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Responding to Anonymous' 19-Jul-09 (09:36) query... if an Authority Having Jurisdiction (AJH) requires that the installation comply with the USA National Electric Code (NEC or NFPA-70). then, yes, you are right, and the fuse in the grounded conductor is not correct! Regards, Phil Corso...

Responding to Ashish's 14-Jul-09 (13:00)... you are dead wrong! As proof that unbalanced currents on the y-side of a Dyn transformer do not result in balanced currents on the D-side consider the extreme cases, i.e. fault currents on the LV or y-side: Case 1, three-phase fault. LV windings a...

Ashish, the CT connections must be opposite to those of the power transformer's winding connections. 1) The D-side CTs must be connected in Wye, and the y-side CTs must be connected in Delta. 2) Typically there may also be a slight error because the CT ratios can not be exactly matched...

Responding to Nemo's 07-Jul-09 (01:33) query... additional detail is required: For example, what is meant by "permissible load xfmr 640?" Contact me off-list for more questions! Regards, Phil Corso (cepsicon [at] aol.com)

Sorry CSA, Power input of a single-phase motor is: Power = Volts x Amps x Power Factor. Regards, Phil Corso (cepsicon [at] aol.com)

Koshy, I have additional questions. Contact me off-list. Regards, Phil Corso (cepsicon [at]aol.com

Koshy... Apparently during run-up of the STG driver, there is sufficient residual magnetic flux in the motor to produce a terminal voltage. Thus, if you close the breaker out-of-sync, the resultant torque produced will cause the coupling failure (not an unusual happenstance.) This then...

Andrey, I suggest you visit the USA Government EPA website. Regards, Phil Corso (cepsicon [at] aol.com)

James, be thankful for the thank you! Phil

Santosh... have you done a search of the Control List Archives? Regards, Phil Corso (cepsicon [at] aol.com

Sir, Few queries regarding REF. 1) What is Knee-point voltage of CT's & how to calculate it? 2) Most of the time i read that REF scheme is applied for Delta-Star transformers (Am i correct?). My question is, Can we apply REF scheme for Delta- Delta transformers. If yes then how would be...

Wargas, what did you decide to do? Phil Corso

Caitlin... unfortunately using amperes alone only works if voltage is not varying! I suggeest you use kW as the variable to monitor. Regards, Phil Corso (cepsicon [at] aol.com)

KK Verma... see Control List topic: http://www.control.com/thread/1026226787. Regards, Phil Corso ([email protected])

Robbyk, reur 02-Jun-09... the network you described includes a substantial impedance between the source and the high-side of the 33/11kV transformers. Fault-duty on the 11kV bus is now 15.9 kA (rms, sym!) While a reduction over the earlier case, current may still be too high for the...

Robbyk, the time setting of the earth-fault relay is easy. However, I am more concerned about the system's ability to safely clear an earth-fault: The system described has a short-circuit duty of approximately 720MVA. Earth-fault current in the 11kV system could be well over 100kA (peak!)...

Robbyk can you provide additional detail: 5) What are the kVA sizes of the transformers connected to the 11kV system. 6) Do the 11kV feeders supply only LV transformers? 7) Are the feeders 3x1/C or 1x3/C? If the latter are they sheathed? If so, what is sheath material, lead, steel or...

Wagas, here is an idea based on a study provided for a Pakistan Ammonium Plant in the early '70s. The idea was to simultaneously vary the speed of all process drives, by varying the generator's speed! Following is my suggestion: 1) Provide two 13.8kV busses; one 50 Hz, the other 60 Hz. 2)...

Wagas, operating a 60 Hz machine at 50 Hz is do-able, at least theoretically! That said, then, what are the concerns? 1) I suggest you review jojo's comments in Control.com's thread # 1026249406, responding to a similar question posted in July '08. 2) Adding to his comments, problems can...