VFD and GFCI

[kwired]

210.8.....is all about RECEPTACLES.
Remove the receptacle and install disc/OCPD in place of the receptacle. NO gfci needed.

That works great with equipment that doesn't frequently get interchanged or even removed when not in use. We have a hard enough time keeping untrained hands out of control panels and other things for this sort of application no need to make them have to wire in such a piece of equipment that does get changed or removed on a regular basis.

 

[Ingenieur]

Which NEC are you reading, that is not in 2014, and in 2017 exception 2 is now exception 1, but is otherwise unchanged.

Another condition if it did apply is the receptacle not be readily accessible. How does one do that at the typical center pivot irrigation site? The cord ultimately ends up at equipment that sits right on the ground regardless of where you put the receptacle.

exception 2 nec 2011 as previously stated
are you saying the op's application is outdoors?

if not, which applies
bathrooms
kitchens
rooftops
outdoors
sinks
indoor wet locations, washdown, etc
locker rooms
garages for handheld portable tools, etc



apparently there is no solution

 

[kwired]

most people that understand process control use adjustable rate feed pumps
not vfd's

http://www.vaawwa.org/file/Committe... Ops Chemical Pump Types and Applications.pdf

I have worked in water/wastewater, pharma, process water treatment
can't seeing a vfd
if a larger pump is required it pumps into bypass metering or a rate control valve

a vfd will vary flow
as feed tank level drops so will suction head (overall head increases) as does flow rate

I also don't see much advantage to using a VFD on the type of pump being used here. traditional pumps used for this have mechanical methods of varying the flow rates, and they are only 1/2 hp pumps normally. They don't run all that many hours per year either so it isn't like they are going to save a lot of energy by slowing down the motor when all is said and done.

 

[Ingenieur]

I also don't see much advantage to using a VFD on the type of pump being used here. traditional pumps used for this have mechanical methods of varying the flow rates, and they are only 1/2 hp pumps normally. They don't run all that many hours per year either so it isn't like they are going to save a lot of energy by slowing down the motor when all is said and done.

should be no real energy difference since

pump hp = gpm x hd x 8.34 / (33000 x eff)
assuming solution's density ~ water
but the point is power ~ mass lifted
basically the same if speed is varied, mechanical rate is varied, or throttled by a valve

a vfd out in the weather sounds iffy

 

[ptonsparky]

Not saving money on energy but the application of chemicals to the field. No sense putting the same rate on if not needed. With GPS the system will change rate as needed.

 

[Ingenieur]

Not saving money on energy but the application of chemicals to the field. No sense putting the same rate on if not needed. With GPS the system will change rate as needed.

a gps based telemetry system
how will it know? soley based on location?
what will send the speed signal to the vfd?
gps on machine sends location to controller (how?) that converts that to a speed signal?
the same can be done by mechical means, a solenoid varies rate
all pointless without measured flow feedback
and converting a gps location to a 0-100% mapped signal sounds messy

if spending that much money on that elaborate of a system get 3 ph

sounds like an overly complicated solution to a non-issue
just use a position pot to index machine rotation
input into plc and map output

 

[ptonsparky]

a gps based telemetry system
how will it know? soley based on location?
what will send the speed signal to the vfd?
gps on machine sends location to controller (how?) that converts that to a speed signal?
the same can be done by mechical means, a solenoid varies rate
all pointless without measured flow feedback
and converting a gps location to a 0-100% mapped signal sounds messy

if spending that much money on that elaborate of a system get 3 ph

sounds like an overly complicated solution to a non-issue
just use a position pot to index machine rotation
input into plc and map output

You have not sat in the cab of a tractor, combine, or any other modern piece of farm equipment lately have you?

 

[Ingenieur]

You have not sat in the cab of a tractor, combine, or any other modern piece of farm equipment lately have you?

same tech as construction machinery doing earthwork cut/fill
load the gps derived plan file in and away it goes
some surface mining equipment is the same
large gps navigated euc's

but that is not what we are talking about

you'll need to translate gps into a signal map
the farmer will need to derive concentrations for the map
sounds like custom programming
basically feed rate varies with arc (or position, pretty much the same thing)

it would seem for a given crop in a given locale radius the soil type, etc, would be fairly homogenous and trimming the rate may not be worth the effort

 

[ptonsparky]

same tech as construction machinery doing earthwork cut/fill
load the gps derived plan file in and away it goes
some surface mining equipment is the same
large gps navigated euc's

but that is not what we are talking about

you'll need to translate gps into a signal map
the farmer will need to derive concentrations for the map
sounds like custom programming
basically feed rate varies with arc (or position, pretty much the same thing)

it would seem for a given crop in a given locale radius the soil type, etc, would be fairly homogenous and trimming the rate may not be worth the effort

The older pivots would require a sector based application rate, but someone obviously believes it is worth the effort. My job is to provide them with needed power within the limits of the NEC. I will try to guide them to 480v which is there now. 230 and below is another can of worms. Trying to talk myself out of work again.

 

[Cow]

The older pivots would require a sector based application rate, but someone obviously believes it is worth the effort. My job is to provide them with needed power within the limits of the NEC. I will try to guide them to 480v which is there now. 230 and below is another can of worms. Trying to talk myself out of work again.

I would do the same thing.

I would lean hard on the customer to lean hard on the supplier/manufacturer to provide 480v rated equipment. It is way too much nonsense to transform your pivot feed from 480v to 120v to 230v 3 phase. We had a similar deal years ago for a pressure washing setup for manure screens. The manufacturer designed a control cabinet based on 120v and used VFD's to get 230v 3 phase. We only had 480v available. They knew that. Too much useless equipment needed to get installed just so the manufacturer only had to build one type of "box" rather than offering different voltages/phase options. They eventually abandoned the system shortly after installation.

I would walk away or offer to replace the manufacturers 120v 1 phase-230v 3 phase VFD with a 480v 3 phase VFD as well as associated control wiring changes, if possible. And only if it was for a good customer.

 

[kwired]

Not saving money on energy but the application of chemicals to the field. No sense putting the same rate on if not needed. With GPS the system will change rate as needed.

Didn't think of that possibility, but makes some sense. Though what I see is you might have corn on one part of field and beans on another part and you more likely just want the system to stop before it crossed into another crop, or at least shut down the chemigation pump, as the other crop likely doesn't need same product applied to it. Even for applying fertilizer I can see different product (or blend of product) applied to a different crop.

 

[Ingenieur]

if all you need is on/off why not an adjustable limit switch

to use gps wouldn't you need a surveyed database?
and the will change with crop planting
a switch on a protactor just adjust the switch along a line of sight

 

[kwired]

if all you need is on/off why not an adjustable limit switch

to use gps wouldn't you need a surveyed database?
and the will change with crop planting
a switch on a protactor just adjust the switch along a line of sight

A lot of modern pivots have GPS or the ability to easily add it. It is used to indicate where the end of the system is located, everything else will be in an approximate straight line back to the pivot point. Not only can it be used for functions that need to know positioning, but often have wireless networking abilities as well and the operator(s) can manage things from their personal mobile devices. They can start, stop, change direction, change speed, possibly control accessory devices. With GPS their app can also tell them the current position of the system. Many also send a notification to the owners phone if operational status changes, even if it gets manually started. I have been out to work on something and had to start system to check operation of things - then owner calls me to ask if I was out there because it notified him it started.


I don't really have any experience wiring or using these, it is somewhat new and mostly handled by the equipment dealers, there are some out there that are retrofitting older systems with such controls though.

Switches at the pivot point have long been used to control different functions. They seem to fail frequently though. I have a feeling the GPS is more reliable, or at very least you get notification of failures when they happen instead of finding out what happened whenever you come back to check on things.

I don't know how complicated the apps are, but doubt any more complicated then entering data for GPS guidance for other operations such as planting.

tom mentioned being in modern farm equipment - tractors, combines, etc. They are not all that similar to what your grandparents might have used if they were farmers. If you are pulling a grain cart alongside a combine so it can unload while still going - they have the ability to follow the combine and stay at correct speed and maintain correct position in relation to the combine - tractor operator just sits there and lets it run itself. More experienced operator maybe doesn't get off track and lose grain on the ground very often, less experienced doesn't lose any either if they use the guidance system.

 

[ptonsparky]

I rent out 30 acres of dry land. I tried to download the PDF of The yields for this field but its too big. From what I can tell the combine records the yield for about every 10 feet of linear movement and plotted to a map with corresponding GPS? coordinates. Depending on the equipment this data can be used to apply fertilizer, seed planting density, etc. Put that same info to a pivot and it can now apply water and chemicals as needed to a particular area of the field.

 

[retirede]

I rent out 30 acres of dry land. I tried to download the PDF of The yields for this field but its too big. From what I can tell the combine records the yield for about every 10 feet of linear movement and plotted to a map with corresponding GPS? coordinates. Depending on the equipment this data can be used to apply fertilizer, seed planting density, etc. Put that same info to a pivot and it can now apply water and chemicals as needed to a particular area of the field.

This technology and its rate of advancement is quite impressive.

 

[kwired]

This technology and its rate of advancement is quite impressive.

People don't always know what goes on other then they see tractors, combines, and other equipment in the field. A lot of technology and precise data being used anymore.

My brother in law was GPS mapping fields about 15-20 years ago for a crop insurance company. They are no different on precision. Why pay out a claim for a loss on 160 acres if they map it out and can see you are only farming 155 acres of the plot? We were asking him questions at Thanksgiving dinner one time and he said he can easily map an area the size of the dining room table we were sitting at and take that out of the total area of the field being mapped, that was several years ago already.

They call it "precision agronomy" at colleges and technical schools.

Years ago even seed was purchased and applied by weight, anymore I believe they consider each seed more so then just a bulk weight, and the planting machines probably are very capable of tracking how many seeds were planted.

 

[STucker]

The specific motor they want to use is 230 volt 3Ph only. I’ve seen a photo of the nameplate. They will be using a VFD that steps the 120v up to 230 then to the VFD that gives them the 3Ph.

If I'm understanding this correctly, they want to use a VFD to act as a transformer, and then a second VFD to do phase conversion and drive the pump? I'm fresh out of school so there's a vast collection of things I have yet to see, but this seems overly complicated...and expensive. Just to pick some brains:

-Wouldn't it be much more cost effective to use a transformer for 120-230V?(Assuming there's a rated enclosure involved)
-If there's already 480V available, couldn't a single 480V drive set to output only 230V accomplish the same task?

 

[winnie]

If I understand the system, there are multiple requirements which, when combined, are mutually inconsistent. Something in the design or requirements needs to change to achieve the customer's desired functionality.

The requirements are:
1) use a VFD to control some chemical application
2) use a cord and plug connection to permit the system to be interchanged with other hardware or to other locations.
3) have the equipment operate at 110V at the receptacle
4) comply with the NEC, which brings in a GFCI requirement.

IMHO you can change one of the following:
1) You could use something other than a VFD to control the process. Ingenieur has been posting several concepts, but I doubt you want to get into re-engineering the application system.
2) You could do something to decrease the leakage current. The PWM switching frequency capacitively couples to the motor frame which causes _expected_ leakage current to flow. Decreasing the switching frequency would reduce this current. Insulating the motor frame is a possibility, but this would _create_ a shock hazard (limited and expected leakage current coupled to the egc is safe, an insulated frame blocking this current means that you get a shock when you touch the frame.) Perhaps filtering between the VFD and the motor could reduce the leakage current. Perhaps get the motor rewound with heavier internal insulation to reduce capacitance.
3) You could change the setup to remove the GFCI requirement, eg. using 480V cord and plug connections, with a 480V input VFD.
4) If this is really a low power system, perhaps you can operate at much _lower_ voltage, eg. a VFD with a 48V DC bus and motor rewound to match.
5) The _receptacle_ has a GFCI requirement, but does the equipment? Could a 120:240V step up transformer be made part of the equipment, with no GFCI on the _hard wired_ connection between the transformer secondary and the VFD?

Something has to give; the question is: what is the easiest/cheapest thing to change.

-Jon

 

[ptonsparky]

If I understand the system, there are multiple requirements which, when combined, are mutually inconsistent. Something in the design or requirements needs to change to achieve the customer's desired functionality.

The requirements are:
1) use a VFD to control some chemical application
2) use a cord and plug connection to permit the system to be interchanged with other hardware or to other locations.
3) have the equipment operate at 110V at the receptacle
4) comply with the NEC, which brings in a GFCI requirement.

IMHO you can change one of the following:
1) You could use something other than a VFD to control the process. Ingenieur has been posting several concepts, but I doubt you want to get into re-engineering the application system.
2) You could do something to decrease the leakage current. The PWM switching frequency capacitively couples to the motor frame which causes _expected_ leakage current to flow. Decreasing the switching frequency would reduce this current. Insulating the motor frame is a possibility, but this would _create_ a shock hazard (limited and expected leakage current coupled to the egc is safe, an insulated frame blocking this current means that you get a shock when you touch the frame.) Perhaps filtering between the VFD and the motor could reduce the leakage current. Perhaps get the motor rewound with heavier internal insulation to reduce capacitance.
3) You could change the setup to remove the GFCI requirement, eg. using 480V cord and plug connections, with a 480V input VFD.
4) If this is really a low power system, perhaps you can operate at much _lower_ voltage, eg. a VFD with a 48V DC bus and motor rewound to match.
5) The _receptacle_ has a GFCI requirement, but does the equipment? Could a 120:240V step up transformer be made part of the equipment, with no GFCI on the _hard wired_ connection between the transformer secondary and the VFD?

Something has to give; the question is: what is the easiest/cheapest thing to change.

-Jon

#3 is what I am suggesting.

The 120V VFD already has the conversion to 240v built into it. I don't know the details. I will in the next hour or so.

 

[ptonsparky]

The system they had here worked just fine with a GFCI in front of it. We ran it thru the whole range of pressures. While the VFD nameplate did say 16+amp input, we never went above 4.4 on my TRMS amp clamp.

I made the suggestion that they include the 480v step down in their equipment. It is not a fly by night operation and they are based in California for whatever that means.