Buy IEC/TR Ed. Short-circuit currents in three-phase a.c. systems Part 4: Examples for the calculation of short-circuit currents from SAI Global. The results meet requirements of IEC and match the example provided in IEC TR section 6. The IEC standard terminology is used in the user. The International Electrotechnical Commission (IEC) is the leading global IEC TR , Short-circuit currents in three-phase a.c. systems – Part 4.

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EasyPower offers a complete and accurate solution to short-circuit calculations in three-phase AC systems using the IEC standard. You can enter equipment data and parameters via user friendly interface. The IEC standard terminology is used in the user interface and reports.

## IEC TR 60909-4:2000

You can obtain the following 06909-4 of short-circuit currents at the fault location for both maximum and minimum short circuit currents:. You can view the currents in various formats such as phase currents for A, B and C phases or in symmetrical components: Lec voltages can be displayed at the buses. The values can be displayed in magnitude, magnitude and angle, or in real and imaginary quantities.

EasyPower uses the equivalent voltage source at the short-circuit location, symmetrical components impedance network, and the voltage factor c as described in section 2. The short-circuit impedances for electrical equipment are modified using impedance corrections factors that are calculated based on section 3.

Impedance correction factors are applied for network or utility K Qgenerators 60909- Gpower stations units with on-load tap changer K Spower stations units without on-load tap changer K SOand two- and three-winding transformers K T.

### IEC TR | IEC Webstore

For minimum short-circuit currents, the resistances are based on the estimated temperature at the end of the short-circuit condition. For minimum short-circuit calculations the motor contribution is excluded. Capacitors and non-rotating loads are not included in the calculations. The program is designed to address short-circuits in meshed networks. The voltage factor c is used to scale the equivalent voltage source in the calculations to account for variations in the system voltage.

This factor is also used in calculating impedance correction factors. EasyPower uses the following c factors as the default for maximum and minimum short-circuit conditions. You can modify these values as needed in the short circuit options. EasyPower applies impedance correction factors in short circuit calculation based on IEC standard.

The transformer correction factor K T for two winding units with or without on-load idc changer LTC is calculated as follows per section 3.

The correction factors for three-winding transformers with or without LTC are calculated using the following equations.

The synchronous generator impedance correction factor K G for generators without unit transformers is calculated as follows per section 3. Z S is the corrected impedance of a power station unit with LTC to the high-voltage side. Z THV ieec the impedance of the unit transformer referred to the high-voltage side without correct factor K T.

U nQ is the nominal system voltage at the feeder connection point Q of the power station unit. The initial symmetrical current is calculated based on section 4. This is ice first step to obtaining most values. Subtransient impedances are used for rotating 609094- with the impedance correction factors. As described in the methodology the solution is obtained using the equivalent voltage source at the short-circuit location, symmetrical components impedance network, and the voltage factor c.

EasyPower calculates the Peak currents i p based on section 4. The following methods are supported for meshed networks as per section 4. The method described above is for 3-phase short circuit. The implementation is as per sections 609094. For rotating machines the current contributions to short-circuit decays over time.

Breaking currents are calculated at 0. DC component of short-circuit current at breaking times: Steady-state short-circuit current I k is eic based on section 4. Motor contributions are excluded. For unbalanced faults, equations 868788 and 89 are used. Asymmetrical currents for the initial and the four breaking time intervals are also calculated for use in protective device coordination.

Asymmetrical currents are calculated as the root mean square of the symmetrical and dc components. Asymmetrical values can be used with protective devices that respond to the asymmetrical currents. Currents flowing through sources, cables, lines, transformers and other equipment are also calculated. Voltages at remote buses are also provided.

These remote currents and voltages are useful for relay setting. IEC section 6 provides a sample calculation as a benchmark test for software programs to compare. The comparison of results is summarized below. Three-phase short-circuit currents for breaking I b at0. EasyPower compares the short circuit results with protective device short-circuit ratings and displays 60990-4 results in the text report and in the single line diagram.

For high voltage circuit breakers, the peak current is compared ic the making capacity and the 6099-4 current is compared with the rated breaking capacity.

Isc and low voltage circuit breakers ratings are compared with initial currents. Switches use the peak current to compare with making capacity. High voltage circuit breaker data comes with the DC time constant.

The EasyPower library is populated with data for circuit breakers, fuses and switches. The short circuit rating is part of iex data library. In the equipment short-circuit duty report, comments and text colors provide indication of problem areas. EasyPower provides the option of showing a warning when the short-circuit duty percent is above a user defined safety margin threshold but below the violation level.

Short-circuit on any bus results in voltage drop in other near buses in the system. You can set a voltage sensitivity threshold in the options such that any bus with voltage below this value will be highlighted red in the single line view and shown in the voltage sensitivity report.

The short-circuit calculation provides the phase angle of the branch currents and the bus voltages at various equipment. The phase angles displayed are relative to the applied equivalent voltage source being at zero angle. Transformers having different winding configurations, such as a delta connection on one side and a star wye connection on the other side, have a designated shift in the phase angles of currents and voltages.

For remote buses and branches across transformers, a phase angle shift is applied accordingly by the short circuit calculations. IEC standard specifies clock number notation and their respective phase angle shift for transformers. EasyPower provides the necessary phase angle shift of remote voltages and currents for IEC rated transformers in the IEC short circuit analysis.

For transformers with delta and start wye winding connections, the clock notations 1,3,5,7,9 and 11 are supported in the database. These have, 90, and 30 degrees phase shift respectively based on the high voltage side taken as the reference. The IEC short-circuit results are integrated with the protective device coordination tools in EasyPower. The following features are supported:. Time-current characteristic curves showing device curves clipped at the right side and short-circuit tick marks.

## IEC-60909 Short-Circuit in EasyPower

EasyPower supports the following four types of short-circuit conditions as per IEC Calculated Values You can obtain the following values of short-circuit currents at the fault location for both maximum and minimum short circuit currents: Display of short-circuit currents You can view the currents in various formats such as phase currents for A, B and C phases or in symmetrical components: Short-circuit currents decaying over time Methodology EasyPower uses the equivalent voltage source at the short-circuit location, symmetrical components impedance network, and the voltage factor c as described in section 2.

Voltage Factors c The voltage factor c is used to scale the equivalent voltage source in the calculations to account for variations in the system voltage. Transformer Impedance Correction Factors The transformer correction factor K T for two winding units with or without on-load tap changer LTC is calculated as follows per section 3. Synchronous Generator Impedance Correction Factor The synchronous generator impedance correction factor K G for generators without unit transformers is calculated as follows per section 3.

Peak current based on method b: This method applies the 1. Peak current based on method c: As per section 4. Also, all synchronous machines use the resistance R Gf in place of R G in accordance with section 3. Symmetrical Short-Circuit Breaking Currents I b For rotating machines the current contributions to short-circuit decays over time.

Steady-state short-circuit current I k Steady-state short-circuit current I k is calculated based on section 4. Asymmetrical Currents Asymmetrical currents for the initial and the four breaking time intervals are also calculated for use in protective device coordination. Remote Currents and Voltages Currents flowing through sources, cables, lines, transformers and other equipment are also calculated. Line-to-earth short-circuit currents for Initial symmetrical rms and peak Short-Circuit Duty Calculations EasyPower compares the short circuit results with protective device short-circuit ratings and displays the results in the text report and in the single line diagram.

Example HV breaker ratings in the device library Figure 4: Ratings for HV breaker in project file loaded from the library In the equipment short-circuit duty report, comments and text colors provide indication of problem areas. Short-circuit duty results displayed in the single line drawing Table 5: Short-circuit equipment duty report Voltage Sensitivity Analysis Short-circuit on any bus results in voltage drop in other near buses in the system.

Highlighting of buses when voltage is below threshold Figure 7: Voltage sensitivity report for buses with voltage below threshold Transformer Phase Shift The short-circuit calculation provides the phase angle of the branch currents and the bus voltages at various equipment. Shift in current angle across delta-wye transformer Integration with Protective Device Coordination The IEC short-circuit results are integrated with the protective device coordination tools in EasyPower.

The following features are supported: View of the single line diagram in the time current characteristics TCC plot for protective devices. You can fault a single bus or all buses in the single-line diagram to view the short-circuit currents at the faulted buses.

You can also view the remote branch currents and remote bus voltages. The short-circuit current through any protective device can be used to clip the TCC curve of the device.