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Additionally, frequency analysis is carried out for each network node in order to reveal the frequency curve of the signals and to provide this as a signal which can optionally be inserted into a diagram.The analysis is also done using the space vector analysis, preferably with the voltages, but if these are not available then with the currents. As the measuring window for the frequency analysis the usual backward look-ing window with a length of 1/Fnom is chosen.NOTEThe calculated values are valid only if there is no status change, (such as fault occurrence or disconnection), within the measuring window. NOTEAll variables calculated by SIGRA are identified by an asterisk. NOTEThe variables calculated by SIGRA cannot always be used to draw conclusions on the reaction of the protection device used to acquire the fault record data.The algorithms on which the protection devices base their internal calculations may deviate from standard SIG-RA conventions. Deviations may occur, particularly in the case of variables which are not perfectly sinusoidal. The calculated values are valid only if there is no status change, (such as fault occurrence or disconnection), within the measuring window.
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Calculations/Definitions6.3 Reference Arrow Definition145SIPROTEC, SIGRA, ManualE50417-H1176-C070-B1, Edition 06.20176.3Reference Arrow DefinitionThe calculations performed by SIGRA are based on the following reference arrow definition:Figure 6-1The reference arrow definition used by SIGRA for calculations6.4Variables in the three-phase systemSIGRA supplements the measured variables of the fault record by calculated variables, using the nodal or Kirchhoff equations in the three-phase system.Calculation is based on the following relations and their conversion (for further details, see chapter 6.3 Refer-ence Arrow Definition):L1L2L3NEIYIL1PIL2PIL2PIL1IL2IL3VL3VL2VL1VL23VL12VL31IE -3 I0IEP -3 I0PVL12VL1VL2VL23VL2VL3VL31VL3VL1VL12VL23VL310Ven3V0=(VL1+VL2+VL3) /3IE(IL1IL2IL3)
Calculations/Definitions6.5 Symmetrical components146SIPROTEC, SIGRA, ManualE50417-H1176-C070-B1, Edition 06.20176.5Symmetrical componentsSIGRA calculates the symmetrical components of the voltage and current system using the three-phase oper-ator a= ej2/3according to the following equations: The complex conductor variables are r.m.s. values of the fundamental component (rated frequency TN).The measuring window is situated on the left of the reference point, e.g. the cursor position, and its length cor-responds to one period of the rated frequency TN.6.6R.M.S. valuesThe calculation of r.m.s. values is based on the following definition of r.m.s. values:The measuring window is situated on the left of the reference point tc, e.g. the cursor position, and its length corresponds to one period of the rated frequency TN.
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