Hi-Low-Hi Motor Starting: An Approach for Starting Deep Well Submersible Pumps
In order to be cost effective, deep-well submersible pump designs typically use medium voltage motors (2,400V and above). Running at medium voltage reduces conductor size, and smaller conductors are beneficial to the design and construction of the well. However, medium voltage creates its own challenges for the operator. The number of electricians trained to work on medium voltage equipment is typically less than those who work on 480V equipment. Availability of medium voltage replacement parts is also a common issue. And finally, the Hazard/Risk Category Classification, as defined by NFPA 70E, is higher when performing tasks on medium voltage equipment.
The standard approach to starting a medium-voltage motor would be to install a medium-voltage motor starter, however another option available to operators is a Hi-Low-Hi motor starting design. This will cost a little more, take up more overall real estate, and will not eliminate all medium-voltage gear, but it will allow the operator to utilize a low-voltage 480V starter. Motor starters, whether they are across the line, soft starts, or variable speed drives, are typically the piece of equipment that requires the most troubleshooting. Installing a starter that is a make and model already used in the water system, and which the electricians are already familiar with, will go a long way in increasing the reliability of a well field system.
This paper will analyze and present a Hi-Low-Hi type motor starting configuration that was designed and built for the Potter County Well Field, which supplies water for Amarillo, Texas. The incoming utility voltage was 13,200V. This voltage was stepped down to 480V for motor starting (and miscellaneous site loads), and then stepped back up to 2,400V for the feeders going to the submersible motor. This paper will address design considerations that are unique to this type of configuration. The overall goal is to provide operators with options when designing their well-gathering systems.