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Responding to Arthur Tua's 10-Aug 822:pm implied query... "when is a motor a generator?" Yes, Arthur, the logic falls apart. The perception that an induction motor can only "generate" when operated hypersynchronously is dead wrong. All that is needed is a prime mover and a source of reactive...

A simpler solution for Arthur Tua's dilemma... An increase in voltage will probably affect the iron saturation. Based on the additional information you presented I believe that your most viable option is upgrading. It can be stated that the single most influential parameter for determining a...

In response to Arthur Tua's 7-Aug, 9:10pm query about the use of a captive transformer... I understand that, although 11 kV is used in Europe, it is not a common insulation grade for motors of a 1,000 kW. The lower voltages are far more common, and cheaper. Thus you might have had an...

Please excuse the pun... I don't want to appear to be beating a dead horse-power, but this is in response to Dan Boudreault's cited example of two motors whose tandem arrangement produced only half of their expected output... If the motors had identical characteristics, then the problem was...

I apologize to Arthur Tua, but I failed to address his comment about the "motor as a generator." Because I prefer Risk Mitigation to Accident Investigation, I tried to provide "food for thought" emphasizing negative reasons. Now, following are two scenarios with which I hope to deter you...

Responding to Arthur Tua's 7-Aug comments: You have not detailed your requirement. As a result, you are getting a number of non-educated guesses as to what/will/could happen. Assuming that you want to mechanically couple the two motors together so that they "share" the total load, then...

Johan, variation is why God made us Unjineers. Anymore requests for my startup/runup BITE stories? Regards, Phil Corso, PE Trip-A-Larm Corp (Deerfield Beach, FL)

Responding to Alvaro Rodriguez' query: Mandatory.. No! Probable... Yes! General Comment, The starting and operational characteristics of a wound rotor (WR) motor and a squirrel-cage (SC) motor are significantly different. Using VSD to turn a WR motor into one having the performance of...

Responding to Arthur Tua's query... some thoughts: 1) Has the 1,000 kW motor manufacturer been contacted with regard to upgrading or uprating the existing motor? 2) It seems to me that the 11 kV rating (are you sure about voltage?) suggests "modifying" the motor's capability. 3) As a...

Responding to Corso's 2-Aug-00, 11:09am response to Jay Kirsch's query: P.E., huh. You are Technically Incorrect: In order for the left-hand side of equations 1) and 2) to correspond to kilo-VA, then, the right-hand side must be divided by 1,000 ! ! ! PRACTICE WHAT YOU PREACH ! ! ...

Sorry, I don't remember original basis for this thread, but: If hi-temp wirng was involved, investigate type MI (Mineral-Insulated). The more common sheath materals are Cu, Al, & SS. Temperature ratings (except for terminations) approach the sheath melting temperature. Regards, Phil...

Responding to Anthony's reply: A slight Technical Correction... you gave the formula for kW, not kVA. Yes, the power company's requirements are some of the ones you listed, but the most important are: energy (kwHr); and maximum demand (Peak kW). The latter is usually over a period of...

Responding to Jay Kirsch's query. Determining the power draw of a 3-phase motor can be done as follows: 1) Input kVAa = SQRT(3) x Ia x Va, where Ia and Va = actual operating values. 2) Rated kVAd = SQRT(3) x Id x Vd, where Id and Vd are taken from the nameplate. 3) Determine the motor's...

Responding to Johan's comments, I understand your "over-simplification" approach, but it is misleading to those who are trying to understand basics: Starting Time Please note that I said "No-Load" runup time. I was not referring to the situation where the load and motor are uncoupled or...

To the List, I wish to correct a statement I made in my 28-Jul response. Runup time IS dependent on size. The general relationship turns out to be logarithmic: t ~ M x Ns / Tm, where, t = time, in seconds. M = Moment of Inertia (that inertia stuff again). Ns = rated full load...

Responding to the recent discussion on the effect of inrush current. Much of what has been said is misleading. Starting Time. Typically, a standard squirrel-cage motor has a no-load runup time of a fraction of a second to about 6 seconds, depending on type, but, regardless of size (except...

As a result of the recent to and fro discourse on whether a 'slug' is added to the motor's MoI or the system's, I must respond to the 3-Phase Heater thread... the intent being to make it more Technically Correct. Call it more of that "PEing contest mentality" I addressed many months ago...

Responding to Paul O'keeffe's query: First identify the currents and voltages: Subscripts y, d, s, and r, denote value in Wye, Delta, Supply, and Heater element (resistive), respectively. Furthermore the line-to-midpoint voltage is Vn = Vs/SQRT(3), say 220 v, for simplicity. Then, For...

Further to my earlier response: You can also connect it to a three-phase source. However, I don't want to mislead you. The ability to connect a two-phase motor to either a single or three-phase source depends greatly on the motor's rating, ie, voltage, Hp, & speed. Regards, Phil Corso, PE...