7anoter4
I beleive you might have misinterpreted Section 7.2.5 of IEEE 141-1993. It does not state that only medium voltage cables have these insulation levels. It is merely stating that fact in the context of design considerations for grounding systems. If you review the references that are...
dpc,
My friend; I am satisfied with the technical decision I made to remove the HRG system due to the insulation levels used in the electrical insulation. Thanks for your comments and I would respectfully agree to disagree with your opinion.
I would recommend that you take a look at ICEA...
davidbeach,
I don't agree with your statement that this is the accepted practice. You seem to ignore what is in the IEEE Recommended Practices and ICEA industry recognized standards which are, in my opinion, the accepted practice.
There is also a publication by GE on electrical system...
jghrist,
You neglected the phase relationship between the voltages. In addition this is an unbalanced ground fault on a three phase system which need to be handled by symmetrical components.
In IEEE 141-1993 Chapter 7 "Grounding" Section 7.2 "System Grounding" it describes the following:
"High-resistance grounding will limit to a moderate value the transient overvoltages created by an inductive reactance connection from one phase to ground or from an intermittent-contact...
David,
The NEC doesn't adrress a lot of issues in industrial applications. I am concerned about the inadequate voltage rating for the power cables used for this type of system when a section is grounded and the two remaining phases have voltages exceeding 800 volts. I think this is a safety...
David,
In the Standard ICEA S-95-658-1999 "Standard for Nonshielded Power Cables Rated 2000 V or less for the Distribution of Electrical Energy" Section 3.3 it defines the 173% insulation level for cables applied on a system where the time required to deenergize a grounded section is more than...
One possibility that I did not see mentioned, is there any way to reduce the required torque of the load during the start. Depending on the type of load (pump, compressor, etc..) it may be possible to close or partially close a discharge valve to reduce the required torque, or unload compressor...
mnewman, in general I agree with the statement. However, for systems that involve two machines (a generator and a large motor) a comparison of the machine's inertia should be done. If the motor's inertia is not significant with respect to the generator's inertia (1/10th of the generator's...
mnewman, in my opinion when calculating the voltage profiles on power systems when starting large motors the generator's transient reatance is recommended because the sub-transient reactance will decay quickly and therefore the transient reactance is a more conservative representation of the...
I recommend that you read the manual for the software in the Dapper Reference Manual page 46 that describes the solution methods used for the load flow analysis.If you have questions I would recommend that you contact SKM Systems Inc. (they will endeavor to answer your questions and I have found...
Make sure to review NEC 430.113 and determine how it applies. For large facilities with large motors that may have multiple sources of power. For example, power to a space heater, lube oil heater, etc.. These sources may require individual disconnects within site of their respective load. I...
On medium voltage distribution systems that are ungrounded it is common for there to be ground detection lamps installed on the switchgear (switchboard). Does this systen have such monitoring? What does it indicate?
If this monitoring doesn't exist you may want to consider it.
I think that a line to line fault on the 12.47 kV overhead line could result in enough current unbalance between the three phase currents on the 4.16 kV side of the transformer to help to explain what is happening.
