I had a power outage here recently so got a pretty good scare... I have a small inverter generator but it will not handle the water pump and the fridge/freezers in the house and etc...and to shuffle it back and forth is a hassle so I got to get another portable generator to handle any problems temporary until I get a more permanent solution next Spring/Summer. Pretty much out of time as winter is about here so... The damn problem is I can't find a good Dual-Fuel (I prefer propane of course) with a good THD and I got 2 new refrigerators, computers, super-duper TV/DVD player, etc. etc. etc. and all my house lights are LEDs. I really don't want to burn anything up due to high THD so...I did hear that LEDs will flicker if THD is high. Westinghouse makes a pretty good dual-fuel (Running Watts (Propane) 8500) but THD is rather high, 23% but they make a darn good gas one (Running Watts 8,500) with <5%. I really don't want to get a gas generator but might not have a choice if THD is that critical. And, if it IS that critical why don't the companies list their generator's THD, it's like pulling teeth to find it. So, what do you know about THD? Does anyone here have first-hand experience with THD? I hear one should be very concerned about it but never ran into anyone that had a problem with it... EDIT: Also, does anyone know of decent 5000-8000 watt dual-fuel generator with low THD?
THD is not as critical with equipment that is built with a Switching Power Supply, since those Rectify the Line AC into DC first thing...I would look for a Propane Conversion Kit for the Gas fueled rig first... Also how is you Well tied in to your Domestic Water System.. If you have a Storage Tank between the Well Pump and House , and just use the Well Pump to fill that Tank, you can eliminate the times that the fridges and Well Pump need to be powered simultaneously, with simple Load management...negating the need for a bigger Genset... Just as suggestion....
THD became important with switching power supplies. THD is the prime killer of an efficient power supply. Volumes have been written about it and having more than one power source will increase your problem. Your first move is to find out your actual problem. To do this you will need a Power factor Meter to determine the actual level of your problem on your wiring system. No way I can cover this on the forum, but a clue as to how extensive this can be in an industrial plant is the hundreds of hours it takes to get a grip on a plants 3 phase distribution grid. A Proper single point ground for all your system is a must as you can have different voltages and a heat build up between phases, even neutrals in different panels can have loads on them and you can have ground loops that waste energy and cause problems in electronics. This problem is the reason a Neutral is now required to be as large as the feeds and is sized different due to unbalanced loads. Sizing the neutral: Sec. 220-22. You must size the neutral conductor to carry the maximum unbalanced current in the circuit (i.e. the largest load between the neutral and any one ungrounded phase conductor). You calculate the first 200A of neutral current at 100%. For all resistive loads on the neutral exceeding 200A, you must apply a demand factor of 70%. Then, you add this value to the first 200A, which we calculated at 100%. And Understanding Total Harmonic Distortion (THD) in Power Systems - Technical Articles
My generators don't put out a very pure sine wave. I have a few computer uninterruptible power supplys (ups) that can easily be plugged in to clean that up. Efficiency isn't that big of a deal to me. Not killing the board on my furnace is. Ups,s are cheap or free after the internal backup batteries die. Just make sure about the starting current on any motors plugged in.
Filters can be added but must be done in a manner to prevent going to far back on the curve. ABB builds large scale automatic units that can return a system back to the 98% PF. This is now a requirement in most city grids. Medium-voltage capacitors and filters - Capacitors and filters | ABB I have installed one system and it was like magic to watch the caps cycle in and the load drop. You can see the wasted current be replaced by a balanced load. 3rd harmonics are a real problem in older parts of any cities due to the unbalanced legs of older buildings.
Very good article. I read it last evening in bed. I didn't realize how bad they effected efficiency - an eye opener. However, my concern isn't so much with Power Efficiency as it's more directed to specifically 'how' THD effects electronic devices and 'what' devices specifically. I did more Googling and pretty much found what I was looking for as "...increased heating in the equipment and conductors, misfiring in variable speed drives, and torque pulsations in motors..." I don't have a electric furnace but I do have a new HVAC system (heat/air conditioning) that could be effected by harmonic distortion which gives me pause and not sure about both my refrigerators which are fairly new... Anyway, thanks to all for comments and information... It helped me form an opinion and think it's best to try and error on the side of low THD if possible especially since I would be purchasing a new generator. @BTPost "If you have a Storage Tank between the Well Pump and House , and just use the Well Pump to fill that Tank, you can eliminate the times that the fridges and Well Pump need to be powered simultaneously, with simple Load management" Yes, I have a 1500 gallon cistern and that is my intent (just run the generator as needed not constantly and load manage) so I can go to a smaller generator unit but, honestly, the cost and size/weight is not much different, of course, fuel usage is... The bigger problem is now trying to locate a low THD, Dual-Fuel generator which I don't think they make...I might have to settle for gas. We'll see. Thanks!
If you are on a battery system and run your fine electronics from an inverter you can eliminalte a lot of problems.
I use a few but my most recent addition is one of the Harbor Freight Honda knock offs, I think it is 8700w or something along those lines. We use it often and don't have any trouble with our electronics computers, phones, routers, etc.
BenP, see that is what I mean, I am not so sure it is a big deal for home users. But, for industry and manufacturing - absolutely! That article concerning THD that HK_User shows in black and white that power efficiency drops like a rock. But, us home users? We don't really care about efficiency as we are making do just until the power comes back on so... So, do we really need to be concern about it because I know loads of people around here (Northern Idaho) are forced onto generators but really haven't ever heard of anything bad happening to their televisions, computers, etc...so I don't know. I read of a guy whose LED lamps flickered - that's it - but my neighbor has LED lights and his Champion generator is 12%-20% THD - no flicker. According to what I read, it can cause more heat and, we all know, heat is a killer in electronics but that variable is not a constant for if it was then all your "electronics computers, phones, routers, etc." would be dead, right? I think what it comes down to is it's definitely 'not good' for the sensitive electronic stuff but it all depends on the build quality of the electronics, how long they are on the high THD generator and - the real determining factor - exactly how high is the THD. I think generally good electronics can take higher THD without any problem, more than we think... But, again, that's only my guess and from reading and asking questions and from people like yourself that actually have experience with it... So, maybe <5% is really necessary...then again maybe it's not.
My house is set up with an apc. The battery bank is always charging while on the grid. Solar and wind panels will be added as I get around to them but I thought it more practical to set up from the rear forward. I read christmas catalogs like that too, back to front.
Our old house had a 48vdc 400ah battery bank to a 2000 watt UPS to run lights etc. Power failure barely blinked the lights. 6.5kw of solar panels and small generator are backup. Solar 12vdc for ham station is full time... Building new system of 2kw solar panel, 60amp MPPT charge controller, 24vdc 210ah battery bank with 3kw sinewave inverter. Lots of choices... as many ways to build a backup as there are people to build them. You build to fit your budget and your needs. as always YMMV
One thing you can do is get a Kill-a-watt meter and check power factor on all your motor loads correct them by adding capactors in parallel to the motor. Replace old heat pump and A/C appliances with more modern inverter versions. LEDs can run a pretty horrible power factor because of the cheap made in china power supplies that run piss poor power factor it can't be corrected with capacitors because it's just phase distortion. Where you need a lot of light use T5 with industrial/commercial rated ballasts. These will run "dirty power" and deal with voltage drops, surges well and run very high power factor. Where cheap LEDs may flash on and off when the voltage drops because of a motor load starting.
