Yes it seems the tables are for voltages for 600v. Could we calculate C values using standard ohms/feet values from IEEE stndards. "C=1/ohms per ft"
Suggest you look at "Short Circuit calculations - the Easy Way" by J.R.Seiver PE & John Paschal PE - ISBN 0-87288 - 745 -6 for another alternative, I got my copy via AMAZON.
Yes this method could be used for simple application such as radial system particularly for low X/R ratio. The accuracy of the result is fairly acceptable. Furthermore, in HV application the direct method could be simplified neglecting the R-values.
For complex system the accuracy and time to prepare a calculation could be questionable.
Suggestion: It appears that the high voltage substation deserves to have applied suitable commercial software the for short circuit and voltage drop calculation for several reasons, namely:
1. The commercial software has programmed various industry standards practices that are usually omitted by a simple approach to the short circuit and voltage drop calculation.
2. Considering responsibility in engineering and design of such HV hardware, the use of commercial software or engineering services that offer such calculation is prudent.
3. Any approximate approach to the calculation and disregard of industry standards may lead to a waste of lot of money.
For the vast majority of substation, the SC is used primarily to determine or validate that the standard SC rating (40 kA or 63 kA) of electrical apparatus and particularly the circuit breaker.
For application far from the standard SC rating, a simple calculation could be satisfactorily in most cases. For complex calc involving non-radial configuration or network application, commercial software could be a better option than simple calculation.
The reason that a simple calculation could be used may be found by a quick review of a typical non-utility substation.
· Substation is connected to the power grid via a transmission line (typically few miles).
· Substations connected to a generating plant are connected to the HV switchyard via a step-up transformer.
· On Industrial facility this connection typically is with step-down units.
The short circuit available at the interconnection point is normally available from the utility. The SC available at the plant side or generation station could be available or relative easy to determine.
Regardless the configuration of the substation (ring bus, bkr 11/2, single bus, etc) the model to determine the SC at the substation is not too complicate. Furthermore, there are components that require rating verification as follow:
· Breakers are typically rated for SC current at 40 kA. The next std. rating is 63 kA.
(Circuit switcher if used could be 31.5 kA or 20 kA.)
· Disconnect switch, surge arrester, inst. transf., pwr transformers and many electrical apparatus are rated to withstand SC similar to the breaker rating.
· Voltage drop is not an issue for HV facilities. LV installation could be different.
· The SC forces on busses and associated support insulators normally are designed based on the bkr SC rating and not in the available SC. Loading combination of wind, snow or seismic could be more severe than SC.
· Grounding grid design SC current in most cases is based on a fraction of the bkr SC rating regardless available SC current.
. Transformer SC withstand capability is achieved by appropiate protection coordination.
