Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Weressl...
Josh said he had 2400V switchgear available.
Regards, Phil
Josh said he had 2400V switchgear available.
Regards, Phil
Maximum recommended motor hp served at 480v??
- Thread starter joshtrevino
- Start date
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weressl
Esteemed Member
Indeed, he did. SoOrry....
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Josh...
If you are faced with afuture upgrade to 4,160V, then purchase a Dual-Voltage motor: initially to operate at 2,400 V (Delta connected); and later to operated at 4,000V (Wye-connected) in the future!
Jraef...
Your comment about MV-qualification of techs' is almost verbatim to what I was told when I presented my study to raise HPI-plant LV-distribution voltage from 480V to 830V!
Regards, Phil
If you are faced with afuture upgrade to 4,160V, then purchase a Dual-Voltage motor: initially to operate at 2,400 V (Delta connected); and later to operated at 4,000V (Wye-connected) in the future!
Jraef...
Your comment about MV-qualification of techs' is almost verbatim to what I was told when I presented my study to raise HPI-plant LV-distribution voltage from 480V to 830V!
Regards, Phil
iceworm
Curmudgeon still using printed IEEE Color Books
- Location
- North of the 65 parallel
- Occupation
- EE (Field - as little design as possible)
The "motors are scarce" part surprizes me. As was mentioned, it is just a matter of connecting the coils Wye or delta. I don't think I have ever seen a 2400V, 4160V, 480V (over 250Hp) that is 'off-the-shelf". No matter which voltage one chooses the motor is going to be built.
ice
iceworm
Curmudgeon still using printed IEEE Color Books
- Location
- North of the 65 parallel
- Occupation
- EE (Field - as little design as possible)
I keep hearing this but I never get any reference as to exactly who is mandating this qualification or what it amounts to.
Another issue is, what is meant by "work"? Original installation? Un-bolting connections to change out a motor?
Changing bearings? Pulling maintenance on an MV CB?
The state usually requires a COF for original installation. All else doesn't require any state certification.
Osha (and NFPA 70E) talk about "qualified". However, other than saying one has to understand the hazards and how to mittigate (paraphrased), gives no clues about how one might do this. And one has to understand the specific LOTO for the equipment (again paraphrased). All of the companies I've worked for - the company decides exactly what "qualified" means.
I've looked up all the references given in other threads (the threads I have seen, anyway). So far, all certification organizations were self-certifying - as in the specific organization is the one to issue a certification because they say they are the ones to certify.
I'm not suggesting that any ordinary shoe clerk can undertake MV maintenance. I'm saying I don't know of any state or federal mandate for certification for in-plant MV maintenance. This is not to say that some (state of federal) agencies could easily require some specific certification to work on their gear.
Help me out here - what am I missing. And it could be that the state I'm in is silent on the matter - and all other 49 require a specific certification.
Color me clueless on this issue
ice
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
OSHA.
Got this from an inspector once with regards to a project where we installed some MV soft starters, and the City got dinged for not having a "qualified worker" to deal with them.
"29CFR1910.269(x) defines a qualified person as ?one knowledgeable in the construction and operation of the electric power generation, transmission, and distribution equipment involved, along with the associated hazards.? OSHA 29CFR1910.269(a)(2)(ii) also requires that qualified persons ??shall be trained and competent in the skills and techniques necessary to distinguish exposed live parts from other parts of electric equipment; the skills and techniques necessary to determine the nominal voltage of exposed live parts; the minimum approach distances specified in this section (1910.269) corresponding to the voltages to which the qualified employee will be exposed, and proper use of the special precautionary techniques, personal protective equipment, insulating and shielding materials, and insulated tools for working on or near exposed energized parts of electric equipment.?
weressl
Esteemed Member
Let's clarify this. OSHA requires qualified workers for all voltage levels, not just Medium Voltage.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Yes. It's just that you can get qualified on 600V when you get an electrical license. MV certification is a separate course that not all electricians take. In the case where I learned this, the City had to send one of their staff electricians to get certified. When he was done, he demanded (and got) a raise. Smart cookie...
iceworm
Curmudgeon still using printed IEEE Color Books
- Location
- North of the 65 parallel
- Occupation
- EE (Field - as little design as possible)
No, that's not true.
The word "involved" tells me the qualification is equipment specific. Having a COF does not automatically grant "qualified" status for any equipment 600V and under. I'm absolutely not knocking the electricians. There is plenty of screwie stuff out there that one would have to be somewhat nutz to crawl into without special training - and the special training may only be reading the book. But once the training is documented (slip of paper in the file), that's called qualified.
Interestingly, COF holders are generally legally okay to install any in-plant equipment regardless of voltage - they just can't pull maintenance on it with out also being qualified.
Exactly. And the city should have gotten slapped for even considering sending in a maintenance tech without special training on the specific equipment. That is, qualified for the specific equipment - not a general MV certification.
Assuming this was an electrical tech, she should have already had arc-flash and shock hazard training. About all that is left is the equipment specific training for this particular gear - and again, that could be as simple as reading the book, I don't know. It really depends on the complexity of the equipment.
I have not seen any evidence that there is a state or federal mandated certification to do maintenance on in-plant MV equipment.
I have not seen any evidence that installation of MV equipment requires any certification past NEC journeyman COF.
I'm serious - help me out. I need to know where I'm getting this wrong.
ice
I would suggest that a "general MV training" does have some merits, and that equipment-specific training for MV equipment would be added on top of the general MV knowledge as needed for the specific equipment at the facility. Maintenance and construction each have numerous working practices that are quite different for MV vs. LV. For MV and LV work, think about: how to terminate a cable, how to acceptance test a cable after installation, how to test for the absence of voltage, and how to take current or voltage measurements.
Each of these basic skills needs to be established at MV first before any equipment-specific knowledge is considered. Knowledge of common MV starter and MV switchgear components could be addressed in the "general MV" training as well. After the basic understanding of MV working practices is developed then equipment-specific training can be added. Different MV starters have different ways of isolating primary voltage, applying test power, different relays have different front panel interfaces, etc. This equipment-specific training is often provided at the end of the equipment commissioning process by the folks that commission the equipment. If the audience has the general background knowledge it is fairly effective to compare and contrast the new equipment from other equipment the audience is familiar with, point out different features, and have everyone operate the equipment.
iceworm
Curmudgeon still using printed IEEE Color Books
- Location
- North of the 65 parallel
- Occupation
- EE (Field - as little design as possible)
jd -
I agree with everything you said - with one minor exception. I would say, "lots of merits"
ice
jahounou
Member
- Location
- Washington DC
Overheating of motor has to be considered.
Overheating of motor has to be considered.
Whether you decide to use 500HP @ 480V or 1000HP @ 480V, you need to consider the fact that motor will overheat which could increase the failure time. Refer to IEEE std 620 (thermal Limit curves) for further information.
There are other factors that should be considered as well like replacement strategies, delivery time of a new motor/availability of motor during downtime etc...
Jean-Jacques Ahounou, PE
Overheating of motor has to be considered.
Whether you decide to use 500HP @ 480V or 1000HP @ 480V, you need to consider the fact that motor will overheat which could increase the failure time. Refer to IEEE std 620 (thermal Limit curves) for further information.
There are other factors that should be considered as well like replacement strategies, delivery time of a new motor/availability of motor during downtime etc...
Jean-Jacques Ahounou, PE
weressl
Esteemed Member
What are you trying to say? Nobody is talking about overloading a 500HP motor to 200%?!
Not enough.
Perhaps you were misled.
For a maximum size of 500 hp motor, minimum transformer size is 2.5 MVA at 480V . The total load shall not exceed 2.0 MVA per NEC.
iceworm
Curmudgeon still using printed IEEE Color Books
- Location
- North of the 65 parallel
- Occupation
- EE (Field - as little design as possible)
Really? I didn't know that. Where exactly does the NEC say that? Please cite article numbers.
ice
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
I did not know there were any minimum sizing requirements for transformers to be found in the NEC. Where might I find them?
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Searching the term "MVA" only returns one result for the entire NEC pdf that I have, and that has nothing to do with maximum sizes.
The closest I could come to this concept is that in 240.2, the definition of an "Industrial Facility" for purposes outlined in part VIII of that section must be 2500kVA (2.5MVA) or greater, which then indirectly implies that anything UNDER that 2500kVA level does not qualify. No idea how that all fits in with what this discussion is about, but my curiosity was raised as to where that comment came from. Seems to be maybe some sort of misunderstanding perhaps?
The closest I could come to this concept is that in 240.2, the definition of an "Industrial Facility" for purposes outlined in part VIII of that section must be 2500kVA (2.5MVA) or greater, which then indirectly implies that anything UNDER that 2500kVA level does not qualify. No idea how that all fits in with what this discussion is about, but my curiosity was raised as to where that comment came from. Seems to be maybe some sort of misunderstanding perhaps?
weressl
Esteemed Member
Fundamental.....
Hmm..
Which NEC rule says the load current of an equipment not to exceed 80% of its current carrying capacity?
- Location
- Massachusetts
- Status