I would like to obtain the magetizing impedance characteristic, voltage versus current, of motors and transformers, on site, 4160 V system. I don't think it is so easy, as voltage would need to be varied from below 4160 to above, or use of some frequency methods. Does someone know if this can be...
In Ieee 242-2001, "Recommended practice for protection and Coordination of Industrial and Commercial Power Systems", Table 15-2, a value of 0.12 sec. is given for relay tolerance and setting errors, static relays, coordination time interval, field calibrated relays.
I'm wondering what the true...
IEEE 242-2001, p605, suggest a coordination interval of 0.12 between fuse and upstream static relay. Others, suggest similar values such as 0.10, for example, http://siemens.siprotec.de/download_neu/applications/SIPROTEC/english/Appl_03_Coordination_of_Overcurrent_Relais_with_Fuses_en.pdf
I...
Has anyone seen references on the effect of probe depth vs probe spacing using the Wenner 4 point method. It is easy to see statements that spacing to probe depth should be 10 or 20 to 1, and formulae are available when spacing is not much greater than probe depth. However, exact backup is not...
For 5 kV switchgear, main or feeder breakers, I expected enclosure type to be Box. However, I am looking at a study where Open type was used, which gives a lower calculated incident energy. Has anyone seen something on this?
We have multiple motors to start, at 6.3 kV, 50 Hz. The power system is weak. We have looked at the following system:
http://powersystemanalysis.com/EasyMVStarting.pdf
My question is if anyone can see some areas of improvement on the switchgear part.
Has there been any concensus on which currents to use as bolted fault current on MV, Hi-R grd systems. I ask because arc flash standards caution against overly conservative fault calcs. However, fault calculation standards are just that. I have a max level from Ansi C37 momentary 0-1 cycle. For...
For industrial systems, I am used to seeing power factor correction capacitor discharge resistors, in minutes. A special design appears to have a discharge in seconds or perhaps a fraction of a sec. Does anyone know of limits on quick capacitor discharge.
Has anyone seen references with cooling and heating thermal time constants for dry type transformers. I'm also wondering how to best measure that on site.
When a 4160 V motor is started by an AC Drive, and the AC Drive is used to start other motors as well, then the motor must be transferred from the AC Drive to the main power. My concern was that the motor must be disconnected from the AC drive before transferring to the main. That would seem to...
Does anyone know of a source for methodology to calculate motor acceleration by a drive. The load torque will vary from standstill to full rpm, so that seems to eliminate the formulae in the Nema application guide, for a more exact calculation.
My first thought was that with a frequency ramp...
I am trying to understand and interpret tripping curves presented by IEC LV MCCB manufacturers, specifically thermal magnetic. These are normally presented as single curves. There must be non-tripping time and current-breaking time with tolerances. For US devices, we usually see the min/max or...
Ansi equipment on 50 Hz project. 4.16 KV vacuum CB's designed to previous C37 constant MVA rating, not the newer standards in the C37 series which have constant KA ratings.
Tables in the C37 standards, on preferred ratings, are at 60 Hz. Is there a procedure to use these standards for 50 Hz...
On a programming level (C++, etc.), I want to read items from the autocad drawing to import other applications sharing the data, to save re-entry time. This would be separate and external to autocad. Does anyone know where the autocad database details are available. Would this require a certain...
I am looking for modern books and references on calculation of torsional vibration, such as the torque harmonics of a reciprocating compressor. The ones I have are ancient, by Ker Wilson and Nestorides. Any popular modern ones or were those the final word?
I find that at least one motor manufacturer allows their marketing staff access to motor performance data for manipulation, recalculation, etc. At design stage, we get sloppy spreadsheet submittals, obviously assembled by sales staff. Some data is obviously calculated by sales persons, and...
If a VFD's supply voltage sags for several seconds in the order of 10%-15%, and the VFD is previously at full load, rated voltage and 60 Hz speed, then what is the typical drive response. Will it shut down on low voltage or overcurrent? This is a common problem.
