VFD drive

4 comments

Rate

Anonymous Poster	VFD drive 11/29/2009 3:00 AM
	In VFD input current and output current is different i.e.input is less than to output current.what is formula or in what ratio of both current.
	Reply

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

These comments received enough positive votes to make them "good answers".

JohnDG Guru Join Date: May 2006 Location: Reading, Berkshire, UK. Going under cover. Posts: 9684 Good Answers: 468	#1 Re: VFD drive 11/29/2009 4:44 AM
	I_OUT = (I_IN x V_IN) ÷ (V_OUT x E) Where E is the efficiency. __________________ "Love justice, you who rule the world" - Dante Alighieri
	Reply Good Answer (Score 2)

Joe Sparky Power-User Join Date: Jun 2009 Location: New Zealand Posts: 403 Good Answers: 5	#3 In reply to #1 Re: VFD drive 11/30/2009 1:00 AM
	Its a funny thing VSD input and output loading but when you look at it you are correct, output voltage will vary as will the current depending on the load, I suppose the only time that the input and output current will be the simular is when the motor is at full load, and at the frequency that the motor was rated for and even then then they wont be the same because of the efficency. Power factor has been corrected so of coarse current will be different. Also JohnDG, sorry have not got back to you on my bressbrake application, have had to go overseas a few times since we last communicated, and I havent had to much time to think about the application further. Next I am off to China for a project then Veitnam then the Philipinnes, when I am in the Philipinnes I will have more time to look at the pressbrake application. Cheers Joe
	Reply

JohnDG Guru Join Date: May 2006 Location: Reading, Berkshire, UK. Going under cover. Posts: 9684 Good Answers: 468	#4 In reply to #3 Re: VFD drive 12/02/2009 6:32 PM
	No sweat, Joe. Be safe, John __________________ "Love justice, you who rule the world" - Dante Alighieri
	Reply Off Topic (Score 5)

Aldego Commentator Join Date: May 2009 Location: Centurion, South Africa Posts: 87 Good Answers: 5	#2 Re: VFD drive 11/30/2009 12:23 AM
	There is no ratio between the input and output current of a vfd. The reason why the input current is lower than the output current is because of the difference in the power factor to the vfd and to the motor. The power factor in to the vfd is constant at approximately 0,97 regardless of the percentage load on the motor. The power factor however to the motor changes anything between 0,2 to 0,8, depending on the percentage load on the motor shaft. If you use the formula P = √3 * Vl * Il * Cosø to calculate the line current Il you will find that the input current to the vfd is lower than the output current, and that the motor current change as the power factor changes. The input current remains constant with the change in load on the motor. __________________ R T F M .......
	Reply Good Answer (Score 2)

These comments received enough positive votes to make them "good answers".

Copy to Clipboard

Aldego (1); Joe Sparky (1); JohnDG (2)

	Got Something to Say?
	Ask a Question Start a Discussion

	Aerospace
	BioMech & BioMed
	Chemical & Material Science
	Civil Engineering
	Communications & Electronics
	Education and Engineering Careers
	Electrical Engineering
	General Discussion
	Instrumentation
	Manufacturing
	Mechanical Engineering
	New Technologies & Research
	Software & Programming
	Sustainable Engineering
	Transportation

	Site Directories
	Forum Directory Blog Directory User Group Directory RSS Feeds CR4 Rules of Conduct CR4 FAQ Site Glossary Who's Online (92 right now) Show Members