Gr8blu / xnuke,
Thank you for your time replying. It is certainly more clear to me now, but I need to fully absorb the depth of what has been said to finally get there. I am always thinking of how to relate topics (any topic) to someone who asks me, and I need to visualize things to be able to...
Hi Hoxton,
Thank you for the reply, but to my knowledge these currents do actually exist, and they counter rotate and therefore cut the rotor at 2x fundamental frequency. This causes rapid overheating of the rotor ends (in particular) and eventually ruins the machine.
I don't understand the...
Searched the thread archive for this one, but didn't find what I was looking for.
After showing someone how to calculate NPS currents from Generator data, they asked my a question that I had never even asked myself, and couldn't answer - What makes NPS currents rotate counter to the rotating...
No argument there, but as there are hundreds of them on this site (and thousands on other sites), and the fact that Manufacturers keep making them, Projects keep installing them, and Standards keep quoting them, then the question still stands.
I did nearly have an epiphany though - a sudden...
Follow up:
I have come across NETA 2015 Standards stating the following:
Sec 7.16.1.1.B.4 Test motor protection devices in accordance with manufacturer’s published data. In the absence of manufacturer’s data, use Section 7.9
and
Sec 7.9.1.11 49R Thermal Replica Relay: 1. Determine time delay...
Quick one for the North American audience:
Are there any standards (NEMA/NFPA/NEC or other) that specify that thermal overloads need to be current injection tested periodically, and/or after replacement?
There are pro's and con's for testing them - pro's are obvious, but the con's are that they...
Thanks waross,
Sometimes it doesn't take much for the penny to drop. By reading your opening few lines I suddenly realised where I was going wrong - all phases simply take their positions relative to the grounded point, and not the hull assuming a potential of the phase(s).
I take it that my...
I have attached a hand drawing of what I believe are the vectors for an Ungrounded Star, and an ungrounded Delta system, and shown it with a ground fault, on different phases, on the two different voltage systems.
Link
Please comment on them - good or bad.
The first one (Ungrounded STAR)...
Fuse4,
Thanks for the reply.
I'm not sure that I will be going out to buy the book specially for this, but it does look to be the kind where I could find out the answer.
I take it that because you are the only responder (and I appreciate that), the question cannot be readily answered by other...
I am having a bit of trouble getting my head round a problem regarding to systems of varying voltages running in Isolated Earth configuration. It is a floating vessel which comprises of a Topsides earthed system at 13.8kV, and feeders from the Switchboard go to the Marine side (Hull)...
@electricalpete: no you were not fooled by my title. I was indeed after the electromagnetic influences that tend to slow a Rotor down when load current is increased on the Stator of a Generator - that's it. I was not after an explanation on Isoch/Droop or Proportional/Integral control loop...
Gents,
Thank you very much for your insights and clear explanations.
@electricpete: Very interesting paper you have published there - like you say, the convention is to show (like I simplistically have) Stator coils in the air-gap, and I have actually wondered in the past what effect there is...
I need to roll out an electrical generation presentation to groups of Technicians to help underpin their understanding of generation principals. I was separately discussing with one of them about why Generators tend to slow down when load is applied, and how the Governor is increased to correct...
Waross,
I like the alternative way of looking at this very much - thank you very much indeed.
I have attached a hand-written pdf file depicting this. Looking at it this way makes me think how simple the original question was to answer (and why didn't I think of doing that...) - just goes to...
