Hello from iraq
here is my problem i have 22 generators ranging from 30 KVA to 135 KVA. i am starting to experiance wet stacking(not enough load on generator) i need a 75% load to run with out damaging the engines. all are not acheiving 75% some are reaching 50% and others 35%. what i would like to do is build a load bank so i could bring the generators closer to 75%. and be able to test the generator set before i put them online for service. the other problem i have is there is no radio shack in iraq so all parts must be local purchased (real pain in the @#$) i can not find a diagram of a load bank or parts list. if you could piont me in the right direction. if i had pitchure of the parts needed it would help make purchase easier. generator info 100KVA = 50hz at 400volts,152 amps, 3phase, the 135 and 114 KVA = 400volts at 50hz, unsure of amps, also 3phase, any help would be great, thanks to all you supporting us over hear.

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Robert B. Poland

 

Surely the answer here is to determine why the problem has arisen ?

How is regulation achieved?
Given that the engine speed is a function of frequency, How is the excitiation generated within the alternator, thus the amount of power output......

Trying to build a load of the size required aint going to be easy.......

 

Water is a good heat sink and electric hot water heater elements should be easy to acquire. Here in the USA, standard heater elements are 4500 watts at 220 volts. If you series two of these and then arrange 3 pairs in wye, you have about 24KW load in sufficient water. I tried cooling a 4KW heat pump with 250 gallons of water, it overheated in 20 minutes, so to run 50KW for 20 minutes you need 3200 gallons of water. I don't know how big a tank you would need to run 50KW continuously, it would depend on the surface area and whether there was a stirring pump.

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see my website: www.geocities.com/russlk

 

Radio Shack! HA :lol: For the amount of power dissipation, you won't find the resistors you need in an electronics store!!!

I agree with Russlk's idea of hot water/stove/oven elements, but also, perhaps, you will need a big radiator to cool the water. Maybe a few old car radiators (with electric fans) would work.

 

Hi Robert,

I am going to assume that the generators are operator-attended, yes ?
I assume they are switched in or out by the attendant, yes ?
A typical load bank for this type of thing is an electrode boiler.
Such a device is easily made, it is just what it sounds like,
electrodes in water. The water within it is usually pumped around a
system so that it shouldn't boil dry within the boiler.
It can be used as a load balancer where the load varies, and optimum
loading can be maintained on the running generators.

Clearly if the outgoing load falls sufficiently, one of the generators
would be taken off-line, the object is not to waste output unnecessarily.

The other advantage of pumping the boiler water around a system is
that this method leads to build up of deposits in the boiler if you
don't pump it round vigorously, and sampling of the system water is
necessary regularly. The chemicals used to dissolve and keep such
fur and deposits in solution will need regular topping up, and every
so often will need draining and fresh solution put in. I don't think
these deposits or the chemicals used are poisonous or aggressive,
no more than any hot water system.

Side comment:
Running diesel generators at low loads can cause excessive wear,
unlike a vehicle engine, their internal construction is 'optimised'
to run continuously at set speeds, and at near-maximum loading.
Running at low loads, but at the same set speeds, causes thrust
loading at different angles on the rotary component parts of the
machine. That doesn't normally matter much so long as its not for
very long, but where loading is unpredictable it is customary to
employ a 'dummy load' as a ballast or sink which can be easily
adjusted.

An electrode boiler with motorised electrode immersion fits this
need pretty well. Very often the heated water can also be put to
sensible use.

Hope this helps, Regards John

 

Indeed a difficult problem to solve.
Can't you swop the generators for better balancing? i.e. Use the 100kVA instead of the 135kVA generator and the 30kVA instead of the 40kVA.
You should try to at least load a generator to 30% of its rating to prevent wet stacking. Are these generators used for Standby only? If so then wet stacking shouldn't be a concern since they don't run for long periods. (OK maybe you guys have a lot of power failures?)
Second option would be to increase the combustion temperature of the engine. Throttle the Air intake slightly (ever noticed how the diesel engine overheats when the air filter is clogged?) If you could raise the temperature just a little bit (higher rated thermostat?) it would surely elimininate wet stacking.
Third option is to use 220V (1000W)heater elements mounted on a rack with a fan.
This works really well. You can use ordinary 10A circuit breakers to switch each(or pairs) element into circuit.

Chilli

 

This site:
http://www.load-bank.com/
may be of interest.

 

Hi Robert, Chilli, Chippie, Russlk, Phasor,

The switching of these in and out is not usually a simple matter.
It is not clear what type of breakers are being used, or if the
switching is automated or just the synch and closing is automated
or if the synch and closing is done by the operator.

If the equipment is older stuff thats being pressed into service
its probably all operator controlled, but if its newer stuff then
it could be almost all automatic.

The load can vary a lot quite quickly, winding some sort of dummy
load up and down to compensate is the normal way that such a
power station as described by Robert would operate.

The operator might have a console on which to instruct the levels
of load that different generators cut in or out,

Or if its more hands-on the operator would optimise the situation
as he sees fit, with manual switching. Switching generators in and
out requires practise and understanding of the synch and power
factor systems and controls. Doing it wrong could cause a lot of
damage, and maybe injury. Later systems would have safeguards.

Many larger 3ph breakers have operation counters attached because
they have to be serviced after a number of operations.

One advantage of an electrode type boiler used as a load is that
the breaker feeding it may mostly be left in the 'ON' position as
when the electrodes are wound up out of the water, the load is
removed.

If such a unit had to be made on-site, the construction could be
as simple as a winding assembly to raise and lower conductors on
guides into and out of a water container, suitable precautions as
to insulation.

Older breakers were not made for frequent or hourly use, newer ones
probably can cope with more frequent use, but it would not be
normal to shuffle generators around to optimise loading in this
situation. Those diesel units are intended for long running at
fairly steady loads at or near 85 - 90 per cent of their maximum.

Regards John

 

John, I agree with what you say but have you ever seen what happens when you run 50+ Amps through water(ideally salt water 'cause of resistance)?
There is a hell of a chemical process going on!! H2O will become Hydrogen!! Even worse is salt water. NaCl will break down in Sodium & Chloride! And that even at an AC Voltage! I've tried the wind up system myself and changed to resistance loading very quickly again. The other drawback with water is that the resistance tends to change according to water temperature.
He also mentioned that he wants to test the generators only before he put them online.
One other thing to remember is that Polandrb is in Iraq and that he cannot run down to the next hobby store.
Which makes me think...... If it is only for testing purpose... How long would you want to test a generator for the cylinders becomming cocked?(Wet Stacked)


Chilli

 

Hi Chilli,

Yes you're right, gasses are generated within such water heaters,
but so long as the water is pumped round it is simply allowed to
vent away at a suitable point. And also other chemicals and
calciums are formed, these would be kept in suspension using
additives, until the water is changed.

I was assuming that a power station is involved, but we don't
really know, these could be just a collection of trailers in a
hospital car park, loosely linked into the local grid.
In which case wire elements cooled by fans would be a sensible
choice.

I think there are two parts to this, the load balancing and the
testing of a generator after servicing, before handing over for
duty.

Its looking as though Robert isn't coming back, so we may
never know.

Cheers, John

 

settled then. :mrgreen:

 

Water heaters will work, yes, but to keep sediments and deposits to a minimum, use a riffle-box (not rifle). Looks kinda like a washboard. Pump the water over it and the crud settles out. Cheaper than filters.
Also use a sacrificial anode. Drop a bucket of used, empty brass casings in the water. They corrode away while your elements get to live another day.

__________________
<ckd>
"Chance favors the prepared mind."--Louis Pasteur (1822 - 1895)

 

Place I worked for had 4 generators to power a 48 story high rise building. For load banks they used heater elements and a fan to blow air from inside the generator room across the elements to outside. It not only worked as a load bank but doubled up as plant room ventilation. Look at HVAC for heating elements, they used to be used a lot for central plant heating, now days they tend to use smaller in duct heaters on floor for better control.