Line reactors and Power quality 6

[John2025]

Hi All,
I haven't been around for a while since I retired to sunny Puerto Rico.
I live in rural PR and the power quality is pretty poor, lots of outages, varying voltages and switching transients from the POCO. The volts are typically too high (right now 130s each leg) and it jumps up and down a few volts abruptly. I've had my A/C (2 Fujitsu inverters, 1 @ 5kw, 1 @7.5kw) burn out twice. I have surge suppresion at the individual units and at the main panel. Getting any useful response from the POCO or the A/C contractor has been unsuccessful so far. They just keep replacing boards.
SO, do you think line reactors for the A/C units would help with transients? I can get them pretty cheap from Automation Direct. I thought about ferroresonant xformers, but that doesn't sound very promising. I'm thinking of going off-grid with solar someday, but I need to get some other things done first.
Any thoughts?
Thanks, John

 

[waross]

During my years in the third world, I had to deal with a lot of power issues.
There are small, economical voltage monitors available that disconnect your equipment if the voltage is too high or too low.
These plugged into a receptacle and would accept the plug from a refrigerator or freezer.
If the incoming voltage is chronically high, consider an autotransformer to knock off 10 or 15 Volts.
The transformer will also act as a series reactor.

[link ]Bill[/url]
--------------------
"Why not the best?"
Jimmy Carter

 

[John2025]

Bill,
That sounds like a good plan. I'll wire the output of the monitor to a suitable contactor into the xformer and that should get me proper voltage, over/under protection and a reactor.
Thanks.

 

[waross]

By the way, there is a difference between my experience and your situation.
We used to lose a lot of refrigeration equipment to low voltage and your issue is high voltage.
Generally, low voltage takes out the refrigerator motors and high voltage takes out the electronics.
The monitoring devices will protect against sustained voltage excursions, you may consider surge arresters to protect against transients.
I suggest using the transformer at all times. The monitor and contactor may not act fast enough to protect against a sudden, sustained voltage increase.

[link ]Bill[/url]
--------------------
"Why not the best?"
Jimmy Carter

 

[djs]

It has been my experience that ferroresonant transformers provide the best protection for line quality issues. Expensive but pretty much bullet proof. The only time I have seen that these units have a problem is when there is a large amount of harmonics on the incoming line. They give you under voltage protection, over voltage protection and transient protection. Also note the size of your loads 5KW and 7.5KW.

 

[itsmoked]

djs; But those things are soooOOOoooo inefficient it's painful. I remember them running so hot they'd steal your fingerprints at first touch.

John; You're in solar heaven. I'd cut that POCO loose completely. Solar panels are dirt cheap now. Yes inverters aren't dirt cheap but pretty inexpensive. Yeah, batteries aren't cheap but work well now.

Here's a typical 'all-in-one' type inverter solar charger: MPP-PIP-LV5048

That's 5kW and you can gang fistfuls of them together (something like 6). They'll provide 120V,208,and 3 phase as desired.

You can also use them without solar. You can use them and some amount of battery and the they will take in crummy utility power, dump it on the batteries and invert out clean sinewave power continuing to run uninterrupted if the utility drops entirely. For further backup support you can run an inverter generator into them if the utility goes dark and what your loads don't use will be stuffed in the battery bank.

Might be worth checking it out or sketching up a system for yourself.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[jraef]

The best thing Line Reactors for your power electronics is to slow down the rise time of transients. In your case, you are likely seeing a lot of "grid switching" transients as the power suppliers try to keep up with demand amid a crumbling infrastructure. When grid power is switched from one source to another, capacitors on the line create ringing transients. When those get to the rectifiers of your inverters while the motor is running, they can cause damage to the rectifiers, DC bus and or transistors.

What happens is that the diodes in the rectifier conduct during only a portion of each sine wave, when the incoming voltage exceeds the "Forward Conduction Threshold". If, during a transient ringing effect, the sine wave entering one diode is too low, that diode fails to conduct into the DC bus. But the transistors on the other end STILL fire into the motor, depleting the DC bus capacitors. Capacitors charge and discharge almost instantly, so if one or more diodes is not contributing and the DC bus caps are depleted, the NEXT diode that conducts has to supply ALL of the energy taken out of the caps, and that can cause a current spike of up to 20x the rating of the diodes. One or two occurrences every year is probably inconsequential, but several times per day is causing incremental damage to the diodes, the capacitors and stressing the transistors.

Adding the line reactor slows down the rise and fall rate of the ringing transients, allowing the energy movement across the rectifier to be spread out more evenly between the diodes. It ALSO drops the line voltage a little bit, but not enough to get excited about.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[John2025]

Great info guys, I think I understand my options now. Thanks!
Hi Keith, have you used those inverters? They're really attractively priced.

 

[itsmoked]

I am using one of them, the LV2424, and will be getting another shortly. I will be using them ganged to get me 120/240 split phase power as currently with one I only have 120V. I will be using them to get me thru our crummy local power company's so called 'Safety Power Outages'. I have about 40kWhrs worth of batteries. Some new some used. I'm slowly adding solar panels.

This is 'sort of' what I'm talking about: Hand Truck Solar System: 2.4kWh LiFePO4, 2.4kW Inverter, ATS, 1.4kW AC Charger, 1.8kW PV Input

I'm doing this except I'm using two of those inverter/chargers, three times that much battery, and I've rolled my own battery management system (BMS) using a PLC.

With your bigger electrical loads that's why I suggested the bigger inverter model.

That guy in the video is very a very sharp guy with years of experience.
He has a page that has some interesting stuff.His site. Dig around in it.

A new forum completely dedicated to this stuff set up by Will.[URL unfurl="true"]https://diysolarforum.com/[/url] I'm in there as "Keith C".

Those MPP inverters are not what I'd call 'bomb proof' but one very nice aspect is if you have problem or fry a board the company will actually mail you replacement boards. (The benefits of no stupid lawyers.)


Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Keith;
It sounds as if John may have switching transient issues as well as high supply voltages from time to time.
How will the front ends of those units stand up?
What mitigation can you suggest?
Are those units self protecting?
Will they accept grid overvoltages?

I live in rural PR and the power quality is pretty poor, lots of outages, varying voltages and switching transients from the POCO. The volts are typically too high (right now 130s each leg) and it jumps up and down a few volts abruptly.

"it jumps up and down a few volts abruptly" Often associated with switching transients.

[link ]Bill[/url]
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

Bill;
Those particular all-in-ones have a UPS mode which has trigger points like;
Low Loss Voltage = 95Vac
Low Loss Return Voltage = 100Vac
High Loss Voltage = 140Vac
High Loss Return Voltage = 135Vac
Maximum Voltage = 150Vac
42 to 63Hz without alarming.

It also states; "Output power derating:
When AC input voltage drops to 95V, the
output power will be derated."
And, the derating chart continues down to 65Vac input.

So I 'think' they'd be okay with his conditions. As soon as something excessive happens the inverter disconnects from the mains and continues running the loads on battery.

It might still make sense to include a line reactor in front of them as a moderator if things are really nasty.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Sounds good Keith.
Thanks for the explanation.

[link ]Bill[/url]
--------------------
"Why not the best?"
Jimmy Carter

 

[John2025]

On a somewhat related note, I was looking at using an SSR in front of these inverter style A/C units to speed up a shutdown on high voltage ( Carlo Gavazzi has a monitor that will respond in <200ms), but it doesnt look like the SSRs will reliably shut off when the load is to a rectifier. Is that really true? Any alternatives besides mechanical relays ( contactors)?

 

[John2025]

Sorry for the delayed response. I've been entertaining the neighbors by waiting for the local poco to come check the out-of-spec voltages. Needless to say, they never responded. So as an update: I've finally ordered an Outback inverter (8kw, split phase) and a Kilovault 7.5 kwh lithium battery. I'm going to run the grid power through the inverter to deliver clean power and use the battery for about a day's worth of backup when the power goes out. I can use my existing 5kw generator to charge the battery for longer outages. Earlier I bought a 5kw line reactor that I'm going to put on the input to the inverter with some more surge protection. I'll limit the inverter input to 4kw or so and use the battery to take up the slack when needed. My average usage is less than 1kw. Once I get my roof squared away ( previous owner thought concrete roof with zero pitch would work) I'll add solar panels and "cut the poco loose" as Keith would say. Thanks again, you guys are great!