Many motors should not be operated in reverse because their cooling fans only cool them properly when turned in one direction. When this is the case there should be a direction arrow stamped on the motor. Most smaller motors (for example almost all 460 volt motors) are bidirectional and their...
By now I'm guessing that JigaWatt has made his decision and acted on it. But here's another piece of advice which might be more of a cliche. My dad used to tell me that a good way to make a decision after weighing all of the factors and still being undecided was to flip a coin. When you catch...
There is no hard and fast rule as to which state you should get your PE in. You can take your EIT (FE) anywhere, as far as I can tell. If you live and work near the Indiana/Illinois border you can choose to get your PE in either state, although it is probably more common to get it in the state...
A lot of great responses here. The original question didn't specify utilization voltage or application (underground, cable tray, conduit) which would be strong determining factors.
Tree resistance has been discussed, which would suggest EPR for underground or wet applications.
Temperature...
In justifying the purchase of a spare 13.8 kV breaker for a 15kV metal-clad lineup I was asked a question about the failure modes of a medium voltage breaker. Our breakers are vacuum interrupter type. I've heard of catastrophic breaker failures happening, but the ones I'm most interested in...
I posted a question in the Electrical activities area and received a response that led me to http://www.xldp.com which specializes in professional liability insurance for engineers, architects, and environmental people. I have yet to talk with an agent of their company but at least it's a good...
We are looking at adding Hydran oil monitoring systems to our important transformers. Probably model 201R. From reading the literature, it only makes sense to monitor gases in the oil continuously, thereby determining if some overheating, arcing, or low magnitude fault is going on inside that...
If you can obtain a copy, I recommend reading "The Whys of the Wyes", a General Electric publication numbered GET-3388B and dated 1967. That paper points out that the first 3-phase transformers were all wye-wye but that the numerous problems of this design have significantly reduced their use...
In anticipation of doing some consulting in the near future I have applied for Professional Liability Insurance (PLI) but I don't expect a response for a week or two. Meanwhile I'm trying to estimate the cost for putting together my rates. I have a few questions for the forum.
1. Is it...
I am waiting for quotes on Professional Liability Insurance and the percentages listed above are scaring the heck out of me. Is it typical for PLI to cost 10 to 25% of billing fees?
If you have two separate power sources you must choose a transformer vector to make the two sources match. For example you may have a primary source at 35kV and have a backup from a 12kV distribution system. It is likely that these two are not in phase with each other so you must choose...
A lot of good information is imparted above, but some key points are missing. Improving the cooling will improve the thermal characteristics of a generator, which is important for steady state and any long term operational parameters. But if you're concerned about occasional motor starting...
We have a 10/12.5MVA sealed transformer operating at 13.8 - 4.16kV and our recent oil tests gave "unacceptable" results for the power factor. The transformer consistently has a positive pressure nitrogen blanket on it, approximately 3-5 psig. I think it is very unlikely that water is...
I am amazed at the increase in price for the T&D book. I looked inside the cover of mine and see that I paid $85 for it buying it from ABB in August of 1991. Those two new chapters had better be good! Out of all of the books on my shelf, this is my go-to book. I agree with the positive...
I am confused by the situation you describe. While the machine is running there should be an oil film which causes the driven end bearings to be somewhat insulated. The shaft grounding brushes should shunt off any shaft voltage, reducing the current through that bearing to 0 or very close to...
Since you say a 2MVA transformer we'll assume you're talking low voltage, 480V or similar. I would agree with recommendations above to use aluminum busway, not nonsegregated phase bus duct. It is smaller, less expensive, and simpler to disassemble if you need to do so.
I agree with RonShap on...
In retrospect it may have been best to use oil-filled. But since this is an existing installation I don't want to have to build new foundations and deal with oil catch basins & oil water separators. So I have ruled out oil-filled.
Years ago I attended a Square D presentation where they sang the praises of cast coil or cast resin transformers. It was even stated that they have been successfully operated underwater in the ocean, showing how wonderful the insulation system is for wet or dirty environments. I know one...
The ANSI/IEEE C57.12 series covers this for US standard transformers. Generally C57.12.00 should have what you need, although other standards in the series cover various types of transformers.
Check out thread237-35734. It's in the electric motors and controls engineering forum on this site and a nearly identical question is asked and answered.
