Answer / yousef madhi

Suppose That the line voltage on DELTA connection
V(line)= V
and the line current I(line)= I

as we know in DELTA connection the phase voltage equal the line voltage and the phase current equal to the line current times 1/root(3)

then V(phase)=V(line) = V
and I(phase)=I(line)/root(3) = I/root(3)





In STAR connection if again the line voltage equal to V(line)= V , the phase voltage will equal to line voltage time 1/root(3)

V(phase)=V(line)/root(3) = V/root(3)

and as per Ohm's Law (V=I*Z) and in both connection (star & Delta) we have the same winding impedance, any change in Voltage will change the current in the same amount.

so the phase current for star connection will be equal to

I(phase-star)= I(phase-delta)/root(3)
=(I/root(3))/root(3)
= I/3

and as we know in star connection the line current equal to the phase current

I(line)=I(phase)= I/3





Conclusion:

the line current in star connection is reduced by 1/3 time the line current in delta connection

Answer / vknt

in star connected winding net resistance across the line
voltage will be less as the winding across line volt are in
series.

in delta connected winding the net resistance across the
line voltage will be more as the winding across line volt
are in parallel. (one winding will be in parallel with
series combination of other two. so net resistance is less
than the resistance of one winding in delta)

Answer / vijay maurya

According to ratio line V equal to phase V upon root 3 . So
that decrease the V, decrease the current

Answer / sibi mathew

When motor is started there is no power. the only factors which effects the current is the impedance of the winging.
i.e. the current I=V/Z. So since the phase voltage in star connection =phase voltage xroot3,starting current is reduced to one third of delta connection.

Answer / abhishek goyal

STAR : decrease the voltage
decrease the torque
decrease the speed
decrease the current
as per electrical formula

Answer / kalidass

Initially there is no back emf in motor while starting. If
apply high voltage the motor will draw more current. That
is why the motor always satat with star connection.(low
voltage )

iii) A shunt motor runs at 70 rad/sec from a 460V supply and takes in an armature current of 100A. Resistors of 2.52 ohms and 1.64 ohms are connected in series with the armature and in parallel with the armature respectively. The field excitation remains direct from the 460V supply but the generated torque is halved. Determine the new running speed. Neglect brush voltage drop. The armature resistance is 0.4 ohms. [15]

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