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1 Serial : Ch1_EE_C_Power Electronic_6818 Delhi Noida Bhopal Hyderabad Jaipur ucknow Indore Pune Bhubanewar Kolkata Patna Web: info@madeeay.in Ph: CASS ES EECRICA ENGINEERING Subject : Power Electronic Date of tet : 6/8/18 Anwer Key 1. (c) 7. (c) 13. (c) 19. (c) 5. (d). (c) 8. (b) 14. (c). (d) 6. (b) 3. (a) 9. (d) 15. (d) 1. (a) 7. (a) 4. (b) 1. (b) 16. (b). (b) 8. (c) 5. (c) 11. (c) 17. (a) 3. (c) 9. (c) 6. (c) 1. (d) 18. (d) 4. (c) 3. (b)

2 C18 EE Power Electronic 7 Detailed Explanation 1. (c) he output voltage waveform of the circuit i i S C C t S D S t S t according to the waveform voltage acro inductor i zero, ince inductor i hort circuited for dc. voltage 1 1 voltage 3 hence, the three voltage are 1,, 3. (a) Given chopper i a buck chopper o, α I I max I I I min I OFF t I I I hi i applicable only at boundary of continuou and dicontinuou condition α (1 ) C α Ι f 4. (b) he revere recovery characteritic of a power diode i hown below. In the figure revere recovery time t rr compoed of t a and t b. t a i the time between zero croing and peak revere current I RR and t b i meaured from revere peak I RR value of.5 I RR.

3 8 Electrical Engineering I F t rr.5 t rr t a t I RR If the characteritic are aumed to be triangular (i.e. abrupt recovery) then from the figure charge tored i t b Q R area ABC 1 I RR trr...(i) di I RR t a dt di t a t rr, then I RR t rr dt...(ii) from equation (i) and (ii) Q R 1 dt di trr 5. (c) he fundamental rm value of output voltage i, rm m ph in m 3 in option c i, (c) urn off time in a emi conductor device increae with minority carrier. Since minority carrier are abent in MOSFE, it turn off time i le. 7. (c) Even harmonic are alway zero for a halfwave ymmetry waveform. 8. (b) It i a 6 pule converter, hence firing frequency i 6 time the line frequency. 9. (d) o turn off the SCR the anode current hould go le than holding current which i 5 ma. I h R olt 9 i the voltage level to be maintained to turn off the SCR out of the given option. For 1 olt, 9 i a 4.5mA 3 1 [ i a < i holding ]

4 C18 EE Power Electronic 9 1. (b) I a 3-φ upply 3- φ emi converter R E b I R E b If I i droped to zero then, E b When I drop to zero, at that intance of time, voltage aume a value equal to the intantaneou value of the motor back emf. 11. (c) he diode will tart conducting at an angle θ 1, where 1 15 θ 1 in Arrange value of charging current, 1 1 I θ ( m in ωt E) d( ωt) R θ1 I 4.97 A power delivered to battery i, P E I P W co (d) di dt max max A/ µ dv dt max di R dt max /µ ec 13. (c) 1 α α α.6667 I ( ) f or I α f

5 1 Electrical Engineering I ( ) A 14. (c) Rm value of output voltage, rm Rm value of fundamental component of output voltage, Rm value of all harmonic voltage, oh () (198.7) or HD Ditortion factor µ oh or 48.34% , rm (d) Here, ml l average output voltage of a 3-φ diode bridge rectifier i 3 ml then E I R average value of battery charging current, I E A R 8 3 Fundamental component of ource current, i S1 inωt I RMS value of fundamental component of ource current, RMS value of ource current i, I 3 I S 1 I S I 3 1/ Input HF or HD I S 3 Ι 1/ I 1 I / 1.31

6 C18 EE Power Electronic (b) O m ωt 17. (a) t rr t rr If revere recovery time i taken into conideration, the diode D 1 and D will not be off at ωt, but will continue to conduct until t t rr ω the reduction in output voltage i given by cro hatched area. Average value of thi reduction in output voltage i given by r t rr 1 m in ωt d( ωt) m r ( 1 coω t ) with zero revere recovery time, average output voltage m for f 5 Hz, the reduction in the average output voltage, rr m r ( 1 co ωt ) rr co percentage reduction in average output voltage 9.55% D t CH O A D 66 on off t Since the give chopper i a tep up chopper, 1 1 δ

7 1 Electrical Engineering or, δ or, δ 3 he output voltage pule width i off. on on off 3 or, on off or, off 5 µ 18. (d) Effective on period of a voltage commutated chopper i on on I C (8 1 ) on (c) Circuit diagram of cla-c commutation i hown below. S R 1 R C I (max) 1 Peak value of current through thyritor i: I, max 1 R 1 R A. (d) String efficiency η Current rating of whole tring Current rating of one SCR number of SCR in tring 54 6 np

8 C18 EE Power Electronic 13 Now, Derating factor 1 tring efficiency.1 1 η or, n p 54 or, 6.88 n p or, n p (a) he output waveform of line voltage i, ine 3 ωt,rm,line,rm,line 3 1 dωt (b) S 1 3 I contant load current S O A D 4 he dc load current, i given by ω m I [ coα co( αµ )] et µ 1 be the overlap angle for firing angle α 1, then ω m I [co α co( αµ )] m [ co α 1 co( α 1 µ 1) ] or, co α co (α µ) co α 1 co (α 1 µ 1 ) or, co co (15 ) co 3 co (3 µ 1 ) or, co (3 µ 1 ) or, co (3 µ 1 ).8319 or, 3 µ or, µ ω

9 14 Electrical Engineering 3. (c) 3-φ R 1 Ω 4 arge Inductor 5 Hz (c) For firing advance angle of 6, α Average output voltage, 3 m coα 3 4 co(1) or, 7.9 A i negative, thi converter i operating a line-commutated inverter. he polarity of load Emf E mut be revered. Now, E I R or, I (1) oad current, I A Rm value of load current, I,rm I A Power delivered by the battery to the ac ource through the line commutated inverter i: P I P W P 158 W Negative ign indicate that the power i delivered from load to ource. 3 A CH 1 mh.5 Ω For a motor, t E a I a r a he minimum peed of a dc motor i zero. hi give motor counter emf E a α I a r a or, α (3.5) or, α Maximum poible value of duty cycle i 1. Now, α E a I a r a or, 1 KN 15

10 C18 EE Power Electronic 15 or, N 15 5 rpm.1 Range of peed i < N < 5 rpm, and range of duty cycle i <α<. 5. (d) RMS value of fundamental component of load voltage on 4 n RMS value of fundamental current, I 1 1 Z1 7.1 Now, Z n Z 1 R R 1 nω nωc 1 ω ωc or, Z 1 or, Z 1 Ω 1 (6 7) I A Phae angle, φ n φ 1 tan 1 1 nω n ω C degree R 1 (6 7) tan 45 1 he fundamental component of current i 1 a function of time i i 1 I1in( ωt φ1) or, i in (ωt 45 ) A 6. (b) During on period of witch, the circuit behave a S d dt i

11 16 Electrical Engineering I or, S dt or, S ( on ) I...(i) During off period, the circuit behave a hown below, D or, d dt i or, ( off ) I...(ii) Equating both the equation. on off on on or, α 1 α When α <.5 the circuit operate a a tep down chopper. In cae α >.5, thi circuit operate a tepup chopper. 7. (a) he minimum value of firing angle α load phae angle φ φ tan 1 ω R or, φ 1 6 tan he maximum value of rm load current I or occur when α φ But, at thi value of firing angle, the power circuit of ac voltage controller behave a if load i directly connected to ac ource. herefore, maximum value of rm load current i: 3 3 I o,rm 31.9A R ( ω ) 4 6 Maximum power,,rm I R (31.9) W Power factor at thi power Io, rm R I I, rm I,rm R lagging 3

12 C18 EE Power Electronic (c) Pule width 7 d 5 d 36 he output waveform can be decribed by Fourier Serie a n 1,3, 5 4 n in in nd inn ωt n 7 4 in 7 in7(36 ) in7ωt 7 7rm in in7(36 ) 7 7rm.1 9. (c) S m R Ω m ωt α ωt I ωtd ωt R R 1 m in ( ) α m ( coωt α ) R m I avg [1 co ] R α aking m a contant for both the cae. R 5 I a 1 coα 1 coα 1 or, 5 I a 1 co(4 ) 1 co(8 ) or, I a 33. A. hu, 5 A < I a < 5 A

13 18 Electrical Engineering 3. (b) Power delivered to load, P 1 I, rm co φ where 1 Rm value of fundamental output voltage I,rm load (or) output rm current. 1 4 dc Power delivered P 1 I,rm co φ co kw P

Delhi Noida Bhopal Hyderabad Jaipur Lucknow Indore Pune Bhubaneswar Kolkata Patna Web: Ph:

Serial : LS_N_A_Network Theory_098 Delhi Noida Bhopal Hyderabad Jaipur Lucknow ndore Pune Bhubanewar Kolkata Patna Web: E-mail: info@madeeay.in Ph: 0-4546 CLASS TEST 08-9 NSTRUMENTATON ENGNEERNG Subject