Power System Analysis
Different analytical studies are performed on the power system in order to determine its capability to accommodate different loading conditions and withstand faults under both transient and steady state operation.
• Load flow analysis
Load flow analysis is performed for balanced and unbalanced AC systems as well as DC systems to achieve the following;
o Verify equipment ratings and their capability to accommodate the loads.
o Calculate the steady-state voltage drop across feeders and identify the locations where the voltage drop exceeds the limits specified by the applicable standards.
• Short-circuit analysis
In this analysis, different types of short-circuit faults are calculated at different network buses including balanced and unbalanced faults for AC and DC systems. The voltage and current profiles throughout the fault period are plotted and investigated for the following purposes;
o Evaluate equipment and protective devices suitability to withstand the fault current
o Evaluate the impact of transient undervoltage condition on electrically operated loads.
o Evaluate the need to install reactors on certain network branches to reduce the fault current
• Motor starting analysis
This analysis evaluates the voltage sags that occur during the starting one or group of motors.
With building an appropriate model for the motor and its driven load, the motor starting torque, current and voltage drop can be calculated. This voltage drop and the voltage drop on other buses and loads affected by the starting of this motor must be within the limits specified by the applicable standards.
The motor starting analysis takes into consideration the number of successive cold and hot starts of the motor depending on the limitations set by the motor control scheme.
• Protection coordination study
Once the capacity of the equipment and protective devices are set out, the selection of protective devices, relays, and trip units can be made taking into consideration the coordination requirements of these devices at the calculated fault level.
Time-Current Coordination (TCC) curves are plotted for all devices in series to ensure that they are properly coordinated and a sequence-of-operation report is generated showing the tripping and clearing time of each protective device and the sequence at which these devices will operate.
• Arc flash calculations
Arc flash has always been a safety concern for people working in energized equipment. A lot of standards were developed to evaluate the arc flash and to assign the appropriate PPE to be used. NFPA 70E and IEEE 1854 are the most popular among these standards.
Arc flash studies involves evaluating the arc flash due to faults at different network buses and on the line-side of draw-out breakers with the equipment bus gaps modelled properly.
Knowing the fault clearing time of the protecting device, the arc flash released energy can be evaluated and the required PPE category can be advised.
Further improvement to the calculated arc flash values can be suggested such as reducing the fault clearing time of certain protecting devices or activating the instantaneous tripping mode of these devices when someone is working on the protected equipment.
• Harmonic analysis
Harmonics in power systems is one of the major causes of increased systems losses and instability in the system during switching operations.
Harmonics generated by different system components are evaluated and mitigative actions are proposed to reduce the harmful orders.
• Transient stability analysis
This analysis deals with different voltage and current transients that may occur due to switching operations or sudden changes to network loading.
For large networks with above or underground cables extending for long distances, the capacitive charging of these cables plays an important role in transient over voltages and may affect the selection of the switching devices. Charging current analysis is performed on such networks and is included in the overall transient analysis of the system.