in star connection
line voltage is=(3)^(1/2)*phasevoltage
line current is=phase current
in delta connection
line voltage is =phase voltage
line current is =(3)^(1/2)*phase current

power ratio=( ((3)^(1/2)*phasevoltage*phase current)/((((3)^
(1/2)*phasevoltage*phase current))
so power ratio is =1.

Power ratio between star and delta is 1:1
because power in star=line voltage(3^1/2*Vph)*line current
(Iph)=3^1/2VphIph
power in delta =line voltage(Vph)*line current(3^1/2*Iph)
=3^1/2VphIph

IIly in star connected vphase=Vline/rt3,
Iline=Iphase
ie Power = rt3 vpahseIphaseCos
ie. in both star and delta power remain same
therefore the Power ratio = 1.

The power transformation ratio in the transformer is
1:1.Only the voltage and currents are subjected to
change.Pri MVA=Secondary MVA. Except to compensate for some
losses.

i think transformer just step up or step down voltage or
current only but power remains same(constant).so ratio of
p1 to p2 is 1 when same transformer connected in star or
delta.

If placing 3 resistors in Delta rather than Star will end
up with 3 times more heating power. This is because you
have sq root of 3 times more voltage across each resistor
in Delta and hence end up with the sq root of 3 times more
current through each resistor. The sq root of 3 of more
voltage times the sq root of 3 of more current than, star
connected resistors means 3 times more power. Capacitor
are often connected in Delta for power factor correction as
this offers 3 times more reactive power than in Star
connection, though be aware they need to be able to cope
with line voltage across each Cap in Delta.

If placing 3 resistors in Delta rather than Star will end
up with 3 times more heating power. This is because you
have sq root of 3 times more voltage across each resistor
in Delta and hence end up with the sq root of 3 times more
current through each resistor. The sq root of 3 of more
voltage times the sq root of 3 of more current than, star
connected resistors means 3 times more power. Capacitor
are often connected in Delta for power factor correction as
this offers 3 times more reactive power than in Star
connection, though be aware they need to be able to cope
with line voltage across each Cap in Delta.
Thanks

Now assume any type of load; for simplicity assume it a
only resistive load.

And let it be ?R? per phase.

For Delta connected load:

Calculation for per phase power; PD= I2R

Where I ? load current (per phase)

And,

I = ?3Vs/R {as line voltage of the supply is directly
applied to the phase of the delta load}

So,

Pd = (?3Vs/R )2R = 3Vs2/R watts per phase.

For 3 phases:

P3D = 3Pd = 3*3Vs2/R = 9Vs2/R watts.

Now for Star connected load:

PS = I2R = (Vs/R)2R = Vs2/R watts

For 3 phases: P3S = 3PS = 3 Vs2/R watts

Conclusion:

P3S / P3D = 3Vs2/R / 9Vs2/R = 1/.

Is This Answer Correct ?

25 Yes

57 No

Baswaraj

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Dear sir,
we are getting voltage fluctuations suddenly for 2 or 3
minutes again it becomes normal. we checked each and every
connection some times we are getting 110 volts like that
from earth to neutral again it is reducing we are getting
supply from 45 kva DG set give earthing properly.

WHEN THESE TRANSFORMERS WINDINS CONFIGURATION ARE USED?
SPECIALLY EXPLAIN REGARDING STEP UP AND STEP DOWN KEEPING
IN MIND.AND REGARDING LOAD ALSO.
a.star to delta
b.delta to star
c.delta to delta
d.star to star
ALSO EXPLAIN WHY V USE 415/415 TRANSFORMERS IN TUBEWELLS?

How to run 1ph motor(230 VOLTS its full load amps
is 4.5 ampa))with 480 volts main(we didn hav
neutral)Thn we go for step down transformer.Our load 10
amps,so we conisder this amps in primary are secondary side?