GMD, GMR and Waterfall Charts

Waterfall charts are useful tools in design when there is a very wide range of possibilities and something needs to be done. A good example of this is cable selection. A waterfall chart for cable selection makes the life of an electrical designer in creating cable schedules.

I have almost always used waterfall charts for cable selection in my projects. Some people who are not familiar with this tool are adamant about its usage but those who use them regularly got a different perspective. Motor starting, earth fault, and voltage drops are just some parameters that could be integrated into waterfall charts to make them even more useful.

A project that I was involved with was in its concept definition stage. I was assigned to do in-field distribution reticulation for CSG upstream facilities. The underground distribution could be done much easier using a waterfall chart but overhead distribution will be a different story.

For overhead, GMD and GMR are needed to be able to get the line parameters. Likewise, several voltages were considered, in the case of this particular project, the voltages considered were 11kV, 22kV and 33kV. Later on due to the significant load and distance of distribution, 66kV and 132kV were likewise considered.

The usage of a waterfall chart in design is limitless. All that is needed is your imagination.

Some useful waterfall charts can be downloaded below. These are natyive files which could easily be modified to suit your particular needs.

  1. High Voltage Cable Sizing - Undergground
  2. Single Phase Cable Selection
  3. Cable Selection for Motors