Power system studies performed on industrial networks include 

1.  Load flow : (Popular tools-ETAP, SKM)

Load flow study is generally used to determine steady state system voltage levels and power flows under different system operating conditions. All power equipment should be Rated for the maximum power that can flow through it under any system operating condition. The system voltage levels should be close to 1p.u. under most operating conditions.

Challenges: a) system load fluctuations  b) equipment outages(planned or unplanned) scenarios generally present problems in meeting the above objectives.

Standards: IEEE Std 141, Chapter 3 for steady state system voltage tolerances

Things to keep in mind: 

Lower the system loading higher the system voltages (Not true for systems with active voltage control device, like Transformers with On-load tap changers, Generators with AVRs, etc)

When system studies are performed with non-test values of equipment impedance, impedance tolerances ( Z+Tolerance) should be used to calculated lowest possible system voltage. (IEEE C57, 9.2)

Cable impedance varies with cable temperature. Cable impedance at maximum cable operating temperature (Often 90^oC) is used in Load flow studies to calculate maximum voltage drops. This becomes significant when the cable lengths are very long.

Results:

Transformer off-load transformer tap setting (Transformer off-load tap changer settings generally help keep system voltage with in the range specified in the IEEE standard. If not, the overall system design should be reviewed, on-load tap changers, VAR compensator can be considered to solve system voltage problems.

Check of equipment power ratings. (The system design generally does not require a software tool, the software is used only to check the design. MVA method is a very useful tool for engineers designing industrial power systems without the help of a software tool.)

 2.  Short circuit : (Popular tools-ETAP, SKM)

The objective of the short circuit study is generally to establish the short circuit ratings of electrical equipment (switchgear, MCC’s etc) per a standard. Generally ANSI(C 37) in America and IEC 60909 in Europe. The equipment short circuit rating should be more the short circuit current current available at the equipment terminals to prevent damage to equipment (Note - Equipment is protected only if the short-circuit condition is limited to a specified short time).

Important Definitions :

Rated short-time withstand current (Ik) - The rms value of the current that the switchgear can carry in the closed position during a specified short time under prescribed conditions of use and behavior. 

Rated duration of short-circuit (tk) - The interval of time for which switchgear can carry, in the closed position, a current equal to its rated short-time withstand current. 

Rated peak withstand current (Ip) - The peak current associated with the first major loop of the rated short-time withstand current that switchgear can carry in the closed position under prescribed conditions of use and behavior. (This rating indicates capacity of the equipment to withstand mechanical stress, which is maximum at peak short circuit current.

 3.  Motor starting : (Popular tools-ETAP, SKM)

The objective of the motor starting calculation is to determine if the electrical system can support starting of large motors in the system while maintaining the voltage at the motor terminals and other buses within acceptable limits.

 4.  Transient stability : (Popular tools-ETAP, SKM)

 5.  Protective relay coordination and Arc flash : (Popular tools-ETAP, SKM)

The objective of the relay coordination calculation is to determine the ratings, settings and characteristics of the overcurrent protective devices in the system to assure a secure and reliable system protection. This system study includes load flow, short circuit and motor starting calculations only. The objective of the arc flash calculation is to estimate the incident energy in the event of an arc flash and determine the personal protective clothing requirements at typical working distances. This system study includes load flow, short circuit and motor starting calculations only.

 6.  Switching transients : (Popular tools-ATP, PSCAD)

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