IEC909 Improvements ^{Version 3.12.0 : Feature 6735 11/03/2022}

ERACS' IEC909 calculation has been significantly improved. It has been aligned with IEC 60909-0:2016 and 60909-0:2001 and includes several new features.

Editions of the Standard

Firstly, the major improvement is that the module now supports both IEC 60909:2016 and IEC 60909:2001. The inclusion of IEC 60909:2001 is really for backward compatibility and by default, the module will choose the IEC 60909:2016 edition of the standard.

The module still provides support for the 1988 edition. Again, that is for backward compatibility and for re-running any studies that you have previously performed.

A control, that is labelled Edition of Standard, has been added to the study setup windowl and enables you to choose one of these options:

• IEC 60909:2016
• IEC 60909:2001
• IEC 909:1988

Maximum and Minimum Fault Calculation

ERACS now enables you to perform 'maximum', 'minimum' and 'user-defined' fault level calculations.

A control, labelled C factor, has been added to the study setup panel and enables you to choose one of the following options:

• Max: maximum fault levels will be calculated using voltage factor c_max specified in the appropriate Voltage factor table according to the edition of the standard that has been selected. Impedance correction factors are calculated for synchronous machines and transformers (if 2016 or 2001 edition is selected).
• Min: minimum fault levels will be calculated using voltage factor c_min specified in the appropriate Voltage factor table according to the edition of the standard that has been selected. Impedance correction factors are set to unity.
• User-defined: the new set of Voltage Range controls will be enabled to allow you to define the voltage factor, c, to be employed.

Peak Short-Circuit Current Calculation Method

Two additional methods of calculating the peak short-circuit current, i_p, have been provided:

• Method B: Factor к (Kappa) is derived from the R/X ratio of the short-circuit impedance employed by the initial short-circuit current calculation.
• Method C (Kappa depends on system configuration): Factor к is derived from the R/X ratio of an equivalent frequency impedance seen from the short-circuit location and considers the type of fault and subsequent connection of the sequence networks.

Access to the new calculation methods is provided by an option that has been included in the study setup window. The option is labelled Peak Short-Circuit Current, i_p, Calculation Method and these options have been provided: 'C (Kappa depends on system configuration)', 'C (Kappa set to three phase short-circuit value)' and 'B'. By default, the option is set to 'C (Kappa depends on system configuration)'.

Impedance Correction Factor for Network Transformers, K_T

When Edition of Standard is set to 'IEC 60909:2016' or 'IEC 60909:2001' and C factor is set to 'Max', a transformer impedance correction factor, K_T, is calculated and applied to all network transformers.

Results Displayed on Single-Line Diagram

Summary Box and Busbar:

• Voltage Correction Factor.
• Nominal Voltage (kV).
• Initial Symmetrical Apparent Power (MVA).
• Symmetrical Breaking Capacity (MVA).
• X/R ratio (peak).
• R/X ratio (peak).
• X/R ratio (dc).
• R/X ratio (dc).
• Factor Kappa.
• Factor Kappa Product.
• Breaking Time (s).
• DC Current at Breaking Time (kA).
• Positive Sequence Driving Point Impedance (pu).
• Positive Sequence Driving Point Impedance Angle (°).
• Negative Sequence Driving Point Impedance (pu).
• Negative Sequence Driving Point Impedance Angle (°).
• Zero Sequence Driving Point Impedance (pu).
• Zero Sequence Driving Point Impedance Angle (°).
• 2Ph-Eth Initial Symmetrical Short-Circuit Current in Phase 2 (kA).
• 2Ph-Eth Initial Symmetrical Short-Circuit Current Angle in Phase 2 (°).
• 2Ph-Eth Initial Symmetrical Short-Circuit Current in Phase 3 (kA).
• 2Ph-Eth Initial Symmetrical Short-Circuit Current Angle in Phase 3 (°).
• 2Ph-Eth Initial Symmetrical Short-Circuit Current to Earth (kA).
• 2Ph-Eth Initial Symmetrical Short-Circuit Current Angle to Earth (°).

Grid Infeed:

• Identifier.
• Voltage Factor.
• Partial Initial Short-Circuit Current (kA).
• Partial Initial Short-Circuit Current Angle (°).
• Three Phase Fault Infeed (MVA).
• Three Phase Fault X/R Ratio.
• Single Phase Fault Infeed (MVA).
• Single Phase Fault X/R Ratio.
• Positive/Negative Sequence Resistance (pu/r).
• Positive/Negative Sequence Reactance (pu/r).
• Zero Sequence Resistance (pu/r).
• Zero Sequence Reactance (pu/r).

Synchronous Machine:

• Identifier.
• Voltage Factor.
• Power Factor.
• Impedance Correction Factor.
• Factor µ.
• Partial Initial Short-Circuit Current (kA).
• Partial Initial Short-Circuit Current Angle (°).
• Rated Current (kA).
• Corrected Positive Sequence Resistance (pu/r).
• Corrected Positive Sequence Reactance (pu/r).
• Corrected Negative Sequence Resistance (pu/r).
• Corrected Negative Sequence Reactance (pu/r).
• Corrected Zero Sequence Resistance (pu/r).
• Corrected Zero Sequence Reactance (pu/r).

Induction Machine:

• Identifier.
• Factor µ.
• Factor q.
• Partial Initial Short-Circuit Current (kA).
• Partial Initial Short-Circuit Current Angle (°).
• Rated Current (kA).
• Locked Rotor Current (kA).
• Locked Rotor X/R Ratio.
• Locked Rotor R/X Ratio.
• Positive/Negative Sequence Resistance (pu/r).
• Positive/Negative Sequence Reactance (pu/r).

Transformer:

• Identifier.
• Voltage Factor.
For two-winding transformers:
• Impedance Correction Factor.
For three-winding transformers:
• Impedance Correction Factor – Winding 1 to 2.
• Impedance Correction Factor – Winding 1 to 3.
• Impedance Correction Factor – Winding 2 to 3.

Transformer windings:

• Corrected Positive/Negative Sequence Resistance (pu/r).
• Corrected Positive/Negative Sequence Reactance (pu/r).
• Corrected Zero Sequence Resistance (pu/r).
• Corrected Zero Sequence Reactance (pu/r).

Synchronous Machine Power Factor

Facilities have been added to the synchronous machine data entry form that enable you to explicitly define the power factor that will be employed by the IEC909 calculation module to calculate the machine’s impedance correction factor, K_G.

Synchronous Machine Resistance

An option that enables you to choose the resistance that will be employed for synchronous machines during the calculation of the peak short-circuit current, i_p, has been added to the study setup window. The option is labelled Synchronous Machine Resistance for ip Calculation, and two choices have been provided: 'Fictitious resistance defined in the standard' and 'Stator resistance from library dataset'. By default, the option is set to 'Stator resistance from library dataset'.

Grid Infeed R/X Ratio

An option that enables you to choose the R:X ratio employed by grid infeeds has been added to the study setup window. The option is labelled Grid Infeed R/X Ratio and two options have been provided: '0.1; i.e. Rq = 0.1*Xq, Xq = 0.995*Zq' and 'Value provided in the grid infeed’s data entry form'. By default, the option is set to 'Value provided in the grid infeed's data entry form'.

Initial Short-Circuit Current for Two-Phase to Earth Studies

For two-phase to earth fault calculations, ERACS now calculates I"_kE2E, I"_k2EL2 and I"_k2EL3. All three values are written to the Excel formatted results file and can be selected for display on the single-line diagram.