Current Direction Sensor with Switching Contacts

Do you have any voltage stabilization strategy? Any pictures of your setup?

http://www.wmea.net/Technical%20Papers/5-WMEA-Nov-2009-Power-Trak-Plus-r2.pdf

http://www.miningelectrical.org/files/66541946.pdf

Nice dragline. Only the one here has 6 stepping feet and is 20 times bigger. The power company has to start up 5 extra generators to make this monster spin.

The machine room is as big as an 3 story apt. building. The digging goes on for the 10 th year already.

There has been a post, quasi similar problem some time ago.

Answers came up to use "single phase reverse power relay" and IEEE relay types

32, 67AC, 87, 91 and 92.

Most of these are really not suitable for this small application, except maybe the WILMAR, but this has only 0-5 Amps reading capability, so that you will need to make a current transformer to your 10 or 20 Amps circuit. The Wilmar is pricey.

A different approach may be:

Considering your Inverter is in shutdown mode. This implies that there is no current flowing (only voltage from the grid is connected to your inverter connector) or perhaps only a very small current, compared with the 10 or 20 Amps it can deliver to the grid when working.

You could take a AC relay with easy accessible coil and.... not use the (voltage) coil at all and transform it to a current coil with a few turns of wire that can easily have your 20 amps transported. The number of turns depends on the sensitivity (build and springs) and the desired amperage to make the switch.

Perhaps there is room around the existing coil, otherwise make space by removing the existing coil.

Once the work condition is achieved, your inverter delivers power and the current activates the relay. The contact points NO and NC you can play with for further experiments.

Since I expect that the NC contact is of most use for you, be also aware that in the dark your relay needs some more sophistication like e.g. a photocell or timer relay (dark light needs to be taught)

This relay must be in the dedicated line between the inverter back feed to the grid.

Work safely and

Good luck.

The problem that you may encounter is the "anti islanding" mode of the inverter which prevents it from outputting any power if the grid supply is missing or deficient, as in a brown-out such as you are likely experiencing.

Therefore to get your inverter to output to a battery bank you will either have to bypass that control feature - (dangerous for linesmen and likely illegal), or provide a battery fed inverter supply to the grid tie inverter to get it to fire up to the MPPT for battery charging and then prevent islanding.

A better method may be to simply install a change over relay that is activated by the drop in mains voltage that diverts the output from the pv array straight to a suitably sized MPPT regulator to charge the batteries directly and then feed to another inverter to supply essential circuits.

You would not want to then use that battery supply to re-energise the grid tie inverter due to the islanding concerns that I mentioned previously, and you would need to isolate those essential circuits from the mains to prevent backfeed with another C/O relay.

The inverter starts up as soon the grid is back in shape.

The idea is to charge the batteries from the solar array through MPPT when the inverter is off.

So the inverter is sleeping (or in test mode) and has no output function then.

Thank you.

"Therefore to get your inverter to output to a battery bank you will either have to bypass that control feature - (dangerous for linesmen and likely illegal), or provide a battery fed inverter supply to the grid tie inverter to get it to fire up to the MPPT for battery charging and then prevent islanding."

I am sorry If you read that I want to charge the batteries with the inverter

Just want to use the brown out and start up periods to connect the solar panels straight to batteries and use the "collected energy" afterwards when it is dark.

So I do not change anything that can affect anti-islanding.

Brown outs can appear several times per hour, but the start up procedure (automatic) takes 5 minutes. (times the brown outs this can be a considerable loss of efficiency)

Could what you be looking for is a solar powered UPS? If yes, this is very doable. I don't bother supplying power to the grid. There are two ways to accomplish this, one is to modify a suitably sized UPS, the other is to purchase a suitably sized commercial grade inverter.

A UPS is nice as it provides seemless switching when the power fails, the inverter system requires no modification. The UPS will have to be modified to permit charging from a solar panel and will need a suitably sized battery. Some UPS's apply 1/2 line voltage to the battery terminals regardless of whether it is in line or battery mode. This will damage the panels and your MPPT. You will have to remove the charging circuit from the UPS, this may be difficult, as most manufacturers will not supply schematics.

The recommended way is to purchase a suitably sized flooded battery, inverter, and battery charger, and a line voltage rated relay. You will need an "old school" charger that is not microprocessor controlled. (When power is restored, micro p chargers need to be reset, "old school" chargers just do what they are supposed to do and mostly work on flooded batteries only). When the AC fails, the relay drops out allowing charging via the panels, at nite the MPPT prevents the panels from discharging the batteries. When the AC is restored, the relay energizes, allowing the batteries to charge via the charger.

it is a similar approach, only power wise UPS are not designed to work on 300-500 Volts DC. The system I use is 5kW+.

For some lights backup, I use a UPS, but powering it straight from a solar panel is weird. I just have the connected batteries charged from the grid (and Inverter) supply, which requires no modification of the electronic circuit of the UPS.

The only thing I did is, replacing the batteries of the UPS by a out the box one.

Considering that the UPS can handle the battery charging current.

I try to find a solution for the 10kW or more that goes nowhere when I experience a brown out.

Thank you for thinking with me

When mains voltage is V sinωt. the current from the inverter has to be I sin ωt and not I sin (ωt+/-180). That decides direction of power flow between the mains and the solar inverter- assuming the mains voltage peak and inverter voltage peaks are same. So direction of current has to be detected with reference to voltage waveform of the grid which can be done by very simple circuitry.

The off topic comes from me.

While there is nothing wrong with your contribution, it has nothing to do with this post, nor gives it any suggestion to be an answer to it.

There is a lot of misunderstanding here, probably because Solar is not taken seriously and therefore implemented and understood.

In a grid tie inverter, your formula is one of the main parameters to start the inverter and provide a real time copy of the grid features. Powering back the grid has then only to do with amplitude difference between the grid value and that of the inverter.

The solar grid tie inverter should have a dry contact to activate when the inverter is active or inactive. I would suggest looking at the drawings to see if it has one. If so (and

most good ones do) monitor the contact and then operate a relay to shift the solar power from the inverter to the MPPT charger to the batteries. The batteries could then be fed back to parallel the grid inverter when the power system is clear and sunlight not available. I don't know if you have the knowledge to make this happen or not. There are other ways of making it work.

Possibly the best solution would be to ebay your present equipment and simply purchase a combination grid tie/island inverter with a built in charger. They are making these now and they have all the detection/switching and nec stickers to keep everyone happy. It will involve some careful load management or larger solar arrays. (Yours sound very small) In my area one company is marketing one that is combined with a Tesla Wall. Users have reported good results.

I remember the first time I went out for PM on a dragline. This was a really large one that a football stadium could be place inside the main structure. A Semi could turn around in the bucket. I had an easy day just checking motors and transformers but my co-worker tuned the drives which took a little time. When the operator went to checkout operation, He told me to hang on tightly because I had to stand at the back of the control room. I couldn't believe how fast the swing motion could accellerate that large a mass and in general how fast it could dig!

I am really surprised however that you are experiencing your problem. The transformers in the manufacturers we supplied electrical componets for called for specially designed transformers to block out the transients from the drives (that's what contains the SCRs) so that interference on the transmission line should not happen. I would complain heavily to the power company, elected officials, and anyone else I could aggravate.

I think this issue has not been understood. GP is looking for a current switch. First it is necessary to find out direction of the current. So what determines direction of the current? For that the reference has to be the mains voltage. Amplitude, frequency, phase of grid voltage as well as inverter voltage has to be monitored by a DETECTOR block and current direction with reference to grid voltage has to be measured. If grid current is zero for any reason, grid could be cut off (not shown here) and load is allowed to operate from inverter.

When current is zero, the inverter does not work at all.

Solar panels have to connect to charge the batteries under this condition. Inverter is in standby and will start the start up and control cycle.

That is fine. This can be taken note of in the software part.

I am no exert on solar however something does not make sense here to me. Perhaps I missed a vital point.

If you install an under-voltage relay on your side it will disconnect your grid export and the inverter should supply your premises and battery bank without any interference to the electronics of the inverter and without interruption to your supply from the panels.

I am puzzled why the inverter produces no voltage when the grid is disconnected as the panels will still be supplying the inverter which in turn is supplying the premises and battery bank.

However, on reviewing, I found the Selectronic Solar Hybrid On Grid Inverter will do all this for you without interruption to your supply and it will still charge the battery bank.

Quote : Security of Backup Power

During a power outage, the SP PRO solar hybrid systems will supply the load from the renewable energy source whilst storing any excess energy in the battery bank to be used as needed. This gives the user continuous power and peace of mind.

http://www.selectronic.com.au/grid/

A regular grid tie inverter has NO 50/60Hz autonomous sinus generator in it. It is designed to have a look at the grid and copy or clone the wave form when it fits the working specs. No grid power means this inverter just doesn't generate anything. Bad grid conditions out of specs means this inverter goes in standby.

A combined inverter that can deliver back up power and grid tie features generates it own sinus and synchronizes it to the grid. These systems need a Transfer switch to disconnect the grid (safety features to the lines men) when on back up, just like a backup generator.

These inverters promise you a trouble free heaven on earth, but most of them are prone to expensive service costs (say repairs). I won't name makes that have just contributed to spending more money than your solar system provides.

However they actually work well in heavenly good grid conditions on earth. Problems with saturation (sinus top flattening), brown outs, duty cycle deviations or other non symmetrical events drain your wallet.

On the other hand, these systems run better in battery mode and not grid tied. Problem then is that you need to have a "oversize" battery bank. Batteries don't like to be charged and discharged with currents they are not designed for.

Batteries may run hot, swell, evaporate, explode if not taken care of properly. A non ventilated battery house can be a ticking time bomb. If you design the battery size for 1 or 2 days backup, you are inviting troubles.

Thanks.

A undervoltage relay will not do the job during the start up checks. Since the inverter is connected to the grid, the voltage is present almost all the time.

A current relay will switch states when the inverter goes from active to standby and vice versa.

This is a simplified diagram how it works.

The solar battery charger is not here. The turns around the relay coil determine the sensitivity