Fire Pump Starting

[timm333]

I have to start a 100HP fire pump motor; the maximum allowed voltage drop at motor starting is 15%.

Can this be accomplished with a stand-by generator of 300kW? Thanks for your help.

 

[dpc]

Maybe. You'll need to do a motor starting calculation. Check with engine-generator manufacturers - they have software to help with this.



David Castor

http://www.cvoes.com

 

[davidbeach]

Given my drothers, I'd never put a fire pump on a generator where the fire pump was more than about 20% the size of the generator. When it's bigger than that you'll get better all around performance and satisfaction with an engine driven pump.

 

[waross]

You may direct connect the pump to the generator and start the generator with the pump online. This assumes a either dedicated generator or other loads may be connected once the generator and pump are up to speed.
You may have to feed the controls and the AVR power with a UPS. This starting method is the poor mans VFD and is the easiest on both the motor and the generator. One point to be aware of, should the fire pump be stopped for any reason, the generator will have to be stopped and restarted to restart the fire pump.
But back to your original question:
300 KW should start a 100 HP motor. A PMG option on the AVR will help hold the voltage up.
Why a 15% limit on voltage drop? Who has set this limit?
Will there be other loads on the gen-set?
With regards to David's suggestion of an engine driven pump;
I was involved in discussions concerning back-up power for a fire pump where a diesel engine was suggested. This was in an area exempt from most codes and operating procedures were seldom followed. A strong argument was made to use a back-up generator for both lighting and A/C in the offices and for the fire pump. Human nature and local conditions being what they were, a problem with the backup supply for lights and A/C would probably be fixed fairly soon, whereas a problem with an engine dedicated to a fire pump would probably NOT be fixed until after the next major fire.
There are good reasons to not run a diesel generator at 20% load or less, but if other loads are available so that the fire pump is part of a greater load the total load on the generator is over 50% or the rating, David's suggestion has merit.

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

 

[e1n2g3i4n5e6e7r8]

The Starting current of 100hp pump is in the order of 800Amps (assumed 400V system). When we convert 800Amps into power it works out to approximately 445KW, which is within the capacity of the generator set. But we need to confirm, the response time of generator is well within the starting time of the pump set. For this we need to have… 1 The starting curve of the pump which gives the current Vs time graph to get from the pump supplier, and… 2 The voltage response time from the generator set supplier. If the second is shorter than the first one, means you can straight away use this pump with this gen set, one other point to consider is the electrical load on the generator at the time of pump starting. If it is not more that 10KW electrical load on the generator at the time of pump starting, it is OK to use these configuration. Still I feel the engine driven pump could be the suitable solution.

 

[waross]

A 100 HP motor is about 100 KVA. Generally a three to one ratio will start a motor across the line. A 300 KVA generator will be 240 KW. With 300 KW you should be ok to start. You are 300kW/240kW = 125% of a dependable rule of thumb.
But I won't waste time on voltage drop until I know why you must limit the voltage drop to 15%. The best way to check this is with software from Caterpillar, Onan, F.G. Wilson or other manufacturer. The locked rotor KVA/HP may vary from an extreme low of about 1.6 KVA per HP for a code A motor to over 20 KVA per HP for a code U or V motor.
If you have to know the voltage drop to three significant figures you may want to check the locked rotor code letter.

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

 

[sspeare]

waross, I'm just trying to help: the start-up voltage drop has to be 15% or less, per the Fire Pump Standard (USA):

NFPA 20, 2010 edition: Article 9.4 "Voltage Drop."

There is an exception for bypass operation with a VFD, but if we're talking across-the-line, the original timm333 post is correct: voltage drop is limited to 15%.

timm333: you might consider a VFD. I was able to easily start a VFD-driven fire pump, 125 HP, using "only" a 235 KW diesel generator. When I was trying to size the generator with manufacturer's software, some of their selections were as high as 500 KW. I finally got together with a sales rep who worked with me to get the KW down, using an over-sized alternator and some other techniques. The job worked just fine. If you're interested, here is contact info for that sales rep:

Contact:
Scott Gagliardi
Alternative Power Systems
412-951-4080 (Pittsburgh, PA)
800-894-4455

Tell him Jeff Miller, P.E. of Upstreet Architects gave the referral.

 

[jraef]

I think a VFD or even a soft start is serious overkill for this, but I would go soft start on a Fire Pump before I'd go VFD. 3:1 has never failed me for X-Line even when I've had to stay at 10% VD on a centrifugal pump. It's just not that hard of a start.

Assuming it's a centrifugal and not a gear pump for chemical foam... Different story there.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[waross]

Do you have other critical loads on the generator or will it drive just the fire pump?

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

 

[timm333]

sspeare, is the VFD allowed for fire pump application?

 

[sspeare]

Yes, for several years variable speed drives have been allowed for fire pumps. The VFD job I referred to in my post was built around 2005 - 2006. Get the edition of NFPA 20 Fire Pumps that applies under your Bldg Code. The latest NFPA 20 is the 2010 edition. The VFD requirements for electric motor-driven fire pumps are in 10.10 of the 2010 edition of NFPA 20.

The VFD manufacturer I used was Master Controls; here is a link:

 

[timm333]

Thanks ... Another thing is that although the main load on this generator is a fire pump, but it also has some other loads like lighting and HVAC.

I want the automatic shedding of HVAC at the time of starting of fire pump. What kind of circuit breaker shall be required for this?

 

[sspeare]

The load shedding is not done with a breaker. I shed the non-motor loads during start-up with timing relays inside the automatic transfer switch (ATS). Your best bet is to call the sales rep I named in my previous post. He sells the ATS as well as the generator. He can help you work out the starting sequence; he knows all about this stuff. Even if he doesn't cover your territory, he can tell you who your rep is.

By the way, do you realize that an emergency generator is not necessarily required for an electric motor-driven fire pump? If the generator is absolutey required by the scope of work, or your plant standards, OK. But you might want to study 9.3 in the 2010 edition of NFPA 20. An emergency generator is not always required, believe it or not.

 

[jraef]

It should be mentioned that there are VERY SPECIFIC secions of the National Electric Code that pertain to Fire Pump installations, and there are VERY SPECIFIC and separate UL files for controllers used on Fire Pumps. You cannot use any just starter or VFD that you want on those, it must be specifically listed as a Fire Pump Controllers, such as the case of that Master Controls version.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376