PowerPoint Presentation · 3. A 500 kVA transformer has constant losses of 500 W and copper losses...

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1. A transformer has 300 W as iron loss at full load. The iron lossat half full load is? [HPCL A.M.T, 2019]a) 300 Wb) 0 Wc) 600 Wd) 150 W

2. The relationship between number of turns of primarywinding (N1) and number of turns of secondary winding (N2) ofan isolating transformer is: [BSPHCL JE, 2019]a) 𝐍𝟏 > 𝟐𝐍𝟐b) 𝐍𝟏 < 𝟐𝐍𝟐c) 𝐍𝟏 = 𝐍𝟐d) 𝐍𝟏 > 𝐍𝟐

3. A 500 kVA transformer has constant losses of 500 W and copperlosses at full load are 2000 W. Then at what load, is the efficiencymaximum? [ESE 2007, AAI Electrical, 2016]a) 250 KVAb) 500 KVAc) 1000 KVAd) 125 KVA

4. A 25 KVA single phase transformer has 260 turns in primaryand 40 turns in secondary winding. The primary is connected to1500 V, 50 Hz mains. Calculate primary and secondary current,respectively, on full load. [ESIC, 2019]a) 54.16 A, 8.32 Ab) 8.32 A, 54.16 Ac) 16.67 A, 108.3 Ad) 108.3 A, 16.67 A

5. In generators and transformers, the Percentage reactance ofthe circuit is defined as [BSPHCL JE, 2019]a) The percentage of total phase-voltage drop in the circuitunder no load conditionb) The percentage of power lost with respect to powertransmitted from the sending sidec) The percentage of total phase-voltage drop in the circuitwhen full load current is flowingd) The percentage of total phase voltage lagging total loadcurrent

6. The material used in constructing the core of a transformer isgenerally [BSPHCL JE, 2019]a) Non-Magnetic materialb) Mild Steelc) Cast Irond) Silicon Steel

7. Scott-T transformer connection is used for the conversion of[BSPHCL JE, 2019]

a) Three phase to single phaseb) Single phase to two phasec) Single phase to three phased) Three phase to two phase

8. Transformers are devices which transform electrical energy fromone electrical circuit to another. These two circuits are electricallyisolated from each other. Transformers are: [BSPHCL JE, 2019]a) Rotating devices working on the principle of mutual inductionb) Static devices working on the principle of mutual inductionc) Rotating devices working on the principle of self inductiond) Static devices working on the principle of self induction

9. Which is the INCORRECT statement? Unlike shell typetransformers, core type transformers have. [BSPHCL JE, 2019]a) a single magnetic circuitb) less lossesc) cylindrical winding or concentric windingd) two limbs

10. A delta/delta connected three-phase transformer can beconnected in parallel with? [SAIL (RSP) OCTT, 2019]a) Star/deltab) Delta/starc) Star/stard) Star/zigzag

11. If the iron core of a transformer is replaced by an air core thenthe total iron loss in a transformer will? [SAIL (RSP) OCTT, 2019]a) Increaseb) Decreasec) Remain unchangedd) Become zero

12. When two transformers of different KVA ratings are connectedin parallel, they divide the total load in proportion to theirrespective KVA ratings only when their? [SAIL (RSP) OCTT, 2019]a) KVA ratings are identicalb) Efficiencies are equalc) Per unit impedances are equald) Equivalent impedances are equal

13. Which of the following combination of 3-phase transformers canbe successfully operated in parallel? [SAIL (RSP) OCTT, 2019]a) Δ –Y or Δ -Yb) Y-Y or Δ -Yc) Δ -Δ or Δ -Yd) Y -Δ or Δ -Δ

14. In practice, in a transformer having electrical losses (ironlosses and copper losses), no load current. [BSPHCL JE, 2019]a) lags the applied voltage by 90°b) leads the applied voltage by 90°c) lags the applied voltage by less than 90°d) leads the applied voltage by less than 90°

15. High moisture (water) content in oil used in transformerwill: [BSPHCL JE, 2019]a) Improve its voltage regulationb) Save the transformer core from being rustedc) Reduce dielectric strength of oil and lead to flashoverd) Reduce its density

16. Transformer action requires. [EDCIL DDA. JE, 2018]a) an increasing magnetic fluxb) an alternating electric fluxc) a constant magnetic fluxd) an alternating magnetic flux

17. Voltage regulation and efficiency of four transformers A, B ,C & D are as given below: [DMRC, 2018]A-5% regulation & 94% efficiencyB-2% regulation & 96% efficiencyC-5% regulation & 97% efficiencyD-2% regulation & 97% efficiencyThe transformer that is in a good working condition is:a) Ab) Cc) Dd) B

18. A 0.75 KVA, 220/22V, 50Hz single phase transformer has HVwinding resistance of 1 ohm and leakage reactance of 6 ohm. Whatwill be the equivalent resistance and equivalent leakage reactance ofHV winding with respect of LV winding? [N.P.C.I.L, 2018]a) 0.01 ohm, 0.06 ohm respectivelyb) 0.1 ohm, 0.6 ohm respectivelyc) 10 ohm, 60 ohm respectivelyd) None of these

19. A single-phase transformer has 400 turn on primary and 50 turnon secondary. Cross sectional area of core is 80 cm² and Flux densityis 12Wb/cm². If a 440volt 50 Hz Ac supply is given to the primaryside, what will be the induced emf and frequency on secondary sideof the transformer? [N.P.C.I.L, 2018]a) 50 volt, 50 Hzb) 55 volt, 50 Hzc) 75 volt, 25 Hzd) None of these

20. Following statements are made regarding the Open Circuit Teston the single phase transformer [EDCIL DDA .JE, 2018]1. It is performed on L V side.2. It is performed at rated current.3. It helps in calculation of equivalent leakage impedance.4. It is performed on HV side.5. It is performed at rated voltage.6. It gives magnetizing current and core loss.7. It helps in determination of voltage regulation.8. It gives turn ratio.From these, which statements are correct?a) 2, 4, 7b) 2, 4, 6, 8c) 3, 4, 5, 6d) 1, 5, 6, 8

21. The magnitude of the induced emf in the primary winding, willbe…….but opposite to the applied voltage. [SSC-JE, 2018]a) Higherb) Almost equalc) Lowerd) Negligible

22. In a transformer, if the iron losses and copper losses are 40.5kW and 50 kW respectively, then at what fraction of load will beefficiency be maximum? [ESE, 2014]a) 0.80b) 0.57c) 0.70d) 0.90

23. In a transformer zero voltage regulation is achieved at a loadpower factor which is. [ESIC-JE, 2016 & SSC-JE, 2018]a) zerob) leadingc) laggingd) Unity

24. A 10 KVA auto transformer, turn ratio is 0.4. Find the powertransferred inductively: [SSC-JE, 2018]a) 4k VAb) 6k VAc) 10 kVAd) 0 kVA

25. For the transmission line, if booster transformers are to beused, preferred location will be: [SSC-JE, 2018]a) at the receiving endb) at the sending endc) at the intermediate pointd) anywhere is the line

26. In which transformer, the tertiary winding is used: [SSC-JE, 2018]a) Star–deltab) Star–starc) Delta–deltad) Delta–star

27.The no load current in a transformer is: [SSC-JE, 2018]a)Sinusoidalb) non Sinusoidalc) Trapezoidald)stepped

28.Transformer cooling and insulation oil must be of: [SSC-JE, 2018]a) low viscosityb) high viscosityc) low BDVd) low resistivity

29.Single Phase transformers can be used in parallel only whentheir voltages are: [SSC-JE, 2018]a) Equalb) Unequalc) Zerod) None of these

30.Which is to be short circuited on performing short circuittest on a transformer? [SSC-JE, 2018]a) Low Voltage Sideb) High voltage Sidec) Primary sided) Secondary side

31.A Single phase 50 Hz transformer has high voltage and lowvoltage windings of 2200/220 V. What is the Transformationratio? [SSC-JE, 2018]a) 10b) 1/10c) 1d) None of these

32.An Isolation Transformer has Primary to Secondary turnsratio of. [SSC-JE, 2018]a) 1:2b) 2:1c) 1:1d) Can be any ratio

33. In case of core type transformer which type of winding isdone near the core? [SSC-JE, 2018]a) Low voltageb) High voltagec) Primary windingd) Secondary winding

34. The core Flux in transformer depends mainly on. [SSC-JE, 2018]a) Supply voltageb) Supply voltage, Frequency and Loadc) Supply voltage and Loadd) Supply voltage and Frequency

35. If the voltage applied to a transformer primary is increased

by keeping the𝐕

𝐟ratio fixed, then the magnetizing current and

the core loss will, respectively? [ESE 2006, VIZAG MT, 2017]a) decrease and remain the sameb) increase and decreasesc) remain the same and remain the samed) remain the same and increase

36. Two windings of transformer are designed as: [EDCIL DDA. JE, 2018,]a) primary and H.V. windingsb) H.V. and L.V. windings or equal voltage windingsc) secondary and L.V. windings or primary and L.V. windingsd) primary and secondary windings

37. To conduct Sumpners test on a transformer: [N.P.C.I.L, 2018]a) Only one transformer is sufficientb) Two identical transformers are neededc) Two un–identical transformers are neededd) AT least three transformers are necessary

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(28) In a steam power plant…………heats the feed water on its way to the boiler by delivering heat from the flue gases: -

(A) Superheater (B) Economizer

(B) Preheater (D) Turbine

(29) Power generation of thermal power plants is based on: -

(A) Rankine cycle

(B) Otto cycle

(C) Diesel cycle

(D) Carnot cycle