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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...

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 -...

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...

I am investigating possible arcing of connections on the primary side of a wye-delta transformer feeding a 6-pulse, three-phase SCR-based exciter. The arcing led to a small electrical fire so there isn't a lot of evidence left of where things might have started. The transformer is 18kVA and...

All, I have a 480:120/240V single-phase transformer. The secondary side has the standard four wires out and are wired in parallel to only put out 120V. The transformer nameplate says "Percent Imp (2) 2.8" and it is 15.0kVA. Does the "(2)" in the first nameplate suggest that the % imp is...

I am being asked to supply test procedures that I have used to test relay logic wiring on MV Switchgear for a publicly posted follow-up bid process. I only shared these with people inside our company until now and the previous swgr was tested only with my full attendance and oversight This is...

Sorry, this is probably a bit obtuse. I have a multi-conductor 600V rated cable running from a switchboard to an excitation panel. The cable uses only four of the 14AWG wires in it for switching a relay in the panel and two other feedback contacts to the switchboard, numerous other spares in...

All, We have a 4160 island power system that is high-resistance grounded (broken delta PT tertiaries only on one common bus switchgear cubicle, not each cubicle set of PT's, alternators actually floating). The switchgear has vacuum breakers and so came with small surge "limiters" that were...

I've noticed in some fault current and arc flash studies I've seen lately, that the low voltage systems produced higher incident energies (cal/cm2) than those for medium voltages of similar power levels. My sample size is probably just too low and I know that it is probably quite complex. I am...

All, We have a 4160V, ~3MW diesel genset that went through some bad juju with arcing in the entrance cubicle of its attached switchgear cubicle. Previous loss of PT fuses on shutdown led the voltage regulator to take it very high on ramp up from idle to rated (perhaps as high as 150% and for a...

All, I am investigating the upgrade of an old 5,000Hp 150rpm DC motor to AC for a pump application. Am curious about an "off-the-shelf" induction machine operating off PWM versus synchronous due to up-front price. Appears that an 8-pole induction machine is not stretching this too far but...

All, I have read some whitepapers that indicate that IEC 60034-18-41 & -42 are superior to American standards NEMA MG 1, Section 31, IEEE 522, etc when it comes to helping avoid premature insulation breakdown of motors downstream of PWM VSI's: "New IEC standards for qualifying stator...

All, We are looking at upgrading an old Ward Leonard loop with DC gens to AC synchronous generators. The DC motors involved would be retained. We are a remote operation with utility power an impossibility. I am trying to estimate what levels of ripple current one would expect from ~1600kW...

All, Could anyone suggest any industry standards or otherwise as to the maximum energizations per time frame one should limit oneself to with transformer inrush? Will be doing some testing soon involving four identical 2800kVA three-winding transformers, 600:375:375VAC, with multiple breaker...