iii. No-load current 3. If the ratio of V/F has been kept constant and the observed value of hysteresis loss at rated frequency of 50 Hz is 18 W, the measured value of core losses is 35 W, Find the total core losses at the frequency of 60 Hz. Q2: a) Determine the efficiency of three-phase 400 kVA, 11kV/ 380 V transformer at over-loading condition by 15% of its rated with unity power factor load. The copper and iron losses at full load are 16 kW, 4 kW respectively. b) State one or more of the ways to reduce the losses that taken place in transformers. Q3: At the parallel operation of three-phase transformers: a) Give an explanation for the following cases: i. Two-lamps are glow-up ii. Three-lamps are glow-up b) Two three-phase 11kV/ 380 V transformers are connected in parallel to serve a load of 36 kVA at unity power factor. The secondary side current for one transformer is 14.1 A, determine the load sharing for each transformer and the current of the other transformer. Q4: a) In the experiment of performance study of three-phase wound rotor induction motor, what are the effects of adding an external rotor resistance on the following? 1. Motor Slip 2. Motor efficiency 3. Motor starting torque

iii. No-load current 3. If the ratio of V/F has been kept constant and the observed value of hysteresis loss at rated frequency of 50 Hz is 18 W, the measured value of core losses is 35 W, Find the total core losses at the frequency of 60 Hz. Q2: a) Determine the efficiency of three-phase 400 kVA, 11kV/ 380 V transformer at over-loading condition by 15% of its rated with unity power factor load. The copper and iron losses at full load are 16 kW, 4 kW respectively. b) State one or more of the ways to reduce the losses that taken place in transformers. Q3: At the parallel operation of three-phase transformers: a) Give an explanation for the following cases: i. Two-lamps are glow-up ii. Three-lamps are glow-up b) Two three-phase 11kV/ 380 V transformers are connected in parallel to serve a load of 36 kVA at unity power factor. The secondary side current for one transformer is 14.1 A, determine the load sharing for each transformer and the current of the other transformer. Q4: a) In the experiment of performance study of three-phase wound rotor induction motor, what are the effects of adding an external rotor resistance on the following? 1. Motor Slip 2. Motor efficiency 3. Motor starting torque

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 3.51P: The ratings of a three-phase three-winding transformer are Primary(1): Y connected 66kV,15MVA...

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Similar questions

For 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) No
Why is it important to reduce the moisture within a transformer to acceptable levels during transformer installation?
An ideal transformer has no real or reactive power loss. (a) True (b) False
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.
In 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) False
Three single-phase, two-winding transformers, each rated 450MVA,20kV/288.7kV, with leakage reactance Xeq=0.10perunit, are connected to form a three-phase bank. The high-voltage windings are connected in Y with a solidly grounded neutral. Draw the per-unit equivalent circuit if the low-voltage windings are connected (a) in with American standard phase shift or (b) in Y with an open neutral. Use the transformer ratings as base quantities. Winding resistances and exciting current are neglected.
Rework Problem 3.14 if the transformer is delivering rated load at rated secondary voltage and at (a) unity power factor, (b) 0.8 power factor leading. Compare the results with those of Problem 3.14. -
A single-phase, 50-kVA,2400/240-V,60-Hz distribution transformer has the following parameters: Resistance of the 2400-V winding: R1=0.75 Resistance of the 240-V winding: R2=0.0075 Leakage reactance of the 2400-V winding: X1=1.0 Leakage reactance of the 240-V winding: X2=0.01 Exciting admittance on the 240-V side =0.003j0.02S (a) Draw the equivalent circuit referred to the high-voltage side of the transformer. (b) Draw the equivalent circuit referred to the low-voltage side of the transformer. Show the numerical values of impedances on the equivalent circuits.
For an ideal 2-winding transformer, the ampere-turns of the primary winding, N1I1 is equal to the ampere-turns of the secondary winding, N2I2 (a) True (b) False
A single-phase l0-kVA,2300/230-volt,60-Hz two-winding distribution transformer is connected as an autotransformer to step up the voltage from 2300 to 2530 volts (a) Draw a schematic diagram of this arrangement, showing all voltages and currents when delivering full load at rated voltage. (b) Find the permissible kVA rating of the autotransformer if the winding currents and voltages are not to exceed the rated values as a two-winding transformer. How much of this kVA rating is transformed by magnetic induction? (C) The following data are obtained from tests carried out on the transformer when it is connected as a two-winding transformer: Open-circuit test with the low-voltage terminals excited: Applied voltage =230V, input current =0.45A, input power =70W. Short-circuit test with the high-voltage terminals excited: Applied voltage =120, input current =4.5A, input power =240W. 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.
Consider Figure 3.4. For an ideal phase-shifting transformer, the imda nce is unchanged when it is referred from one side to the other. (a) True (b) False
The ideal transformer windings are eliminated from the per-unit equivalent circuit of a transformer. (a) True (b) False