Previous in Forum: Understanding DC Drives   Next in Forum: DC Current Measurement
Close
Close
Close
5 comments
Rate Comments: Nested
Anonymous Poster

Power Factors and Transformers

12/02/2006 12:42 AM

Sir ,

plz let me know what will be effect on transformer if one's maintaIN POWER FACTOR exceeding unity i.e -99 or -98 , whether there is some effect on transformer efficency , and what is thre formulla how to collect load on transformer

thanking you

Kapil Bansal

Kapil.k.bansal@gmail.com

Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Associate

Join Date: Nov 2006
Location: Chennai - India
Posts: 29
#1

Re: Power factor

12/02/2006 4:05 AM

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

__________________
Every Problem has its own solution
Reply
Guru
Hobbies - HAM Radio - New Member United Kingdom - Big Ben - New Member Fans of Old Computers - Altair 8800 - New Member Canada - Member - New Member

Join Date: Jun 2006
Location: Toronto
Posts: 3968
Good Answers: 120
#2
In reply to #1

Re: Power factor

12/03/2006 12:44 AM

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

__________________
Per Ardua Ad Astra
Reply
Guru
United Kingdom - Member - Olde Member!! Engineering Fields - Instrumentation Engineering - New Member

Join Date: Jul 2006
Location: Dunstable, England
Posts: 2821
Good Answers: 45
#3

Re: Power Factors and Transformers

12/03/2006 2:14 PM

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 little knowledge is a dangerous thing - Googling is far worse!
Reply
Guru
Hobbies - HAM Radio - New Member United Kingdom - Big Ben - New Member Fans of Old Computers - Altair 8800 - New Member Canada - Member - New Member

Join Date: Jun 2006
Location: Toronto
Posts: 3968
Good Answers: 120
#4
In reply to #3

Re: Power Factors and Transformers

12/03/2006 3:18 PM

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.

__________________
Per Ardua Ad Astra
Reply
Active Contributor

Join Date: Oct 2006
Posts: 14
Good Answers: 2
#5

Re: Power Factors and Transformers

12/04/2006 9:58 AM

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.

Reply
Reply to Forum Thread 5 comments
Copy to Clipboard

Users who posted comments:

aurizon (2); capacitorbob (1); Electroman (1); mahalingam (1)

Previous in Forum: Understanding DC Drives   Next in Forum: DC Current Measurement

Advertisement