Vertical motors are electrically similar to horizontal motors, but are mechanically constructed differently because of the unique cooling requirements. Generally, enclosures are designed to handle a wider range of environmental conditions than Horizontal motors. Where footless requirements are required, it is common to apply vertical motors due to the many application advantages to the driven equipment.
Vertical motors are primarily designed to drive pumps. This means they are designed specifically to handle axial or radial thrust. Turbine, mixed flow and propeller pumps usually have high axial thrust; while centrifugal and non-clog pumps normally require a combination of radial and axial thrust. In order to make the ideal selection, it is necessary to have a complete description of all thrust conditions.
Temperature of Insulation Systems
Insulation systems are classified by NEMA by their ability to perform at a specified temperature rise over an ambient temperature constantly for a specified length of time before deterioration and failure.
NEMA MG1-12.421 - Open Motors are rated as follows: #
Full Load Temperature Rise by Resistance Method
Class B 80°C at 1.0 Service Factor, 90°C at 1.15 Service Factor
Class F 105°C at 1.0 Service Factor, 115°C at 1.15 Service Factor
Large Apparatus - NEMA MG1-20.40#
Class B - 80°C by resistance at full load
Class F - 105°C by resistance at full load
The old NEMA 40°C rise referred to in many specifications is an obsolete method of asking for longer life. With the standard that a decrease in temperature of 10°C increases life by a factor of 2, it then becomes obvious that by ordering a higher grade of insulation or reducing load by 10% is a more economical approach to increase life.
Even though motors have a 1.15 Service Factor, we recommend they be operated at 1.0 service factor. A motor operating at 90°C rise over a 40°C ambient will have half the life over one at 80°C ambient.
Reed Frequency and Vibration
Vertical pumping systems must be designed to operate out of the critical zone. If the motor and pump operate near the system’s critical zone, failure due to vibration can be expected.
The reason new Vertical Motors are sold to pump manufacturers is that they must take into consideration thrust, operating conditions and pump system critical frequency/speed. Since the mass is in a vertical plane, there are more problems than Horizontal Motors because of lower system resonance. Oil whip and bearing instability problems in the pump can be more of a problem to motor life.
We recommend to avoid excessive vibration, the natural frequency of the pump system should not be within 25% of operating speed.