How do you determine reactive power in three phase?

Answer 1

Total 3-phase real power = sqrt(3) x VLL x ILL x cos (theta) = 3 x Vp x Ip x cos (theta)

Total 3-phase reactive power = sqrt(3) x VLL x ILL x sin (theta) = 3 x Vp x Ip x sin (theta)

where: ?LL denotes line-to-line and ?p denotes phase-to-ground quantities

Therefore, S = sqrt( P2+Q2) =

= sqrt[32 x Vp2 x Ip2 x cos2 (theta) + 32 x Vp2 x Ip2 x sin2 (theta)]

= sqrt[32 x Vp2 x Ip2 x {cos2 (theta) + sin2 (theta)}]

= sqrt[32 x Vp2 x Ip2 x {1}]

= 3 x Vp x Ip (works for the line-to-line case, as well)

Hope this helps,

Chris

Answer 2

For a three phase real power calculations we are using the formula:

P=Sqrt3*V*I*PF

PF:Power Factor =1 if the load is pure resistance like the light

V: Voltage

I: Current

Answer 3

Real power (W, watts) is apparent power (VA, volt-amperes), times power factor. Power factor is the cosine of the phase angle between voltage and current. For a resistive load, such as a toaster, power factor is unity, so W is VA. For an inductive load, such as a motor, with a (typical) power factor of 0.92, W is VA times 0.92.

Also, in terms of reactive power, real power (W) is reactive power (VAR) times the reactive power factor, which is the sine of the phase angle between voltage and current.

To clarify "true", "apparent", and "reactive" power, the phasor sum of VA and VAR is equal to W. Think of the unit circle, where zero degrees is resistive, generally shown as north. For the example case of the inductive load at 0.92 power factor, the angle of the phase angle is -23 degrees, or typically shown as 337 degrees. VA in this case, if W equals 10000, is 9200, while VAR is -3919.

Phase has nothing to do with the equation, since you need to consider each phase on its own merits, and add up the results. However, do not forget that you need to be consistent, in that you always use star or delta voltage. If you switch systems, star to delta or delta to star, don't forget the 1.732 (square root of 3) factor in the calculations.

Answer 4

Apparent power is a function of power factor, true power over apparent gives you the power factor.

All items of current using equipment have losses

you may have a motor that claims a power of 1000w but actually reads as 1150w

1000/1150 =0.86 (a poor power factor)

Answer

Apparent power (expressed in volt amperes) for a three-phase load is exactly the same as for a single-phase load in that it is the vectorial sum of the true power (expressed in watts) and the reactive power (expressed in reactive volt amperes). For a balanced load, it can be determined from the equation: 1.732 x Vline x Iline. For an unbalanced load, it is more complicated to calculate, as you will need to determine the apparent power per load.

Answer 5

The general equation for apparent power in a balanced three-phase load is as follows:

Apparent Power = 1.732 VL IL (where L = line values)

This will tell you what the transformer is delivering. If you want to know what the transformer's rating is, then you'll need to know the transformer's rated secondary line voltages and currents, and substitute these values into the above equation.

Answer 6

Kw