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Responding to Yogesh's Mon, Dec 30, 10:25am transmittal of actual operating data: 1) The low PF is due to the low load-factor. A power-factor correction-capacitor will compensate for motor-current losses in the cable between the source and the motor. It will not reduce the motor's internal...

My earlier responses on this subject may indicate that I'm obsessively fixated on motor starting time! Well, I AM. I have witnessed or investigated numerous catastrophes involving excessive starting time. Those of you who have read my past responses are aware of my definition of catastrophe...

Further to my earlier responses to K. Gurumurthy's Fri, Dec 27, 11:16am query: Assuming that more than one flashover has occurred, that location is random, and that vacuum bottle integrity has not been compromised, then, an approach to the solution for case a) follows: Use the...

1) Responding to Hakan Ozevin's Fri, Dec 27, 5:08pm comment regarding 'loss difference': Using the original posted figure of 5.5 kW as the output value, then motor's operating at 1/3 of its rating. At this load the motor's efficiency is ca 63%, corresponding to an input of 8.7 Watts. A new...

Further to my earlier response to K. Gurumurthy's Fri, Dec 27, 11:16 am, query: Question 6) refers to a closed-transition resistor used in (some) European practice. It is not normally supplied in USA designs. Regards, Phil Corso, PE (Boca Raton, FL) [[email protected]]

Responding to K. Gurumurthy's Fri, Dec 7, 11:61 am, query: The two most frequent reasons for flashover are: a) transfer current is too high, which means that transition occurs before motor has sufficiently accelerated, thus, inrush current is too high. b) voltage across AT starter...

Further to my earlier response, slip mesurement can determine acual output: If an rpm meter is unavailable (and the location is unclassified, or determined to be non-hazardous) use a fluorescent lamp connected to the same supply as the motor's. It is now a "strobe" light. The resultant shaft...

Responding to Yogesh's Mon, Dec, 10:15 am, query: Is your stated 5.5 kW value a) the measured input? Or b) the calculated output? If a) and assuming a 4-pole, 50 Hz motor, the motor is operating at about 33% of its rating. This determination is based upon using a typical efficiency vs...

Responding to J. Raefield's Sat, Dec 21, 11:38am, reply: Liquid rheostats for reduced-voltage starting have also been used in the primary supply to ordinary induction motors. My Sat, Nov 20, 4:32pm, response on subject can be found in List Archive. Regards, Phil Corso, PE (Boca Raton...

Sorry Bob, but I couldn't pass on this one! During the golden, olden days... before the introduction of hi-tech programmable devices ... this application was easily done with a few relays. Admittedly, the relays were of the protective-relay type used by electrical power engineers! Regards...

Responding to Antonio Herrera's Wed, Dec 18, 12:34pm reply: If you want general information. Contact the service/test/repair divisions of any Large ELectrical Apparatus manufacturer. Typical are: General Electric. Westinghouse. Asea Brown-Boveri (ABB). Allis-Chalmers (now...

Responding to Quingye's Wed, Dec 11, 4:10pm, query: The most succinct definitions in the literature, besides those in old faithful, yep you guessed it, the IEEE Std 100-1992, are the those in Struthers-Dunn's handbook "Relay Engineering." It lists the following terms...

Responding to Antonio Herrera's Thu, Dec 12, 11:42am, query: Where are you located? Regards, Phil Corso, PE (Boca Raton, FL) [[email protected]]

Further to my earlier response to Ramesh Parmar: In the past I was advised that instructions via E-mail were too confusing to follow. Therefore, if you send me your Fax # I will forward the procedure, complete with schematic and vector diagrams. This offer is also made to anyone interested...

Responding to Anthony Kerstens, Mon, Dec 2, 5:05 pm, query: Are you sure that you haven't overlooked a resistor-like or fuse-like device? If so it is actually a positive-temperature-coefficient (PTC) resistor. Some manufactures had switched to this device to replace electro-mechanical...

Replying to Ramesh Parmar's, Sun, Dec 1, 4:50 pm, query: The thread, starting on June 02, was titled "ENGR: Power Consumption for Motor w/VFD!" It covered procedure to determine kW, kVAR, power factor, and efficiency, regardless of waveshape, harmonics, or the degree of unbalance...

Unless one or both drives are equipped with with a "slip" drive, such as a VFD, they can not be coupled, unless... well, that part of the story is in located in the AList Archives. Search for: "Motors in tandem," or "Motors coupled to the same shaft," for analysis and experiences of this...

Responding to Andrew Lovelace's Mon, Nov 18, 3:40 pm, query: The simplest suggestion is to install a bi-directional Wattmeter or two reverse connected Wattmeters. A second suggestion is to employ a Watt-measuring transducer, having the built-in current and potential transformers to provide...

Responding to Alex Ruderman's Tue, Nov 19, 5:29 pm: Thank you for contributing your expertise to the ALIST's store of information on VFDs. Are you published? And, is it available for public purchase? Regards, Phil Corso, PE (Boca Raton, FL) [[email protected]]

Responding to Jay's Thu, Nov 19, 2:04 pm, query: If pipe thread is per USA ASA standard, then tap-drill size for a 1/2 inch nominal pipe size, having 14 threads per inch, is: a) 11/16 inch for tapered thread. b) 23/32 inch for straight-thread. Ref is "Standard Handbook for Mechanical...