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Gen Size For A 100 Hp motor

Gen Size For A 100 Hp motor

Gen Size For A 100 Hp motor

(OP)
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

RE: Gen Size For A 100 Hp motor

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

RE: Gen Size For A 100 Hp motor

(OP)
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.  

RE: Gen Size For A 100 Hp motor

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

RE: Gen Size For A 100 Hp motor

(OP)
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.

RE: Gen Size For A 100 Hp motor

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.


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RE: Gen Size For A 100 Hp motor

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

RE: Gen Size For A 100 Hp motor

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 ?

 

RE: Gen Size For A 100 Hp motor

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

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

RE: Gen Size For A 100 Hp motor

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.

RE: Gen Size For A 100 Hp motor

(OP)
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.

RE: Gen Size For A 100 Hp motor

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

RE: Gen Size For A 100 Hp motor

(OP)
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?

RE: Gen Size For A 100 Hp motor

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

RE: Gen Size For A 100 Hp motor

(OP)
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.

RE: Gen Size For A 100 Hp motor

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

RE: Gen Size For A 100 Hp motor

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!
 

RE: Gen Size For A 100 Hp motor

(OP)
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.

RE: Gen Size For A 100 Hp motor

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

RE: Gen Size For A 100 Hp motor

mash,

An induction motor at standstill has a really poor power factor of maybe 0.2 - 0.3. It consumes a lot of reactive power which causes high current to flow from the generator, but doesn't transfer much energy into the load. The engine only provides active power, not reactive power, so the high current drawn during the start which is maybe 6 - 8 times normal running current doesn't equate to a 6 - 8x overload on the engine.

I wonder if the AVR is behaving correctly during this start? Knowing the type of governor would be helpful too.

Does the engine shut down during the DOL start or does a breaker trip?
  

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

RE: Gen Size For A 100 Hp motor

Hi Scotty;
You are correct, except that I would expect the real power overload on this combination to be near or over the capability of the gen set. I have a customer who regularly starts a motor of about 80HP. on a 275kW set. This is a 3550 RPM motor with a relatively high starting current ratio. The motor starts but the lights dim and the gen-set leans into the motor mounts and blows black smoke until the turbo spools up.
Note, the lights dim a little when the motor is started on the grid also.
A naturally aspirated engine would handle the block loading a little better.
I have had other experiences with gen sets where the protection had to be "softened up" before large motors could be started.
It is not just the real power and the reactive power. It is also natural aspiration versus turbos, AVRs and some voltage collapse versus PMG excitation, gen set rotational inertia, governor response to block loading, and protection settings.
On this size of set, I would expect a droop governor with 3% proportional band. No integral or derivative. The electronic governors that I have seen have similar performance to the mechanical governors but I haven't seen a wide enough variety of electronic governors to be an expert on them.
Running an electronic governed set in parallel with a mechanically governed set worked quite well when the mechanical set was warmed up. When the sets were cold at first start in the morning, we couldn't get the large motors online due to governor lag on the mechanically governed set. After 5 or 10 minutes of warm-up, both the electronic governor and the mechanical tracked well together and shared the load well. The lag of a cold governor would be an additional factor adding to speed and voltage drop (UFRO).

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

RE: Gen Size For A 100 Hp motor

I would expect the 275kva or 220kw genset to start the 100hp motor across the line.   Starting DOL I would expect to see the AVR life span shortened significantly.

Electronic governors are superior to mechanical or hydraulic
mechanical.  I can not say now many Woodwards we have tossed in the dumpster.

We just built a set using a  8.1 liter engine with 394hp rated at 275kw.  We installed a 360kw alternator without pmg.   This set will start a 150hp motor across the line. Then it starts a 75hp across the line which we did plan on soft starting.   Then several small motors are started.  This unit replaced a 350kw gen set with a 14 liter engine.  Our customer  saves significant  fuel consumption.

RE: Gen Size For A 100 Hp motor

"Starting DOL I would expect to see the AVR life span shortened significantly."

Really? Can you explain why? I admit most of the AVRs I work with are considerably larger than this entire genset but I am surprised that small ones don't have limiters and protection to prevent life-shortening damage during routine operation. I think I've only seen one AVR blow on a rental set and that was when we had it loaded right up across two lines as a 1-phase primary injection source. We kept testing going with a DC power supply hardwired to the field, then reported the fault afterwards. noevil
  

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

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