Soft Starters An introduction into soft starters.

AC Variable Frequency Drives A brief introduction to VFDs
Shunt DC Motors A brief introduction to Shunt DC Motors
Series DC Motors A brief introduction to Series DC Motors
Compound DC Motors A brief introduction to Compound DC Motors

Power Factor Correction Introduction to power factor correction
Power Factor Calculations Basic power factor calculations
Power Factor Controllers Introduction to Power factor Controllers
Power Factor Introduction

Hi

I keep coming across web pages that have verbatum copied much data out of my site at http://www.LMPhotonics.com I even found one site that claimed copyright for the material!!

The information on http://www.LMPhotonics.com is my own material, I own the copyright etc.
I guess that copying is a form of flattery, but it would be nice if people asked or acknowledged the source of their information!!

Original page http://www.LMPhotonics.com/pwrfact.htm

Some cloned pages and documents:
http://www.vanrijnelectric.com/vanrijnelec...rcorrection.htm
http://www.geocities.com/vijayakumar777/po...owerfactor.html
http://www.tvss.net/pq/pf.htm
http://igs.nigc.ir/igs/STANDARD/artic/CAP-07.pdf
http://www.myelectrical.com/book/xmlPage.a...tchgear/PFC.xml
http://www.emc-ltd.net/blog/?page_id=16
http://motor.djwxw.com/Technology/Pages/20...07/TT_689_1.htm
http://user.chol.com/~sis1226/powerboss/2.doc page 11 of Powerboss Compact Operation Guide Version 2
http://www.pdhonline.org/courses/e144/e144content.pdf page 30
http://www.ug4e.com/PowerFactor.htm
http://mansoori-electry.blogfa.com/post-20.aspx
http://www.stemselectronics.net/powerfact.htm
http://www.sayedsaad.com/montada/showthread.php?t=4035


plus others.
Best regards,

I often see statements from "reputible" sources suggesting that the use of oversized motors causes energy to be wasted.
In many cases, this is not true, infact there can be an advantage in using an oversized motor.

For example, from a manufacturers data sheet (attached) I see the following:

11KW motor.
100% load 89.2% eff

15KW motor
75% load 89.7% eff

22KW motor
50% load 90.7% eff

So, if I have an 11KW load, I would be most efficient to use the 22KW motor at half load, followed by the 15KW motor at three quarter load and least efficient to use the 11KW motor at full load.
The oversized motors would run cooler, and therefore would last longer as well. The disadvantages of using an oversized motor would be that the start current will be higher and the capital cost is also higher.

I find the same if I compare the 30, 45 and 55KW motors, and others as well.

As I see it, the use of an oversized motor does not waste energy, it actually can save energy!!

Best regards,

Hi

Most of the soft starters out on the market that have a current limit, have a maximum current limit setting that seems to vary from as low as 400% current, to around 550% current.

Some soft starters are designed for a maximum start current of 400% and that is a thermal limit. You could oversize the starters to increase the thermal limit, but there is a problem with the current limit setting.

With modern "Hi Efficiency" motors, the locked rotor current has trended upwards from an average of around 600 - 650% to an average of 700 - 750%.
This means that to develope a high torque start as required for loaded conveyors, mono pumps, loaded drying drums and high inertia loads, the start current is required to be well above 400% rated current.

With the standard motors that were used 20 years ago, it was very rare for a start current to be required to be above 500%. Today, to achieve the same start torque, the current may need to be closer to 600%.
This raises the issue, "what are the manufacturers doing to enable soft starters to be used in these applications?" If you considerably oversize the starter in order to remain within reasonable thermal limits, you loose the protection features of the soft starter and you need to add external protection devices.
With some starters, you can turn OFF the current limit and operate in an open loop voltage ramp mode. This may be OK for a loaded conveyor, but would not be any good for a high inertia load.

Are there any starters out ther that cater for the 580% start current required in starting the loaded conveyor referred to in another post?

Best regards,

Hi

I have upgraded this forum to a new script which offers a number of advantages (but costs me more).

I believe that all the data from the previous forum has been ported across except the U2U inboxes.
If you find any problems with the operation of the forum, please let me know either via the private message facility on this forum (you need to be registered and logged in) or via Contact Me

Best regards,

Hello

The forum is now lodcated at a new address
http://www.lmpforum.com - this is much easier to remember than the old address.
Please update any links that you have.

Best regards,

Hi

I am interested in finding out how designers determine the ratings they put on to their soft starters. There are many different ideas and techniques, but in the real commercial world out there, it is important to both retain reliability, and to retain commercial competitiveness.

I will post my ideas and experience shortly.

Best regards,

Between the 4 May 2003 and 7 May 2003, we experienced major server problems which resulted in our site being moved to a new server. Unfortunately, some data was lost, but we are working to recover as much as possible.
New registrations to this forum will be lost and you may need to reregister.

9 May 2003 fix registration problems.

Best regards,

We welcome students to this forum, but request that postings and discusions related to assignments and projects be posted to the students area. You will get much more support there.
Best regards,

For a paper on the power factor controller energy savers (Based on a NASA algorithm) have a look at http://www.lmphotonics.com/energy.htm
The technology works, but it well over stated and over sold.

Anybody had any experience with medium voltage soft starters??

I am looking for good technical sites about soft starters.

Anybody got ideas on good techniques and filters for reducing the harmonics produced on the supply by large drives? Lots used in rural areas for irrigation and resultant supply distortion is causing problems.