Diesel Generator Starting Time

To supply vital loads during a power break, use an Uninterruptible Power Supply [UPS] between the mains and the vital load.

It depends on how fast your crystal ball is....

(I'm getting sleepy and will try to think better tomorrow.)

The ideal time for it to start is just before the power failure. As this isn't possible to predict you have to use your judgement or as PWS suggests use a UPS to make up the shortfall.

You have the details, we don't! It's down to your judgment.

If you have critical systems that require constant power, PWS is correct, you need a UPS....Sized according to those critical systems on a separate distribution circuit...

http://www.apc.com/products/category.cfm?id=13

Agreed with TonyS....the best time would be the time slot between UPS can support the load. In big systems only critical load is supplied by UPS rest of the load will be fed by Diesel Gen only. Generally, Diesel Gen should start feeding load within 6-8 sec.(what we did with our system) because even if we consider the outdoor lighting. Refinery, oil and gas stations don't want to go for blackout for long and it is practical to resume power back as soon as possible.

If your system requires no power failure , them you want to use UPS system . UPS will give back up for some time . Diesel generator will start as time set by you . And will be restored by DG. So no power failure. NORMAL time to start is 3 sec in auto mode.

An interruption of power can be very short or sometimes very long. Instantaneous interruption lasts only a few cycles before the utility breaker recloses. A delayed reclosure will take maybe 30 seconds depending on the utility setting. There may be more that one delayed reclosure. You need to wait until these events have completed their cycle and then have the generator pickup the load. I would check with the utility to see how long they suggest. However, depending where you are, they may not have a clue.

Unfortunately, UPS backups can not handle heavy loads. Inductive loads can require 700% more starting current than operating. Inductive motors can be found in many types of equipment: machinery, pumps, compressors..etc. It would be necessary to know for what type of facility the emergency power is needed, because what might be considered "vital" to a hospital is different than one that houses computer equipment.

The key requirement for any emergency diesel system is first to insure that is has a sufficient rating to supply all of the loads that it will be required to power. Even with sufficient power it is necessary to shed and sequence the load in order to maintain frequency and voltage. The time the system must be able to accept full load may be controlled by government agency or an industry standard (or both). Three seconds is pretty darn quick, but not unachievable.

It all depends on the nature of your load. Some loads could accept few seconds others you have to think of a split of a second, in which you may have to apply a no-break system such as in airports, highly sensitive control centers etc .

it takes around 4-5 sec to crank the DG set via starter motor

After, 13-15 sec when normal voltage of DG set develops, it gets closed on dead bus.

what is cranking actually? Is it starting the diesel generator from zero conditions?

regards,

sks

Why are you asking these questions?

You clearly don't have a clue what you're asking about!

Per NEC, it is not more than 10 seconds. Here is the extract from NEC Article 700.12

"Current supply shall be such that, in the event of failure of the normal supply to, or within, the building or group of buildings concerned, emergency lighting, emergency power, or both shall be available within the time required for the application but not to exceed 10 seconds".

- MS

I know that a substation breaker can go thru several timed openings. So when do you start counting to 10. Is it after the last opening of the breaker?

What do you mean by "start up time"?. Is it time delay set in starting timer or total time elapsed from the moment failure occurred to the moment of supply return from generator?.

well, i am unaware about the starting time set up in the timer, would be grateful if you could elaborate........i mean - time from city supply is off to the time the diesel generator supply comes to a load.

regards,

sks

Sounds like a project for school.. Yes? I suggest you read the DG manufacturers handbook! There are differences in every DG you can obtain.

Small 4 cylinder 75Kva DG start in several seconds whereas large V16 RR engines takes forever to start, then you have to wait for the autosync to work, then the load shedding system to kick in, then the autobreakers to close.... an eternity if you are in darkness.

Does this project include autostart? You haven't actually mentioned it! If you don't have autostart, then the time to restore power is directly proportional to the speed the Man can run to the emergency generator house to switch it on!

well........i saw this in my earlier work, when the supply was essential........but they mentioned 3s to 4s for emergency supply for DG, as there was UPS as well.......which could serve supply to the ICU patients.........!!

thanks anyway.......

ICU: Intensive Care Unit, a VERY important place in ANY hospital that and operating theatres.

Pity you had not mentioned this before!

In the UK, ICU and Cat 1 theatres have a dedicated power supply, backed up with UPS for ventilators, Heart monitors and all manner of equipment designed to keep the patient alive while undergoing surgery or recovering in ICU. That in itself is not enough to run either department for long, only while the DG is kicking in. Theatres have their own dedicated DG which will because of its size, that is, less than 250Kva.. will start and supply power within a few seconds, supplying essential/critical equipment first, then ancillary equipment second.

ICU in many cases is connected to the theatre DG, or they have a larger UPS for essential/critical equipment and for general power, they will have to wait until the main DG starts, then that only supplies services that have been designated a priority during a power cut.

As for times of starting and restoring power, you still must refer to the instruction book, or test it yourself!

However.. CAUTION. if you are in a hospital environment, and you are thinking of a test, do it when there are no operations.. as I don't think you'll get a thank you from the surgeons if suddenly they are plunged into darkness while removing someone gall bladder!

You must have ATS Panel in place -Automatic Transfer Switch? It would take 30 seconds or less to automatic start the generator and provide power back on.....

[Speaking from Experience :)]

Standby Diesel Generator (DG) sets get started automatically in case of failure of main (grid) power with the help of automatic mains failure (AMF) panel in case of sustained under voltage or no voltage. DG set may start within a period of 6 to 8 sec but its circuit breaker will be closed only when it has attained full voltage. Normally the scheme takes care of maximum three consecutive crankings through starter motors, powered by battery. If it fails to start even after three attempts, the starting process is aborted and it requires manual intervention for trouble shooting.

DG power is fed to emergency distribution board for essential loads. The emergency distribution board receives power from two sources i.e grid power and DG power through change over contactor/ circuit breaker. Capacity of DG set is selected on the basis of maximum demand of essential loads, taking into consideration the starting KVA of the largest motor with all other loads including emergency ligting being connected.

For critical loads like automation equipment, computers, life saving equipment and associated lighting where uninterrupted power is required, UPS of adequate capacity and backup time should be used. If long duration power failure is anticipated, UPS may also be fed from emergency DB.