You can enter equipment data and parameters via user friendly interface. The IEC standard terminology is used in the user interface and reports. EasyPower supports the following four types of short-circuit conditions as per IEC 3-phase short circuit Line-to-line short circuit with earth connection double line-to-earth Line-to-earth short circuit. Corresponding voltages can be displayed at the buses.
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You can enter equipment data and parameters via user friendly interface. The IEC standard terminology is used in the user interface and reports. EasyPower supports the following four types of short-circuit conditions as per IEC 3-phase short circuit Line-to-line short circuit with earth connection double line-to-earth Line-to-earth short circuit. Corresponding voltages can be displayed at the buses. The values can be displayed in magnitude, magnitude and angle, or in real and imaginary quantities.
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. 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 KQ , generators KG , power stations units with on-load tap changer KS , power stations units without on-load tap changer KSO , and two- and three-winding transformers KT.
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. 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.
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. Transformer Impedance Correction Factors The transformer correction factor KT 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. Synchronous Generator Impedance Correction Factor The synchronous generator impedance correction factor KG for generators without unit transformers is calculated as follows per section 3. 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. 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. As per section 4. Also, all synchronous machines use the resistance RGf in place of RG in accordance with section 3.
Symmetrical Short-Circuit Breaking Currents Ib For rotating machines the current contributions to short-circuit decays over time. Breaking currents are calculated at 0. Steady-state short-circuit current Ik Steady-state short-circuit current Ik is calculated based on section 4.
Motor contributions are excluded. For unbalanced faults, equations 86 , 87 , 88 and 89 are used. Asymmetrical Currents 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. Remote Currents and Voltages 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. The comparison of results is summarized below.
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. 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.
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. 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.
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. 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.
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.
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.
For phase currents, the maximum current of the three phases is used. Earth ground trip functions for low voltage circuit breakers or relays use the symmetrical earth ground current. This is the 3I0 value 3 times the zero sequence current.
In a system of low voltage breakers with ZSI, when the current through any circuit breaker exceeds the short time pickup its restraining signal is sent to upstream circuit breakers. The upstream circuit breakers do not trip instantaneously whereas the most downstream circuit breaker trips fast, enabling selective coordination. Figure 9: Time-current characteristic curves showing device curves clipped at the right side and short-circuit tick marks.
IEC 60909: ‘Far from’ Generator Short-Circuit
The Redline version provides you with a quick and easy way to compare all the changes between this standard and its previous edition. The Redline version is not an official IEC Standard, only the current version of the standard is to be considered the official document. IEC specifies procedures for calculation of the prospective short-circuit currents with an unbalanced short circuit in high-voltage three-phase a. The currents calculated by these procedures are used when determining induced voltages or touch or step voltages and rise of earth potential at a station power station or substation and the towers of overhead lines.
According to the IEC 60909
IEC-60909 Short-Circuit in EasyPower
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