VFD retofitting for pumps 5

[Sam993]

I would like to know how difficult is it to replace the induction motor for an existing pump with VFD motor. what are the things which we have to change. Regards,

 

[Valvecrazy]

300 HP is a large pump for me. I don't know much about anything larger. However, for the size of pumps and motors I deal with I like the old Auto Transformer soft starts instead of the electronic ones. Sure it saves on the demand charge to use a soft start but, you don't have to use the same system to control the pump once it is up and running. Dealing mostly with submersibles, the auto transformer style gets it up to the minimum speed quicker which is needed for the kingsbury type thrust bearings.

I have almost no problems with the auto transformer soft starters. No electronics, just a couple relays, transformers, and a timer. I can't say that about the VSD's and electronic soft starters I have used.

 

[itsmoked]

Why would you have a problem with an electronic Soft Starter?

Soft Starters cost less than Auto Transformers and provide a bunch of other features too!(like safety monitoring)

Most are completely out of the circuit once the start is complete as they have bypass contactors in them. They can also soft-stop the loads too, (just ask them). They take up about 1/6 the space.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Valvecrazy]

Electronics do have their place. Just with the size and kind of pumps I mostly deal with, electronics can be more trouble than they are worth. Sure the electronic soft starters are smaller, lighter, cheaper, they don't have as much meat in them. Heavy duty mechanical relays and transformers are going to be larger, cost more, and weigh more but, I believe they are more dependable.

I have probably sold or installed an average of 1,000 pumps a year for the last 30 years. When you are responsible for this many pump systems, simplicity and dependability are the key. Nobody cares if it is electronic or mechanical when water stops coming out of their faucets. They just know who to call and scream at, their pump man.

If the bypass relay of the electronic soft starter is not large enough to handle and across the line start, when the electronics fail, somebody is out of water. When somebody is out of water, they are chewing on my butt.

I studied electronics. The guys I went to school with, think it is funny that I use what I learned about electronics to help build completely mechanical systems. I can add an electronic monitor of several different kinds when needed. I can also bypass these electronic devices and get the pump running and water pressure restored when needed. Many times the electronics in a monitor, drive, or PLC cause me more out of water conditions than the failures they are designed to prevent.

Because the pumps I work with are correctly sized for the application, very little reduction in speed is possible. Most of these pumps will not lift water out of a well and build enough pressure to buck the static head unless they are spinning about 90% of full speed. This means when a soft starter is programed to get the pump to full speed in 30 seconds, for the first 25 seconds the pump is not spinning fast enough to start moving any water. Head falls off by the square of the speed, which is so quick that a soft stop doesn't do much good either.

If the drive or soft starter can start or stop the pump at 90% of speed and gradually go up from there, it might help with the water hammer. However, when a pump comes on it is usually because a demand already exist. The longer it takes to get the pump to match the demand, the more amplified the transients are.

That is just my two cents but, I have a very narrow market. ½ HP to 300 HP pumps that supply cool, clean water on demand. I know there are lots of other applications where electronics are worth there weight in gold but, I believe most of my applications are better off without it.

 

[BigInch]

That's why I'm amazed to see a lot of VFDs on, or being sold for, well pumps. If the well pump is sized correctly (as almost 100% static head) a VFD doesn't do anything good.

http://virtualpipeline.spaces.msn.com

 

[itsmoked]

Hmmm, I have used VFDs on several occasions just to get 3ph out of single ph so the down hole pump can be a less expensive more dependable 3ph instead of a capacitor dependant 'one lunger'. Then you set them up to spool up in 2-3 seconds and you can avoid the twist and slap headaches. You can also modulate the flow rate to match the demand and avoid the start stop cycling and pressure variations. You can also prevent over draw on a problematic well. If I ever do another well for myself I would definitely grab for these features. Of course I'm an EE and love water works games so I'm probably a tad more interested in the (certainly) added complexity.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Valvecrazy]

You got me on the single phase to three phase conversion. I have used drives for the same purpose myself but, only when I must. However, I do not have any more problems with single phase motors than I do with three phase so, I still use 15 HP and smaller single phase submersibles and make my own 15 HP single phase centrifugal pumps. When the demand is already present before the pump starts, 2-3 seconds can still give the twist and slap headaches.

I use Cycle Stop Valves to "modulate the flow rate to match the demand and avoid the start stop cycling and pressure variations." I can also prevent over draw on a problematic well with the same simple valve. These valves react almost instantaneously which eliminates amplifying transients or "twist and slap" When a demand is there, they meet it instantly. When the demand changes, they change the flow rate instantly. A slow response from a drive or speed controlled valve in these cases, is what amplifies the transients.

I have even used these valves to control the pump system when a drive is converting single phase to three phase and acting like a soft starter.

If you choose the right pump, throttling with a valve will give you the same reduction in power as a drive. Simple control is what makes a dependable pump system.

I love electronics. I have all the latest gadgets. I would just never use one of them to control my pump system. I am a little annoyed when my computer, cell phone, TV, or even my electronic thermostat go south on me. However, when water is no longer coming out of the faucet, it is more than just an annoyance. The simpler a pump control system, the more likely water will come out of the faucet when you open it.

 

[Sam993]

I have got a chance to visit a motor manufacturer last week, and I met a design engineer who is above 60 years. His reply to this question: yes you can install VFD but you have to remember the following:
1-You will have a temperature increase about 10 deg C. So, if you are running away below from its rated capacity you should not have any problem. This is because the sine wave from VFD is not perfect sine wave.
2-Verify mechanical vibration, i.e. not running through a critical speed.
3-By installing VFD you should remember that that its efficiency is around 98%. If it is installed in a substation you need additional power to remove that heat, so you should calculate these losses and additional maintenance cost and compare these expenses Vs other alternatives.

Best Regards to all

 

[itsmoked]

All true.

I would add that you need to be careful if the distance between the VFD and the motor gets beyond about 100 feet.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[Artisi]

Just buy a new pump suited to the application and sleep easy at night.

 

[MortenA]

I looked and i looked - and finally had to use "seach" for the word "fan" before i found that Biginch allready had said what i think is the most important issue relating the the actual initial question: Cooling of the engine may be a problem if you add VFD. If the fan on the motor does not have its OWN motor then cooling may be inadequate. There may be some other requirements re. temperature monitoring for the motors that should be checked.

Best regards

Morten

 

[pumpking]

If you guys and gals come to Sunny 'ole Europe, you can use a satanrad IEC European frame motor with inverter - just make sure you have thermistors fittted as thermal protection.

Lots of interesting discussion though, learnt alot - thanks !!

Ash Fenn

http://www.cdrpumps.co.uk