Avoiding Possible Problems in Submersible Motors

Submersible motors have been used in municipal water systems for years. There are plenty of advantages associated with these motors—they are immune to many of the environmental factors that commonly affect hollow shaft motors, and they do not require the drive shaft and bearing systems seen in conventional line shaft turbines.

That being said, submersible motors are still susceptible to different types of problems. These motors rely on water as an internal lubricator. While the motors are extremely reliable when used within their design limitations, there are plenty of situations in which they are used in applications that accidentally exceed these limitations.

Here are some of the most common problems associated with submersible motors, and occasions for submersible pump repair in Hillsborough County, FL.

Temperature

One of the most common problems affecting submersible motors is overly hot temperatures. This can be caused by pumping hot water, overloading of the motor, a loss of cooling flow, scale buildup and frequent starting and stopping of the motor.

Submersible motors must be able to cool themselves, which usually occurs by transferring the internally generated heat of the motor into the water flowing past the motor and then on into the pump. The thrust bearing in the motor supports the thrust weight of the water column that gets lifted up by the pump. A thin film of water forms between the parts of the thrust to provide lubrication. If the water starts to boil, this lubrication evaporates, and the bearing surfaces collide with each other directly, causing rapid heating and inevitable failure of the bearing.

Hydraulic loading

Hydraulic shock loading (or water hammer) occurs when a fast-moving column of water hits an obstacle in the system, or otherwise experiences a sudden change in velocity. This is often caused by the use of multiple pumps on a single common supply manifold. When a pump turns off or on, the water hammer forms. A water hammer can also happen if there is actuated valving.

Voltage

All motors, including submersible motors, require a sufficient voltage supply at their terminals. One of the most common causes of motor failure in submersible applications is a lack of the proper voltage or, conversely, sudden spikes of high voltage. Under-voltage usually occurs as a result of sizing the drop cables too small, or low voltage being supplied to the site by the utility grid.

Voltage spikes are often caused by lightning, a utility switch gear opening or other motors turning off. This can be a serious problem in a field that has multiple pumps and motors, as every time one of the motors turns off, the inductive energy stored in the motor’s magnetic circuit goes back into power lines. This could cause power outages.

Motor seals

The motor shaft has seals that prevent well fluid from entering the motor. Both water- and oil-filled motors require these seals to keep abrasives from affecting the internal bearings of the motor. If these seals fail, abrasive materials can enter the internal motor bearings and cause corrosion, which in turn leads to improper operation and eventual failure.

For more information about the most common problems with submersible motors and how to avoid them, or if you need more information about submersible pump repair in Hillsborough County, FL, contact our team today.

Categorised in: Submersible Water Pump