Diesel Generator - Testing Scenario

myaseen,

In answer to your questions: -

1) I've always been told by engineers and technicians alike, No more than 15min, allowing for the 5minute run-down cycle. So 10 minutes unloaded run + 5 minutes run-down.

2) Not knowing where in the world you are, I can't recommend a local brand.
Ideally you should have a Loadbank equivilent to 100% of the Generator Capacity, which has a controller to maintain a minimum load (ie set some where between 40% and 60% of generator capability). The load bank can then be manually cranked up to 100% for annual testing, without risk to the site it supports.

If you are in or near Australia, I use Sephco SmartLoad (www.sephco.com.au) Loadbanks. I've installed four (4) so far on Critical Sites and had no problems with the units or installation or compatibility with generators.

Regards,
Sapper

thanks for your feed back.

Although you may try to get your load bank sized for your generator capacity, please remember to load test the unit based on the ENGINES rated output and not the generator that is in most cases rated higher than the mover.

Tim,

Absolutely...I should probably be more specific, but when I refer to the rating, I'm refering to the rating of the Set as opposed to either the Prime Mover or the Alternator.

I have a good example at one of my smaller sites.

Prime Mover = 400kW
Alternator = 1100kVA

The Set Rating is 365kVA or 316kW as designed. The Alternator is oversized to cater for Harmonics and out of balance situations.

So Yes...you've got to have all the information and get a dummy load to match the rating for the Set, not one component or the other.

Regards,
Sapper

Good answer. In the USAF we were advised to conform to manufactures requirements thus we were not allowed to run UNLOADED for any amount of time.Each gen set was adapted to have a load bank.This made possible the application of a load as soon as the operating temperature was reached(usually within 3-5 minutes) at that point in time we applied the load banks resistive load for the duration of the 18 min. bi-monthly test. This reduced "wet stacking" to almost non existence.We also applied the load bank along with building load to approach the 75%,most manufacturers recommend.This run was accomplished once (1) a month,come rain, or sunshine.Our engine maintenance problems were reduce to almost NASA.All generators were backing up facilities and had auto transfer switches.We were getting 10% start up-transfer-re-transfer-shutdown.Prior to installing load banks and testing as proscribed, the start rate was around 90%.Yes load banks work.The annual run for 2 hrs at 100% is a great way to be assured the gen set will perform as designed.

No more than 15 minutes at no load is ok.

The standard test in the UK is 8 hours at full load followed by 1 hour at 10% overload then 1 hour at full. Tempertures and pressures should return to normal full load readings within 1 hour after the 10% overload hour has finished.

Depending on your situation, location, etc. you can easily make a load bank with a large tank filled with salt water solution and three phase rods suspended in souch a way that they may be lowered easily to increase load on the generator.

Certainly if you are in some large plant or somthing you will not concider this, but I've found myself in remote locations such as south Mexico and parts of South America where this was the only option on units up to 3000 kw.

The only draw back is the fact that depending upon the size of the tank in regards to the load being applied you will boil the solution rather quickly.

I have often wondered about just lowering the rods off the side of a dock

In the US Air Force we are required to have the generator match the building load, as near as possible. The requirement is it must be ( the building load ) 75% of the rated KW of the generator. Thus, a 100 KW generator may be assigned to a building whose total load is 75 KW.The use use a load bank ( portable) is used once a year to reach 100% of the gen set's rated KW.This gen set is ran for 2 hours at 100% load. The 10% overload someone spoke of is, a normal built in, factor of each gen set,to insure the motors,etc that start up will not cause the windings of the Generator to become over heated.It is a factor for only temporary use.It is not recommended to be sustained for any period of time. The engine ( prime mover ) may not be able to hold the safe temperatures of the coolant (use 50% antifreeze) due to ambient temps,placement of the generator and other factors.Closely monitor operating temps and pressures during near full load test runs.Attached ( built in ) load banks are used to bring the load up to 75%, when necessary.These can be on during the normal 1 hour test runs each month. We test all generators every 2 weeks.Once each month the building it is wired into is transferred,using an automatic transfer switch, to the generator.All meters are closely monitored and readings are recorded.If the load average is blow the 75% we schedule the generator to be replaced with one which will more closely match the requirements.In the meantime we use a load bank,consisting of resistive rods to attain the 75% load. Hope this helps you, We have virtually eliminated "wet stacking", and any emergency generator failures to start,due to lack of maintenance.

This is the first time I am writing on this blog, and I really like it.

I have a question about acceptance testing of DG Sets. In our case we run it on 100% load for 4 hours and then 110% load for 1 hour. However, some vendors contend that although it will run at this time successfully, but will shorten its life in the long run.

My question is if there is any international standard (IEC, BS, IEEE, etc) which stipulates or supports such testing? Or best pratices in major Telco or other operators, or manufacturer recommendations?

Any comments will be highly appreciated.

Putting things into layman's terms from the mechanical side of things you are making the engine do 10% more work (create 10% more heat) than it was originally intended to do for an extended period of time.

The effects largely depend on the machines auxiliary equipment like cooling system, ventilation and the like.

I have done these "full load +" tests and found bad oil coolers, etc that would have never been identified until it was too late otherwise. So with that said, these tests can be a good thing if properly administered and all points carefully monitored.