AC Current Flow Detector

Current Sensor Relays - Relays - Grainger Industrial Supply

AC Current Switch/DC Current Switch/Current Switches/Current ...

Thank you Lyn.

I am checking for the second link, but they are closed for inventory. Mosy of the detectors are detecting current, measure it and switch. The system I am searching for has a different task: on one side, I have a solar inverter, that measures the grid and produces a little more amplitude to send current back into the grid.

I want to detect this moment and stop the reverse current to flow into the grid, because the watthour meter is adding my production onto my bill.

When this happens, I want to switch on a dummy load to store power in it that I can release later, even when no sun.

I could use an old watthourmeter (power meter type) and the wheel direction gives me the current flow. I could work with a black dot and a photocell and just let the disc rotate the visual part of the disc (with a stopper) But I am looking for something easier to use (ready made)

A different way could be a break-in in the dashboard of TED and get the display to switch, but I have no clue how to fix that either. When the display needle is right from the zero, I should be able to switch.

The picture is coming with the next post.

You should ask which direction the power is going, not the current. A Power meter measures the voltage waveform and the current waveform and takes the product of the two. It should read positive if you are receiving power from the grid and negative if you are supplying power to the grid.

Here is what I monitor on the dashboard.

The needle moves exactly real time. In my earlier response, I was wrong. I need to detect the zero point and switch when the needle is on the left side.

I am curious as to what program or device that is on.

Also I would think that something using such a program along with the program itself would have a function for a digital output that could be used to drive a relay with a small single channel output interface circuit.

Hi TCM

This is a part of the display I get wireless from a TED 5000 system. It is a system with 3 Clamp- on devices, each with a controller that talks over the grid (PLC power line communication) to an interface, that is conected with my WAN modem. The system works as a real time data logger on a virtual dashboard display.

Each CT gives information about the measured current and the voltage of the line it refers to. With some clever algorithms it also computes the NET power = the sum of the main load, minus the solar production (algebraic)

It also has inputs for price of a kWh, with different possibilities. Meter reading dates and calculates, real time production, real time money spent and made and how high the bull will be at the next meter reading day.

I also do data posting with Bidgely.com, but they are not ready for the solar or wind part yet. They provide a data base for years. TED does that only for a few months.

(memory to small)

I am sure I can get all the required data out of this program since it is an open architecture. I am just too stupid to find out how on short notice, but I am working on it.

This link is very useful. Monitoring and managing is OK, controlling only for Nerds.

http://www.smartgridnews.com/artman/publish/Technologies_Home_Area_Networks_Reviews/Home-Energy-Management-TED5000-Provides-Real-Consumer-Value-But-Scores-Low-on-Standards-Based-Interoperability-2636.html

dvmdsc-

Use/adapt a current sensing transformer. It does exactly what you want to do.

http://www.electronicproducts.com/Passive_Components/Off-the-shelf_current-sense_transformers.aspx

Good Luck, Old Salt

Old Salt,

Thank you for thinking with me. Unfortunately it is not that simple:

I made a sketch of what is going on and hope it shows up clearly.

On the left side we have a power supply, delivered by the sun, solar panels and an inverter. To keep it simple, say the inverter can deliver maximal 1000 Watts and to do so it produces power waves in phase with the grid, only with a slightly higher amplitude.

On the right side we have the grid coming in and passing the power meter. (here shown as the 2 coils - one current + one voltage coil that make the meter work.

I didn't draw (show) a load, but just consider this parallel with the meter.

When we use 1000 Watts there will be no current flowing back to the grid (load and production are the same)

But in both cases when we have a difference of say 200 watts (starting at 0.00X1 Watt) A current transformer will measure the same value, whether I use 800 Watts or 1200 Watts. The systems lacks intelligence to detect from where to where the current flows. I need a one way street, a check valve.

TED uses 2 measuring points and 4 CT's and gives the CT's a virtual +- polarity to achieve a value to give the needle in the dashboard a direction.

That is missing in the principle CT set up you have posted. I might overlook something but need elaboration, because my elevator......, even worse: I have no elevator. Greetings, D.

Old Salt,

The system may work. I give you a G.A. for that.

The practical setbacks are that a lot has to be installed and connected, while I did that before with the TED 5000 system. I am enabled to SEE already what is going on and with little invasive measuring.

The power meter, I have drawn is a theoretical presentation of a disc meter that rotates and spins a mechanical display. This type of meter reacts immediately on the direction (or sense of distribution) while measuring at only 1 place (within a foot)

Some of these meters also work with CT's which makes it even more comfortable.

Observing an installed meter, the rotating disc shows us what is going on: most run CCW when power is drawn from the grid and change to CW when the grids accept power.

Visualizing is not the problem. The task is to use this view and make it initiate a action to automate.

I did not tamper enough with meters to find out if blocking the disc will produce e.g. enough heat to destroy the meter, but a single blackened dot on the disc could travel from left to right in the display (when a stopper limits the movement in the window)

and a Photocell relay could detect it and switch my needs.

Cost: old meter - $25.00 (ebay) one with 2 small CT's = $40.00 (less invasive)

Photocel with relay - $10.00, Small alu needle to stop the disc, and some time to work it out.

This works probably. Only, it is just another self made experiment that is difficult to market later, because it is 2013 and this belongs in a museum. (not saying that all old things are worse - even old salt can be good, if not, the best.)

Having two light sensors looking at the dot and noting which one senses "first", also noting the time differences (short and long period - before and after the dot), will tell you which direction the disk is revolving. A small PIC or similar can easily do the math and output the signal.

It could also detect when the two are balanced, and the disk is stopped, if such a condition can or could occur. PICs are wonderful.

As speed is not quite so critical, even a PIC with a form of BASIC could easily do the job and also be exceedigly cheap, from about $1.00 upwards plus interface. You should achieve a working unit for under $10.00 in all...plus a tiny bit of simple BASIC programming....

Having more dots would allow faster updating if required.

The PIC could eventually be programmed to store data and give such data up to say a PC to show when and where power was taken/produced.....

It could be a nice project as well as teaching you something new.....

PICAXE Chips are available locally in most countries, these are the ones I would recommend. See here:-

http://www.picaxe.com/

Also there are PICAXE forums online where you can learn more and ask questions and get help, all for free.

All PICAXE documentation and all the "needed" software are free to download and use via a USB or serial cable attached to almost any age or type of PC using Linux, Windows (any!!) or a Mac.

The chips can run up to 40MHz, depending upon the chip.

It is far far cheaper than using Arduino or its derivatives.

Thank the UK government for running such a useful program and making the chips freely available to anyone anywhere...with just a few dollars/UK Pounds....the postage often costs more than the bits and pieces!

Hi Andy,

I really don't know of this is the place to discuss it, since I notice that not many people are getting involved yet.

The TED system that I have now and where the graphs and photos come from has a 3rd party posting/polling possibility.

It creates and supplies an API stream that can be addressed through:

https://TED5000/api/LiveData.xml.

Each query initiates a list of all the possible parameters on a 8 page format.

The power information of MTU (CT system) 1 and MTU2 show as 2 undefined lines in a long list. What I need is to take these 2 values and compare them and process them to initiate a switch.

If you want I can produce this list and the 2 details I need to use. Unfortunatey I need to automate a query request every, say 2 seconds to have real time info to work with.

This query and also how to get only those 2 values that need to be programmed and processed to the switch. Here I fall short in the mean time (too stupid, I guess). I am trying to find something on the market that can be used, also without my computer on all the time.

The information comes as a .xml file, but there are other format available.

I will also look into your suggestions, but building something is quite unpractical, more because I have all the parameters available in the API.

Thank you.

D.

No problem.

Don't forget that ideas and tips here, though generated for a single person, you in this instance, they remain online and can be found and used by others.....so nothing gets wasted!!

I am looking for a platform that can do a query all the time:

polling the API sheet every 2-3 seconds

That doesn't need permanent computer connection to work and will be able to derive 2 values, compare (value and +.-) and make or interrupt a programmable switch.

Here the info- check for the 2 Fat lines, Thanks.D

This XML file does not appear to have any style information associated with it. The document tree is shown below.
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I highlighted 3, because the computed result to work with appears also.
Thanks for any illuster thoughts

If you want to supply current on either / or bases or sum of current bases? You must not send current back into grid as that is something impossible for you to achieve as load on that side may be anything beyond anticipation and also you may not get paid for it.

Junction point will always have same potential and this is the summing point. Rectifiers are best way to prevent reverse flow of current.

That is simply not true.

There are suppliers of certified equipment in most western countries at least (this may not be true where you live) that allow even a private person to generate electricity in some manner and if he has too much, to supply the country grid.

They usually get paid a pittance for each KWH, but even here in Germany, many have solar systems on the roof, supply daily power to the grid.

The equipment may NOT be home built, only certified and tested suppliers may sell and install it. Lots of rules and regulations to follow for a good correct install.

Its not cheap, but I have understood from the owners that lice around here, that they actually make enough to pay for the installation and have free electricity for their private usage!!!

Andy Germany:

You have a point and I agree that the law are different for different countries.
You also should know very well about grid synchronization and power summing method and must be registered to have a paid allowed service for selling power to the grid.
It is not a bad idea.

India is still very backward in having its own power and one reason is highly subsidized Government Power Supply. Unless you match the cost both ways, you deter people from having their own. There is a factor of 5 to 10 high production cost so no one feels like having unless industrial projects fail to run due to poor supply from Government power grid. There are some private grid also who are allowed to hike the price and this may sound bad but ultimately is good for the country.

I get 10kW/Hr for $1 from Government Supply and for Industry they may charge just half of that.

You can compare the cost from other sources easily for me and for your country as well.

I think this person requires little more technical reference help so find some suitable link for information for him.

In periods of crisis the most inventive countermeasures are created.

We have to be creative because when half of your income goes to your power bill, there is something to work on.

Here power costs approx 40 $cents per kWh. Solar has an extremely short payback time this way. And when choosing the right inverter, requires only to keep the panels clean from bird sh*t here.

This situation is to be expected for other parts in the world too.

dvmdsc:
As I pay only 10 $cents per kWh and industry pays 5 $cents per kWh and many don't pay at all here in India so that is it. It is an end of the road for innovation.
Most of the people use very little power. I use about 300 units per months and some time 500 units. 1 unit is 1 kWh. Most of the people only 100-150 units per month.

0.40 $ / KWh ?!?

.

Ouch!

.

I am in Central Florida and just pulled out my utility bill to check: 312 KWh cost me $45.25 and that includes all taxes, fuel adjustments, and the $11.90 charge just for the pleasure of being their customer.

.

So all in, that is about 0.145 $ / KWh. Are you really getting charged almost three times as much in South Florida? At that rate, you should demand that the power company install a meter that works correctly instead of charging you for power you provide to the grid!

You needn't make a trip to Pirate Island to gawk at milk being sold at $7/gal or even greater.

.

Luxury brands of organic milk at many grocery stores reach $7+/gal in gallon and 1/2 gallon sizes. But you can find milk going for more than $7/gal almost anywhere it is sold....just add up the price for a gallon made up of 1 pint containers.

Walk into any retail store that sells McArthur milk, or most any brand. Check out the price on the pint or 1/2 pint (I don't know why they don't just say 'cup').

.

Unless there is a 'sale', price for 8 pints or for 16 1/2 pints will typically exceed 7$ by a good margin.

.

Some will argue that people are paying for convenience, but paying more than double the price per unit for something 1/8th the size doesn't strike me as very convenient.

.

Even more unsettling is the amount of Zephyr Hills bottled water sold in or in close proximity to Zephyr Hills. The premium is significant, and IIRC it is from the municipal source.

Update: now $8.33 per gallon

truth is not a compromise

I think your electricity bill is comparable to my electricity bill in India so that tells only one part of the story. Other part of the story is that Petrol / Gas here cost about $1.8/L and perhaps Diesel $1.5/L. That means that the alternative energy generator resources are highly expensive in India. I simply can't use a generator for home unless there is no power at all from electricity supply. I use two truck Batteries and 1.5 kW Inverter to hold on power for power breaks.

It is very simple: the graphs (green) show how much a day produced. When the blue stays under the zero line, you have produced more than used. When it shows above zero the use has been higher than the production.

We have a very good location here as these are results from a 4800 Watts array.

Frankfurt has perhaps 50% insolation and way lower price per kWH and still uses it. PV panels help really.

AC or DC?

Assuming for a moment that it is DC:-

Why not simply use properly sized blocking diodes to stop back feeding?

Cars of a certain vintage had a center reading ammeter that showed the direction of (DC) current flow.....not difficult to make yourself either.....between generator and battery.

Do you want an older simpler method, or should it be bang up to date?

By the way, a dummy load just wastes the power (usually as heat), it does not store it.....

You appear to not fully understand what you want/need........

Hi Andy.

Let's use the AC from the grid at home. My posts are getting big and long to read them all. I understand that.

The "dummy is a load of batteries" that equals the net voltage" and will be switched on charging when there is an overproduction of solar during the day time. At night, we fool the inverter and let it produce grid tied power out of the batteries.

(With DC there is no problem- the diodes can do it - only it is AC)

We can design a bridge with 4 IGBT's, MOSFETS or Thyristors in a very complicated setup with microprocessor to do about the same, but that is way out of budget)

The dashboard meter on the computer (TED interface) does exactly what your battery ampere meter does. (the one with 0 at the center)

The magnificent thing about is that it happens with AC load and production.

Thank you for bringing this on. D.

AC flows both ways 50 or 60 or 400 times per second.

Thank you.

However in the schematic I posted you can see there are 2 AC power sources. The inverter copies the frequency, the phase so that there is no shift. We must think in the positive or negative part of the sinus only. As amplitude.

With 2 generators and the load between there is a direction of current flow and that is determined by the difference in potential (real time). This is why inverters can feed back to the grid. And also why generators can be put in parallel.

Polarity does count also for AC measurements. CT's have a mark (like a red dot) on one side. If you work with CT's, you need to respect that or the measurement is wrong in a kWh meter.

I didn't give it much of a thought, but probably with 4 CT's in Wheatstone bridge, and 2 close to each generator the phase and voltage (current) differentials results can be used to compute a working value.

Since TED 5000 succeeded in doing it, it is possible.

Most of all I would get a hint to retrieve the values out of the TED interface to with some program and a switch interface determine the setting on which I activate the battery charger.

The dashboard pictures I get to monitor with the TED 5000 software (wireless on router) and computer. Only I have no way of processing them to control.

I post another picture of the day data of the system. The bars are solar production,

main and load.

dvmdsc:

I don't under stand it at all. There must be some clear rules for middling with power grid.

Assume that I collect lightning power and feed it to the grid for 10s synchronously 60Hz or whatever it may be then do I get paid for it? I don't think so.

There has to be some kind of consistency in operation. It is OK to load the line as you need it bases but how much are you allowed to feed-in and for how much minimum period to get paid for it?

I am asking all these as I am net involved in this type of power generation so please don't mind my silly logic.

Hy Shyam,

As long as you have no agreement with the power company, and no special sophisticated netmetering device, so that e.g. your meter is spinning backwards, the tariff is about equal for energy used and energy produced. There is a slight loss of a few watts that the meter consumes by itself to make the disk spin. Normally the company pays this in a regular setup. Once you produce power into the grid, that becomes your loss, but it isn't really a lot, unless you are operating an old and worn down metering device. (In one particular case the meter was using 200 Watts, before any spinning was noticeable)

If you can harvest lightning and convert it to the grid, you have made it for the rest of your life. I don't think you'll need to work anymore.

Unfortunately this is not simple. We don't have the apparatus to input the lightning to and harvest it, and also not enough lightnings that will feed your captor.

The inverter you are using is not grid tie compatible. Yours has a frequency generating device in it and your 12 volts is converted (chopped) to 50 or 60 Hz and transformed upward to meet your required voltage,

A good grid tie inverter works different. Without a grid, it doesn't work at all, because it uses the grid sinus to clone the frequency, duty cycle,phase, shape and inverts this into a PWM power source that has a little more voltage than the grid reference. The AC chopper here is often a HF unit and operates between 15kHz to 100 kHz, depending on the design.

This higher voltage makes the current flow into the grid. You actually raise the grid voltage a little bit.

There are a lot of misunderstandings in PV solar, or wind inverters and how they work. I only detailed one specific type, but some work on a different base.

dvmdsc:
Ok, you believe that you are adding some power to the grid properly so it will be useful and meter moves reverse way for you when you feed power to the grid. I doubt if our meters can move the reverse way at all. I have never checked this out.
Did they tell you that the meter can move reverse way or you have assumed it?
What if grid have no power and you feed something to the grid and at that time no synchronization is required so meter will move the reverse way, as you have said here. Obviously one one can use that power being so low into the grid, but you still get paid for it.
Power failure is very common here.
I understand synchronization and also potential difference that makes power to flow (V1-V2)/Z where grid load is the load. Basically the current flow may be controlled rather than voltage to have some uniform flow of energy keeping V-injected a variable.

Dr. Shyam

In my post # 14 you can see the graphs of daily power situation:

green - pointed downwards is the solar production (now typically 65% compared to July)

The gray'ish color column upwards is what the house has used that day.

(a day ends at midnight on the grabber)

I can monitor everything you can dream of, even PF. And the weather too.

The blue column is the result what the meter adds or subtracts - when the column sits under the zero line, that is how much the meter has spun backwards.

The meter I have now spins backwards when the sun shines and it runs very fast.

When you watch it too close, you'll get dizzy.

The display counter is attached to the shaft of the disc and counts backward (only gears between) Most of the meters I have seen with a disc can run backwards. Only the ones with a one way clutch spin only forward. But I never have met one or read about one.

When the grid power is off, the meter is not spinning and the inverter does not generate any power out of the panels, because the grid wave form that it needs as pilot, is gone too.

For safety reasons: when the grid interrupts for say a second, the inverter goes in start mode and takes 5 minutes to run a batch measuring test on the grid before it kicks in.

The strings I use produce up to 380 Volts DC per string. (19 panels in series).

Unfortunate you cannot just make a current feedback, without working the amplitude. The more power you feed back, the higher the potential differential is. This depends on the impedance of the net and the start voltage.

In my place, to put 4000 Watts back in the grid that is e.g. 240 V AC/60 Hz, I generate 247 Volts. Efficiency of the operation is between 96 and 98% when working. The inverter runs on 4 watts ( and uses only DC from the panels)

dvmdsc:
Absolutely interesting one.

You should read the posts more carefully, especially the one you have just commented on, IT WAS SAID QUITE CLEARLY THAT THEY ONLY WORK WHEN THE GRID IS LIVE!!!

I quote:-

A good grid tie inverter works different. Without a grid, it doesn't work at all, because it uses the grid sinus to clone the frequency, duty cycle,phase, shape and inverts this into a PWM power source that has a little more voltage than the grid reference.

Partly because you don't want to be trying to feed a city after a mains failure....that can never happen.

It is a concept that some have a problem understanding.....

OK. I understood.

consider this: IEEE relay type 32, directional power relay.

Thank you.

Good find. I will check with ABB. Although this is a 3 phase system and I see they use the 3rd phase with a CT as reference.

I understand the principle of operation.

I only have 2 phases and no neutral. Perhaps there is a bypass?

As far as I'm aware, its normally impossible to have 2 phases.....3 phase with one missing, I don't think so!! Even then, you would only have 120° (or 240°!) between the phases, how uncomfortable.

You have the US system I believe, which is a single phase at 220VAC, which can be centrally tapped for 2 x 110VAC, with the center tap as neutral.

This basically can also mean, you have two phases at 180° to each other or two ends of the same phase.

The neutral, for safety reasons, will be at some point also grounded, usually at the last transformer....but possibly elsewhere.....it may even be grounded as it enters your building for example. Local laws apply.

Its a fairly common system for domestic power where 60Hz 110VAC is the norm.....

Andy,

You are right. I have only 2 legs of a 120/240 VAC/60 Hz.

I do not use the neutral at all, so according your post it is a single phase net 240 VAC.

Thank You. D

http://www.testequipmentdepot.com/yokogawa/pdf/2039.pdf

I would think you could use a portable power factor meter with programmable alarm contacts to monitor the direction of current flow and switch the power via a set of contactors.

Here is a good link to start with.

I am sure that contacting the technical services support division at Yokogawa, GE, Westinghouse, Sweitzer, or ABB wouls yield some schematics as well as good advice on what would work the best.

There is a company in Tucson Arizona Arizona Electrical Aparatus that deals in used metering, test, and other electrical equipment which is a great source for low cost, reliable solutions.

http://www.testequipmentdepot.com/yokogawa/power-energy-meter/pr300.htm

Maybe this one would work for your application.

Try googling 'single phase reverse power relay' and you will find exactly the item you require.