soft start or VFD

[Jraef]

430.52 breaker should be 250% ...

Slight correction... breaker COULD be up to 250%. The only thing stopping you from using a smaller breaker is the risk of nuisance tripping. VFD = no inrush, no nuisance tripping.

Another slight correction to an earlier comment; I never recommend selecting a VFD based on HP alone, because motor FLA varies a lot between motors, especially as pole count increases. I always recommend buying VFDs and Soft Starters using your motor nameplate FLA. You can’t go wrong that way. I did a project a few years ago where the user bought qty 6, 250HP 480V VFDs in advance to get it in the budget, but it turned out the pumps had 250HP 12 pole motors, and the FLA was 366A, “250HP” VFDs were rated for 302A. Oops... restocking charges were reduced but still painful.

 

[Jraef]

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.

To answer your questions;

Water hammer breaks pipes and flanges, it doesn’t cause breakers to trip. Your breaker is tripping because a 150A mag-only (MCP) breaker is too small for a Size 4 starter. Someone must have cobbled that together themselves, making it illegal because you cannot use MCP breakers in the field, they must be part of a LISTED factory built assembly, and no factory would have put that small of an MCP on a Size 4 starter.

If you change to a soft starter or VFD, you cannot use an MCP on them either, so you must change the breaker either way. If that breaker is a 150A Frame, you can change to a 150A Thermal-Mag (called an “inverse time” breaker in the NEC and it should be fine. If that MCP is a 250A frame with a 150A Trip Rating, you could replace it with a similar MCP with a higher trip setting and leave the starter as-is (assuming it too is rated for 100HP).

If you add a valve, you would put it down stream of the pump. But you must also add a way of controlling it, otherwise it is pointless. That then will require adding a controller of some sort and someone will need to understand how that works and how to program it, troubleshoot it etc. A good quality Soft Starter or VFD will have everything you need to do this, self contained in it.

As to SS or VFD it still comes down to what was said in the other thread; if there is value in varying the flow, use the VFD. If it is ALWAYS going to run at one flow rate, use the Soft Starter.

 

[mannyb]

To answer your questions;

Water hammer breaks pipes and flanges, it doesn’t cause breakers to trip. Your breaker is tripping because a 150A mag-only (MCP) breaker is too small for a Size 4 starter. Someone must have cobbled that together themselves, making it illegal because you cannot use MCP breakers in the field, they must be part of a LISTED factory built assembly, and no factory would have put that small of an MCP on a Size 4 starter.

If you change to a soft starter or VFD, you cannot use an MCP on them either, so you must change the breaker either way. If that breaker is a 150A Frame, you can change to a 150A Thermal-Mag (called an “inverse time” breaker in the NEC and it should be fine. If that MCP is a 250A frame with a 150A Trip Rating, you could replace it with a similar MCP with a higher trip setting and leave the starter as-is (assuming it too is rated for 100HP).

If you add a valve, you would put it down stream of the pump. But you must also add a way of controlling it, otherwise it is pointless. That then will require adding a controller of some sort and someone will need to understand how that works and how to program it, troubleshoot it etc. A good quality Soft Starter or VFD will have everything you need to do this, self contained in it.

As to SS or VFD it still comes down to what was said in the other thread; if there is value in varying the flow, use the VFD. If it is ALWAYS going to run at one flow rate, use the Soft Starter.

The breakers are 150a therm mag breakers. They are both set at max settings. Thanks for SS idea that was my first choice. I dont want to throw money at the problem especially if im not sure what the problem is. I dont like just changing parts. I appreciate everyones ideas because at least it gives me a starting point. The 100HP pump sits within 10' of reserve tank with a hand valve. I thought I could close the valve 1/3 or more orl ess during start up and open as needed after it starts up.

 

[Dzboyce]

I installed a 150 hp lineshaft turbine Pump earlier this summer. My utility company was willing to allow an across the line starter in this location. I usually use CH Irrigstion Pump panels. I ended up using a soft start panel. It was only $500 more than the across the line starter. I also got a quote for VFD in a 3r panel. The quote included a line reactor. The utility requires them above 60 hp. It was about $8k more than the soft start panel. All these panels are suse rated.

when you need to buy a 100 amp or larger mccp, or a contactor, consider buying a complete Pump panel. You get the second component for about 1/4 price.

 

[ptonsparky]

ATL Pump panels are very reasonable in pricing. I can’t begin to buy a Size 4 starter for the price I pay for a PP. Plus none of my closest suppliers stocks the starter only

 

[Jraef]

Pump panels are essentially a “loss leader” for manufacturers of motor control equipment. They don’t make enough money on them to be sustainable. But they do it with the theory in mind that when the starters wear out, they are replaced at full price. However most people have long ago figured out that it’s cheaper to just buy a whole new pump panel than it is to replace the starter inside. Yet the industry keeps going this way.

 

[ptonsparky]

Pump panels are essentially a “loss leader” for manufacturers of motor control equipment. They don’t make enough money on them to be sustainable. But they do it with the theory in mind that when the starters wear out, they are replaced at full price. However most people have long ago figured out that it’s cheaper to just buy a whole new pump panel than it is to replace the starter inside. Yet the industry keeps going this way.

I like it:thumbsup:

 

[Phil Corso]

Re Jraef's last comment:

It also justifies the increase in future maintenance-cost funding !

Phil

 

[Besoeker]

Pump panels are essentially a “loss leader” for manufacturers of motor control equipment. They don’t make enough money on them to be sustainable.

We got by for decades.

 

[kwired]

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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250% is maximum per NEC, with exemptions to increase it if that won't hold during starting. 200 amp breakers typically will hold while starting a 100 hp motor across the line. If they have magnetic trip adjustment available the chance is even greater.

 

[mannyb]

250% is maximum per NEC, with exemptions to increase it if that won't hold during starting. 200 amp breakers typically will hold while starting a 100 hp motor across the line. If they have magnetic trip adjustment available the chance is even greater.

I have spoken to SS suppliers and VFD suppliers and both say that the 150a therm mag breaker is sized to small. They both say the soft start wont work in this application but the VFD would work. They both agree that the breaker would still need to be increased to 200amp if a SS or VFD is installed or not. I did hear that the 150a Thermag breaker was sufficient for existing application and my question is could it be that simple as to just replacing breake to 200amp? Eithet way the VFD would probably be cheaper due to high cost of breakers in area but my question also is. IS the breaker to small for 100hp motor?

 

[kwired]

I have spoken to SS suppliers and VFD suppliers and both say that the 150a therm mag breaker is sized to small. They both say the soft start wont work in this application but the VFD would work. They both agree that the breaker would still need to be increased to 200amp if a SS or VFD is installed or not. I did hear that the 150a Thermag breaker was sufficient for existing application and my question is could it be that simple as to just replacing breake to 200amp? Eithet way the VFD would probably be cheaper due to high cost of breakers in area but my question also is. IS the breaker to small for 100hp motor?

So the breaker knows if it is in a new or existing application??

Bottom line is whether or not you ever cross the instantaneous trip curve with the motor current. Soft started or VFD controlled motors have much greater chance of never crossing that line. You can even have different performance with a long motor circuit vs a short motor circuit. The long circuit has enough more resistance it "chokes" that starting surge enough it may hold where the short length has low enough resistance it easily crosses the trip curve of the breaker when starting.

Once it is past that initial starting surge of current 150 amps thermal trip curve is going to be just fine for a 100 HP motor.

 

[ptonsparky]

IS the brearer to small for 100hp motor?

hmmm ...it repeatedly trips at first start of motor...we have no data concerning the actual startup current at these times...we have no idea what the current is when the motor starts thereafter. We dont even know what current is while it is running. We dont know the voltage at any of these times.

All we know is the breaker trips.

I'm not sure. I think maybe the overloads are set too low.

 

[iceworm]

.... IS the breaker to small for 100hp motor?

Following other posts. Most of this has already been said.
Yes
Following is true provided the motor is not something screwie. For a Code G, Design B (which is most):
As already said, for an inverse time Breaker, 250% Full Load Current, next size up okay.
430.6.A.1, T430.250, 100hp ==> 124A FLC x 2.5 = 310A
Next standard ampere rating = 350A
Adjustable instantaneous trips are not needed (unless you have something screwie)
150A TM CB is ridiculously small.

And you may not have to pull new conductors
430.22, conductor ampacity is 124A x 1.25 = 155A
Normal wiring methods ==> 2/0

If there is any doubt, get a Time Current Curve from the mfg. It will likely be on there website. Lay out a reasonable motor starting current. Start at 6X FLC tapering off to FLC at the usual motor starting time - maybe 10 seconds, maybe 5 seconds. The motor starting curve has to be under (as in day light between the curves) the CB TCC.

I'm kind of surprised it starts at all on the 150A CB considering Locked Rotor starting Current is in the 700A range for a few seconds.