2. What is meant by energy efficiency of a transformer? A 20-KVA transformer has a maximum efficiency of 98 percent when delivering three-fourth full-load at u.p.f. If during the day, the transformer is loaded as follows: 12 hours No load 12 kWh, 0.8 p.f. 20 kW, u.p.f. Calculate the energy efficiency of the transformer. 6 hours 6 hours (Electrical Technology-III, Gwalior Univ., 1980)

2. What is meant by energy efficiency of a transformer? A 20-KVA transformer has a maximum efficiency of 98 percent when delivering three-fourth full-load at u.p.f. If during the day, the transformer is loaded as follows: 12 hours No load 12 kWh, 0.8 p.f. 20 kW, u.p.f. Calculate the energy efficiency of the transformer. 6 hours 6 hours (Electrical Technology-III, Gwalior Univ., 1980)

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 3.4P: A single-phase 100-kVA,2400/240-volt,60-Hz distribution transformer is used as a step-down...

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The transformer of Problem 3.16 is supplying a rated load of 50 kVA at a rated secondary voltage of 240 V and at 0.8 posr factor lagging. Neglect the transformer exciting current. (a) Determine the input terminal voltage of the transformer on the high-voltage side. (b) Sketch the corresponding phasor diagram. (c) If the transformer is used as a step-down transformer at the load end of a feeder whose impedance is 0.5+j2.0, find the voltage VS and the power factor at the sending end of the feeder.
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.
Consider a source of voltage v(t)=102sin(2t)V, with an internal resistance of 1800. A transformer that can be considered as ideal is used to couple a 50 resistive load to the source. (a) Determine the transformer primary-to-secondary turns ratio required to ensure maxi mum power transfer by matching the load and source resistances. (b) Find the average power delivered to the load, assenting maximum power transfer.
For the transformer in Problem 3.10. The open-circuit test with 11.5 kV applied results in a power input of 65 kW and a current of 30 A. Compute the values for GcandBm in siemens referred to the high-voltage winding. Compute the efficiency of the transformer for a load of 10 MW at 0.8 p.f. lagging at rated voltage.
Consider Figure 3.25 of the text for a transformer with off-nominal turns ratio. (i) The per-unit equivalent circuit shown in part (c) contains an ideal transformer which cannot be accommodated by some computer programs. (a) True (b) False (ii) In the - circuit representation for real c in part (d), the admittance parameters Y11 and Y12 would be unequal. (a) True (b) False (iii) For complex c, can the admittance parameters be synthesized with a passive RLC circuit? (a) Yes (b) No
A transformer with a 10:1 ratio and rated at 60kVA, 2200/220V, 60Hz is used to step down the voltage of a distribution system. The low tension voltage is to kept constant at 220V. (a) What load Impedance connected to the low-tension side will be loading the transformer fully at 0.8 power factor (lag) ? (b) What is the value of this impedance referred to the high tension side?
A Transformer with 10:1 ratio and rated at 50-kVA, 2400/240-V, 50-Hz is used to step down the voltage of a distribution system. The low-tension voltage is to be kept constant, if the transformer has: R = 2.2 0, R2 = 0.014 Q, X, = 4.1 0, X2 = 0.03 0, then, a. What load impedance connected to low-tension side will be loading the transformer fully. b. Calculate the equivalent resistance as referred to primary. c. Calculate the equivalent reactance as referred to primary. d. Calculate the equivalent impedance as referred to primary. e. Calculate the total Cu loss.
A 2,300/240-V, 60-Hz, 4.6-kVA transformer isdesigned to have an induced emf of 2.5 V/turn.Assuming an ideal transformer, finda. The numbers of high-side turns Nh and low-sideturns Nl .b. The rated current of the high-voltage side Ih.c. The transformer ratio when the device is used as astep-up transformer.
A 120:480-V, 10-kVA step-up two-winding transformer is to be used as an autotransformer to supply a 120-V circuit from a 600-V source (a step-down autotransformer). When it is tested as a two-winding transformer at rated load, unity power factor, its efficiency is 97.9 %. 1.Show the connection diagram of the transformer converted as an autotransformer and identify which is the series winding Nse and the common winding Nc.
A 150-kVA single-phase transformer has a core loss of 1.5 kW and a full-load Cu loss of 2 kW. Calculate the efficiency of the transformer (a) at full-load, 0.8 p.f. lagging (b) at one-half full-load unity p.f. Determine also the secondary current at which the efficiency is maximum if the secondary voltage is maintained at its rated value of 240 V
A 270 kVA transformer has primary and secondary winding resistances of 0.6Ω, and 0.0016Ωrespectively. The iron loss is 2.25 KW and the primary and secondary voltages are 7kV and 320 Vrespectively. If the power factor of the load is 0.6 lag, find the efficiency of the transformer for 20% of fullload.
Each motor is rated at 80 hp but is only loaded mechanically as follows: Motor # % Loading 1 40 2 50 3 70 The relationship between % of full load for each motor and efficiency (they are all the same) is given by the graph below: a) What is the minimum required transformer rating in kVA? b) By what percentage could the required transformer rating be reduced if a capacitor bank were installed in parallel with the motors, improving the power factor of the loadcentre to unity?