Here is an interesting article from the U.S. Dept of Energy about how variations in voltage can affect electric motor performance.
Table 2 gets right to the point.
http://www.eere.energy.gov/industry/...m/article_id=7
Rob
Here is an interesting article from the U.S. Dept of Energy about how variations in voltage can affect electric motor performance.
Table 2 gets right to the point.
http://www.eere.energy.gov/industry/...m/article_id=7
Rob
Last edited by Rob Will; 02-04-2008 at 11:58 PM.
Contributor
Uh...you're a brave man Rob Will...and only 2 days to recover after the 110/220 motor wiring post got started. With that said...
LET THE VERBAL GAMES BEGIN!
I just can't wait...I really love this site....all the free entertainment intermixed with the camaraderie and excellent woodworking information.
Dennis
Last edited by Dennis Miller; 02-05-2008 at 12:19 AM.
Contributor
I don't see anything controversial in Rob's post or in the paper. The paper (especially Table 2) just outlines what to expect if you run your motor at a voltage that is above or below the rated voltage.
Mike
Last edited by Mike Henderson; 02-05-2008 at 1:15 AM.
Go into the world and do well. But more importantly, go into the world and do good.
Does anybody have a chart showing typical amperage requirements for various HP single phase motors?
I realize that this will vary depending on the particular model. Just looking for a range or average for "good" quality USA made motors.
Thanks,
Rob
Last edited by Rob Will; 02-05-2008 at 9:53 AM.
Contributor
Your NEC book will have a table of motor currents, however they are only aproximate values. They are for normal speed motors, normal torque curves.
If you are sizing overload protection or feeders, use the motor nameplate value.
Amperes
HP /@115V/ @230V
0.5 /9.8 /4.9
0.75/ 13.8/ 6.9
1.0/ 16/ 8
1.5/ 20/ 10
2/ 24 /12
3 /34 /17
Regards, Rod.
PS. My 3 HP tablesaw motor (General 650) is 12.5 amperes VS 17 from the table above. As stated use the nameplate information from your particular motor.
Last edited by Rod Sheridan; 02-05-2008 at 10:35 AM. Reason: added post script
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The chart in the article confirmed something to me I knew from experience. That is, motor current increases with a drop in voltage. I have blown a few fuses in my day discovering that!
Some thing to consider, at least for the one phase customers, was mentioned by Dr. Bill Wattenburg on his KGO radio show. Bill said that electric power ultilities (he cited California) tend to run their voltages towards the higher end of their specification limits and that they do so for higher profits! The spec limits he mentioned for 110v were 105v-125v. Double that for 220v.
http://www.kgoam810.com/viewentry.as...=PERSONALITIES
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Not quite.Originally Posted by Eric Gustafson
There usually is some voltage droop characteristic in the voltage ouput of a power plant; as load on the distribution system rises, voltage naturally falls.
Because of this, the power plants tend to be set at the high end of the band to accomodate unexpected peaks in loading, thus ensuring that the voltage on the distribution system stays above the minimum.
Brownouts (sharp reduction in voltage when a large load is added) usually damages equipment, since that equipment will draw above it's rated current at low voltages.
There is a limited side benefit of less I^2 R losses (ie, the higher the voltage, the lower the current, the less energy is wasted in resistive heating of the power lines). But this is a pretty minimal benefit, since the real way to prevent those resistive losses is to use 78 kV transmission lines, not just keeping line voltage 13V higher then 230V nominal.
Back OT, the best explanation of efficiency of motor operation vs input voltage is here in a letter to the editor at Popular woodworking, where the popular myth that the electric motor "runs cooler", since the higher voltages mean lower internal current flows and less internal resistive heating:
http://www.popularwoodworking.com/features/240V.html
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If Dr. Wattenberg would like to contact me,I'd be happy to explain the inaccuracy of his statement.
A power plant puts out 345,000 volts to the grid. This voltage is developed by a large generator that is hooked to a steam driven turbine.The weight of the turbine and the generator is in 100's of tons. It is spinning at 1800 rpm. it is an incredibly large rotational mass of energy.
"We" the power company have no control over the 115vac at your house. We put 345,000 volts to the grid. The grid is controlled by a central power authority that exists outside of the regualted body of electrical generators. The power is "pooled". We can't apply more voltage, or less voltage. We supply 345,000volts whether at 1000 megawatts, or 100 megawatts.
When electricity is demand is low. "Load" is taken off the generator by limiting the amount of steam to the turbine. When demand is high, "Load" is picked up, and more steam is capable of supplying the turbine.
Each Generator connected to the grid has to share equal load, or the grid can become unbalanced. It is the grid demand that dictates the power in Megawatts that each turbine generator is putting to the grid.
Intentionally dropping the regulated output voltage of a turbine connected to the grid has the very realistic potential to cause catostrophic destruction of the turbine and the generator. It simply is not done.
All generators are "synched" to the grid to ensure that the whole system is controlled at 60 hz. A deviation of grid frequency in fractions of a HZ for less that one complete cycle will trip the output breaker of a power plant to protect the turbine generator. Everything is very tightly controlled.
This is a 100,000 ft bird eye view of electrical generation. I've been doing this for almost 25 years. There is a lot to it.
Dr Wattenberg lacks an elementary understanding of power generation/distribution.
Last edited by Mike Cutler; 02-05-2008 at 11:57 AM.
Member
What's interesting (or possibly confusing) about the 3-phase table is that when a motor is run under-voltage, its startup current will be lower. I think this might be because a 3-phase motor gets rotating sooner than the single phase equivalent.
Either that, or the table is simply referring to the maximum startup current without regard to the length of the startup curve.
Member
Certainly, I am no one to criticise you, Dr. Wattenburg, or anyone else for that matter. But, based on his creditials, it is safe to assume he has more than an elementary understanding of electricity, distribution, and generation. He wrote a report entitled, " ADVANCED SWITCHES FOR SOFT BLACKOUTS CRITICAL INFRASTRUCTURE PROTECTION UNANTICIPATED DISCOVERY OF EMERGENCY VOLTAGE EDUCTION FOR GRID PROTECTION."
The report was prepared for the California Energy Commission Public Interest Energy Research Program by Dr Wattenburg and the Chico Research Foundation. The following is a excerpt from that report:
"In meetings with the ENERGY COMMISSION and the governor’s office in late June 2001, the three major investor owned California utilities agreed that they could reduce the load on the grid by 250 to 300 megawatts by lowering distribution line voltages by 2 ½% in portions of their systems (but no lower than 117 volts) during power emergencies. "
Anyhow, I only mentioned it because it is something to think about.
Contributor
Eric
I have the CEC-500-2006-058 report in front of me now. It's 114 pages and had to be printed. I didn't see an HTML option.
On cursory view of the abstract. The implementation of this plan may have had plants operating outside of their design basis.
It also looks like the deck was skewed against the residential rate payer.
let me look at it a bit.
Member
MIke,
The discussion on EVR (Emergency Voltage reduction) and its discovery starts on page 19 of the report. It seems both you are Bill Wattenburg can be right. You are discussing how power is applied to the grid. Dr Wattenburg's approach is applied to major distribution lines. According to the report, Southern Caifornia Edison has automated voltage equipment at the substation level they can use to acheive the voltage reduction.
The last sentence of the report quoted below caught my attention as different from what Wattenburg had said on his show. He said the reason they keep substation voltage high is that the consumers will pay more. He also had said that the voltage rating plates we see on motors vary not because of design differences, but largely because nominal voltages vary across the planet. 110v is more like 120-125 in the US, but may be as low as 105v in Japan. Again, according to Wattenburg, motors for all markets come off the same production line. I found all of this interesting considering the article that led to the original post.
"ENERGY COMMISSION Commissioner Dr. Arthur Rosenfeld asked the
Southern California Edison (SCE) to do an EVR test on a major distribution line. SCE has automated voltage adjustment equipment in its substations. They could do the test very easily and quickly at any time. They were rightfully worried that lowering the voltage would result in customer complaints or damage to customer equipment."
Contributor
Eric
I don't really like the wording in that last paragraph. "Voltage Adjustment", is "voltage regulation". Yes we can "adjust" the voltage, but the purpose of the equipment is to regulate the voltage out, and maintain stability under varying load conditions. While SCE, and PG&E stated their concern for consumer equipment damage, I suspect they were equally as concerned with their own equipment damages.
The substations aren't controlling 115 and 220, they are controlling much higher voltages which are stepped down by transformers on the poles. The only place 115/120 exists is after the service panel.
If SCE is going to do this, they would have to have a feed forward strategy in place with no feedback.
I don't see how the consumer is paying more? Your billed in kilowatt hours, T&D costs, and Federal and state taxes. I could theoretically increase the voltage but the net effect would be a drop in current, and the power would be close to the same. I'm just not seeing the big benefit for SCE and PG&E. Their contracts are structured to supply X amount of power to the grid, at X amount of dollars. It's actually in their best interest for the consumer to use less power. This way they don't have to purchase power contracts for additional power to meet their contractural obligation. They also, most likely, have a mechanism that kicks in that allows them to sell their "excess power", above a certain percentage, at the going market rate, which can be much higher than retail rates, by multiples.
I don't like the fact that the report itself seeks to spec Dr. Wattenberg's patent as the sole device for the "soft blackout" in the event that California adopted the EVR approach. Little bit of conflict of interest there. I also observed that he had a patent he was specifying for the vehical barriers. Interesting.
This EVR was a knee jerk reaction to a "power supply" shortage that existed on paper only. Had they ever implemented the policy they may have found thereselves in an even worsening position. They may not have been able to import power from outside the state to meet their demand at any cost. Kind of a domino effect.
The actual culprit was the poorly thoughtout and implemented deregulation bill that California signed into law. I've sat through a few seminars on the mechanics of that situation. It's the "model" for states on how not to implement deregulation. It also shelved the deregulation efforts of many states, which was a good thing. It's just too bad that it had to happen at the California rate payers expense. Of course, our situation here in CT isn't that much better. We didn't learn quick enough.
I still don't see where PG&E and SCE are actually lowering the voltage to increase profit, or how he is supporting that statement. That part I'm not catching. Am I missing it somewhere?
Motors can run within a band of voltage, but there is a trade off in longeveity. Would someone with a home shop see it? I doubt it, we're just not taxing a motor enough, we don't typically run them long enough, cycle them enough, nor operate them in a hot enough enviorment to statistically be able to quantify a decrease in life.
The document that Rob points to in his post is nothing earth shattering, or new. Any electrical engineer has volumes of info available to correctly spec a motor based on application and location. If they don't the motor manufacturer has the info.
As long as the motor is being run within it's design criteria. It's longevity can be predicted.
I would also assert that, while table 2 is informative, why would someone knowingly want to operate a motor in a low/high voltage enviorment?
If anyone suspects that they are not getting the correct voltage to the motor. Stop and get it fixed.
Thanks Rod, yes I found that chart at 430.248 in the NEC.
That's a good question Mike but I don't know much about electricity.
So if I have a machine tool pulling 24 amps @ 115V on a 50 foot long 12 gauge wire fed by a 20 amp breaker..........
Can somebody tell me if this is ok for my electric motor?
Rob
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