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Responding to Sandy's Sep 11 query: The Rule-of-Thumb (darn, did it again) capacity of the power supply, up to the point of connection of the motor, should be five to six times the motor's hp rating. In this case the motor is about 1,500 hp. Thus, required system capacity should be about...

MAMOOAMH, why would you recommend an AT starter for the upgraded MCC! I believe the first step would be to find out why the Wye-Delta was originally chosen (low inrush current, low torque, other)! If reduced starting-current is the primary reason, and the motor is adequate, other more...

John, thanks for being so observant. I was beginning to believe that no-one read my comments. First, the dropped R1. You are correct. I neglected to mention that since R1^2 is much so smaller than the term (X1+X2)^2, it can be ignored. Second, the missing parenthesis. Once again, you are...

Bearing lubrication and bearing failure analysis is a discipline unto itself, requiring much more information than you provided. Such information includes: bearing type; duty; lubrication type; method of lubrication; detailed operating history; etc. Assuming a web search and the motor vendor...

Responding to off-list requests for my offer (Tue, Aug 27, 4:08 pm) to provide proof that max torque is independent of rotor resistance: Based on the pi model of an induction motor: T = [(V1^2)(R2/S)] / [ (R1+K(R2/S)^2 + (X1+KX2)^2 ] Where: T = torque. V1 = stator input...

The 'buck" stops here! What do you need to know? Regards, Phil Corso, PE (Boca Raton, FL)

Sorry, but I take exception to the comment that an external fan will adequately cool a TEFC motor. The internal fan precludes extreme air-gap temperature. Remember, the rotor generates most of the heat. In addition, internal air circulation improves heat transfer to the carcass! Regards...

Also investigate the effects of power restoration following a short-duration interruption! Regards, Phil Corso, PE (Boca Raton, FL)

In a former life, I received a patent on an EOL device that detected, and diagnosed, three faulted conditions... open-circuit, short-circuit and ground-fault. If you are interested, let's talk! Regards, Phil Corso, PE Boca Raton, FL ( TAL-2 @webtv.net )

Responding to Walt's Fri, Aug 30, 11:02 am: Walt, I strongly disagree. Sometimes it's the operator! Sometimes the tech! But, most of the time, it's the engineer! Regards, Phil Corso, PE (Boca Raton, FL)

Alright, here is one of many "Disasters" I have investigated: A client had a TMR system on a reactor, but to save money opted to use only one set of three temp xmitters to serve both the shutdown and control subsystems. Over a weekend one of the 16-channel A/D cards failed to function...

I was on a navy ship where a 2 of 3 voting scheme for boiler drum-level consisted of three sailors watching the same level guage. When more than one saw high level, then... ! Regards, Phil Corso, PE (Boca Raton, FL)

Gentlepersons: I was trying to be facetious! Just needling the programmmmer folks! But, at the same time I was also trying to provide a direction toward a possible (practical?) solution. Regards, Phil Corso, PE (Boca Raton, FL)

Please send additional information: a) What is the nameplate data of the existing 50 Hp motor? b) Is the power company saying that only a 208 volt, wye-derived source, is available? c) What is the Hp limit on the 240 volt source you have found? The fact that it is a delta-derived source...

Of course... but why? The only reason I can think of is that you don't want to install the six motor leads between the wye-delta starter and the motor. Please clarify your query! Regards, Phil Corso, PE (Boca Raton, FL)

Check Archives for ENGR: Bites or ENGR: Believe It, True Event Regards, Phil Corso, PE (Boca Raton, FL)

Your understanding that (maximum) torque is not dependent on rotor resistance, is correct. The torque equation contains several expressions involving rotor resistance divided by slip. Differentiation with respect to slip yields slip (max). This value does not differ greatly from rotor...

Following are some additional thoughts, but from a "technically correct" viewpoint: F) The service-person is technically correct. Grounding the AT's neutral could reduce triplen harmonics. Note I said could, not will, because reduction is possible only if the AT is the source of harmonics...

Responding to Rick Miller's query (Tue, Aug 20, 11:59 am): Your interpretation of the sum you presented is correct. The following are presented for emphasis: a) Branch three current rating shall be taken as the manufacture's full-load input rating for the power converter, not the full-load...

Responding to Paul Gruhn's reply to A. Milad (Fri, Aug 16, 1:20 pm): Your position that Fault-Tolerance " is usually reserved" for TMR is biased. It is however, a major marketing tool... and those who promoted it are to be lauded for its (marketing) success. Fault-tolerance was the norm...