Power Factors and Transformers

Good day for you....

As per electrical theory and also in mathematical equation power factor is cos φ for pure sine wave....

also cos φ never exeeds 0 to 1 so no negative or greater than 1 will come to picture...

Also transformer is a step or step down device that is V1/V2 = I₂/I₁=R₁/R₂ .

so dont worry about the power there input power is always equaly to output power..

so there is

as the power factor deviates from unity you get increased currents and IR drop in the line = hotter operating temperature and lower efficiency.

Large users must pay extra if they change the power factor. often companies operate power factor correctors (usually special reactance motors that create the required power factor lead/lag etc.

http://en.wikipedia.org/wiki/Power_factor_correction

As transformers are always rated in VA you don't need to be concerned about the power factor of the load. Just keep within the VA rating of the transformer...

John.

A large user will pay for the virtual VA he uses, even within the ratings, and it is far cheaper for them to have a corrective motor or capacitor to get a balance. You only buy it once and it save you money forever.

Maintaining a high power factor keeps the transforming losses to a minimum. Divide the old power factor by the new power factor and square it. Subtract that percentage from the number one. That is the percentage you will save of the transformer losses. Example: you improve from 80% PF to 99%. You will then save 35% of the transformer losses. The big question is ... what are my transformer losses? Most transformer manufacturers will admit to 2%. 35% of 2% is .7%. That is a kilowatt savings. Now, if you go over 100% PF and start leading, the current made by the capacitor flows back onto the transmission lines through the transformer. You actually start to increase the transformer load. This adds a pressure to the system that increases the loadside voltage. You don't want that. Never leave on capacitors that exceed a 10% KVAR/KVA ratio. In other words you can add 100KVAR fixed to a 1000KVA transformer without increasing the voltage substantially. If you need more than the "Basic 10%", you better be sure the load profile supports it 24/7. If not, automate the KVAR. Hope this helps.