6KV GEN

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delreer Associate Join Date: Jan 2015 Posts: 26	6KV GEN 01/13/2015 1:19 PM
	I run the generator and adjust the engine RPM so that I get 60Hz open load, why is it when I load the gen my Frequency drops by 2 Hz? Also, open load voltage on the gen is 105 V , when I load the gen it spikes to 134V then stabilizes on 119V. Why is this? My load are 4 lamps of 1KW metal Halide. (the lamps are connected to a ballast transformer, each light has its own ballast transformer).
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#1 "Re: 6KV GEN" by RAMConsult on 01/13/2015 2:38 PM (score 2)

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#6 "Re: 6KV GEN" by lyn on 01/13/2015 5:02 PM (score 1)

RAMConsult Guru Join Date: May 2007 Location: NYC metropolitan area. Posts: 3230 Good Answers: 444	#1 Re: 6KV GEN 01/13/2015 2:38 PM
	First I believe that you have a 6kW generator, not 6kV, and that you are trying to start all four fixtures at the same time, not one after the other. If that's the case then everything is behaving normally. The frequency drops under load because typically these small generators have a simple spring based governor with no means to compensate for sudden large load application, the sudden load being the cold start of the metal halide lamps which draw far in excess of 1kW each when cold. The voltage changes significantly because the voltage regulation is typically very poor on these small machines, usually they are self excited by drawing power off the generator terminals and if a large sudden load is applied this reduces the terminal voltage and in turn reduces the voltage/current to the field. That being said the reason that the voltage rises in this particular case has to do with the starting circuitry/characteristics of the metal halide lamp. The ballast has a large capacitor as part of the starting circuit. As we know capacitors raise the voltage of the circuit supplying them, that's why your terminal voltage rises. Once the lamp starts the circuit draws less power and becomes more inductive due to the magnetic ballast and the voltage drops to what you see. Your frequency probably recovers a bit but not to 60Hz because your load is near the upper limit of your generator. __________________ “Tell me and I forget. Teach me and I remember. Involve me and I learn.” Ben Franklin.
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delreer

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Join Date: Jan 2015

Posts: 26

#2
In reply to #1

Re: 6KV GEN

01/13/2015 3:04 PM

Yes, my mistake, the Gen is 6.6KW.

I actually tested at no load, one load, two loads, three loads, and four loads. I allowed 10 min per load test to allow for the light bulb to warm up and reach it's steady state. this is what I found out.

Generator Load [LAMPS ON]	Frequency [Hz]	Voltage [VOLTS]	Test Length [min]
None	59.69	102.9	5
1	59.4	113.5	10
2	58.9	113.9	10
3	58.5	118.6	10
4	58.01	124.8	10

Once I was done wit the test I checked open load again to determine if the frequency and voltage would go back to what I had recorded at the beginning of the test and it was not.

Generator Load [LAMPS ON]	Frequency [Hz]	Voltage [VOLTS]
None	59.69	102.3

After the loads were open, the generator did not recuperate to its original values.

Any ideas?

RAMConsult Guru Join Date: May 2007 Location: NYC metropolitan area. Posts: 3230 Good Answers: 444	#3 In reply to #2 Re: 6KV GEN 01/13/2015 3:24 PM
	Thanks for the feedback! I find nothing abnormal in your results. As the load increases the frequency drops, you are experiencing the droop characteristics of the governor. As the lamp fixtures warm up the capacitors become power factor correction capacitors, and the more in parallel the higher the voltage becomes. The return to no-load results are also typical, and within the normal bands for these types of machines, especially when you consider the difference in temperature of the components between a cold start and at the end of a full load run. What exactly troubles you? If you require tight control the light output for brightness, color temperature, etc. then you will need much more sophisticated control systems for frequency and voltage. __________________ “Tell me and I forget. Teach me and I remember. Involve me and I learn.” Ben Franklin.
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delreer Associate Join Date: Jan 2015 Posts: 26	#5 In reply to #3 Re: 6KV GEN 01/13/2015 4:52 PM
	I am trying to determine whether to set the frequency at no load or to fine tune it after the lamps have been runing for a while. Or after reading the comens of it really matters to do it either way. (Will it hurt the gen, lamps, or engine if the freq deviates from 60.2 to 58 in the long run?). Thanks for the help.
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lyn Guru Join Date: Oct 2008 Posts: 42355 Good Answers: 1693	#6 In reply to #5 Re: 6KV GEN 01/13/2015 5:02 PM
	No, no and no. The deviation is minuscule. If you are running a clock and checking it once a year, maybe.
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delreer Associate Join Date: Jan 2015 Posts: 26	#7 In reply to #6 Re: 6KV GEN 01/13/2015 5:06 PM
	Thanks Lyn!
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RAMConsult Guru Join Date: May 2007 Location: NYC metropolitan area. Posts: 3230 Good Answers: 444	#8 In reply to #6 Re: 6KV GEN 01/13/2015 11:02 PM
	A generator whose frequency varies from 60 to 58Hz looses on average 1Hz or 1.67%. So after 24 hours an analog clock running at 59Hz will read 24 minutes behind a 60Hz clock. The lights don't care, but anything synchronized to the line frequency may. __________________ “Tell me and I forget. Teach me and I remember. Involve me and I learn.” Ben Franklin.
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lyn Guru Join Date: Oct 2008 Posts: 42355 Good Answers: 1693	#4 Re: 6KV GEN 01/13/2015 3:44 PM
	I doubt that it Hz your lights to run at 58.
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