Loading generator without a load bank. 1

[Cbrunner]

I don't have a load bank (or access to one). I need to load a generator engine (about 120HP) to make sure it's enclosure is not going to produce problems like overheating. I have read in many generator manuals about a method of shorting the generator coils and externally exciting the windings to drive generator capacity to 80% (to cause heat in the rotor/stator and dry windings). My hope is that this would be enough to load test this generator unit, as I doubt it would ever see more than 80% of it's rated capacity.

Has anyone ever tried this? Any thoughts/recommendations?

Thanks, Chris

 

[rbulsara]

NO. and do not do it! Even if you succeed it will not put any real load on the engine. It will be all reactive current.

Hint: Renting a load bank will cost a lot less than the cost of the generator.

Rafiq Bulsara

http://www.srengineersct.com

 

[davidbeach]

Lots of discussion in past threads, some here more in forum238, about how to build a temporary load bank. Look for posts by waross. But Rafiq is right, a rental load bank is the real way to go.

 

[waross]

You may short the generator windings and use a reduced field voltage to induce current in the generator windings. I have used this procedure to dry out a hurricane damaged generator.
BUT, This only loads the generator thermally. The load on the engine is practically nothing. The watts produced by 80% current times zero voltage (shorted leads) is not much. The engine may not even notice the load.
You need a load bank.
If you want to do it on the cheap, you will need the following.
A secure area to set up.
Three large plastic barrels (50 Gallons).
Six scrap leaf springs from a truck or older car. The length should be a little more than the depth of the barrels.
A sack of salt. 10 or 20 pounds. maybe more.
Cables capable of carrying the load current for the duration of the test and some terminal lugs.
Clamp on ammeter.
Lots of make-up water.
Step one, arrange the barrels in an area where it is possible to exclude unauthorized persons.
Step two, fill the barrels with water.
Step three Make a hole in one end of each leaf spring and bolt a terminal lug to the spring.
Put two leaf springs in each barrel, at opposite sides.
Connect the generator breaker to the the leaf springs. One neutral to each barrel and line conductors to the other three leaf springs.
Connect the generator for 120|208 Volts.
Start it up and turn it on. (At 120 Volts.)
Check the current and add salt until the current comes up to 80%. It is best to do this in rotation, bring each barrel current up 20 or 30 amps and go on to the next one. Repeat until all three barrels are drawing the current that you wish.
Check every hour or so and add water. The water will be boiling and you will need to add a lot.
Yes, I know. There are fewer and fewer jurisdictions where the old school solutions are acceptable.
By the way, outdoors is best. There will may be several hundred tons a day of water vapor produced.
Actually this may be border line for three barrels. You may need six, two barrels per phase.
OR, rent a load bank.
Good luck.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Cbrunner]

Thanks for the input everyone, I appreciate it.

Chris

 

[lectricwes]

Waross:

"outdoors is best"?? How about outdoors is essential!! Hydrogen and Oxygen gasses will be generated. If done indoors these gasses could collect and stratify and become dangerous around anything with an open flame or spark igniters.


cbrunner:

I've looked at a couple of your previous posts and found:

"Ok, I'm a hydraulic guy - and although I do a lot of control work my level of electrical "enginering" is quite limited"

Take the advice given ... rent a load bank.

Be safe.

 

[catserveng]

Some other field options if you can't readily get a load bank,

Industrial electric space heaters, have been working in the northern US and found for smaller gens these worked pretty good, and were available from local rental supply places.

Commercial electric water heaters, sounds funny but a small shop I know in Wisconsen used them for a time after their load bank died while waiting for a replacement.

Lighting loads, takes a lot of lights, but there may be some right where you are, like a big warehouse. One of the CAT dealers in South America used their part warehouse lights as a small load bank for a number of years.

You don't say where you at, maybe if you said, someone may have a more specific recommendation for you.

Like Waross, I've shorted generators many times to dry them after field cleaning. I've also made a lot of money over the years repairing/replacing generators where it was improperly done.

Waross gave you a really good field salt box idea, just keep everyone far away, if you're in the US, I'd say forget it unless you are in a really remote place due to liability concerns.

Hope that helps, Mike L.

 

[Cbrunner]

Thanks for the constructive ideas Mike - I have 1/2 a load bank now that I'm working on finishing, just don't have the funding to purchase the contactors right now.

The bank I'm finishing is made from commercial heater banks, 100kw of them.

I had read about the drying procedure, and not realizing it was the reactive current working on the generator - I thought it would load the engine. I had read about the salt box resistors elsewhere - but I think that's going to be a lot of work for what I need....

 

[nawao]

Why not parallel to the grid? You can export as much Kw as you need to load test your units and not need to spend money in equipments that you will use only once.

 

[davidbeach]

Undoubtedly quite expensive to make it possible to parallel to the grid and a single run of limited duration probably can't justify the cost of the interconnection process.

 

[waross]

I know of one country where it would take engineering studies, several years and then an act of congress. The process is not economically feasible for installations of less than several mega-Watts.
Other jurisdictions are less stringent but not cheap for the approvals and connection equipment.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[FreddyNurk]

In Australia, we've borrowed the engine manufacturer's load bank more than once, as well as borrowed the utility's load bank, and finally rented one through Aggreko.

Some were cheaper than others, but all were relatively easy to use, and quicker than trying to build your own.

Waross' suggestion is good, with the exception of all the safety legislation floating around. I don't know of any site around here where we would get away with that these days.