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Responding to Tim Mitchell's Fri, Nov 20, 2000, 11:35am query: Before recommending cable and protective design criteria, please provide the following: (a) Are you sure that transition is only 20 ms (2 cycles @ 50 Hz)? Reason: maximum asymmetrical first-cycle peak could reach 4,800...

Responding to Faizal's Wed, 13-Sep, 1:17 pm query... Please elaborate on the information you need, or provide additional detail regarding your study's goal: a) When referring to control and block diagrams do you mean the "open" and "close" control circuits of the breaker? b) When...

Responding to Johan's Sun, 10-Sep, 3:10 pm comments... we're getting closer: Now reconnnect B stator so that it lags (or leads) A stator by 120 deg.. The mathematical model I used is the same as that used for the "hot" terminal problem. However, for this application let Ea represent motor...

Responding to Johan's Tue, 5-Sep, 3:35pm comments... I appreciate your dilemma with your students. Therefore as an aid to understanding the phenomena, try this: Consider two stators driving a common rotor. Stator 'a' develops a rotor emf, Ea, producing rotor current, Ia. It lags the rotor...

Responding to Richard King's Mon, 28-Aug, 10:50am query: Although you mentioned having investigated a trip-wire solution, have you considered a system having the following characteristics: 1) "Loop" a "bare" trip-wire so that it is offset about 1 meter around the boom's perimeter. The...

Responding to off-list queries about... phasor sequence convention. First, let me state that there is no conventional way to label phasors. The method one uses depends on the text he or she used in school. One can choose any direction for the reference phasor. But once selected, then...

Ec the info for Brian Joles in my Wed, 30 Aug, 2:05 pm: Using USA convention, a line-to-line voltage vector that is labeled Vca, is a vector directed from line c to line a. Following is the derivation of vector Vca from the line-to-neutral voltages Van and Vcn. If line voltage between phases...

Responding to Bruce Durdle's Thu, 31 Aug, 7:40 am, comments.... overloads? Yes, both motors showed different overload magnitudes. The mathematical model shows that stator current is sensitive to actual loading. Perhaps the following will clear up some of the murky waters. Generally...

It is not clear what you mean by Reheater Protection, so I will presume that you mean: 1) failure of the reheat temperature control logic; and 2) failure of the reheat loop piping, spray water and temperature control valves. No, the NFPA has no restriction! In general the factors to consider...

Responding to Brian Joles', Wed, 30 Aug, 10:15 am, questions... speaking of single-phase: A1) No. Boost & Buck refers an arrangement of transformer windings arranged whereby the output voltage is higher (primary & secondary windings additive) or lower (primary & secondary windings...

Responding to Bruce's Tue, 29 Aug, 3:37 pm comment... Different size motors. The mathematics are similar if their speed-torque curves are identical, ie, full loads occur at the same slip. The combination can then be modeled by equating the larger motor's electrical characteristics in per-unit...

Responding to Johan's Mon, 28 Aug, 2:02 pm comment... I will proceed on the basis that my Thu, 24 Aug, 4:42 pm explanation, "Motors in Tandem" is still unclear. Consider the equivalent circuit for motor "A". A voltage, Es, is impressed on the stator's phase "A". A voltage, Er, is produced to...

Off-liners have asked me to explain, in lay terms, why the "CAUTION" flag for tandem-coupled motor applications. All electrical machinery have a "load-angle!" It doesn't matter that they are DC or AC, synchronous or induction, squirrel-cage or slip-ring, operated sub- or hyper-synchronously...

Respondng to Heather's query: Get Radio Shack's publication, "Getting Started in Electronics!" It is Orer No. 62-5003. The booklet has several simple, and reliable, variable DC circuits using FET's. Regards, Phil Corso, PE Trip-A-Larm Corp (Deerfield Beach, FL)

When you say the fluid couplings are fully engaged do you mean "locked-up?" If so, and if the 4 drives have identical characteristics, and they are fed from the same power source, then the overload of two could be caused by the phenomena I addressed earlier, ie, their respective rotors are...

Responding to Johan Bengtsson's 10-Aug, 8:24am comments.... Yes, you did miss something. There is no "self adjusting" feature when the two rotors are locked at some arbitrary angular displacement of their shafts. An aside. Referring to Donald Pittendrigh's 14-Aug, 2:56 pm observation...

Clearing up some misconceptions of my own: 1) Wed, 09-Aug-11:38 am, response to Dan Boudreault - I mixed USA and European practice. The mechanical shift equation should have been, (120°/# polepairs) or (240/#poles). 2) Thu, 10-Aug-4:21 pm, response to Arthur Tua - the phrase in...

Arthur, I have one last (?) thought... Do I understand you correctly? Is the goal of the "retrofit exercise" to reconfigure the SWRO plant so that the six 1,000 kW machinery trains will be reduced to just three 1,200 kW ones? If so, then how can you justify relocation, modification, and...

Arthur, there is another concern to investigate... Were the 11 kV motor feeders sized for: a) Short-circuit withstand duty? b) Earth-fault duty? c) Motor's present capacity? Including Service Factor allowance? d) Future motor's capacity? Regards, Phil Corso, PE Trip-A-Larm...

Further to my 10-Aug 4:21pm response to Arthur Tua... Gut impression. The scenario you described is not unusual. It analogous to excess energy recovery systems utilized in refineries, chem plants, etc. It can be shown that reliability is inversely proportional to the number of operating...