Large motors and soft start

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John Hasler
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Re: Large motors and soft start

Post by John Hasler » Sun Jun 09, 2019 3:23 pm

I would be amazed if there aren't overloads.

The 50 A is reactive current.

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Bentworker
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Re: Large motors and soft start

Post by Bentworker » Sun Jun 09, 2019 3:37 pm

I'm on the Wye-Delta bandwagon.

Probably the most cost effective. Might even be able to cobble one together with used parts.


If blowing the utility owned fuses on the high side of the transformer still worries you…

You may be able to make out the nameplate information of the transformers that serve you with a decent set of binoculars or a spotting scope from the ground (nameplate is normally on or near the brackets on the tank). Also depending on the type of fuse, the fuse may be externally marked well enough to look up the fuse curve. If you get curious enough to break out the optics and take a look post up what you find. For obvious reasons you don't want to get any closer than ten feet to any high voltage goodness...

By going to a Wye-Delta starter my gut says that you'll be fine, since you got 5 starts out of it at last time at about twice the locked rotor current than a Wye-Delta setup will have.
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Harold_V
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Re: Large motors and soft start

Post by Harold_V » Sun Jun 09, 2019 4:00 pm

Just want to let you folks know I'm reading each and every comment, and I thank you for the time you're dedicating to help me solve my dilemma.
In regards to the current the unit draws when up to speed, but idling, it should be noted that the control circuits are all 120 volts. There's a relatively large internal transformer that provides the necessary voltage, hooked to the A & C phases, with both of those indicating the 50 amps mentioned. What I didn't mention was that the B phase (the high leg) displays only about 42 amps current.

I was impressed with the numbers provided for the performance of time delay fuses, with time intervals being quite generous. I need to discuss this with PUD, to see if they might have similar options for fusing the primary.

There are no other users on this service. The three transformers are in my yard, near the shop, with the fused disconnects (for the primary) about 500 feet away. That may be in my favor, as what they do with the service doesn't interfere with other customers.

Of interest, perhaps. Power factor, I believe, is playing a role in this problem. I know the unit is not in unity, but because I don't have the cooling system operational yet, I am unable to excite the generator. Once the unit can be fully loaded, with the generator operating at unity, that will change. At that time PUD may discover that a capacitor bank is necessary. Shifting power factor so the motor operates at or near unity may help solve the problem.

This power supply has a set of five water cooled capacitors that are involved in the generator output, which is at 400 volts, @ 3,000 Hz., single phase. There's a large number of relays that switch the caps in or out of the circuit, with meters that display voltage, amperage, wattage and power factor. I am able to control power factor from the generator, as the furnace is constantly changing in operation. Any switching of caps is done with the field not excited, so the change is not done under power. All of this occurs in the process of using the included switch device. None of this should be confused with the fact that the motor is not in unity with the power supplied by PUD---which may also require a cap bank.

It has taken me a lot of study to understand how this unit works. I am out of my element, to be sure.

H
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rrnut-2
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Re: Large motors and soft start

Post by rrnut-2 » Sun Jun 09, 2019 4:10 pm

That is the same way our old MG set operated as well. They bought Inductothem PowerTrak's and a lot of the "watching of the meters" went away. At that point, the only meters were KW, furnace Volts and Frequency. The new units now, it's all done automatically with the microprocessors.

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Bentworker
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Re: Large motors and soft start

Post by Bentworker » Sun Jun 09, 2019 4:31 pm

Do you get billed for Kvar hours? FYI- out west small commercial where I am are paying $.60/kVar hour.....compared to about $.14 kWH.

On the subject of fuses...

The utility picks a primary fuse based on the size of the transformer. The transformer has a damage curve, it can be a little overloaded for a long time, or really overloaded for a short period of time and be on the “safe” side of the damage curve. They select a fuse with similar curve, so that the fuse will blow before the transformer suffers damage (hopefully).

I very much doubt they would be agreeable to installing larger fuses, I probably wouldn’t ask, because the last thing you want to do is attract utility attention to your giant inductive load with horrible power factor. You might find yourself paying for larger transformers, power factor correction etc...
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liveaboard
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Re: Large motors and soft start

Post by liveaboard » Sun Jun 09, 2019 5:21 pm

A friend of mine has a large wood planer with a star / delta start switch.
It's a manual 'star-delta' rotary switch, which is a standard item on this side of the pond.
I used that machine a LOT. made cabinetry and furniture, doors and windows.
The procedure is to switch it on start mode while it speeds up; due to the weight that has to get spinning, that's about 4-5 seconds.
Then switch it over to the run setting.
The switch also had a sprung momentary reverse position, for stopping the blades.
Otherwise they'd keep spinning for a long time.
The planer is 7HP; a toy compared to Harold's monster. At least 50 years old too.

spro
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Re: Large motors and soft start

Post by spro » Sun Jun 09, 2019 7:11 pm

I agree how this worked, yet these days I don't have any motor near 7 hp. My experience was more test runs and maintenance of fair huge generators for immediate back up, when losing phases of commercial supply. Phases would come back as the commercial power was dealt with at much larger scale. Switch gear had to be continually improved to detect the way it may go. Consider a few turbine generators already up to speed and powering crucial equipment, then interruptions, as the commercial feed started and stopped. There were signals , if you were right there, to switch it before the engines wound down. Never want them to wind down. Never want the Cats to get an "all clear" signal when the storm or whatever, wasn't over.
There were tons and tons of battery backup ( More tons than this, in the old days). Dedicated battery banks to start the emergency engines and somebody like me checked them regularly.
Of course the near worst thing was two feeds fighting. During generations of switch gear and receding memory, it was timing where this may apply. if you see noticeable difference or even a reading on your gauges, it means it isn't totally disconnected from your starter circuity .

John Hasler
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Re: Large motors and soft start

Post by John Hasler » Sun Jun 09, 2019 7:28 pm

Bentworker writes:
I very much doubt they would be agreeable to installing larger fuses, I probably wouldn’t ask, because the last thing you want to do is attract utility attention to your giant inductive load with horrible power factor. You might find yourself paying for larger transformers, power factor correction etc...

The utility did the measurements for him so they already know what he's up to. I don't think they'd be willing to go to larger fuses, but they *might* be will to go to ones with a more favorable curve. I think that a wye-delta starter is the right solution, though.

spro
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Re: Large motors and soft start

Post by spro » Sun Jun 09, 2019 11:09 pm

Phases must be in sync with supplied power but getting there is the pickle. Loads; as in entire banks of equipment, must be switched on in priority rank and balanced among many less critical loads. It was that entire floors of a building wouldn't go dark because there was immediate battery back up. While that was happening, the great turbines and engines were coming up to speed.
They had to sync together and the LMC ( load management center) had to detect quite a few things. I saw about four changes and upgrades and safe to say now there were many more.
There was a time when many people were dedicated to the power plant of one building. It was all hands on..then. They cleaned every switch and did everything according to bsp practices then. I worked in that same building a few years to see the last of the huge "White" generators being dismantled and scrapped. The building is from around 1911 and sometime around WW1 there was a total black out in Wash DC. These buildings, These massive power plants were switched into the grid to provide power to Wash DC during those those crucial times.

armscor 1
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Re: Large motors and soft start

Post by armscor 1 » Mon Jun 10, 2019 12:48 am

Worked in an oil refinery where we had a GEC Alstolm 10 Mega Watt motor, 11KV, about 13000 HP driving a Sulzer axial blower supply air to our Cat Cracker, the beast was Direct on Line and we had to contact electric utility provider before starting so they were prepared for the sudden load change.
I was responsible for the maintenance and upkeep of the motor and switchgear.
On startup every cabinet and piece of equipment in the MCC would rattle and shake and all the UPS's in the refinery would switch to battery supply due to the power dip.
Took 17 seconds to get to speed!

K. Brouwers
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Re: Large motors and soft start

Post by K. Brouwers » Mon Jun 10, 2019 6:01 am

Hello Harold,
My vote is to try hook up a Y delta starter first. We have a wide-belt sander these are a bit hard starting it has a y delta starter. The machine starts and runs on our 15Hp rotary converter on a 100A 220V line. I think you could also use a vector drive but thinking of having to buy one for a 50Hp motor makes me weak in the knees. :lol:
IMG_8908.JPG
This is a photo of the contactor set up. (sorry its sideways tried to fix it either turn your head or the screen) :wink: The White contractors are the y delta switching relays they are controlled by the timer (round dial on little square block) The main contactor is the black block.

It is set up with ordinary magnetic contractors. so you would need to get a timer and two magnetic connectors as you already have the main contactor in your machine. You could probably get a schematic from the internet.
Hope this helps.. I am also electrically challenged so I am sure you can do this.
Cheers
Karel

armscor 1
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Re: Large motors and soft start

Post by armscor 1 » Mon Jun 10, 2019 8:03 am

Hi Harold,
It is absolutely imperative to know what type of motor you have.
1, Does it have 6 terminals?
2, Is it configured for Star or Delta?
Easy way to check is to isolate supply and remove terminal box cover, if 6 terminals and you have 2 links in series it is a Star connected motor and Star/Delta starter is out of the question.
If you have 3 links in parallel it is Delta configured and Star /Delta starter is possible.
Hope this helps.

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