d) the real and reactive power supplied to the primary winding.
A single-phase 100-kVA, 2400/240-volt, 60-Hz distribution transformer is used as astep-down transformer. The load, which is connected to the 240-volt secondary winding, absorbs 80 kVA at 0.8 power factor lagging and is at 230 volts. Assuming anideal transformer, calculate the following: (a) primary voltage, (b) load impedance,(c) load impedance referred to the primary, and (d) the real and reactive power supplied to the primary winding.
A 200 – MVA, 15/200 kV single-phase power transformer has a per – unit resistance of 1.2 percent and a per-unit reactance of 5 percent (data taken from the transformer's nameplate). The magnetizing impedance is j80 per unit.a. Find the equivalent circuit referred to the low-voltage side of this transformer.b. Calculate the voltage regulation of this transformer for a full-load current at power factor of 0.8 lagging.c. Assume that the primary voltage of this transformer is a constant 15 kV. And plot the secondary voltage as a function of load current for currents from no load to full load. Repeat this process for power factors of 0.8 lagging, 1.0, and 0.8 leading.
2) A single -phase power transformer of 150 MVA, 15/200 kV has a Resistance in unit of 1.1% and reactance per unit of 4.5%. The Magnetization impedance is J95 per unit. a) Find the equivalent circuit of the transformer referred to the bass side voltage. b) Calculate the transformer voltage regulation under conditions Nominal and F.P. 0.9 in delay.
The label values of the single-phase transformer whose electrical equivalent circuit is given below are 20 kVA, 15400V / 240V, 50 Hz. This transformer Calculate what is required below. a. What is the value of the active power measured in the short circuit test? b. What is the value of the active power measured in the idle test? c. Voltage regulation was found to be 0.1% at 0.8 back power factor. Accordingly, using any method you want Find out how many kVA the transformer draws from the network (primary apparent power).