Concept explainers
A single-phase
Open-circuit test with the low-voltage terminals excited:
Applied voltage
Short-circuit test with the high-voltage terminals excited:
Applied voltage
Based on the data, compute the efficiency of the autotransformer corresponding to full load, rated voltage, and 0.8 power factor lagging. Comment on why the efficiency is higher as an autotransformer than as a two-winding transformer.
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Chapter 3 Solutions
Power System Analysis and Design (MindTap Course List)
- 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.arrow_forwardFor a short-circuit test on a 2-winding transformer, with one winding shorted, can you apply the rated voltage on the other winding? (a) Yes (b) Noarrow_forwardWhy is it important to reduce the moisture within a transformer to acceptable levels during transformer installation?arrow_forward
- 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) -.arrow_forwardIn developing per-unit circuits of systems such as the one shown in Figure 3.10. when moving across a transformer, the voltage base is changed in proportion to the transformer voltage ratings. (a) True (b) Falsearrow_forward9. The no-load current of a single-phase transformer is 5.0 A at 0.3 power factor when supplied from a 240-V, 50-Hz source. The number of turns on the primary is 200. Calculate (a) the maximum value of the flux in the core, (b) the core losses, and (c) the magnetizing current.arrow_forward
- What are the objectives of implementing an open circuit test on single phase transformer?arrow_forwardThe core of a three phase, 50 Hz, 11000/550 V delta/star, 300 kVA, core-type transformer operates with a flux of 0.05 Wb. Find (i) number of H.V. and L.V. turns per phase. (ii) e.m.f. per turn (iii) full load H.V. and L.V. phase-currents.arrow_forwardFind the elements of the equivalent circuit attributed to the secondary of a single-phase transformer. The no-load voltages in the primary and secondary circuit are 200 volts and 400 volts, respectively, with a frequency of 50 Hz. The primary no-load current at the voltage of 200 volts is 0.7 amperes and the loss of the core is equal to 70 watts. The resistance and reactance of the primary are 3.2 ohms and 1.25 ohms, respectively. The resistance and reactance of the secondary are 0.6 ohm and 0.07 ohm, respectively. Draw the equivalent circle, showing the values of its elements.arrow_forward
- Find the elements of the equivalent circuit relative to the secondary of a single-phase transformer. The no-load voltages in the primary and secondary circuit are 200 and 400 volts, respectively, and at a frequency of 50 Hz. The primary no-load current at a voltage of 200 volts is 0.7 amps and the losses in the core are 70 watts. The resistance and reactance of the primary are 3.2 and 1.25 ohms, respectively. Secondary resistance and reactance 6.0, 0.07 ohms, respectively. Draw the equivalent circle, showing the values of its elements.arrow_forwardTwo transformers A and B have the following data Transformer A: 6600/440 V, (250 KVA ) requires ( 6%) of rated voltage to circulate (90%) of full load current at power factor (0.25) when the low voltage winding is short circuited and the no load loss is equal to (2500 W). Transformer B: 6600/420 V, (600 KVA) requires (9%) of rated voltage to circulate (80%) of full load current at power factor (0.16) when low voltage winding is short circuited and no load loss is equal to (4500 W). Calculate the followings: If both transformers are connected in parallel to supply a load (1.2 + j 2.3) ohm, find the output power of each transformer.arrow_forwardTwo transformers A and B have the following data Transformer A: 6600/440 V, (250 KVA ) requires ( 6%) of rated voltage to circulate (90%) of full load current at power factor (0.25) when the low voltage winding is short circuited and the no load loss is equal to (2500 W). Transformer B: 6600/420 V, (600 KVA) requires (9%) of rated voltage to circulate (80%) of full load current at power factor (0.16) when low voltage winding is short circuited and no load loss is equal to (4500 W). Calculate the followings: The terminal voltage when transformer A is supplying half load at power factor (0.6) lagging and transformer B is supplying (85%) of full load at power factor (0.85) leading.arrow_forward
- Power System Analysis and Design (MindTap Course ...Electrical EngineeringISBN:9781305632134Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. SarmaPublisher:Cengage Learning