Capacitor Usage

It depends upon the tariff being charged for electrical power. Is there a penalty for low power factor at this installation, then?

As aluminium has a high thermoexpansion coeff, what affects adversely contacts in case of an aluminium cable, a capacitor near the motor would "absorb" some reactive current otherwise circulating in the line - the contacts would be safer.

Why would you use a 90 kw motor to do a 20 kw job? A motor operating with that little load would have a lower PF than 0.88. How did you measure this?

we hav been using it for 4 years...that time we needed 9okw motor...but nw its changed...i measured that pf at its feeder...there is a meter for it...

Forget the capacitor ... the problem isn't that your motor has bad PF, it's that it's very often operating under low load. This means that motor efficiency is very low. And given that this is for a coal griner, which is very similar to a rock crusher, the load is very variable too.

Get yourself an Integra intelligent motor-controller, which is made by Somar in the United Kingdom (England). Here's Somar's website:

http://www.erepublik.com/en/organization/1620606

Believe me, this is THE solution. The device will reduce power consumption, reduce power spikes, improve power quality and PF, etc. One of my colleagues has applied it to very good effect in a gravel quarry, which has a large rock crusher in it.

Good luck!
DZ

Oops! Correction .. the website address is:

http://www.somar.co.uk/

Cheers!
DZ

I would advise some caution applying soft starters / voltage controllers to achieve energy savings.

Generally, they can reduce starting peaks and reduce running current at light load by reducing motor terminal voltage, however, real energy savings are quite small, often people confuse the power reduction achieved with actual work done as the motor will run slower when at reduced voltage giving reduced power consumption but ALSO reducing work done anyway.

They're useful devices but their advantages are often overplayed by sales hype where consumption is concerned. There will be a marginal improvement in motor efficiency at light load, a bigger improvement in pf and reduced starting currents as long as it produces enough torque to accelerate the load. A big peak load can lead to motor stalling if the motor magnetic delay constant is longer than the physical load increase time.

With classic soft-starters and voltage regulators, I'd agree. The thing is, though, that this Integra product has lots of other software-based capabilities built in. An engineer who's proficient in their application can make these things work wonders by configuring Integra units for particualr uses.

Honestly, have a look at these things and at any application notes that may be on the website. I don't sell these things, but for some applications, I'm a big fan.

Cheers!
DZ

Hi DZ,

I had a quick look on the website before commenting just to confirm what the unit is / does.

You're right for some applications they're fine, but any jazzy features don't get around the basis that its a voltage controller with inherent limitations. Faster stable control would need an encoder and a special motor to optimise performance (similar to some lift applications), otherwise its a risky choice on 'harder', 'faster' jobs, in my experience.

Don't be too fooled by the sales blurb and so on, its not able to save much energy but does increase the pf (good if you don't have separate pf correction). The 'real' power savings people perceive are reduced speed (increased motor slip) / reduced power doing the job more slowly, generally, therefore, taking longer or altering final product output that goes by without notice.

The motor efficiency savings are very real but marginal when you consider motor efficiency differences at 25% and 100% full load are not so very big nowadays but still could maybe save 1 or 2 kW on a 90kW machine. However, the controller itself also uses energy with a typical thyristor watts loss / Amp being the major component.

Good luck in your applications, if you have energy saving potential in your application (not in the motor!), consider VFD too.