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tresi
11-19-2007, 10:20 PM
I need to power up a piece of equipment with a 200 horsepower 480 volt 3 phase motor driving hydraulic pumps. Of course it needs to be running yesterday and the power company says it will be at least 2 months or more to get 480 volt power to the location. The boss has access to a 200KW generator. While this would run the motor it would not have the capacity to start it. Would changing to a soft start motor starter allow this generator to start this load? How does one figure the ampacity required to start a motor with a soft starter? We've consulted an electrician who said this would work with a soft starter but he couldn't tell me how to figure the math he just said it should work. Of course the cost of a 200 HP soft starter is way too high to go by what anybody says should work. I'm going to see the formula and do the math myself before we tell him to order the starter and commit to this. Can anybody here shed anylight on this ?

turboblown
11-19-2007, 11:11 PM
You could also use a smaller "jack motor" to spin the big motor and the load up to a low RPM before starting the big motor. You'll need a bit of reduction ratio between the small motor and the large motor to achieve this. All you need to do is get a few hundred RPM at the big motor before starting it. Just make sure you use a one-way clutch so once the large motor starts, it doesn't over-spin the small motor since the reduction ratio works backwards now. By getting the large motor & load to a low RPM, it will really reduce the starting load. If you can get it to the RPM above the starter winding cutout (depending on motor design), you may have a very low start current demand on the 200HP unit.

Depending on mechanical load, a "soft start" may not always work since most of these reduce the breakaway torque as a result of the lower starting amperage draw.

tresi
11-19-2007, 11:45 PM
Thanks for the tip of a jack motor. I don't know if that would work or not or yet. The machine is a twin ram baler and it's about 1400 miles from me right know. Most of these machines have a pump coupled to each side of the motor so I don't hold out much hope for the jack motor. I'm told that the building has 1400 amp 208 service so we're trying to see if the machine is capable of being wired for 208. Most of these machines can be ordered from the factory with a soft starter as an option so it's possible it could be equipted with one all ready. I'm telling the boss if he wants me or the local electrician to tell him more he's going to have to spring for plane tickets.

slamdvw
11-20-2007, 10:27 PM
How about a VFD rated to the motor? They'll start a motor with almost no inrush current...

Sober_Pollock
11-20-2007, 11:06 PM
How about a VFD rated to the motor? They'll start a motor with almost no inrush current...
That's how we do it in the mills.

We have tons of air moving equipment (two to three hundred horse power) that we use VFD's on so that we can load them up slowly during cold start up because the starting load is horrendous when the air they move is cold (Not so bad when it gets up to eight or nine hundred degrees). We used to use dampers on the inlet side for this, but this was problematic and the VFD's just seem to be a perfect solution.

I've never done it with a hydraulic pump, but right off hand I can't see any reason it wouldn't work.

A 200Kw generator and a VFD sure seem like an expensive proposition though. This piece of equipment better earn a hell of a lot of money!

6010
11-20-2007, 11:10 PM
Tresi,
Most 480 volt three phase motors can be wired 208 three phase if all 9 motor leads are run to the pot head. Usually this is the case unless the company that does the rewinds hooks some of the leads internally and only brings out the three power leads. They do this when they are fimilar with their customers distribution system. If you ask someone at the epuipment how many leads are coming into the pot head and they tell you 9 then you can wire the motor Delta and this will be the low voltage or 208 three phase. Keep in mind when you wire the motor for 208 three phase the motor will pull twice the current and require bigger wire to handle the current. Of course if someone at the equipment can eyeball it they can tell you the Full Load Amps when wired for low voltage.

I have experience with soft starts but we used them for different reasons. We used them on large pumps to avoid water hammer and on large conveyor belts to ramp up the start and lessen the stress on the conveyor belts and rollers. You probably need to refer this question to tech support for the manufacturer of the soft start you are considering. I know they can limit inrush current but I don't have any information to help you size one and never had to consider this aspect of their use, only ramping the motor speed up to keep from tearing up equipment. Tell the manufacturer what you have to do and he can tell you if his soft start is capable of it.

tresi
11-21-2007, 07:59 PM
That's how we do it in the mills.

We have tons of air moving equipment (two to three hundred horse power) that we use VFD's on so that we can load them up slowly during cold start up because the starting load is horrendous when the air they move is cold (Not so bad when it gets up to eight or nine hundred degrees). We used to use dampers on the inlet side for this, but this was problematic and the VFD's just seem to be a perfect solution.

I've never done it with a hydraulic pump, but right off hand I can't see any reason it wouldn't work.

A 200Kw generator and a VFD sure seem like an expensive proposition though. This piece of equipment better earn a hell of a lot of money!
A 200 KW generator rents for $5000 per month. I'm guessing $250+or- 50 per shift for fuel. I will take a look at VFD's

tresi
11-21-2007, 08:07 PM
Tresi,
Most 480 volt three phase motors can be wired 208 three phase if all 9 motor leads are run to the pot head. Usually this is the case unless the company that does the rewinds hooks some of the leads internally and only brings out the three power leads. They do this when they are fimilar with their customers distribution system. If you ask someone at the epuipment how many leads are coming into the pot head and they tell you 9 then you can wire the motor Delta and this will be the low voltage or 208 three phase. Keep in mind when you wire the motor for 208 three phase the motor will pull twice the current and require bigger wire to handle the current. Of course if someone at the equipment can eyeball it they can tell you the Full Load Amps when wired for low voltage.

I have experience with soft starts but we used them for different reasons. We used them on large pumps to avoid water hammer and on large conveyor belts to ramp up the start and lessen the stress on the conveyor belts and rollers. You probably need to refer this question to tech support for the manufacturer of the soft start you are considering. I know they can limit inrush current but I don't have any information to help you size one and never had to consider this aspect of their use, only ramping the motor speed up to keep from tearing up equipment. Tell the manufacturer what you have to do and he can tell you if his soft start is capable of it.

This solution is being looked into also. I rewire motor for voltage changes all the time. Big motors aren't always set up for dual voltage. To run this on 208 would really take some big wire. I haven't looked it up yet but I think it would take 500MCM copper not aluminum.

tresi
11-21-2007, 08:21 PM
Thanks to all who've offered advice. Here's a welcome update. Rather than a 200 HP motor it has 2 100 HP motors each with it's own starter. I still have research to do but I beleive that the motors start independently so this greatly reduces the current inrush during starting. I shouldn't name who wants the boss to have this site up and running yesterday but most of you have visited one of their super center this week and have been greeted at the door by someone in a blue shirt or smock so money is the last factor. Get this, said project is being used as a way to prove that they are a green company. Just how green is it to run a 200HP baler off of a diesel generator everday for 2 or 3 months?

turboblown
11-21-2007, 08:21 PM
This may sound stupid, but for a temporary solution, why couldn't you just use a Diesel/natural gas/gasoline powered engine to run the pump?

Just rent a skid-mounted engine unit and couple it to the pump. Select one with the proper PTO drive ratio (or even direct).

In a real pinch, one could even fab a skid and install a simple 305 Chevy or whatever flavor of engine with a 2 barrel carb HEI ignition. All you'd need is fuel, a radiator, 12V battery, exhaust system and drive coupler to your pump. This could be built in a day or two for under $1000.00 and drive a pump just fine that needs 200HP.

turboblown
11-21-2007, 08:27 PM
Oh....regulating RPM would be easy too! If you need 3450 RPM, set the throttle for 3450 RPM at maximum hydraulic load. Install an MSD 6AL ignition system with a adjustable rev limiter chip (set for 3450 RPM).
When under load, the engine is set for the correct RPM. When the load decreases, the RPM will increase and the MSD unit will randomly drop cylinders to lower the RPM to 3450. This wouldn't be something to do if it were to run for years, but for 2 months it would work fine.

Another way us to use a RPM-sensitive switch (another MSD goody!) to drive a vacuum valve that will regulate the vacuum going to the distributor advance pot. When RPM is high, vacuum will dump and retard the timing and drop RPM. Just make sure the cooling system is capable of the extraq heat when the timing leaves.

tresi
11-21-2007, 08:32 PM
This may sound stupid, but for a temporary solution, why couldn't you just use a Diesel/natural gas/gasoline powered engine to run the pump?

Just rent a skid-mounted engine unit and couple it to the pump. Select one with the proper PTO drive ratio (or even direct).

In a real pinch, one could even fab a skid and install a simple 305 Chevy or whatever flavor of engine with a 2 barrel carb HEI ignition. All you'd need is fuel, a radiator, 12V battery, exhaust system and drive coupler to your pump. This could be built in a day or two for under $1000.00 and drive a pump just fine that needs 200HP.
I haven't seen this machine yet but any recycling baler I've ran across just would be impossible to mount and couple an engine to it. The pumps need to turn at 1750 rpm max. A load for a 200 HP electric motor would probably take a 450+ HP gasoline engine.

JeffB
11-21-2007, 09:08 PM
Man, a baler with that kind of power would bale cardboard back into wood! I recently replaced a motor on a baler for a small supermarket that makes pallet sized bales about 4 feet high, and that was only a 10 HP motor running on 208.

denrep
11-21-2007, 09:19 PM
... Here's a welcome update. Rather than a 200 HP motor it has 2 100 HP motors each with it's own starter...

Glad to hear it, you're in now. 200kw will start those easily. I've been hesitating about posting some other, not so conventional, "across the line" motor starting tricks.

I think the 200kw will start a lightly loaded 200hp motor. Especially if the 200kw is a prime rating, rather than standby rating. It does make for a long two seconds! With that little spin turboblown mentioned, it would certainly do it. If the pumps are full of cold oil, or have a restrictive flow path, that's another story.

Caterpillar Cummins and others offer extensive generator sizing for motor starting formulas. However, I figured that you're lacking too many input variables for them to be much help.

Good Luck

tresi
11-21-2007, 09:37 PM
Man, a baler with that kind of power would bale cardboard back into wood! I recently replaced a motor on a baler for a small supermarket that makes pallet sized bales about 4 feet high, and that was only a 10 HP motor running on 208.
It's a big twin ram auto tie baler. Main ram 16" bore @ 3500 psi. 340,000 or so lbs of compaction force.

denrep
11-21-2007, 09:54 PM
It's a big twin ram auto tie baler. Main ram 16" bore @ 3500 psi. 340,000 or so lbs of compaction force.

Hey, how much to make a coffee table out of a Ford pickup? :laugh:

turboblown
11-21-2007, 09:58 PM
If the hydraulics allow, have them in recirculate or bypass until the motors start. Some pumps start making pressure against the regulator the instant they flow. If you can recirculate the fluid until started, you'll make things easier by removing a large amount of load on startup.

Sequence the two motors about 5 seconds apart when starting. You can have motor #1's contactor start the instant the "on" switch is closed and have motor#2's contactor's coil go through a 5 second octal-style delay timer. One switch will start the motors 5 seconds apart when you hit one switch. The octal timers can be had from Grainger or any industrial supply house. You may also want to investigate using a gas-turbine genset for a rental. You can get a .5-1 megawatt unit that will make enough power (and then some) for that unit and it's QUIET and efficient on any liquid fuel. It will run on kero, Diesel, gasoline.


BTW, even though the gas engine won't work for your machine, a 2:1 reduction drive using a 5-6" wide Gilmer belt and cogs would put the engine in the powerband and double the torque and run the pump at 1750 easily with enough HP & torque. Engine RPM would be 3500. We did this on a tire shredder a few years back with a carbed Subaru engine. It lasted almost forever- bungee straps (radiator retention devices) and all.

6010
11-22-2007, 03:08 PM
To run this on 208 would really take some big wire.
You can parallel the motor feeders to keep the wire a little more manageable.

A 100 Hp motor has a Full Load Amp rating of 273 this is nominal based on the 2008 code. However, there is no substitute for looking at the motor name plate especially when picking out overloads.

I
still have research to do but I believe that the motors start independently so this greatly reduces the current inrush during starting.

I imagine you will find the machine has two start buttons wired in parallel so the two motors have to be started independently, unless the start operation is automatic. If this is how it is, the control voltage for the machine operation would probably come through normally open contacts on each of the motor starters so that both motors had to be running before operating the machine.

If you are going from 480 to 208 the primary of the control transformer will have to be changed along with the motor wiring and motor overloads.

Hope you can get it going OK


Speaking of compactors - I just finished eating Thanksgiving dinner and I feel like a compactor myself. :laugh: :sleeping:

tresi
11-22-2007, 07:43 PM
I've dealt with paralleled conductor a lot in my past aircraft work. Sometimes you just can't get wire that big or get that big wire to go threw all of the tight bends required. We are considering setting a buck/boost transformer to boost the 208 up 480. This will make the wiring easier and cheaper. Once the power company can supply the 480 service the buck/boost transformer could be used the other way to supply a 208 panel. All options are being researched and when all is said and done availability of equipment and parts on short notice may decide just how this cat gets skinned.

6010
11-22-2007, 08:57 PM
I would like to know more about that buck/boost. The only ones I know about only take care of a little sag in the line say 40 or 50 volts or make small changes in supply voltage. I would be interested in how that one works out.

denrep
11-22-2007, 09:02 PM
We are considering setting a buck/boost transformer to boost the 208 up 480...

All options are being researched and when all is said and done availability of equipment and parts on short notice may decide just how this cat gets skinned.

That's probably a good solution.
I don't know if you could call it buck-boost anymore, rated at
208 - 480 with a running load capacity of at least around 120kva!

But the more I think about this; How tough could a transformer swap be? They must be on site. Distribution must have capacity, to have that much kva potential at 208v. This is a big customer. I'll bet if a call was made to the power company, inquiring about service termination, - " Are we under contract? We're exploring generating our own green power, if we can't buy 480 by a certain day" - You'd see some action.

William McCormick Jr
11-22-2007, 09:08 PM
I've dealt with paralleled conductor a lot in my past aircraft work. Sometimes you just can't get wire that big or get that big wire to go threw all of the tight bends required. We are considering setting a buck/boost transformer to boost the 208 up 480. This will make the wiring easier and cheaper. Once the power company can supply the 480 service the buck/boost transformer could be used the other way to supply a 208 panel. All options are being researched and when all is said and done availability of equipment and parts on short notice may decide just how this cat gets skinned.

You might need a big buck boost transformer.

Here where I live you are required to call the power company any time you install an electrical device over 15 horse power. The reason is that it can take the power lines off the building if not done right.

I did that once. I was starting a giant 3/8" 12 foot shear, and looked out side to see white smoke. I melted the connectors to the building off.

We all know that a motor draws high amperage when starting. Almost an infinite draw at first and then less and less as it reaches sync with the hertz that sets its speed. The problem with generators is that they do not always supply the same kind of powerful start that an induction motor needs.

When you use a buck boost transformer on an induction load, if the voltage drops the duration of starting amperage goes up and exponentially increases the amperage you need to start. So a motor rated at 125 amps, getting low voltage may draw as much as 200 amps at a lower voltage or more. Sometimes creating a crater where the transformer used to be.

You may pop breakers and rightly so, because of the duration of locked rotor amperage at even a slightly lower voltage.

You could probably start a large motor, with an inexpensive resistor bank made of finned strip heaters. You could formulate the amount of amps you want to be able to pass through your heaters to limit the current to the rated generator output.

Then when you start the motor through the heaters only the amperage you predetermine will pass through the heaters. After the motor comes up to speed and it will come close with no load, you can engage the full current in parallel to the resistor bank. This is a cheap soft start.

Sincerely,



William McCormick

tresi
11-23-2007, 12:17 AM
Yes, A buck/ boost transformer was the wrong term to use but you got the idea. 1400 amp 208 service is currently supplied to the building. The local power company is envolved in this project. THe power company says that the reason it will take them 2 months to supply 480 service is that there lead time to get a new transformer for there transformer vault is 2 months. A 150 KVA transformer is said to be on hand at distribution center for a regional electrical supply house, bigger may be available. Why the temperary measures if 208 can be boosted up to 480 for this machine? The power company claims that they can sell 480 volt power cheaper than 208. I thought that they sold electricity by the kilowatt.

6010
11-23-2007, 09:14 AM
I would ask them if there were any that weren't being used at the moment that could be moved. I know where I live there are plenty of plants that are closed that will never be opened again. These transformers have a long service life. I can't understand why they wouldn't be trying to use some of the newer ones before installing brand new ones. Chances are all the wire in these plants has been stolen and sent to the scrap man anyway - industrial users favored copper. Get your customer to put some pressure on these guys - I think they could do a little bit better.

Alan N
11-23-2007, 04:58 PM
Don't know about your part of the universe, Billy, but a 3/8", 12 foot shear is no giant in any sense of the word.

Must be a really rare "sometimes " on the cratering transformer. The pwoer company folks i know say they may smoke and smolder when they go bad but none of them have seen one leave a crater.

If you're going to try to impress us with fabricated stories they need to be just a little more believeable. Your current level of storytelling is bordering on science fiction, heavy on the fiction but containing far too little science.

Stilll waiting for documentation to support some of your wild tales.

tresi
11-23-2007, 07:13 PM
I would ask them if there were any that weren't being used at the moment that could be moved. I know where I live there are plenty of plants that are closed that will never be opened again. These transformers have a long service life. I can't understand why they wouldn't be trying to use some of the newer ones before installing brand new ones. Chances are all the wire in these plants has been stolen and sent to the scrap man anyway - industrial users favored copper. Get your customer to put some pressure on these guys - I think they could do a little bit better.

Probably the the biggest factor my boss had the idea that he was going to call the power company and they would have everything on the shelf and were going to drop everything and work whatever hours it would have took to get 480 volt service by now. Maybe the would to repair storm damage but new service gets done on their time table.

William McCormick Jr
11-23-2007, 08:47 PM
Don't know about your part of the universe, Billy, but a 3/8", 12 foot shear is no giant in any sense of the word.

Must be a really rare "sometimes " on the cratering transformer. The pwoer company folks i know say they may smoke and smolder when they go bad but none of them have seen one leave a crater.

If you're going to try to impress us with fabricated stories they need to be just a little more believeable. Your current level of storytelling is bordering on science fiction, heavy on the fiction but containing far too little science.

Stilll waiting for documentation to support some of your wild tales.

I am an amazingly happy fellow, rather content with who I am.

I built equipment for a plant that had a couple transformers blow. Before I built the equipment. Ha-ha.

My friends at K&G knew what the problem was and took information to contact them and explain it.

Many years earlier the father of the fellow who runs the rewinding company, blew a transformer off the pole. By connecting a 100 horse power electric motor directly to the secondary lines coming into the panel box.

Bypassing the main breaker. And perhaps the meter pan or the meter pick ups. To test the motor at full starting amperage. It just took the transformer off the pole.

Main breakers usually have a smaller current limiting, usually copper coil that limits current flow. So do the individual circuit breakers also have such a device. So they bypassed two limiting devices. But at that time they did not know what would occur.

Look at Square "D" breakers used down in Florida. The sub-panel breakers are rated at 75,000 amps throughput. Imagine what came through large 2/0 or 3/0 or 4/0 wire right from the transformer for several commercial buildings.

Attaching a large induction device like that directly to the secondary lines, draws so many electrons from the transformer, that it ARC's (Anode Rectified Cathodes) and becomes a small bomb. Probably with the energy of a stick of dynamite. That is why almost always no one is killed it is not extremely powerful.

Some of the underground transformers I believe have melted down with limb destroying energy, and have killed.


The new transformers at the printing company in question when they moved to the new building, were twenty feet from the Airport fence.

They can also blow off a pole, literally disintegrate. I am surprised that experts did not know that.



Sincerely,



William McCormick

Alan N
11-23-2007, 10:03 PM
I am an amazingly happy fellow, rather content with who I am.

That's easy to change, just put down the pipe.

tresi
11-27-2007, 09:23 PM
OK, It's been confirmed that this machine can be ran off of 208 volts, There is more than enough unused ampacity in the building to run the machine and
we've hired a electrician in the local area to do the job. The power will supply 480 service when they get around to it to get cheaper rates. Let's see the total of all motors on this machine 210 horsepower, running 208 volts, 100 ft plus from the machine to the service panel thats going to one heck of a lot of copper to get the job done.

slamdvw
11-28-2007, 07:19 PM
lot of copper... not to mention the grunt of the transformers when that badboy starts!!

tresi
11-28-2007, 09:21 PM
lot of copper... not to mention the grunt of the transformers when that badboy starts!!
Not all that bad. Even with overhauled pumps the hydraulic pumps make a lot more noise until the fluid gets up to 100 degrees or so. The prestart warning horn has been known to make people pee themself.

William McCormick Jr
12-03-2007, 11:20 PM
Not all that bad. Even with overhauled pumps the hydraulic pumps make a lot more noise until the fluid gets up to 100 degrees or so. The prestart warning horn has been known to make people pee themself.


I had mentioned using heaters in a resistor bank.

Most people today think of heaters and the ones they have tested, radiant type oven heaters have high amps when starting and as soon as a couple cycles pass they heat up and draw a fraction of what they are rated for in watts.

However some companies make constant ohm finned strip heaters. They start and run with about the same ohms. Watlow is such a company. With these heaters calculating the amount of amps you want to flow on start is easy.



Sincerely,



William McCormick

William McCormick Jr
12-03-2007, 11:37 PM
This might be an interesting bit of information. In a Wye hookup heaters draw more amperage then in Delta configuration from the same power supply. A good deal more.

To someone that is used to hooking up induction motors and watching them go slower in Wye, naturally without knowing this they would assume the heaters would do the same. They do not.


Sincerely,



William McCormick

turboblown
12-04-2007, 09:05 AM
Gee, I thought that an induction motor would run at its rated speed dependant upon frequency within its rated load capacity?

So in other words, a Wye and a delta don't both run at 60Hz?

kbeitz
12-05-2007, 06:30 PM
Install another motor with a heavy flywheel and about half the Hp and wire in so it would be in line with your motor...
When your motor starts the smaller motor will work like a rotary phase converter and take a good part of the load off your pinnel box...

William McCormick Jr
12-05-2007, 10:58 PM
Gee, I thought that an induction motor would run at its rated speed dependant upon frequency within its rated load capacity?

So in other words, a Wye and a delta don't both run at 60Hz?

Hertz do tell the tale of how fast a motor will turn, in relation to how many different coils there are in the motor, at the motors rated name plate voltage.

More separate induction coils less speed. More hertz more speed.

Wye however severely undervolts a repulsion induction device, by keeping a constant voltage in the windings that all have a common point. The motor is slow to start, because it does not draw serious starting amps.

It is more like an electro magnet, rather then a repulsion induction device at a voltage almost half of the name plate voltage and hooked up Wye. The phase voltage is exactly 1.73 times less then the line voltage in Wye configuration.


Delta spikes the individual coil between two line legs with full line voltage. So that your line voltage is the same as your phase voltage.

That constant voltage you get from Wye, has a slightly different effect on constant ohm heaters. They draw more amperage at the rated voltage in Wye. About 1.73 times more. Ha-ha.


Sincerely,



William McCormick

William McCormick Jr
12-05-2007, 11:20 PM
Gee, I thought that an induction motor would run at its rated speed dependant upon frequency within its rated load capacity?

So in other words, a Wye and a delta don't both run at 60Hz?

Hertz do tell the tale of a motors speed, in proportion to the number of seperate coils the motor has. At the rated volts in the proper configuration either Wye or Delta. More Hertz more speed, more coils less speed.

Wye cuts voltage in two ways to a repulsion induction device. One it keeps a constant voltage in the coils. Reducing the repulsion induction effect, and it reduces the phase voltage by a factor 1.73 times less voltage then the line voltage. Or better put Line voltage divided by 1.73

Delta on the other hand, feeds each coil with line voltage so your phase and line voltage are the same.

When you drastically reduce voltage by hooking the motor up Wye when it was calling for Delta, yes it will go very slowly, it will slip, or be out of phase and not even pop a heater. That can be a problem and cause a motor to run all night long, and not be cooled off by the fan. Smoking the windings that can fill a factory with smoke.

But with fixed ohm heaters that means that you will be drawing approximately 1.73 times more amperage if the heaters are fixed ohm heaters and hooked up in a Wye configuration. Because of the more constant DC like current flowing through the heaters.


Sincerely,



William McCormick