Power system analysis software: Intro

Power system analysis software ranges from basic, commercially available, generic packages to large, complex programs developed for a specific customer. The latter serves the needs of a single comprehensive electrical system and may be integrated in real time to an electrical SCADA system with real input from the field.

The former programs are usually more user-friendly, require simulated input, and are used on a wide scale by consultants, industry and utilities.

A wide variety of programs are available today to perform all sorts of electrical analyses, as will be demonstrated in this section. Of all these, the programs that are undoubtedly used most frequently in power distribution design and analyses are the load flow and fault analyses studies.

A load flow study determines the voltage, current, power and reactive power in various points and branches of the system under simulated conditions of normal operation. Load flow studies are essential in optimizing existing networks, ensuring an economical and efficient distribution of loads, and plan future networks or additions to existing networks. The currents that flow into different parts of a power system immediately after the occurrence of an electrical fault differ substantially from the current flowing in steady state conditions. These currents determine the ratings of circuit breakers and other switchgear that are installed in the system, specifically the current flowing immediately after the fault and the current which the circuit breaker must interrupt. Fault calculations consist of predicting these currents for various types of faults at various locations in the system. The data obtained from fault calculations are also used to determine relay settings.

Network studies used to be extremely time-consuming in the pre-digital computer days, and often not very accurate. However, very powerful electrical analysis software in modern times has restricted human efforts to the input of equipment data and the interpretation of the study results. Network studies can now be done in a fraction of the time it used to take, with much more accurate results. This has greatly aided in more efficient power systems being designed, implemented and maintained. The real-time information that can be obtained from a power system automation system is a great aid to, and parallel with, network studies. Firstly, the steady-state information continuously obtained, archived and trended can tremendously assist the results of load flow studies. Secondly, the information obtained from disturbance records, as well as sequence-of-events recordings, can be used to determine the correctness of fault calculations and stability studies, as well as to verify the effectiveness of the electrical protection.