Hydro electric Generation

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Power Solutions

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Hi All,
Had a call for a 35 kW residential hydro electric generator that was not producing voltage.
Found a Prime Line Induction generator made by Marathon Electric. The previous owner had installed his own meter at the generator shack that is about 400 ft from the house. Looks like a poor connection that just kept getting worse till failure. We removed the meter base and installed a junction box. Got it up and running.

First glance and I almost walked away, lots of code issues, but I'm here to make the world a safer place and the customer said he would do what it takes to make it code compliant.

I do not view this as a separately derived system. Correct me if I'm wrong please. There is no ground between the generator and the house, only two hots and a neutral. And I believe there should be. Customer says he had documentation that said no grounding but cant find it. Am I off base here? Was probably installed in the 60-70s? So maybe a code revision since installation?

Thoughts?
 
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zbang

Senior Member
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Roughly 5346 miles from Earls Court
Is there a bonding jumper anywhere?

Since it's an induction generator, it has to be grid-tied and then would rely on the service's SBJ. Whether or not there's a separate EGC to the generator shed is a separate item.

Kind of sounds like this may not be the worst of the issues. Might want to give Marathon a call, too.
 
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SceneryDriver

Senior Member
Location
NJ
Occupation
Electrical and Automation Designer
Power Solutions said:
Hi All,
Had a call for a 35 kW residential hydro electric generator that was not producing voltage.
Found a Prime Line Induction generator made by Marathon Electric. The previous owner had installed his own meter at the generator shack that is about 400 ft from the house. Looks like a poor connection that just kept getting worse till failure. We removed the meter base and installed a junction box. Got it up and running.

First glance and I almost walked away, lots of code issues, but I'm here to make the world a safer place and the customer said he would do what it takes to make it code compliant.

I do not view this as a separately derived system. Correct me if I'm wrong please. There is no ground between the generator and the house, only two hots and a neutral. And I believe there should be. Customer says he had documentation that said no grounding but cant find it. Am I off base here? Was probably installed in the 60-70s? So maybe a code revision since installation?

Thoughts?
Click to expand...
Was conduit used as the EGC, and by now the conduit has rusted away due to age? Any evidence of ground rods at the generator? When it was installed (you stated 60s - 70s) code allowed for local ground rods bonded to the neutral at the remote structure that if there were no additional metallic paths between two buildings. Now, you have to pull an EGC to the remote structure, as well as drive the ground rods.

How is the generator controlled / prevented from motoring if water flow drops off?

This sounds like a cool project, even if there are code issues to be addressed. Please post some photos if you're able; very interesting.


SceneryDriver
 
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hillbilly1

Senior Member
Location
North Georgia mountains
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Owner/electrical contractor
Micro hydro is the way to go, payback is much quicker than solar and wind, though more limited to where it can be used.
Will be installing a system this spring for a friend of mine. His will not be grid tie, it will be the prime mover. If it works out well, I will be installing a smaller system at my house.
 
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Power Solutions

Member
So, no ground rods at the generator. Conduit, what little there is is PVC with 2/0 Alu 3 conductor URD exposed most of the 400 ft. I did look up the manufacture yesterday but did not have time to call.
 
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Power Solutions

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Question on the induction part. Since the generator is grid tied, how does it drop out if the utility has a loss of power. Wouldn't the generator keep feeding it's own field?
 
synchro

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Power Solutions said:
Question on the induction part. Since the generator is grid tied, how does it drop out if the utility has a loss of power. Wouldn't the generator keep feeding it's own field?
Click to expand...
For an induction generator to produce power there has to be "slip" between the rotor and the rotating magnetic field created by the current in the field windings, and the rotor has to be driven at a higher than synchronous rate relative to the connected power source. This relative motion is needed to induce currents in the shorted turns of the "squirrel cage" within the rotor in order to provide excitation for the rotor. So in an induction machine there needs to be a separate power source connected to the field windings that is asynchronous (i.e., at a non-harmonically related frequency) with the rotor's rotation rate in order for power to be created as a generator (RPM faster than synchronous) or consumed as a motor (RPM slower than synchronous).
 
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zbang

Senior Member
Location
Roughly 5346 miles from Earls Court
synchro said:
So in an induction machine there needs to be a separate power source connected to the field windings that is asynchronous (i.e., at a non-harmonically related frequency) with the rotor's rotation rate in order for power to be created as a generator (RPM faster than synchronous) or consumed as a motor (RPM slower than synchronous).
Click to expand...

That makes it sound like the machine needs to be separately excited, but by their nature induction generators self-excite; the only power source needed is the shaft rotation. (And, they don't have field windings, per se, anyway.) They do need to rotate faster than sync speed to get the slip to make the excitation (that's the whole point of "induction" here).

Marathon has a description of this at https://www.marathongenerators.com/generators/docs/manuals/SB317.pdf
 
synchro

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
From page 3 of the Marathon document under the heading Applications:

"An induction generator cannot generate electricity in a stand-alone mode."

"The kVA of capacitor correction applied should not exceed the no-load, or magnetizing kVA of the induction generator. Excessive capacitance has the potential to cause the generator to go into a self-exciting mode should the utility fail even momentarily. This self excited mode will typically have voltage and frequency deviations sufficient to cause damage to the generator, and perhaps even to the connected load."
 
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Power Solutions

Member
Ok, think I getting it.
Next question, how do we figure voltage drop due to distance since we are inputting power from both ends of the conductors? Or is it not a issue because of that?
 
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