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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. You can obtain the following values 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: positive sequence, negative sequence, zero sequence and the 3I0 value 3 times the zero sequence current.

Corresponding 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 Q , generators K G , power stations units with on-load tap changer K S , power stations units without on-load tap changer K SO , and two- and three-winding transformers K T.

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 tap 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 is 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 the first step to obtaining most values. Subtransient impedances are used for rotating machines 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 1. The product 1. The method described above is for 3-phase short circuit.

The implementation is as per sections 4. 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: Following section 4. Steady-state short-circuit current I k is calculated based on section 4. Motor contributions are excluded. For unbalanced faults, equations 86 , 87 , 88 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. Table 3: Three-phase short-circuit currents for breaking I b at0.

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

Fuses 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 the 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:.

Figure 9: Time-current characteristic curves showing device curves clipped at the right side and short-circuit tick marks. Toggle navigation.

EasyPower supports the following four types of short-circuit conditions as per IEC 3-phase short circuit Line-to-line short circuit Line-to-line short circuit with earth connection double line-to-earth Line-to-earth short circuit. Figure 2: 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.

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. Figure 3: 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.

Figure 5: 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.

Figure 6: 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.

Figure 8: 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.

This will display the curve only up to the maximum current the device will see. For TCC clipping you can choose one from initial, breaking and steady state currents. You can insert tick marks arrows in the TCC plot to indicate the short-circuit current through the device. You can display short-circuit tick marks for initial, breaking and steady state currents. For breaking current you can choose from 0. For phase TCC clipping and tick marks, EasyPower automatically selects the asymmetrical currents for low voltage circuit breakers, fuses and electromechanical relays.

Symmetrical currents are applied for relays with DC offset filter.

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## Short Circuits in Power Systems: A Practical Guide to IEC 60909-0, 2nd Edition

This article looks at the calculation of short circuit currents for bolted three-phase and single-phase to earth faults in a power system. A short circuit in a power system can cause very high currents to flow to the fault location. The magnitude of the short circuit current depends on the impedance of system under short circuit conditions. In this calculation, the short circuit current is estimated using the guidelines presented in IEC Calculating the prospective short circuit levels in a power system is important for a number of reasons, including:. The calculation can be done after preliminary system design, with the following pre-requisite documents and design tasks completed:. This calculation is based on IEC , c , "Short-circuit currents in three-phase a.

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## According to the IEC 60909

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. You can obtain the following values 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: positive sequence, negative sequence, zero sequence and the 3I0 value 3 times the zero sequence current.

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## IEC-60909 Short-Circuit in EasyPower

Do you need a multi-user copy? Our prices are in Swiss francs CHF. We accept all major credit cards American Express, Mastercard and Visa , PayPal and bank transfers as form of payment. Preview Abstract IEC is applicable to the calculation of short-circuit currents in low-voltage three-phase AC systems, and in high-voltage three-phase AC systems, operating at a nominal frequency of 50 Hz or 60 Hz. It establishes a general, practicable and concise procedure leading to results which are generally of acceptable accuracy and deals with the calculation of short-circuit currents in the case of balanced or unbalanced short circuits.