Reduced Voltage Starter?
Reduced Voltage Starter?
(OP)
Is there a minimum motor HP size where reduced voltage, soft start or other controller should be used rather than across the line starter.
This is assuming 3 phase 460 volt motors.
Also assume the driven load does not require a reduced tork start.
Thanks!
TM
This is assuming 3 phase 460 volt motors.
Also assume the driven load does not require a reduced tork start.
Thanks!
TM





RE: Reduced Voltage Starter?
Several miles up the interstate, a new facility is fed from a 13,800 volt overhead line, and its only fairly large motor, a 4160-volt induced draft fan at 600 HP, is on a soft-start, a situation required by their service agreement with the local electric utility company. Full-voltage starting would cause a lot of problems with other customers on that 13,800-volt service as voltage was drawn down by a full-voltage start.
Another consideration for soft-start may be the mechanical requirements of the connected device.
These are just a few of the factors that go into making the decision on full-voltage versus soft or reduced voltage starting.
old field guy
RE: Reduced Voltage Starter?
Depends also on the load as some would rather be started gently.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Reduced Voltage Starter?
thanks
rybrk
RE: Reduced Voltage Starter?
For example, I am in Northern California served by PG&E. Their official cutoff is 25HP at 480V. What that means is that below 25HP you usually don't need to ask. Starting at 25HP, when you apply for service they will ask you how often you will be starting that load, then based on where you are on the grid they may or may not require RV starting. Generally speaking, at 50HP 480V they are going to get more insistant, but even then you can appeal; for instance if your load only starts once per day or even less. I saw a recent applicatios where they allowed 2 x 150HP motors to be sarted Across-the-Line because they ran continuously for months at a time. By the same token, I have also seen them require RV starting on a 15HP motor where the user was at the very end of a 3 phase transmission line served by a relatively small existing transformer. PG&E offered him the choice of usng RV starting or paying for new lines to feed a larger transformer, but obviously the soft starter was going to cost less.
When I lived in Seattle 9 years ago, the cutoff was 15HP from Seattle City Light, but 25HP from Puget Sound Energy, the adjacent utility and 50HP from those served directly by the Bonneville Power Administration. Bottom line, it varies by utility, then varies again within each one.
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376
RE: Reduced Voltage Starter?
You older guys remember that a couple of decades ago, reduced voltage starting was complex and expensive, resitor, auto-tranformer, delta-star, etc. Variable spped drive was even more so, and a nightmare if you needed more than a few horsepower.
The new solid-state stuff makes these options easier to fall back on. In 1970, variable speed was essentially the domain of DC. In the eighties, I saw the first variable speed AC drives, and today I am installing 9000 horsepower variable frequency drives, and integral to the characteristic of variable frequency is the soft-start cahracteristic.
Life is good when it's working, but the old guy with a voltmeter coupd find and fix problems with a autotransformer reduced voltage starter. With the solid-state stuff, well, a good supplier with spares better be available...
old field guy
RE: Reduced Voltage Starter?
Of course, it's simpler to use motor hp as the criteria rather than the actual voltage dip, but it doesn't really make a lot of sense.
RE: Reduced Voltage Starter?
JRaef.com
Eng-Tips: Help for your job, not for your homework Read FAQ731-376