Dear Friends,

I have a fuel hydrant system, which driven by pumps 380VAC (3 phase) and 150 KW. The hydrant system is operated by pumps permutation (ON and OFF) to fulfill the pressure and flow demand.

Now, I have to modify the system so that the pump motors can be controlled more efficiently. For that I will use Variable Speed Drive.

Anyone can give any comment regarding the modification?

Anyone can give me suggestion which brand and type of the Variable Speed Drive that could fit in such a system and also sounds economics?

Thank You in advance =)

 

hi,

instead of vfds, you can try using a control valve and adjust the flow that way. this would help keep the pumps "on" all the time (turning them on/off all the time is terrible for the motors). control valve would be cheaper than buying vfds for each pump. you would also need a flowmeter to control the valve. turning the pumps on/off is very hard on the motors and requires frequent maintenance. having them on all the time will cost you a little on the electricity bill but would reflect huge cost savings on the maintainence side.

just make sure that you don't shut the valve completely while the pumps are still on. it will blow up the line. program the control valve to stay a minimum of 30% open at any given time.

hope that helps.
rahul.

 

For maintaning line pressure usually very small pumps are used in DOL motor control.

When the demand is high and the pressure drops low the bigger pumps come in and usually stopped manually since such pressure drop indicates some serious thing happened.
Though You can use any VSD check if local authorities permit such a change in your country. Also VFD can fail and a standby DOL on/off system should be retained and must be able to bypass the VFD. So be careful with your piping modifications.

Sekar

 

I have to take the VFD side in this application. Rahul is right about the across-the-line off/on/off transition being hard on motors. It's even harder on your pipes. That's exactly why most VFDs today come with an 'S-Curve' accel/decel profile, for pump applications. Never again will you have the hard hammering you get when starting the pump with a control valve, even if the valve is mostly closed (which, again, is hard on the pump). So you don't have to keep your pump running just to avoid the off/on/off transition. Plus, believe me, it's not just a little you're going to save on your electric bill, it's A LOT, especially if you're using this on a fire hydrant system which isn't being used 24/7/365.

VFDs are definitely the way to go. If you don't need variable pressure, just ON or OFF, look at a softstart but at large HPs, the price difference between a drive and a softstart can almost become negligible (although you wouldn't expect it to!).

If you didn't keep a spare VFD on the shelf, and you needed 24/7/365 availability, you could always put in a bypass contactor to run across the line if your drive went down but if you buy a good drive and take care of it, (e.g. don't leave the enclosure door open), you can expect very reliable performance.

You'll save on maintenance costs and you'll save tons on your electric bill going with a VFD over a control valve. Any electrical distributor worth doing business with will be able to do a energy cost comparison and ROI analysis before you even start.

Good luck!

Walter Weinzinger