Gen Size For A 100 Hp motor 1

[mash98]

We have a 275kva stand by generator and it doesn't start a 100hp pump motor having DOL starter.Can I connect the motor directly to the generator and than start it? as I have read somewhere that this method can be successful if any member have an experience of such starting kindly let me know.

Thanks

 

[itsmoked]

Yes you can usually do the generator starting method. I'm assuming the generator is a diesel or gas generator not some other variety?

The alternative would be a soft starter.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[mash98]

Yes it is a diesel generator.You mean I can try the above procedure where I connect the motor directly to the gen set and by starting the generator it should successfully start the motor to it full speed without being tripped.Just to remind you when I intially started this motor when there was no load on the gen set and I switched the motor contactor on the genset tripped and failed to start it.I would like to know if someone really used this method successfully when the normal starting method fail i.e where we connect the motor on gen set when it speed and voltage reached stability.I would appreciate if somebody could confirm that this method of starting simulate the starting curve when we use VFD for such motor starting.

 

[itsmoked]

The generator starting method certainly has less control than a VFD.

The issue you are having with your generator/motor is that the motor is trying to draw about 600kVA when you DOL. Your generator protection is being triggered.

A soft starter reduces current by effectively reducing the starting voltage dramatically so the motor's starting current is reduced also.

By starting your generator with the motor contactor closed you are doing something similar to a VFD. You are ramping the voltage and frequency slowly. This definitely limits the starting current.

Another alternative you might try first. If this is a centrifugal pump; Restrict its outlet for the start. This greatly reduces the load on the motor. Do not leave the pump restricted for very long or you will overheat the seals.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

If you want further reading on a substantially larger generator/motor start using the same method you can wade thru this recent thread:
thread237-220645

Keith Cress
kcress -

http://www.flaminsystems.com

 

[mash98]

Thanks I have got most of things cleared by visiting the thread itsmoked suggested.It is an amazing forum on entire net where we get the solutions in shortest possible time.

 

[jraef]

Keep in mind that in order to accomplish the "generator starting" method, you must disable some of the protection features of the generator. Some smaller systems such as yours that have integrated solid state protection may not allow you access at that level. And even if you can and something goes wrong, the generator manufacturer is going to walk away from you: you are going to be on your own with that.

A soft starter is still probably a better idea. Cheap compared to replacing that generator.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[waross]

Before I spent any money I would check the instantaneous settings on the breaker that is tripping. When you allow for efficiency and power factor, 100 Hp is close to 100 KVA.
A 275 KVA set should start a 100 KVA or 100 Hp motor.

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

 

[edison123]

Waross is right. A 275 KVA DG shouldn't trip on starting a 100 HP motor even on DOL. I regularly start a 60 HP motor on a 125 KVA DG.

Is your DG tripping on overcurrent or undervoltage ?

 

[waross]

You probably have an inappropriate setting somewhere in your protection scheme.

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

 

[burnt2x]

I second Waross on this! I've tried running a 100 hp pump DOL from a 250kVA genset. Some tweaks on genset/diesel drive should solve the problem.

 

[mash98]

thanks for all I am off for a couple of days and as soon as I go back to my plant I will check all the settings.

 

[rmw]

Not withstanding the excellent electrical advice already given regarding KVA etc, are you trying to start the pump loaded? Is there anyway to start the pump unloaded by shutting off the discharge valve during the start? If you are trying to start the pump in a wide open flow situation, the HP that the pump is requiring could be way out past the OL point of the motor. Look at your pump curve to find out. Notice that the unloaded HP should not be anywhere near your full 100 HP if that is the design point.

If you do that and it still won't start the motor, you have other problems that the EE's need to advise on.

rmw

 

[mash98]

Dear guys I have finally checked this wonderful method with succesful results the following are the data which I obtained during the process.At DOL when the motor is at minimum load the peak current obtianed was 675 amperes and generator engine tripped.And with our Manipulated procedure the peak current recorded was 170 ampere I also checked the intial voltage appeared at genset output which were 100 volts I could not check the frequency but assume it would be around 12 hz as the rated voltage and frequency are 400 and 50Hz respectively.Now I would like to have your comments about my below question.

- If this starting method would have any negative/positve effect on the health of our engine( both long term or short terms) specially with the above provided reduced starting voltage and current?

 

[itsmoked]

Glad it's working for you. Sweet!

A lot of an internal combustion engine's wear occurs during starting when the oil films are not properly set up, etc.

If you are starting and stopping your generator a bunch of times a day, you will be shortening its life due to the many starts.

I'd probably make sure your generator was warmed up fully by starting and running it for a while. Then drag it down to idle close the breaker and bring it back up again.

However waross may have a different take on it.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[mash98]

though I did not know when comencing the procedure but fortuntly did wrm tht up by trying on dol first itsmoked thkx for dvising.I would like more dvice s some mechnicl engineer in my plnt is very pprehensive.You guys would hve by now notice mny spelling mistkes it is becuse now my key bord is not typing prticulr letter.

 

[waross]

I hate it when the keyboard does that.
Engine; you're OK Keith. If this is a standby situation and you must start and go without first warming up the set as Keith suggests then I strongly suggest installing block heaters set to keep the engine at 70 or 80 degrees F. If the engine does not have an oil cooler, investigate the possibility of retrofitting one. With the coolant heater keeping the coolant warm, the oil cooler will help to warm the oil on the initial cold start.
If you can't you can't. Life isn't perfect!
Many standby sets have to start cold or cool and imediately withstand an overload. After the initial abuse the set may run at a light load that is below the recommended load for the engine.
Bottom line: A diesel engine on a standby set has a hard life. We do the best we can and then accept the results.
I'm glad to hear that your motor is starting.
For your mechanical guy; Ramping up is probably a lot easier on the engine than DOL starting. When ramping up, I assume that the engine is able to accelerate up to speed. When going DOL I would expect the sudden overload on the engine to pull down the RPMs briefly before the engine is able to recover. Ramp-up is a lot easier on the engine. (It must be. Ramp-up will start the motor and DOL won't!!)

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

 

[ScottyUK]

Don't forget DOL starts draw a lot of current but relatively little power is drawn from the engine. The mechanical step load isn't as severe as the ammeter makes it look. I'm surprised that the 'generator engine tripped' - what identified it as an engine trip rather than an electrical trip?


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[mash98]

thnks guys for the grt dvices but I just could not get wht scotty sid more current but reltively little power
while the sme dol errticly reduced the engine rpm,overlood the genset und unble to strt the motor.

Still hving the keybord problem probbly will hve the new one tomorrow sorry for inconvinience guys.

 

[waross]

I would expect that starting that size motor on that size genset would drag down the RPMs as well as dim the lights. It is a combination of load and governor response time that slows the engine. The large KVA draw dims the lights.
The UFRO (under frequency roll off) feature of the AVR (automatic voltage regulator) will also contribute to the light dimming. As the frequency decreases the UFRO reduces the voltage in an attempt to reduce the kW load and allow the engine to recover. The UFRO also protects inductive components by preventing saturation at lower frequencies and prevents AVR burnout from saturation and over load at lower frequencies.

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