Answer Posted / thowsif_emerson

The power in watts is equal to volts times amps, but
we must use "phase" volts and "phase" amps to calculate
power.
Calculating these phase relationships requires a little bit
of
trigonometry.

In a "Y" connected circuit, the voltage measured line to
line is not the
true "phase" voltage [phase to neutral voltage], but the
combination of
two voltages that are out of phase by 120 degrees.

Assuming a balanced load, the current in any of the three
phases is the
same as that measured in each line because the line will be
attached to
one end of the phase so there cannot be any difference. We
need the

phase voltage times the phase current to get the phase
power.

There are two phases connected between each pair of lines
in a "Y"
circuit, and since the voltages are not in phase, they do
not add together
to make the line voltage twice the phase voltage. It turns
out through
some basic trigonometry, that the line voltage is equal to
each of the two
phase voltages times the sine of 120 degrees, and the sine
of 120 degrees
is "one-half" the square root of 3. Adding those two halves
together
gives the LINE voltage as the square root of 3 times the
phase voltage.
Or conversely the phase voltage is the line voltage DIVIDED
by the square
root of 3.

So the power in any phase, assuming, again, a balanced load
is
the line voltage times the line current divided by the
square root of 3.

For the three phases, then, the total power is three times
the power in
any phase. 3 X the line voltage X the line current divided
by the square
root of 3. 3 divided by the square root of 3 simplifies to
just the
square root of 3. Multiplying that, as you noted, by the
power factor
converts volt-amps to watts assuming the power factor is
other than one.

In a delta connected circuit, the same problem exists
except with the current measurement. Here, the line to line
voltage
measurement is the phase voltage, but the line current is
composed of two
currents that are out of phase by 120 degrees, and you
guessed it, the
"vector sum" of the two phase current components is the
square root of
three times the current in any phase. And, the phase
current is the line
current divided by the square root of 3, so the power
equation works
exactly the same for both the "Y" and the Delta connected
circuits.

What is the best thing to protect the motor from running over full current. CT or O/L or pressure transducer at the given pressure rating

1476

---

describe the phenomena of vacuum interruption in C.B

1725

---

what is (+) and (-) in generator field detector stand for?

1781

---

how r charge carriers produced

2030

---

Can you used moeller lzm1 mccb in a dc system with 125vdc and 20ka short circuit current , beside is it have 24 or 48 volt shunt ? Beside how long current can through from An MCB shunt contacts? (like Z7-AS 24 V)?

2024

---

what are the possible reaons & remedies if resistance of NGR getting heat up

1790

---

What is the difference between the relay and the circuit breaker?

1055

---

when we gave dc supply to 220v dc motor its rpm is 1200. then we gave 180v. how many rpm of its motor. gave answer with calculation at my ID.... ravizak@ymail.com

2291

---

1.why are not using acb 33kv ht side? is there any problem 2.what is difference between acb,vcb,sf6 breackers? 3.what is the function of invertor and convertor in ups?

2101

---

how the characterstics of control valve being done

2015

---

while doing high potential for 11KV 3 core cable how much leakage current will obtain?, what will be acceptance value?

2817

---

what is the problem when i want to close a circuit breaker by local position it closes well.but when i close it in remote position it trips

1548

---

What is the restart inhabit setting in ABB spam150c relay (Motor protection relay)

3584

---

How does "OUT OF STEP" relay ,for Synchronous motor protection, work?

4282

---

Advantages/Disadvantages of earthing of neutral bus on MSB instead of separate neutral earthing for transformer/DG sets feeding to MSB

2734

---