23. Transformers are rated in kVA instead of kWbecause(a) load power factor is often not known(b) kVA is fixed whereas kW depends on loadp.f.(c) total transformer loss depends on volt-ampere(d) it has become customary.24. When a 400-Hz transformer is operated at 50Hz its kVA rating is(a) raduced to 1/8(b) increased 8 times(c) unaffected(d) increased 64 times.25. At relatively light loads, transformer efficiencyis low because(a) secondary output is low(b) transformer losses are high(c) fixed loss is high in proportion to the output(d) Cu loss is small.26. A 200 KVA transformer has an iron loss of 1 kWand full-load Cu loss of 2kW. Its load kVA cor-responding to maximum efficiency is ....... kVA.(a) 100(b) 141.4(c) 50(d) 200If Cu loss of a transformer at 7/8th full load is4900 W, then its full-load Cu loss would be.......watt.(a) 5600(b) 6400(c) 375(d) 42928. The ordinary efficiency of a given transformeris maximum when(a) it runs at half full-load(b) it runs at full-load(c) its Cu loss equals iron loss(d) it runs slightly overload.29. The output current corresponding to maximumefficiency for a transformer having core loss of100 W and equivalent resistance referred tosecondary of 0.25 2 is....... ampere.(a) 20(b) 25(c) 5(d) 40030. The maximum efficiency of a 100-kVA trans-former having iron loss of 900 kW and F.L. Culoss of 1600 W occurs at....... kVA.(a) 56.3(b) 133.3(d) 177.7(c) 7527.1

23). Transformers are rated in KVA instead of KW because iron losses are depends on voltage and…

3. Transformers are rated in kVA instead of kW because (a) load power factor is often not known (b) kVA is fixed whereas kW depends on load p.f. (c) total transformer loss depends on volt- ampere (d) it has become customary. 4. When a 400-Hz transformer is operated at 50 Hz its kVA rating is (a) raduced to 1/8 (b) increased 8 times (c) unaffected (d) increased 64 times. 5. At relatively light loads, transformer efficiency is low because 7 (a) secondary output is low (b) transformer losses are high (c) fixed loss is high in proportion to the output (d) Cu loss is small.

3. Transformers are rated in kVA instead of kW because (a) load power factor is often not known (b) kVA is fixed whereas kW depends on load p.f. (c) total transformer loss depends on volt- ampere (d) it has become customary. 4. When a 400-Hz transformer is operated at 50 Hz its kVA rating is (a) raduced to 1/8 (b) increased 8 times (c) unaffected (d) increased 64 times. 5. At relatively light loads, transformer efficiency is low because 7 (a) secondary output is low (b) transformer losses are high (c) fixed loss is high in proportion to the output (d) Cu loss is small.

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 3.57P: A two-winding single-phase transformer rated 60kVA,240/1200V,60Hz, has an efficiency of 0.96 when...

See similar textbooks

Similar questions

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.
In developing per-unit equivalent circuits for three-phase transformers. under balanced three-phase operation. (i) A common Sbase is selected for both the H and X terminals. (ii) The ratio of the voltage bases Vbase/VbaseX is selected to be equal to the ratio of the rated line-to-line voltages VratedHLL/VratedXLL. (a) Only one of the above is true. (b) Neither is true. (C) Both statements are true.
An infinite bus, which is a constant voltage source, is connected to the primary of the three-winding transformer of Problem 3.53. A 7.5-MVA,13.2-kV synchronous motor with a sub transient reactance of 0.2 per unit is connected to the transformer secondary. A5-MW,2.3-kV three-phase resistive load is connected to the tertiary Choosing a base of 66 kV and 15 MVA in the primary, draw the impedance diagram of the system showing per-unit impedances. Neglect transformer exciting current, phase shifts, and all resistances except the resistive load.
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
Consider a single-phase electric system shown in Figure 3.33. Transformers are rated as follows: XY15MVA,13.8/138kV, leakage reactance 10 YZ15MVA,138/69kV, leakage reactance 8 With the base in circuit Y chosen as 15MVA,138kV determine the per-unit impedance of the 500 resistive load in circuit Z, referred to circuits Z, Y, and X. Neglecting magnetizing currents, transformer resistances, and line impedances, draw the impedance diagram in per unit.
Consider the three single-phase two-winding transformers shown in Figure 3.37. The high-voltage windings are connected in Y. (a) For the low-voltage side, connect the windings in , place the polarity marks, and label the terminals a, b, and c in accordance with the American standard. (b) Relabel the terminals a, b, and c such that VAN is 90 out of phase with Va for positive sequence.
Reconsider Problem 3.64 with the change that now Tb includes both a transformer of the same turns ratio as Ta and a regulating transformer with a 4 phase shift. On the base of Ta, the impedance of the two comp onents of Tb is jO.1 per unit. Determine the complex power in per unit transmitted to the load through each transformer. Comment on how the transformers share the real and reactive pors.
Consider the single-line diagram of the power system shown in Figure 3.38. Equipment ratings are Generator 1: 1000MVA,18kV,X=0.2perunit Generator 2: 1000MVA,18kV,X=0.2p.u. Synchronous motor 3: 1500MVA,20kV,X=0.2p.u. Three-phase -Y transformers T1,T2,T3,T4,: 1000MVA,500kV,Y/20kV,X=0.1p.u. Three-phase YY transformer T5: 1500MVA,500kV,Y/20kVY,X=0.1p.u. Neglecting resistance, transformer phase shift, and magnetizing reactance, draw the equivalent reactance diagram. Use a base of 100 MA and 500 kV for the 50-ohm line. Determine the per-unit reactances.
A single-phase two-winding transformer rated 90MVA,80/120kV is to be connected as an autotransformer rated 80/200kV. Assume that the transformer is ideal. (a) Draw a schematic diagram of the ideal transformer connected as an autotransformer. showing the voltages, currents, and dot notation for polarity. (b) Determine 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 the kA rating is transferred by magnetic induction?
An ideal transformer has no real or reactive power loss. (a) True (b) False
Consider two interconnected voltage sources connected by a line of impedance Z=jX, as shown in Figure 2.27. (a) Obtain expressions for P12 and Q12. (b) Determine the maximum power transfer and the condition for it to
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.