I have a submersible well water pump motor that is suspended down-hole on about 100 ft of plastic pipe. Whenever the pump starts, it torques the pipe and I fear it may eventually cause leaks/breaks. Is there a way to soft-start this motor? It's a three-phase 3HP unit.
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Motor soft-starters have become so common that there is even a Wikipedia article about them. Just look in the catalog of the nearest industrial electric supply and buy the size you need.
Yes, 3 phase motors can be soft started and such start controllers are readily available.
Two companies that offer them:
There are many distributors that sell soft start controllers online, just do a search for “3 phase soft start” in your favorite search engine.
The solution here is a devise called a torque arrestor. Google "well pump torque arrestor" for more information.
I recommend a commercial soft-start 3-phase motor controller such as one in the ABB Softstarter family. You can look through a catalog and technical information here: http://new.abb.com/low-voltage/products/softstarters. DO NOT try to build one yourself. Experimenting with three-phase line power can lead to problems that cost more than a commercial controller. Another suggestion: Connect a stainless-steel line to your pump to make it easy to hoist. If you try to lift it via the pipe or the electrical cord the pump could separate and leave you in a hole, literally. (I have no connection with ABB.)