First, I really appreciate the replies, and from some very knowledgeable posters that I've learned from just reading threads I'm not even in. FWIW, we have no fuses involved and the transformers will always be unloaded during transformer inrush. Yes, I don't discount the 0.5% probability case...
Hi All,
I was just curious if anyone has any better or contradictory information on transformer inrush probability than this excerpt I found (out of a PhD thesis by Jinsheng Peng, "Assessment of Transformer Energisation; Transients and Their Impacts on Power Systems", Pg. 174):
"Furthermore...
Hi All,
I have worked with two large system integrators on 4-5 different projects the last few years. They have competing views of cable insulation for 690V motors operating off VFD. One recommends a specific VFD cable with 2000V rating, three symmetrical ground wires, shield, etc. The other...
All,
My textbook "Power Electronics: Converters, Applications and Design" by Mohan/Undeland/Robbins has served me well for over 20 years. I've used it for DC drives, LCIs and through to PWMs. It does have fairly good coverage of an AFE's use to interface to a grid. The DC bus voltage of Vd...
Thanks for everyone's helpful discussion! I should clarify, I am only concerned about arc flash energies inside the switchboards that these generators are feeding into. There is a pair of switchboards with bus-tie interconnection and six generators each about 1MW in size. At least one would...
RRaghunath, thanks. But, with the short circuit of the field, it will still be flowing. Won't that mean it will continue generating voltage and feeding the fault? Wouldn't opening a generator main breaker be the fastest way to interrupt that fault?
All,
I am on a project where the systems integrator is proposing an AVR trip for generator short circuit rather than generator OCPD trip. I am concerned about the implications for arc flash incident energies and the time it would take for:
1) the control system to recognize the fault...
All,
To the best of my knowledge, North American standards like NFPA 70E and IEEE 1584 regarding arc flash have no equivalent to IEC 61641 for "arc ignition protected zones". I understand the IEC used to refer to this as "arc free".
In Section 1 (Scope) of the IEC 61641, it ends with the...
I am working with an energy storage application. A three-winding transformer is in use. The utility feeds the primary winding medium voltage. One low-voltage secondary feeds an energy storage inverter with lithium-ion behind it. The third winding steps down the utility power and feeds a...
I am making a speadsheet/chart of different motor costs to the end user (industrial). I used catalog list prices from ABB/Baldor for primarily 6-8 pole machines, TWMC for larger medium voltage and Lafert and Toshiba for PM motors. I also added a curve from USDOE for a more common type, not...
All, I know this has been discussed before in more general terms. Referring to the IEEE Std 141 typical reactance values, they list xd" as 0.16 per unit for 12 poles or less (salient-pole with damper windings). In my experience with low-voltage diesel-driven 4-pole gensets in the 100kW -...
ScottyUK,
That's a pretty fascinating (and large!) application. Thanks for sharing that. I wish I could implement something like that at this juncture. But, the selenium suppressors are needing replaced fairly quickly so I obviously was hoping for a less involved solution. Still, it might...
Gunnar, much appreciated. Unfortunately, the exciter does reverse its voltage output when online to collapse the field quickly and regenerate back. My initial thought along these lines was to just use two avalanche/zener diodes (a typical cathode connected power diode module with three...
I have a project involving large 7000Hp DC motors with 19H fields with a resistance of about 5ohm. They normally need around 20-50A of field current for most all operating scenarios. Currently, the system has selenium suppressors installed for overvoltage suppression if the exciter suddenly...
