Microhydro project, transmission line loss

[Rx7man]

Well, I've been trying to design a microhydro power project, and I contacted a supplier on Alibaba and we're a bit at odds about the recommended transmission voltage, I'd like to go with 480V and a transformer back down to 120/240V on the other end, their 'engineers' say this isn't necessary and that 240V is fine

I'm looking at a 10KW unit, transmission distance is about 500 meters, I'd like to go with 6ga wire at heaviest..

So I plugged my numbers into an online voltage loss calculatorHere's the 240V version, 51V drop (25%) at 40A, a loss of 1000W
https://www.calculator.net/voltage-...=500&distanceunit=meters&amperes=40&x=73&y=14

and here's the 480V version, 25V (5%) drop at 20A, a loss of 500W
https://www.calculator.net/voltage-...500&distanceunit=meters&amperes=20&x=121&y=25

Besides a crazy voltage instability under load, am I missing something or am I wrong? wouldn't transmitting at 480 or even 600V and having a transformer at the other end be FAR more cost and energy efficient? Most Teck cable has a 600V rating on it anyhow

 

[Baluncore]

For such a short run of 500m, buy thicker wire rather than buying high voltage transformers. Select the wire gauge to drop a maximum of 5% voltage over the run. You need to keep the cables cool to protect the insulation.
The cost of transformers and better insulation will be more than the increased cost of thicker cable.

 

[Rx7man]

For such a short run of 500m, buy thicker wire rather than buying high voltage transformers. Select the wire gauge to drop a maximum of 5% voltage over the run. You need to keep the cables cool to protect the insulation.
The cost of transformers and better insulation will be more than the increased cost of thicker cable.

I'd have to go to 1/0 ga wire to get even close (5.4%).. that's absolutely cost prohibitive
Most cable is already rated for 600V

 

[Rive]

Besides a crazy voltage instability under load, am I missing something or am I wrong?

Well, you missed the price tags and price calculations. How much would each variant cost? What is the value of the energy saved during the expected lifetime at the expected average load?
In short, is the transformer worth it or not? You did not even touch that question so far.

 

[anorlunda]

You say that you're at odds with the manufacturer. What does the manufacturer say?

You've been getting good advice here. Economic comparisons are the way to go. Keeping the drop less than 5% at all loads is a good guiding principle. You might find a suitable used transformer, but you need a pair of transformers, which are harder to find.

Do not forget to allow for non-unity power factor, and motor starting surges on the load end. Power losses are a function of total current, not just real current. Motor starting surges should not be a big problem with losses or temperature, but excessive voltage sag during start may cause the start to fail leading to a locked rotor and bad stuff. If you have multiple motors, then you need to consider multiple simultaneous starts upon energization of the system.

Will the cables be buried? If so, beware thermal overheating in summer and frost damage to the insulation in winter.

I saw a video recently of a guy in the Rocky Mountains who did his own microhydro. His major problem was the water freezing in winter. Is that a problem for you in BC?

Does the manufacturer supply the self-protection logic for the generator? Overcurrent; short-circuit, etc. How about voltage regulation and speed governor?

I have seen safety codes in the USA for overhead wires. Anything less than 20 feet above the ground is limited to 600V. You should try to find out what codes are applicable to your location. You may need a permit, a inspection, and a sign-off from a professional engineer. If you violate the codes, your insurance will be voided and the property could become unsalable in the future.

 

[jim hardy]

Since your fuel (gravity) is free, the 20% losses would seem at first glance to not matter.

However - if this system supplements not replaces utility power , your economic study should evaluate those losses at their replacement cost, ie the ten or twenty cents per kwh you pay the electric company.

old jim

 

[russ_watters]

Well, I've been trying to design a microhydro power project, and I contacted a supplier on Alibaba and we're a bit at odds about the recommended transmission voltage, I'd like to go with 480V and a transformer back down to 120/240V on the other end, their 'engineers' say this isn't necessary and that 240V is fine

I'm looking at a 10KW unit, transmission distance is about 500 meters...

My company standard for motor design is 1hp (.8kw) and up is 480V regardless of distance. I think that's overkill but 10kw is a lot more. So no, I don't think you're crazy, but the payback calculation is a good idea.

 

[anorlunda]

Here is the video I mentioned about preventing freezing.

 

[jim hardy]

So I plugged my numbers into an online voltage loss calculatorHere's the 240V version, 51V drop (25%) at 40A, a loss of 1000W
https://www.calculator.net/voltage-...=500&distanceunit=meters&amperes=40&x=73&y=14

and here's the 480V version, 25V (5%) drop at 20A, a loss of 500W
https://www.calculator.net/voltage-...500&distanceunit=meters&amperes=20&x=121&y=25

Besides a crazy voltage instability under load, am I missing something or am I wrong? wouldn't transmitting at 480 or even 600V and having a transformer at the other end be FAR more cost and energy efficient? Most Teck cable has a 600V rating on it anyhow

i don't think you're wrong.
#6 is 1.3 ohms/km so that'll be close to your round trip resistance,
Regulation would be around 1.3 volts drop per amp and at 240 volts and 40 amps that's awful..

There'll be some drop across your transformers too, a very few percent is typical .

so your 5% in the wires plus ~2.5% in each of two transformers gives 10% regulation

To beat that you'll need a voltage regulator with either "Remote Sensing" or "Line drop Compensation" feature.Consider #4 or #2 wire too.

 

[Rx7man]

Thanks for the replies

In the winter, we're good to about -7C with water flowing, much below that we'll shut the system down.. we do have grid power as well.

about thermal heating in the summer, if I have 1kw of power dissipation over 500 meters of wire, I can't see any significant temperature rise, there's so much surface area

I'd only need a transformer on the far end, on the generator side I'd get a unit that produces the voltage I want directly... On the far end, just a quick look on Mouser shows me this unit https://www.mouser.ca/ProductDetail...KmRn7rpQYPb9YzkicGpXv864J5cCSYf8KC62V9cwFnA==
It has lots of voltage options on both the primary and secondary side.. $2K CAD.. not too bad a price.. I'd find something used though for probably 1/4 of that.. I'm looking for used cabling too, I know where there's some that may be salvageable from an old forestry lookout, fair size gauge from what I'm told, price is right, leaves money for other parts of the project

About motor startup, we don't have any large motors, most loads will be resistive except for a walk-in cooler that is rated at 40A locked rotor, 8 amp running, 110v.Another question that the supplier doesn't seem to answer is how stable the frequency is.. turbine has 2 nozzles, manual control on them.. Now again, correct me if I'm wrong, but unless you have a constant load (perhaps a big heat sink), a variance in load will change the RPM of the turbine, thus your frequency.. Start to deviate too much and it's going to wreak havoc on inductive motors, etc.

 

[Rx7man]

I just found this transformer, $550, 600v to 120/240V, 10kva
https://www.phase-quest.com/product/auto-transformer-10kva-240v-600v/
If it reduces line loss from 1kw to 400w and provides much better voltage stability, and allows for smaller gauge transmission line, I think its a no-brainer.

 

[anorlunda]

I looked at that link. I do not see where it says 60 hz. For that much money, it's worth double checking.

The grounding of an autotransformer is different than a regular transformer. What difference does that make? ... I'm not sure, but it would be wise for you to check before laying out money. Once again, codes/permits/inspections become key.

about thermal heating in the summer, if I have 1kw of power dissipation over 500 meters of wire, I can't see any significant temperature rise, there's so much surface area

Heating is a problem only if you bury the cable.

Now again, correct me if I'm wrong, but unless you have a constant load (perhaps a big heat sink), a variance in load will change the RPM of the turbine, thus your frequency.. Start to deviate too much and it's going to wreak havoc on inductive motors, etc.

That's what a speed governor is meant to do. It should be set that a 100% change in load results in a 5% change in frequency. But as I said before, there are a number of other control and protection issues. I expect either a) the manufacturer bundled in an all-inclusive control and protection package bundled it, or b) it is totally up to you to do the control and protection. Before laying out money, I would demand to see photos of the equipment, photos of the nameplates, and the installation and operation manuals. Don't forget voltage regulation as @jim hardy mentioned.

When operating isolated, +- 5% frequency regulation and +- 10% voltage regulation, is a fair assumption. Your motors and other equipment are probably OK with that, but I would double check. (I once lived in Potsdam, NY. It often ran isolated. I was late for school several times because the frequency dipped 5% overnight and that made my alarm clock slow. The point is that a whole town can run at 5% underfrequency with only minor problems.)

I'm envious. I would love to be able to do my own micro hydro project.

 

[CWatters]

Sorry if I missed it but.. Is this a grid tied system? Does that put any constraints on the transmitted voltage?

 

[Rx7man]

Nothing around here is really up to code, we're well out in the sticks.. From the differences between the autotransformer and a 2 coil transformer I can see that you wouldn't want one input line to be a grounded neutral, you'd do a +300/-300V input and then ground the center tap of the autotransformer while on a 2 coil transformer the primary could be completely floating

I have one of those old alarm clocks that counted the AC cycles to keep time.

Let me add to your jealousy, I picked up this little Mitsubishi 2cyl diesel with a Stanford 3ph 120-480v generator for $1500 CAD. I bought it as a bare engine/generator and made the frame.. the engine had never been fired up, 0 hours!

For now I think we'll do it as an off-grid system, frequency control/phasing would make things really complicated... Perhaps if we did decide to grid-tie it (we'd have to see how much we get paid for the power too) we'd get an inverter system designed for grid compatibility.. that's a long ways off though.

This should have plenty of power for our needs though, the system should have about 190PSI and 150-500 L/m capacity depending on creek flow and irrigation.demands.

As it stands, I'm a little skeptical of dealing with this company, they don't seem to know their stuff that well

 

[Baluncore]

about thermal heating in the summer, if I have 1kw of power dissipation over 500 meters of wire, I can't see any significant temperature rise, there's so much surface area

Cross your fingers. Temperature rise damages insulation more than it raises resistance.
When are you going to identify if you will use wires supported on poles, or buried in a conduit?
If you use poles, will the wire be bare or insulated?

 

[Rx7man]

It will definitely be insulated and lightly buried

I'm not that great with thermal dissipation and temperature rise, but I can't see a power dissipation of 1w/m (500W over 500M) causing any trouble at all, let's consider summertime ground temps of 30C..

Something like this.. seems it's rated at 1kv
https://www.gescan.com/products/wire-cable/teck-6-3c-1kv-6245

I'll have to see what that salvage cable is rated at, it's over 1km of cable, so it either has high voltage capability or is of a heavy gauge.. there's snow on the ground now so I wouldn't be able to even find it, apparently it was about 1" diameter (with armor/shielding, etc)

 

[berkeman]

It will definitely be insulated and lightly buried

What kind of conduit do you plan on using?

 

[Rx7man]

What kind of conduit do you plan on using?

Teck cable, see previous post.. I don't know exactly what's available used yet so that may change things.

 

[anorlunda]

Since you said shallow burial, it will be above the frost line. Any micro cuts or abrasions in the sheathing will be subject to freeze/thaw cycles. Eventually, that could lead to insulation failure. That is what makes conduit critical. It is also important to treat the cable gently to prevent trauma before burial.

The conduit also provides waterproofing and it eases the cooling problem. Local codes might dictate armored cable to prevent penetration by a shovel, mower blade, or backhoe in the future.

You have not commented on codes/permits/inspections/sign-offs yet. Please don't tell us that you plan to ignore them.

 

[Rx7man]

In fact I do plan to ignore them.. however, see the link on the cable I posted, it's sheathed, armored and sealed, and designed for the application and direct burial, and I will stay within it's design parameters.

 

[berkeman]

designed for the application and direct burial,

I looked for the "direct burial" part, but didn't see it on the datasheet. I'll look again...

 

[berkeman]

Okay, it does look like I missed it before. Thanks.

I don't see an operating temperature range though (does it include freezing/thawing?).

 

[essenmein]

Not sure if its been mentioned, but how steady is the frequency of the generator? Is it directly mounted ie freq will vary with speed of turbine, or is there some power conversion in there to take the variable freq output of the generator and make 50/60Hz? This will impact the transformer.

I am also envious of your micro hydro, me being me, I'd probably *have* to try to implement some sort of HV DC transmission line, like 1kV or something. :P

 

[Rx7man]

I looked for the "direct burial" part, but didn't see it on the datasheet. I'll look again...

I missed page 2!

Cold temps to -40

 

[Rx7man]

Not sure if its been mentioned, but how steady is the frequency of the generator? Is it directly mounted ie freq will vary with speed of turbine, or is there some power conversion in there to take the variable freq output of the generator and make 50/60Hz? This will impact the transformer.

I am also envious of your micro hydro, me being me, I'd probably *have* to try to implement some sort of HV DC transmission line, like 1kV or something. :P

AFAIK the generator I was quoted doesn't have a mechanical governor, so yes, the frequency would vary with load, part of the reason I'm reluctant to deal with this company.. We have another inquiry/ RFQ out with a russian company that seems more helpful.. I certainly don't want to go adjust nozzles all the time, nor waste water by having a big heat sink to create an artificial load.

I wouldn't think about transmitting over DC, though I could consider rectifying and using a solid state frequency generator to get my AC back.. It actually sounds like it wouldn't be too hard if you want 240 RMS VAC, that's 340V P-P, or +/- 170V... could run the rail voltages a bit higher (even the mains in this case) to give you some allowance for voltage drops.. That's getting too fancy for now.

 

[anorlunda]

This has been a fun thread. I think many of us would like to do a micro hydro project.

However, the original question has already been answered. I would like to let the discussion go on and on. But having us guess at answers that should be the manufacturer's responsibility is silly. I also regret seeing that the OP plans to ignore local laws. Therefore, I will reluctantly close this thread.

We wish you good luck. I hope nobody gets injured or sued.