If you have already used the Quick Check Calculator to determine that a spot network might work in your application, you are ready to use this calculator to make the detailed calculation to know for sure.
This calculator will ask more detailed questions and request information that may be more difficult to locate. Typical values have been entered if you are unable to locate this information. Remember, however, that the accuracy of the analysis relies on accurate data.
Refer to the diagram below to see what information is required, then enter this information into the fields provided in the form below.
Complete Check Calculator
1 The instantaneous maximum rms voltage difference at any time between two sources. Common
causes of voltage differences would include disturbances such as large load, transformer tap changer or
capacitor switching at some point upstream from the network transformer. Utility should be able to
provide this information.2 While there will be differing amounts of phase-shift based on different lengths of lines for the two sources, you must insure that the original sources have identical phase shift and phase rotation where they originate. Phase shift is affected by different transformer winding connections. All transformers paralleled must have the same winding connections (Delta-Wye, for example). Phase rotation is affected by accidentially swapping phase conductors causing a C-B-A versus an A-B-C (for example) rotation.
3If X/R ratio not provided directly, check on the network transformer to see if reactance (X) and resistance (R) is given instead. If so, then divide the reactance (X) value by the resistance (R) value to compute the X/R ratio. If you still cannot locate this data, estimate 6 to 8 for a transformer less than 2000 kVA and estimate 12 for a transformer 2000 kVA and greater.
(updated Aug 8, 2013)