redwan hasan said:
Good evening everyone.
I have two questions to ask you guys.
1. Why voltage regulation of a synchronous motor is negative with a purely capacitive load? I mean why?
2. Why Reactive loss is higher than resistive loss in a power distribution line?
thank you and have a nice day! Really appreciate any help.
Not sure about your 1st question, but I'll take a shot at number 2.
The majority of your reactive losses come from inductive motors. A lot of it gets power factor corrected, a lot of it does not get power factor corrected.
There are certainly resistive losses in the power lines, but since copper or aluminum conductors are very good conductors, the total loss here does not add up the the reactive loss. (The I^2*R losses are not as big as the reactive losses). Reactive losses can be as much as 30% or in extreme cases 50% or more in motors. Just think of the millions of air conditioners running...or the fans running in furnaces in the winter, not to mention the tons of giant motors running in factories.
In factories they are likely to get power factor up to .9. They can't do perfect power factor of 1 because of the harmful harmonics it introduces. In residential, there is very little power factor correction, which also adds a lot of reactive losses.
KVA is a combination of both real power (watts) and reactive power (vars).
If you measure the amps thru a line, multiply this by the volts ( X 1.73 if three phase)... you get the KVA of your motor. If you measure the actual horsepower at the shaft of the motor, this can be converted into watts. Take these watts and divide by the KVA. This is your power factor.
In the power triangle, the bottom horizontal part is the watts. The vertical Y part is the VARS. And the hypotenuse between the two is KVA.
This looks like a pretty good article on the subject. Hopefully it agrees with what I said above!
http://electrical-engineering-portal.com/total-losses-in-power-distribution-and-transmission-lines-1