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IEC 61850 Communication networks and systems in substations ... and beyond It is our intent that you  the domain expert  add to the list of Q&A.
1. Is there a brief example to learn about logical nodes, data, and common data classes? Answer 1 An excerpt of the logical nodes defined in IEC 6185074 (XCBR  circuit breaker) shows the three levels of classes: logical node, data, and data attributes (derived from common data classes). Just click on the data name in the logical node and check the definition of the semantic of the data, ... The above shown pages are not uptodate. SCC has provided a comprehensive tool that provides the complete models defined in IEC 6185074 and IEC 6185073 and an introduction to IEC 6185072. With the purchase of all four (4) parts: IEC 6185074, IEC 6185073, IEC 6185072 and IEC 6185071 you get the complete browsable information model!! Order information. Answer 2 A small subset of the browsable tool is available here [pdf, 2.5 MByte].
2. What is a Logical Node (LN)? Answer A brief introduction of the approach of logical nodes can be downloaded here. 3. What is the scaling of a measured value? Answer Introduction to Floating Point to Integer conversion in IEC 6185073 The formula for the conversion between the floating point value and an integer value is given as follows: f * 10**(units.multiplier) = (i * scalefactor) + offset The following describes the basisc of the scaling of values ("." is the decimal point). Supose the following five values to be communicated or stored. The objective of scaling is to find a minimum integer representation (INT) that can be used instead of a floating point (FP): FP1 = 104.561 The smallest number is 99.459; we can now substract this value from all 4 values (this is the offset): This results in: Now we can multiply with 100 (Scale) to get a reasonable value we can convert to an Integer value: 5.102*100 = 510.2 These numbers can be rounded to get Integer values (which are quite small and close to the original values): INT1 = 510 These values can be stored and communicated. Integer values communicated from a device that provides just Integer processing can be converted to Floating Point values at the receiving side as follows: The received Integer values have to be devided by 100 (Scale) and the offset value 99.459 has to be added: FP1 = 510/100 + 99.459 = 104.559 These Floating Point values are very close to the original values. These explanation helps to better understand the definitions in IEC 6185073 (Common data classes): The instCVal is avlaue that uses Integer and Floating Point representation – one of the two must be provided by any device thathas values of instCVal: mag instCVal.mag.i INT32 offset and scaleFactor are applied to mag.i and mag.f ang instCVal.ang.i INT32 angSVC.offset FLOAT32 offset and scaleFactor are applied to ang.i und ang.f Calculation units.multiplier ENUMERATED [2=>100] is the same for mag.f and ang.f The formula f * 10**(units.multiplier) = (i * scalefactor) + offset can be applied for "ang.i" in "ang.f" and independently for "mag.f" in "mag.f" The fact that there is only one Multiplier (e.g. 103) means that the value "mag" is given 103 (Kilo) as well as the value for the angle "ang" (with a multiplier of 103) a value of the angle of "0.00175 rad" communicated means 100 Grad (1.75 rad). 20080324 




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