Answer / raja

At starting times phase voltage is reduced 1/root(3) times
of line voltage.so motor start safely.after reaching 70%of
speed change to delta.now apply fullvoltage

Answer / subhash sapkal

in star connection winding voltage 1/1.73*line voltage (
there for current is directly prapotional to voltage )

Answer / kayyum

at start in star 1/root 3 times line vtg, and current is
praportional to vtg.

Answer / kumar

all of us know in star Vl=1.732Vp & Il=Ip, at start as current is limited to phase current, thats why motor dosent draw more current.and for delta it is normal cond. i.e.415v. get applied across each wdg. insted of 250(as in star) & line current is limited to 1.732 times phase current. Motor remains in str for 4-5 Sec only.Also power consumption in both cases remain same(can be proved).
But it is also possible that motor can draw more current in star position due application of reduced voltage,also the change in such vtg. will affect torque.
If possible try to find out derrivation for vtg. & current in star & delta connected resistance.

Answer / m.varadarajan

when higher hp motor starts with high current, to reduce
the starting current we are using this connection,it will
reduce 1/root3 times of full load current, after motor
reaches of the rated speed, delta connection applied.this
time full voltage applied to winding and motor run smoothly.

Answer / hitendra

when motor connect in star connection, motor have high
voltage and reduced line current at starting time. becoz
motor secondery side shorted, and motor torque proponal to
voltage.and motor will start in safe mode.after get the 70
percent speed motor run with permissible voltage and current.

Answer / vikramsenareddy

Ans: in star connection line current is 1.732times of phase
current. while taking the phase current we are reducing the
line current. at the same time phase voltage is equal to
line voltage.

sir my exam is on 19/6/2013 under electrical branch pls send me sample aptitude questions as well as sample technical questions for jindal steel and power company

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