Several motors and other loads on conductors

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ptonsparky said:
Wound rotor motors have a lower start up current. High torque. Mine had banks of resistors.

Were you given the motor without the control?
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I believe it’s just the motor so far so I’ll be sizing starters and breakers in a separate panel soon
 
Jpflex said:
How do you tell if it’s a wound motor? Can you tell by liking into windings and I know it’s not series connecting such as field and rotor. As far as resistors I doubt and I believe it isn’t speed controlled. Oddly the speed is under 1200 rpm and NEC says to go off of nameplate amperes instead of FLC table when determining conductor and overload protection
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Ball mill motors have output speeds that are slower than other motors. The ones I have experienced are wound rotors (2.6MW, 13.8kV) which use liquid resistors to limit starting currents. If you have a resistor tank or a set of grid resistors plus a drum controller switching equipment/ shorting contactors, most likely, your motor is a wound-rotor induction motor.
Ours have a shorting mechanism that totally shorts out the resistance inserted into the rotor circuit when the motor reaches full speed.
 
You know that this is a Wound Rotor Induction Motor (WRIM) because the nameplate says it in an Induction motor right at the top, plus it shows the rotor current and voltage data. You are correct that the rotor current and voltage is induced by the stator, so it is not supplied by the source. But you need the data from the nameplate in order to design the resistor control circuit for it. Back when this was made, external resistance control was the only option available and you could not use the motor without that. Nowadays you have the option of shorting out the rotor and using a VFD instead. On a motor that old with an unknown history (ie probably not rewound for use with an inverter in mind), I would stick to resistance control. From the source current standpoint, you are correct in that you will just use the nameplate FLA data. The rotor current is irrelevant for this purpose.

If you have never encountered a WRIM before, designing the resistance control for them when the OEM system is not there for you to rebuild or copy is not something I would recommend trying to tackle on your own. It is complicated and requires a lot of engineering with regard to the load profile and duty cycles involved. This needs someone with specific experience in Ball Mill WRIM applications. There are integrators out there who specialize in mining equipment that the owner should engage with for that part of the project. They on the other hand, typically do NOT tackle the distribution source part of this (unless maybe if it was MV). So you wouldn’t lose the rest of the project to them (typically).

The only other type of “slip ring” motor would be a Synchronous motor, and in that case the word “induction” would not be on the nameplate, and it would have “Field” data instead of rotor data. From the outward physical appearance, especially on really old motors like this, they look very similar to the untrained eye. But the nameplate reveals all.
 
"I’ve worked mostly residential before this job at a mine"
You are taking a HUGE step especially with a mine involved (there are Codes other than the NEC to take into account)
I would strongly suggest you get some help from folks familiar with larger services, ball mills and mines ie: a joint venture.
 
I was initially hired as a helper but company pays way under going rate for All their occupation classifications and therefore cannot get a licensed journeyman or line man for utility high voltage side.

At the ridiculous pay rate I’m at, they have shoved all this responsibility in me. I’ve taken work time to review NEC book, research and plan but I believe the companies snitch told owners I was sitting on the job.

What slap in the face BS I’m going through code And trying to do thing right as it’s my job. If they want to hire cheap then their expectations should reflect that. The trade off is me spending some time to review code or their ass pay triple hourly rate to a licensed journeyman.


Don’t misunderstand I’ve passed the central electronics technicians FCC test and ASE electrical back in my 20s with lots of solid state dc experience but heavy industrial AC and nec codes were new to me
 
Jpflex said:
I was initially hired as a helper but company pays way under going rate for All their occupation classifications and therefore cannot get a licensed journeyman or line man for utility high voltage side.

At the ridiculous pay rate I’m at, they have shoved all this responsibility in me. I’ve taken work time to review NEC book, research and plan but I believe the companies snitch told owners I was sitting on the job.

What slap in the face BS I’m going through code And trying to do thing right as it’s my job. If they want to hire cheap then their expectations should reflect that. The trade off is me spending some time to review code or their ass pay triple hourly rate to a licensed journeyman.


Don’t misunderstand I’ve passed the central electronics technicians FCC test and ASE electrical back in my 20s with lots of solid state dc experience but heavy industrial AC and nec codes were new to me
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Ooofda! Went through that sort of thing with a previous employer. Started as a floor electrician, then draftsman, then designer, then project management. When I balked between the draftsman and designer stages, because I did not consider myself competent, I was told "That is the only work we have for you..." From then on it was kinda toxic with me being somewhat Passive Aggresive. Took a while to find something else (and something else again...) They did end up looking for a true Electrical Engineer/Designer but not many applicants and they wanted 3 times my wages. Heard they got another floor electrician at my old desk now.

My advice: find another job!
 
Jpflex said:
Hi I’m trying to get a general idea on feeder size for ball mill building.

The largest motor has two ampere ratings on nameplate for 3 phase 380 volt source one at 225 amperes and another for rotor current at 150 amperes. Since this is a low RPM motor under 1200 rpm code 430.6A says to use nameplate current rather than FLC based on Horsepower and NEC tables. I assume I go off of 225i ampere rating?

I’m not sure when you would go off of field current vs rotor current. Rotor current is merely induced voltage current from field.

When trying to figure out feeder I’m following NEC 430.24 for multiple motors and loads on a circuit

So far I have two identical large at 225 amperes with one being rated at 125% and the remaining motors at 100%

225i x 1.25 + 225 = 506.25 amperes so far
Plus

2 vat motors 7.5 of 3 phase with 11 FLC amperes each 2 x 11 = 22 amperes

6 more motors at 25 horsepower each or 34 FLC amperes each x 6 = 204 amperes

Ball mill general lighting VA based on outside dimensions 2485.02 sq ft x 1.7VA (workshop?) x 125% continuous load = 5281.28 VA

5281.28 va / 480v x 1.73(3 phase) = 6.35i amperes (Or do I go off of 120 v single phase voltage divider for lighting?)

Total all up = 738.6i amperes BUT table 310.16 only goes up to 665 amperes at 70 degree rating with 2000 kcmils

And there may be more motors being added

What do you do? Does this seem right so far?
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What does the Feeder Feed? Stator or Rotor?
 
xformer said:
What does the Feeder Feed? Stator or Rotor?
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Depends if output secondary windings are stationary or output from rotating rotor. I believe most common is stationary secondary output with rotor being excited thus mitigating sparkling / commutation

But for this huge old motor I would need investigate
 
TwoBlocked said:
Ooofda! Went through that sort of thing with a previous employer. Started as a floor electrician, then draftsman, then designer, then project management. When I balked between the draftsman and designer stages, because I did not consider myself competent, I was told "That is the only work we have for you..." From then on it was kinda toxic with me being somewhat Passive Aggresive. Took a while to find something else (and something else again...) They did end up looking for a true Electrical Engineer/Designer but not many applicants and they wanted 3 times my wages. Heard they got another floor electrician at my old desk now.

My advice: find another job!
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But I need 4,000 more hours before I can take my journeyman’s test
 
Jpflex said:
But I need 4,000 more hours before I can take my journeyman’s test
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Yeah, everyone's gotta start somewhere. Just wish you were in a better situation. If the company is pulling this kinda of stuff with design, there are surely other aspects in the business that are iffy. Don't let them make you remove or install any old MCC cubicles while energized!
 
Jpflex said:
But I need 4,000 more hours before I can take my journeyman’s test
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Sorry, but that situation on a job of this nature seldom, if ever, has a good outcome.
Take TwoBlocked and Roger's advice !
 
TwoBlocked said:
Yeah, everyone's gotta start somewhere. Just wish you were in a better situation. If the company is pulling this kinda of stuff with design, there are surely other aspects in the business that are iffy. Don't let them make you remove or install any old MCC cubicles while energized!
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I write a post a few months ago regarding the company not wanting to buy proper sized fuses and starters with appropriate sized heaters for an assembly of rock crushing motors. Instead the company wanted to use old rusted large starters in junk piles.

When I told the owner about this he said I was just overthinking it. So he went and hired another worker willing to install whatever they supply him.

However, most of the response I got from people on this forum was that I was making a big deal about using rusted starters. They were nonchalant on the heater elements, so I quested whether I should just do it. Furthermore, NEC does nothing to protect an employee who is terminated for not following company orders even if illegal to electrical code.

Some may say there is a shortage of skilled workers and surplus of electrical jobs but I have yet to see that in my area. Therefore I travel 3 and 1/2 hours and stay on job site each week sacrifice time get my work hours for testing purposes
 
Here, there is no Journeyman requirement. I (with 20+ yrs and past retirement age) started at a plant a couple months ago along with a young guy with only poor votech a number of years ago. (Uh, why is there a white wire...) They were desperate enough to give a $6K cash sign on with the 1st paycheck. They are still looking for another and there is a year or more of training. Here they are hiring the "newlyweds and nearly deads."
 
TwoBlocked said:
Here, there is no Journeyman requirement. I (with 20+ yrs and past retirement age) started at a plant a couple months ago along with a young guy with only poor votech a number of years ago. (Uh, why is there a white wire...) They were desperate enough to give a $6K cash sign on with the 1st paycheck. They are still looking for another and there is a year or more of training. Here they are hiring the "newlyweds and nearly deads."
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Dam I wish similar opportunity came to me but in the desert where I’m at there isn’t much. I’m hoping that working under the c10 license of my company as an electrician will count toward my 8k on the job hours prior to qualifying for journeyman licensing testing?
 
Rock crushing operations are notorious for using old junk and sketchy practices. They have little respect for the value of having reliable electrical systems, until the moment when that unreliability starts costing them more in lost production that they would have spent doing it right.

Using old rusted starters can work, for a while, but rust and electrical equipment are incompatible, so expect rapid failure. Using the wrong heater elements however also risks damaging the motors too, which can cause much more expensive down time, not to mention the cost of the motors.

But sometimes you have to just voice your objections and then do what they tell you (so long as it’s legal) then when the failures happen, only mention your objection if they attempt to pin it on you. Otherwise, do as they ask and take the paycheck.
 
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