soft start or VFD

[mannyb]

I posted couple weeks ago. If this sounds familiar because it is I posted about a 100hp 480v 112amps 3ph rotatory pump draws water from a reserve tank to a wash plant tank that also has a large HP tank for washing sand. The 100hp pump is a secondary pump to the primary pump at wash plant. The 100hp pump sits within 50' of primary and breaker trips still. The breaker is 150a magtrip turned up all the way and still trips.

You guys did list a couple options for the problem. Soft start, VFD or Flow valve. I was wondering what is need to size both the vfd and SOft start also If a flow valve is used would it be installed before or after the pump? I wish i could down load the pics but that never seems to work for me so I am limited with info sharing. I will provide as much info as I can on the problem. I believe the pump is to large for application and a hammering effect is causing the breaker to trip.

 

[ptonsparky]

IIRC your breaker is to small.

I don't remember that you stated this was a secondary pump in the other thread.
A VFD would be a good way to regulate the flow in conjunction with the primary pump. You will need feedback of some sort.

A pressure regulating valve would work as well. I have only seen them on the output side of the pump. Either way, you need engineering help.

 

[ptonsparky]

To size the VFD, you call your supplier and tell them the HP, voltage, etc and your application. They will size it for you. I would buy a complete packaged unit designed for a pumping application. You will have to determine how and where the power will come from.

 

[ElectricMatt]

I agree with PTon the breaker should be at minimum a 200, that might even be too small. A vfd would be the best option in this circumstance.

I have seen the application you’re speaking of in several of the rock plants I work at and some of the use vfd with pressure sensors and transducers to manage the vfd based off of the need of the lead pump.

The other option is to add another smaller holding tank closer to the lead pump that is managed by a couple of level probes and the wash plant pump can manage the needed flow to the plant itself.

The second option would be cheaper than option 2, but would most likely still require a larger breaker. Start up on some of these pumps is significant, especially if their is an air gap in the line.

Is there a check valve ahead of the 100 hp pump?


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[kwired]

didn't read your other thread.

Questions -

how many starts per hour will this ordinarily see?

is there any chance of needing to vary the speed, or maybe even ask if you would run more or less continuously and vary speed as needed if you did use a VFD?

Does it ever start against reverse flow?

With current setup does breaker trip immediately upon closing circuit or does it trip during acceleration?

I also agree that the breaker should probably be no less than 200 if starting across the line.

 

[Besoeker]

I agree with PTon the breaker should be at minimum a 200, that might even be too small.

With a VFD I don't see why you would need that.
A regulating valve would waste energy.

 

[ElectricMatt]

With a VFD I don't see why you would need that.
A regulating valve would waste energy.

You are correct IF you have a vfd you could use the 150a breaker currently installed.

As for the check valve I was asking because depending on where it is placed in relation to the pump it could be causing an air gap, pumps will draw significantly more current when they are priming as opposed to when they are loaded.


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[kwired]

You are correct IF you have a vfd you could use the 150a breaker currently installed.

As for the check valve I was asking because depending on where it is placed in relation to the pump it could be causing an air gap, pumps will draw significantly more current when they are priming as opposed to when they are loaded.


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Air won't put as much load on the impeller as a liquid will.

 

[ptonsparky]

OP:

Water Hammer + tripping breaker = PP design from the start.

 

[ElectricMatt]

Air won't put as much load on the impeller as a liquid will.

I went back and reread my post and realized I had said it incorrectly. What I am talking about is head. When priming your line you will see higher current.

What I am getting at, based on my experience, if that second pump is draining the line after the 100hp pump is off then you will see higher head when starting the 100hp pump which will mean higher current until you get the line full of water(primed).




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[kwired]

I went back and reread my post and realized I had said it incorrectly. What I am talking about is head. When priming your line you will see higher current.

What I am getting at, based on my experience, if that second pump is draining the line after the 100hp pump is off then you will see higher head when starting the 100hp pump which will mean higher current until you get the line full of water(primed).




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That I will agree with.

 

[ElectricMatt]

That I will agree with.

That is appreciated coming from you.


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[ElectricMatt]

I went back and reread my original post and I think if you put in a larger breaker, put a time delay off on the 100hp based off the smaller pump at the plant with maybe a check valve after the 100hp pump(to prevent fall) this would be the most cost effective option.

I know a vfd or soft start is also a solution, but that is a substantially larger investment. Having worked with a lot of mining plants myself they want the most cost effective option.

Just an idea, any comments on it?


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[Malywr]

430.52 breaker should be 250%
You should have check valve after pump and bypass valve between pump and check valve with pressure regulator properly set pressure that prevent hammering. Less stress an plumbing and safer for pump. Less current spikes too.


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[Malywr]

Check conductors if they are properly sized for that pump


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[JFletcher]

I'm not sure what kind of pump you have... I come from a Wastewater operations background, and a rotary pump would be a positive displacement pump (like a Lobeflow) ... i.e, you cannot throttle the intake or discharge on those. I would also make sure the pump is not spinning backwards on start (hung check valve) which will basically result in it drawing locked rotor amps until the rotor is moving forward.

Throttling pumps with valves is in my opinion inferior to a timer setup in most cases.

Electrically speaking, the easiest thing you can do is put in a 250 amp breaker. I agree with Tom in that you need engineering supervision to properly address your problems.

Is the 112 amp motor for the pump the original? Is 150 amp breaker original? There seems to be a pretty glaring mismatch there to me for an engineering firm to have missed on commission.

 

[JFletcher]

OP:

Water Hammer + tripping breaker = PP design from the start.

Yep.

 

[mannyb]

All great replies and I appreciate all the information. I do remember the last thread saying the 150 amp breaker was large enough for application without using table 250% because I had trips set at max settings. I also agree its a poor design. I want to help customer with problem and I dont just want to go charging parts. The 200a breaker needed will be expensive no matter they decide. The breaker only trips at start up, once it trips it doesnt do it again. it will run all day and night. The plant runs 24/7 but the equipment when idle for maintenance of other problems will trip at start up but runs all day once started.I agree with that its not the equipment but design and placement of existing equipment. I believe the 100hp motor sits to close to primary tank. The line is a 6' line and it elbows within 20' and then turns towards the primary tank. The secondary pump keeps the primary tank full of water. I think if they could slow the flow for a moment then raise the flow once up and running to keep the nuisance tripping from happening. It is annoying because it doesnt do it all the time but its does it all the time. I will propose the VFD and the larger breaker.

I was considering also installing fuses versus breaker. They dont like fuses because they dont like replacing fuses. I said well you shouldnt need to replace fuses if everything is running and designed correctly. They will change there minds because each 200a breaker is over $3000 dollars. They currently have 2 150a breakers one inside starter and other at MDP.

AT some point They will be relocating and the equipment will be automated and most problems will be resolved and redesigned but for now this is a problem they would like to get resolved.

 

[JFletcher]

I would not go with fuses or a 200 amp breaker... The first time those fuses blow have to be replaced, somebody is going to order 300 or 400 amp fuses to put in play. a 250 amp breaker will probably not be any more than a 200, and will give you the head room to run it at less than its maximum setting.

If the pump is not positive displacement, and there is a valve on its discharge that can be easily throttled, changing the startup procedure to start it against a mostly shut valve would lower its starting current and probably reduce trips. if there are no suitable valves, adding a valve into piping that size could exceed the cost of a new breaker, even if they really should be there.

Edited to add... Taking amperage readings would be a good start in my humble opinion. there could be a mechanical problem with the motor or pump causing it draw more current than it should be.

 

[Malywr]

VFD will help a lot with tricky settings to keep current at start up under 150A and pump will need to speed up a little longer until full speed
How much is VFD vs 250A or 300A breaker if conducts allow it


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