bittu123

 Profile Answers by bittu123 Questions by bittu123

• Nov 8th, 2011

 

You have to draw a phasor diagram. then U will get it easily.

Draw Vr, Vy, Vb with 120 degree displacement. Now draw Ir leading(lagging) Vr by some angle, Say 0. and Iy displaced 120 degree to Ir, same for Ib.

Draw -Vr just opposite to Vr.
Draw Vbr= Vb-Vr, Ur Vbr vector must have 30 degree angle with -Vr.

So, Angle between Vbr and Iy will be (90-0).. remember 0 is phase difference what we assumed earlier.

Now, Vbr*Iy*cos(90-0)= Vbr*Iy*sin(0)=which is nothing but multiplication of (line voltage*line current*sin(0)) and You may say REACTIVE POWER.

See Carefully, Vbr is nothing but line voltage of BLUE and RED phase, which is measured by pressure coil
Iy is nothing but line current of YELLOW phase, measured by current coil.

Hoping, I made clear why current from YELLOW but voltage from BLUE-RED(not from yellow-blue or yellow-red) while measuring reactive power.