Soft starter for potable water well pump (wiring diagram, troubleshooting example)

Introduction to application

This article will analyze a real example of an electrical switchboard for a potable water well pump, containing a soft starter as one of the major components. Besides the explanation of the wiring diagram and working logic, some technical problems which were occurred during start-up and operation will be described also.

Well pump is installed underground, on the bottom of vertical, narrow, about 30 meters long pipe. From that depth, clean water is transferred via a pipeline constructed above the ground to a large reservoir tank at the top of steel made supporting structure in the form of a tower.

The pump’s flow is determined by its construction and hydraulic resistance of the pipeline. This resistance consists of two components:

• Static: which is defined by the height difference between a reservoir as a destination point and pump as source point; and
• Dynamic: which is defined by the friction of pipeline’s inner walls for given flow rate. No flow control by electrical means was required, hence the use of variable frequency drive was not necessary.

Table of contents:

1. Basics about soft starters
2. Example of wiring diagram
3. Troubleshooting example
   1. Problem
   2. Solution