why does generator on hydro turbine produce less current?

[werner]

Hi,

our brushless GEN put out about 6 kW, 3-phase.

Then I lost the loads and system went from 1500 RPM to about 3000, apparently one phase broke off at GEN, the electr. regulator at some point did no longer pass current to loads.
Unfortunately my mechanical safety did not respond.
It burnt up the voltage regulator (likely only the over-voltage fuse).

I had a spare voltage regulator, so put all back together, including re-did all the wiring. Test runs showed that all phases worked well, voltage regulated ok.

So I put system back to full and it seems to run and regulate well.

The main difference is that now I measure only 5.2 kW.

I checked:
- water system, jet are all ok
- GEN turns freely and runs barely warm (capacity is 1o kW)
- the electronic load regulator also is barely warm, as before

As I cannot detect any heat, I wonder if it is possibly that there can be loss due to some type of 'friction' without causing heat? say electromagnetically?
I cannot find where the 800 watts are being lost. Going into winter, it does make a difference.

I have not posted here for a while, so not sure how I know if you answer. If you don't mind, send also to dukeflu(at)gmail.com

regards,

Werner

[Opera House]

On the armature there is a bridge rectifier that rectifies the exciter current.  I know from another engineering forum that they experience problems with these.  It could have been damaged from excessive current One of the diodes could have opened or shorted.  That could create the problems you are seeing.   From experience I know that these diodes are not easy to get at or test.   

[werner]

OperaHouse said:
On the armature there is a bridge rectifier that rectifies the exciter current.  I know from another engineering forum that they experience problems with these.  It could have been damaged from excessive current One of the diodes could have opened or shorted.  That could create the problems you are seeing.   From experience I know that these diodes are not easy to get at or test.

Thanks, I will follow this lead.

Still wonder: how are 800 watts burnt off?  with no apparent heat production?

Werner

[bob g]

are you certain you are still spinning the generator at the same speed that it ran at prior to the failure?

is the output voltage and hz still the same as before?

some drop in hz because of reduction in speed might explain a loss of capacity?

also the generator will only deliver the amount of watts that the load requires, is the load the same as before?
how do you know if it is the same?

any more info? is this a 50hz, 60hz AC machine, from your post i assume a 50 hz at 1500rpm?

is the strainer on the upper end of the penstock, feedwater intake clear? if it is partially clogged with tree's or
a beaver dam, maybe that would limit the output power.

basically i would start at the top and work down a list, making sure you have a clear intake, clear runner/penstock
and clear jets, turbine undamaged, governor bypass working properly, and then look to see if there is a load difference
before to after the failure.

800watts will make a lot of heat, and you don't seem to be experiencing that, you have 5200 instead of 6000watts
i would expect far less if you were lacking a phase, or a phase fault. a field diode i would also expect a much lower output
if any at all if one was faulty.

thats all i got

bob g

[zap]

basically i would start at the top and work down a list, making sure you have a clear intake, clear runner/penstock
and clear jets, turbine undamaged, governor bypass working properly, and then look to see if there is a load difference
before to after the failure.

800watts will make a lot of heat, and you don't seem to be experiencing that, you have 5200 instead of 6000watts
i would expect far less if you were lacking a phase, or a phase fault. a field diode i would also expect a much lower output
if any at all if one was faulty.
bob g

Since a rewind was performed, along with a change of regulator, I would look at that also.

[werner]

Hi Bob,

>are you certain you are still spinning the generator at the same speed that it ran at prior to the failure?
   that's certain, indicated by frequency sensor at axle

>is the output voltage and hz still the same as before?
   also adjusted and confirmed to values as before

>some drop in hz because of reduction in speed might explain a loss of capacity?
   the hydro-side is fix, I adjust Hz (and thus GEN speed) via load controller

>also the generator will only deliver the amount of watts that the load requires, is the load the same as before?
   the electronic load controller monitors Hz and uses excess resistances to burn all necessary to remain at selected Hz

>how do you know if it is the same?
   if the load controller keeps the GEN at 50 Hz, it must burn all the current. At this balanced state, I measure V and A on the 3 phases coming from GEN. These values are not as before, i.e. 800 w less.

>any more info? is this a 50hz, 60hz AC machine, from your post i assume a 50 hz at 1500rpm?
   The GEN can be used 50-60Hz, I have set the controller to keep it at 50, ie 1500 rpm

>is the strainer on the upper end of the penstock, feedwater intake clear? if it is partially clogged with tree's or a beaver dam, maybe that would limit the output power.
   correct, but that I have checked and is ok. Intake and jet are ok, I cannot check insides of 400 yrds of 4 inch pipe, but I cannot imagine that s.t. got into pipe and partially clog 4 inch space, when jet is ½ inch. The first intake rack is with 1/2 inch spaces, second rack with even less.

>basically, turbine undamaged, governor bypass working properly,
   turbine fine, there is no gov bypass

>800watts will make a lot of heat,
   that's is still the mystery

[werner]

>Since a rewind was performed, along with a change of regulator, I would look at that also.

What I meant by "including re-did all the wiring"  was

re-connecting broken phase cable
soldering all other cables which had only crimped ends (in GEN voltage regulator box)

So now all cable have crimped terminals which are also soldered.

[Opera House]

How do you know you lost 800 watts?  If you quoted a number like 6130 watts I would have an idea to what accuracy the original  value was made to.  Is the voltage exactly the same as before?  It is probably not that you are wasting it, but at the limits of what you can generate given the field magnetization.

[werner]

I made measurements across each phase as they come from the GEN. These measurements are not highly accurate.

Initial reading:
229 V       10-11 A
236 V       8 A
222 V       7.5 A
This is about 6072 watts

another one done now again:
220 V       9.5 A
231 V       6.3 A
221 V       8 A
about 5313 w

So the difference now was 700+ watts.
Overall, voltages are adjusted lower now, but increasing them is then reflected in lower A reading.
The difference before/after of power seems large enough that it more than just inaccuracy of measuring.

[bob g]

what is the load?

is it possible the load has changed?

if the load is the same, is it possible some element of the load has been altered
from the overspeed and presumably overvoltage from the failure?

a generator can make voltage, and a AVR can provide for stable operation, but
the load will dictate the amperage in the circuit.

if your hz is the same, the voltage nearly the same, then the amps should be the same "if" the
load is exactly the same.

700watts loss without a sign of heating in the head tells me to start looking at the load

bob g

[Flux]

Far too little information on your method of loading to form any conclusion. You seem to be running on constant load so you may have some form of load regulator that maintains constant load on the turbine and dumps it or sends it to your load as required.

You say that increasing volts on the regulator reduces current so it seems as though you are running at the limit of your mechanical power input from the turbine. If there is no more input power this will happen, you will trade volts for amps to maintain constant watts.

Either something has happened to reduce available input power such as a change in water level or slipping belts or something or your electrical efficiency has dropped.

Finding a small loss in electrical efficiency may not be as easy as you think, bad connections or similar will show very obviously as heat but a faulty diode supplying the field system would increase field loss and you wouldn't be aware of it. You may not even be able to measure field current directly to see if it has changed. If all else fails you may have to take meter readings of each diode individually and see if you have an open circuit one or a shorted one. For your small error I would be more inclined to suspect an open circuit one, usually a shorted diode in a field bridge knocks the performance very obviously.

There may be other factors on the load side that I can't even guess at with such limited knowledge of the scheme.

Flux

[werner]

Hi Flux,

in the initial description I mentioned “electronic load regulator” which I understand is the term of just what you guessed:

-constant load by having ‘users' and dump loads (heater resistances) with regulator monitoring Hz
-it runs thus on max mechanical power, and constant watts, with proportional V/A changes

As the mechanical side seems to be as always (same water column/flow, direct pelton), I find your next comments most interesting:

   ... electrical efficiency ... but a faulty diode supplying the field system would increase field
    loss and you wouldn't be aware of it.

   You may not even be able to measure field current directly to see if it has changed.

From this I gather that it is possible to loose current by “field loss” which I could imagine as s.t. like a magnetic break (?), since the mechanical power is at max.

And that I should test the diodes.

thanks.
Werner

[thirteen]

Not sure about your setup but did the rebuild by chance change the position of where your nozzles hit your wheel. Or maybe possible wearing on your wheel. Just as idea to look at. You also said you rewired everything maybe a different sized wire.

[ghurd]

Following 13s line of thought about physical issues at the turbine,
possibly the electronics or electrical or feed pipe are compromised?

The failure resulted in, or was possibly caused by, a burned up regulator, presumably from excess current?

The broken phase cable could have possibly been a result of, or caused, the failure.

Possibly the coils are partially shorted dues to damaged insulation or wire.
I can imagine how a minor defect would effect the output without much increase in temperatures.

6000W is a lot of power.
700W is not a great deal of loss, percentage wise.

When was the last time the total actual output was measured?
Could it be the pipe is contaminated with barnacles/algae/slimy growing stuff or a twig at an elbow or some other such restrictions?
Could it be the nozzles or Pelton cups are worn?
1000W of loss in those areas would not result in a noticeable temperature increase anywhere.

When you find the answer, please let us know.
G-