Determining When Studies are Necessary

The following are general recommendations for determining when electrical analysis studies are needed:

NEW CONSTRUCTION
Anytime new protective devices are installed, particularly involving relays, both short circuit and selective coordination studies should be performed. Regardless of the sophistication of the relay system, optimum protection cannot be obtained unless the correct relay settings are determined. Correct setting values can only be determined by a study based on all the pertinent electrical characteristics of the equipment in the system.
These studies should be performed prior to the finalization of equipment orders so that changes can be made and delays avoided. This also allows the switchgear vendor to perform the initial settings on the equipment prior to shipment.

For the installation of large motors 100 hp and up, see the PAA section on Motor Starting Transient Analysis.

SYSTEM MODIFICATIONS
If the facilities system has undergone major distribution or load modifications, such as the addition of emergency generators, new utility feeds, transformers or large motors, then a new study for load flow, voltage drop, short circuit and selective coordination should be performed.

ELAPSED TIME
A new set of studies should be performed on all facilities every five years. With the passing of time, unrecorded changes to the system tend to accumulate and utility changes may occur without recorded notification. Frequently, available utility fault currents have substantially increased since the initial installation of the facilities electrical distribution system.

Power System Studies are far less expensive than the legal, business and human costs associated with electrical accidents and malfunctions.

BACK TO “LEARN MORE” PAGE