Trying to measure peak current 3 phase to restaurant  - Page 1
Forum section: electronics / projects

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: March 26, 2015, 05:43:41 pm
content: I do a lot of repairs for a friend , and trying to save some money on electrical bill , they have a markup on the rate that he hits most months .One of the ideas at the time is he thinking about a generator for a few hours each day to keep him from the rate jump point .So my question is what method / gear to measure his consumption peak to help judge generator size , 3 phase .One of my other ideas was to see what can be done to checkout and improve his power factor , most of his high consumption is resistive heating for deep friers etc. , of course there are a number of motors for compressors - inductive , not sure if capacitors need to be added at each motor / or can be add upstream , one cap / caps for all motors / compressors ?

author: IanB
author_rank: Super Contributor
timestamp: March 26, 2015, 05:54:24 pm
content: I think bad power factor would be charged as a penalty factor separate from actual power consumption. So if this was an issue I would expect it to show up as a line item on the bill?Running a generator in parallel with utility power is going to require complex equipment to sync them up is it not? It may (will?) also require a permit from the utility company before it can be hooked up. I wonder if the cost would be justified.Most likely the first and best option would be to measure and profile the power usage over the course of several days or weeks. Maybe the peaks can be leveled a bit by shifting some uses to different times of the day?To measure the power, see if there are smart meters installed. If not, try asking for them. You should then be able to go to a web site and see a historical record of power usage as a trend chart.

author: PeterFW
author_rank: Frequent Contributor
timestamp: March 26, 2015, 06:28:31 pm
content: Quote from: KD0CAC John on March 26, 2015, 05:43:41 pmDepending on the amount of money you want to spend on a generator, the local code restrictions and so forth...Old refrigeration units will loose power like a bottomless barrel.Maybe they should be replaced.Lighting is not to be underestimated, on the floor you might be able to shave of a lot of power if you switch incandecent to CFL or LED.Deep friers can run of gas, maybe a new gas powered deep frier is cheaper then a new generator.The oven burners will most likely be gas allready so there will be a gas line you could put the fryer on.The ovens too could run of gas.

author: Jeroen3
author_rank: Super Contributor
timestamp: March 26, 2015, 06:30:39 pm
content: Yes, it will require specialized equipment to synchronize a generator to the grid. And skilled personnel to commission the installation.It is profitable for horticulture, because they use all products a generator set (with gas engine) produces. Energy, heat and the exhaust fumes.How much power would you want to have for cogeneration?

author: ajb
author_rank: Super Contributor
timestamp: March 26, 2015, 06:43:31 pm
content: You don't necessarily need the generator to be paralleled with the grid. You could use a more traditional transfer switch setup, just like you'd use for backup power. That gives you a lot of flexibility in generator sizing, because you can choose which loads get switched over and thus how big a generator you need. You'd probably want to keep things like room lighting and cash registers on the utility to avoid interruptions when switching to and from the generator. If you put the fridge/freezers on the transfer switch you have the bonus of saving your food if you lose power for an extended period.As for figuring out your current consumption, an decent electrical contractor ought to have a logging meter they could leave installed on the service for a couple days, which would give you a very good picture of your usage profile. Probably wouldn't be terribly expensive, particularly with a potentially lucrative backup generator install job on the table.

author: SArepairman
author_rank: Frequent Contributor
timestamp: March 26, 2015, 06:46:49 pm
content: i think you can use the waste heat from a generator to heat food oil like at kfc

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: March 26, 2015, 07:04:29 pm
content: At this point some may get pissed off , but it does seem to be one of most common things of internet , forums etc.Why is it with forums groups , you almost never get an answer to the questions posed , at least not until many responses that bring up fear .If you do not believe , reread my questions and read the responses ?One came close , asked for a smart meter .I do have clamp-on amp meters , but that would mean exposing power panel and leaving , the meter does have a limited peak watch .It would seem that there may be something to build , verses buy - big buck , but maybe jumpers and wireless to office computer - nearby .For me its about learning , I have been doing electrical mostly residential and some commercial and very little multi-phase , I did just replace 3 phase mercury relays in a boaster yesterday , and built a number of solar systems up to 4kv with transfer switches and other generator systems , so not a total newbie .The problem with using my clamp-on amp probe is the 3 wires / lines .

author: cs.dk
author_rank: Unknown
timestamp: March 26, 2015, 07:11:24 pm
content: Also your clampmeter won't show the powerfactor.

author: ajb
author_rank: Super Contributor
timestamp: March 26, 2015, 07:38:15 pm
content: Quote from: KD0CAC John on March 26, 2015, 07:04:29 pmQuote from: cs.dk on March 26, 2015, 07:11:24 pmThese are all good reasons to get hold of a proper logging meter, and someone who knows how to hook it up safely and unobtrusively.

author: SeanB
author_rank: Super Contributor
timestamp: March 26, 2015, 07:47:45 pm
content: If you want to measure safely in the board just get 5 open core current transformers, and depower the board and place one on each incoming phase then close the board up again, while leading the 6 wires ( you can common one side of the CT output leads no problem) and then outside you can safely have your 5 multimeters with 5A measurement ability to read the transformer outputs. That allows you to have long term reading, or even connect a recorder to each phase to see the usage pattern. As most of the loads are going to be resistive ( heating elements) and the inductive loads will likely already have power factor correcting capacitors on them to make them appear like 0.80 PF loads you pretty much can ignore PF. 5 transformers as likely your incoming is 277VAC 3 phase, along with a regular 240V centre tapped mains line for 120VAC appliances, seeing as this is the USA, elsewhere in the world you only need 3 current transformers with 230VAC mains. For safety short the CT outputs when not in use, or even just use a clamp meter over the line to get a 0-5A reading that you scale appropriately and leave then all shorted.For fridge freezer motors you would have to look, and in most cases they are going to have a PF of around 0.8, so nothing needed. 3 phase motors used for extractors will likely not have any, you would need to see the manufacturer of the motor to see what they recommend for PFC and add it near the motor controller, which will bring the PF up to around 0.9 and reduce line current a little.Lighting is the issue, as commercial fittings will have PFC, but cheaper residential ballast units will not have it, and adding PFC capacitors will improve the PF but increase arcing in switches. You probably would find that lighting is going to benefit the most from simply cleaning the lamps and fittings of grease and dust, which will likely be caked on them. Replace the failed lamps as well, which will make a big difference ( people do not seem to realise that a failed flourescent lamp that has glowing red ends actually is using nearly double the power of a lit lamp, just heating up the ballast) along with replacing failed ballasts with new ones ( buy good quality electronic ballasts, not the cheap ones from HD, go to a lighting wholesaler and buy a decent Phillips or VS unit), and replace incandescent downlighters with decent LED versions ( YT channel Bigclive for ideas on light efficiency) and you will make a difference.

author: Jeroen3
author_rank: Super Contributor
timestamp: March 26, 2015, 07:57:25 pm
content: You can buy (or rent?) a pQube.http://www.powerstandards.com/PQube.php(yes, its expensive)Thats the most advanced power analysis tool I've seen so far that does not require to be operated continuously.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: March 26, 2015, 10:02:43 pm
content: SeanB , that seems to be heading the correct direction , I do have some snap-on ferrites , but my biggest ones may not allow for both the line cable & sense wires , another reason to get more but for large cable , I have a good collection of these ferrites for my hobby - ham radio , with those we need the correct mix for the frequencies being worked .I assume you meant 3 meters not 5 ?I have a few , but only one has the ability to hookup for data gathering .All of the lighting , per code is covered / sealed so not an issue there at least the food prep & cook areas , we are also switching over to LED , just put in a fixture that looks like a 2 tube florescent , but has LED tape .

author: Circlotron
author_rank: Super Contributor
timestamp: March 27, 2015, 02:16:56 am
content: Quote from: Jeroen3 on March 26, 2015, 06:30:39 pmFor a conventional synchronous generator, yes.For an induction generator, no.Easy peasy. All you do is connect a 3-phase induction motor to the AC mains and rotate it with a mechanical source of power. In motor mode it resists being slowed down by drawing power from the mains. In generator mode it resists being sped up by putting power INTO the mains.For 50 cycle mains for example a 4 pole motor runs at 1500rpm no load and typically 1440rpm full load. That's a drop of 60 rpm. As a generator it is working at max when you force it to 60 rpm ABOVE no load speed.

author: SeanB
author_rank: Super Contributor
timestamp: March 27, 2015, 04:32:15 am
content: Quote from: KD0CAC John on March 26, 2015, 10:02:43 pmNo, a current transformer is not a ferrite core, but a toroidal transformer core with a primary made from the mains conductor and a secondary typically 20 turns ( for a 100A/5A unit) that provides a current proportional to the mains current flowing.http://en.wikipedia.org/wiki/File:CurrentTransformers.jpgArticle ishttp://en.wikipedia.org/wiki/Current_transformer

author: Jeroen3
author_rank: Super Contributor
timestamp: March 27, 2015, 08:07:53 am
content: Quote from: Circlotron on March 27, 2015, 02:16:56 amAsynchronous generators are used in wind energy. They're not commonly found strapped to a diesel or gas engine.

author: Seekonk
author_rank: Super Contributor
timestamp: March 27, 2015, 09:46:32 am
content: A while back I was at a Habitat for Humanity resale store and I saw a device that clamped on the outside of the meter glass and would read power. Oddly enough I think it was from Black and Decker and I downloaded the online manual. It came with stickers warning power company it was legal and would not interfere with power reading. It was only part of a complete monitoring system and lost interest in it quickly. Couldn't find the file and don't remember what types of meters it worked on, but it shows there may be systems out there like that.I worked with a company that had the same problem. They had lots of heating devices and the first thing they did each morning was turn them all on. Staggering the turn on's made a big difference.

author: The Electrician
author_rank: Frequent Contributor
timestamp: March 27, 2015, 10:07:17 am
content: Quote from: KD0CAC John on March 26, 2015, 05:43:41 pmYou can rent equipment like this:http://www.ebay.com/itm/261789597241?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AITAs far as getting a generator to supply the extra power, you should run the numbers. Theoretically, one horsepower equals 746 watts, so a 10 horsepower engine driving a generator could theoretically provide 7.46 kilowatts with 100% efficiency. You probably won't even get 500 watts per horsepower in reality, so let's say your friend needs an extra 10 kilowatts--that would require a 20 horsepower engine. The fuel cost will be maybe 2+ gallons per hour; add in the amortized cost of the equipment and what do we get for cost per kilowatt-hour generated? You could get a natural gas powered generator that wouldn't cost as much to run.I suspect you can't generate your own power with your own generator for a lower cost per kilowatt-hour than the power company can supply it to you even at the stepped up rate.I think you would be better off finding a way to reduce heat loss from the deep friers.

author: LaserSteve
author_rank: Super Contributor
timestamp: March 27, 2015, 02:13:12 pm
content: Calibration of a natural shunt formed by a wire in the panel is in order. Watch out for coppers tempco.Job jobbed. Am I off topic?Actually surplus shunts are cheap, but a proper logger shows phase and VARsSteve

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: March 27, 2015, 02:25:38 pm
content: Quote from: Jeroen3 on March 27, 2015, 08:07:53 amI think we are on the same track , just my lack of using all the correct terms , I've used similar setups to tap into other situations for testing monitoring .The part in question - depending on whats being monitored is the core , number of turns - then voltage , current & frequency ?And now adding multi-phase ?I seem to only learn when I run into problems , not much learned when everything is working

author: Seekonk
author_rank: Super Contributor
timestamp: March 27, 2015, 03:12:48 pm
content: I love microprocessors and lots of data, but everyone is getting spoiled. You have an electric meter and a monthly bill. Just going out and checking the meter every half hour should give you enough data to understand the problem. Thinking generator is putting the cart before the horse.

author: flynwill
author_rank: Regular Contributor
timestamp: March 27, 2015, 03:38:23 pm
content: It is really unlikely that a generator is going to save any money. You need to run the numbers, but by the time you amortize the cost of the machine, the fuel and the maintenance I'll bet you're looking at $0.50/kWh electricity or worse.If natural gas is available then the most direct thing would be to move all the direct heat cooking stuff to gas. You'll have to run the numbers, in my neck of the woods (LA Area) gas is about $1/therm the equivalent of $0.035/kWh, where electric power is anywhere from $0.15 - $0.40 depending on where you are. So even if you factor in the lower efficiency of the gas (probably 30-50% for a cooker) you are ahead.If power factor is a concern, you should study his electric bill. If they are charging for it you will see a charge based on kVarH. In my experience this is usually a pretty small charge, but strange things can happen. If he has a large charge for peak usage (based on kW instead of kWh) then it might make sense to see if there is anything to do to level out the usage a bit, but I would imagine that for a restaurant that would be pretty difficult, you pretty much have to have everything going at once during lunch hour.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: March 27, 2015, 03:42:21 pm
content: Quote from: Seekonk on March 27, 2015, 03:12:48 pmYou may not be grasping the issue & solution , to avoid high usage fee / markup , using the generator during peak draw 3-4 hrs on those days to keep from going over the point of incurring the extra rates , if I remember correctly , I think said he has had $1,400 month bill & $500 would be the overage charges .The labor involved in using a meter on 3 phase as you say would be excessive by a huge amount .

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: March 27, 2015, 03:43:52 pm
content: I guess you missed the title of the thread , measuring 3 phase ?So we are looking to get the numbers .Quote from: flynwill on March 27, 2015, 03:38:23 pm

author: The Electrician
author_rank: Frequent Contributor
timestamp: March 27, 2015, 05:44:15 pm
content: Quote from: KD0CAC John on March 27, 2015, 03:43:52 pmYou can rent 3 phase power analyzers for several hundred dollars a month:http://www.trs-rentelco.com/SubCategory/Power_Quality_Power_Demand_Analyzers.aspxhttp://www.atecorp.com/category/ac-power-quality-analyzers.aspxThey will come with clamp on current probes and voltage leads, all rated to at least Cat III. You can get one that will log everything you want to measure--kwh, kvarh, PF, etc.; peak values and average over a day, or any time interval you want.

author: franksanderdo
author_rank: Contributor
timestamp: March 27, 2015, 07:05:31 pm
content: Quote from: The Electrician on March 27, 2015, 05:44:15 pmI can only agree to The Electrician. Use decent Equipment even though it might cost some bugs for rent.If your suspicion is right this will be payed back easily by improving PF and usage.In a mains board any half way diy solution is only dangerous and will not give the results you need.Is there a electrical installation & maintenance company were you can ask to borrow a power analyser?All the BestFrank