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Author Topic: Specifying Generators in Kva  (Read 13830 times)

RYAN LOUDMUSIC JENKINS

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Re: Specifying Generators in Kva
« Reply #20 on: October 13, 2005, 12:28:12 am »

Hey Bennett,

Another thing that helps keep dimmer noise out of the audio is to have them full on or full off, no actual "Dimming."  That what I do and I never hear any buzz from them.  Keep in mind that I only do very basic lighting myself and refer out anything beyond what I can do.  That may be what the light guys have been doing at your events and it really helps.  Also like you said about neat, organized cables, that helps big time too.  If everything crosses at 90' angles whenever possible thats a big help.
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Ryan Jenkins
"Two days until the end of when I don't know what to think.  Three days until I start the cycle all over again!"

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Langston Holland

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Re: Specifying Generators in Kva
« Reply #21 on: October 13, 2005, 10:29:04 am »

Phill wrote on Wed, 12 October 2005

The power factor is the ratio of the dissipated power (in phase sum) to total power (Volt x Amps ignoring phase).


So... Please fix anything broken in the following. :)

1. Assuming the use of Bennett's 36kVA genny in single phase mode, this means there should be 150 amps at 120v available on each of the two hot legs into a purely resistive load.

2. Real world concert equipment places a very non-resistive load on the power source, a product of reactive components and distortion, which reduces the useable amount of power available to run the stuff you plug into the distro.

Question:

Can current and voltage meters be used to monitor the system such that a reading approaching 150 amps (while maintaining a reasonable RMS voltage) on each leg means that the actual limit of the genny is being approached? Or will the current reading be reduced by the mysterious power factor present in the circuit, thus giving one a false sense of security about the "headroom" available to power additional loads? IOW does one have to use one of those fancy and expensive power meters to determine when the genny is about to fuss?
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RYAN LOUDMUSIC JENKINS

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Re: Specifying Generators in Kva
« Reply #22 on: October 13, 2005, 11:50:17 am »

All of these questions could be answered very easily if GE would just put up an easy to find .PDF manual on their web site.  I can go find the specs for just about any generator in two seconds but couldn't find the GE specs.  One of the largest companies in the world and they still can't provide the consumer with important information!!!!!?????

Here is a website that sells generators and has almost all of the generator specs you will ever need.

http://www.portable-electric-power-generators.com/

I refer to this site all the time amd it saves me a lot of time.
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Ryan Jenkins
"Two days until the end of when I don't know what to think.  Three days until I start the cycle all over again!"

Please visit my website at http://www.murphygirl.com

Bob Healey

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Re: Specifying Generators in Kva
« Reply #23 on: October 13, 2005, 01:00:54 pm »

Rob Burgess wrote on Wed, 12 October 2005 22:37

Bob Healey wrote on Wed, 12 October 2005 21:38

I've found I generate the most noise when I have a large excess of feeder cable and no good place to put it.


    You don't figure 8 the excess?

--
Rob



50 feet of cam x 5 in 10 sq ft of space.  Figure-eighted, but doesn't do much.
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Lee Patzius

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Re: Specifying Generators in Kva
« Reply #24 on: October 13, 2005, 01:53:54 pm »

Langston Holland wrote on Thu, 13 October 2005 10:29

IOW does one have to use one of those fancy and expensive power meters to determine when the genny is about to fuss?


Langston,

I just finished installing a bunch of Hitachi 3 phase variable frequency drive inverters, with Simpson true rms ammeter instruments, along with current toroids on a skid mounted process unit here at the plant, and spend another couple of days doing power studies.

I noticed quite a few things that threw me off at first... But I won't go into all the testing procedures, nor the inverter's V/f constant torque output and operation etc., but the testing was very interesting.

We had four ammeters to compare by, a Simpson true RMS, an analog standard Amprobe Clamp around, a freshly calibrated NIST Traceable Amprobe digital True RMS AC/DC clamp around meter, and an analog shunt type ammeter in series.

Even with variable freq drives and horrible motor harmonics (which I reduced with inductive line reactors installed) the Amps was Amps with the exception of one meter. We took the motors to full mechanical load, at various speeds and as always, produced accurate ammeter results.

EXCEPT for the analog shunt type ammeter. It tracked nicely with the others, until the motor was driven beyond it's full load amperage rating. In overcurrent conditions, the analog meter read HIGHER than the true RMS types. The true rms types locked in at 13.xx amps while the shunt type went up to 18 amps.

Anyway, what I wanted to point out was, the generator has to produce the full kVA regardless of the power factor. According to our studies, a clamp around Amprobe will read true amps rms, I supposed in reference to the true Watts, so it may be affected by kVARs. A shunt type analog ammeter did read higher in overload conditions for us though.
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Marty McCann

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Re: Specifying Generators in Kva
« Reply #25 on: October 13, 2005, 03:41:26 pm »

I have used generators in the past for audio applications, and in most case they were large 200 - 400 Amp units (24 - 48 KVA).


Recently I had occasion to use a 5.5 KVA after Katrina.  I had 7 evacuee's from New Orleans staying with me in a 1 Bathroom household.  Along with the pet's, Katrina raised my total household to 9 people, 5 dogs, 2 fat guinea pigs, and one squawking parrot.  Since my water comes from a deep well, and we had no electricity for 8 or 9 days, after the third day of using the above ground pool water to flush the commode, I went to Lowe's and bought a generator rated at 5,550 Watts.

I had no master breaker to disconnect, so I removed the Power companies meter and wired into the 240 VAC buss directly.  When I powered up the gen set and turned on a minimum of lights and such, I was drawing about 4.5 Amps on one leg and 5.2 on another.  I quickly found out how women can not be trusted to be frugal when it comes to power allocation.  After they attempted to plug in curling irons, hair dryers, etc., I had to be the hard nosed EE, and insist on one light per room, refrigerator, and a television.  I would turn on the well pump and it would draw 9.5 amps of current per leg (240 VAC). I would pump enough water to pressurize the storage tank, which was then good for about three flushes of the commode.  (I have a rental house that gets water from the same well).  When I would heat up the hot water, I would draw about 14 amps per leg.  But I quickly realized (from the dimming lights) that even though I was below the max draw of the generator, that I was loosing electrical pressure in the form of voltage drop.  Since I have a collection of multimeter's and Clamp Amp-meters, I began a routine of power consumption maintainence.  The problem is, if you allow too much of a voltage drop, you can actually burn out your electrical motors.  With the Hot water heater elements at max draw and my well pump running, the voltage dropped below 98 VAC, and current draw was 17.5 Amp on one leg and 18.2 Amps on the other.  98 VAC is not good for a deep well pump more than 360 Feet below surface.  Think about this if it was 98 Volts at the panel, and 100 Ft to the well and another 360+ feet to the pump motot, what could my voltage have been at the pump?

After a few days, since my friends from New Orleans brought very few clothes, we had to turn on the washing machine, which would draw nearly 11 Amps more on a single leg.  Even though this was considerably below the max generator capability, the generator would blow the breaker driving the washing machine in 12 - 14 minutes before a complete washing cycle ended.  It was then that I learned to use my above ground pool's pump motor to balance the two legs from the generator, when I did this I could run the washing machine as long as I balanced the line with the pump motor.  

At one point kinda for grins, I turned on the clothes dryer and I was impressed when the generator produced 23.4 Amps per leg (however only at about 94 Volts), after about 6 - 8 minutes the breakers would blow.  With very little current draw, the gen set produced about 124 Volts.  

So I have come to the conclusion that those of us that use generators for audio purposes would still do well to try to at least maintain a reasonably balanced current draw between the two legs of a single phase 240 VAC system.  I would think that this would also apply to a three phase system.  

I wish I would have kept a more accurate log of some the the things that I experienced with this emergency generator.  I did learn that I need to redistribute some of my circuits, as I am drawing more current thru my Red leg than my black when I have a lot of things running at the same time.  I have four different electrical panel boxes in my house to to various additions that were made over a 26 year period.

I also learned not to complain about the 5 or 6 dollars a day that I pay to the electric company for power.  The generator cost me $780.00, but the electricity was 35 - 40 dollars a day, and it was only $2.29 a gal at the time.

marty
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RYAN LOUDMUSIC JENKINS

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Re: Specifying Generators in Kva
« Reply #26 on: October 13, 2005, 04:03:12 pm »

You can't compare the 5500 Watt gasoline generator you were using to a diesel generator.  The gas gen sets just don't have the torque required to keep the voltage up and at a constand 60hz frequency.  Deisel generators are far superior due to the low rpm torque of the engines.  They run at only 1800 RPMs rather than the 3600 RPMs required by gas gererators.  In addition the diesel gen sets give the ability to adjust your voltage to compensate for long cable runs.  Its a whole other beast.  

I am sure I speak for all of us here that we are proud of you for steping up to the plate and providing a roof for the extra people during the aftermath of the huricane.  Spending $800 on a gas generator was a good investment for your circumstances.
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Ryan Jenkins
"Two days until the end of when I don't know what to think.  Three days until I start the cycle all over again!"

Please visit my website at http://www.murphygirl.com

Michael E.

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Re: Specifying Generators in Kva
« Reply #27 on: October 13, 2005, 06:37:33 pm »

My handy dandy Cummins South generator sizing guide shows using a 1.0PF for calculating single phase amps, and 0.8PF for calculating three phase amps. On their premade chart, a common 100KVA genny = 80KW, 333amps per leg single phase 240v, and 278amps per leg for 208v three phase. They don't have a 36KVA, or I'd list it. We size our genny's for lighting at 120%, and haven't had a problem once the genny was actually running (haha). If your genny drops/gains more than .5Hz then something is seriously messed up with it! Most of the Cummins South/Aggreko units we've used can keep themselves within a few volts of your settings easily.
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Tim McCulloch

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Re: Specifying Generators in Kva
« Reply #28 on: October 14, 2005, 12:04:16 pm »

Ryan, to whom are you replying?  TREE VIEW!!!

Tim Mc
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Don Lanier

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Re: Specifying Generators in Kva
« Reply #29 on: October 16, 2005, 06:02:20 pm »

http://www.macgen.com/calcul.html
Great little tool for calculating these mysterious numbers to you non sparky types

Don Lanier
http://www.pearlproaudio.com
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Don Lanier
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Re: Specifying Generators in Kva
« Reply #29 on: October 16, 2005, 06:02:20 pm »


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