Cooling Towers

MACHINERY AND STRUCTURAL REPAIR:

Improve Existing HVAC Electro/Mechanical Components
for Severe and Harsh Environments

Some of our clients were incurring cooling tower shaft bearing failure due to the harsh and wet conditions in the cooling tower cells. This was due to an inadequate bearings that did not isolate the roller elements from the water and the lubricant was being washed out and finally the roller elements developed rust and failed. IDSS installed a more appropriate bearing with the Safeguard triple lip contact seal (see chart below). This bearing change and a more timely greasing schedule has prevented any more blower shaft bearing failures.

Westchester Financial Center

MOTOR BEARING FAILURE

The motor bearings were being subjected to the Variable Frequency Drive producing an electrical discharge on the rotor causing a corona of electricity building up and trying to find a ground which occurs through the raceways and roller elements as explained in detail and graphically demonstrated in the following pages. also at this time the water was filling up the drive end bearing cup and contaminating the lubricant as well as discharging electrically making a puddle of water, lubricant and carbon as shown in the following picture .

Also at this time the water was filling up the drive end bearing cup and contaminating the lubricant as well as discharging electrically making a puddle of water, lubricant and carbon as shown in the following picture.

water contamination of the motor bearings
electrical discharge across the inner motor bearing raceway through the roller elements to the outer bearing raceway’s
although these are sealed bearings, the motor itself is an upward mounted TEC (totally enclosed casing) therefore allowing the water from the tower to run down the motor shaft past the inadequate rubber seal of the motor shaft (which becomes dislodged after time, as seen in following picture).

The following pictures were taken to show the contaminated lubrication that came from the motor bearing cups or reservoir.

MOTOR BEARINGS

Electrically-induced Fluting

The motors are subjected to electrical fields that deteriorate both bearings and windings. View a more detailed explanation of the phenomena of Electrically-induced Fluting.

RECOMMENDATIONS:

Monitor more frequently for upward trending which is an indication of wear & deterioration.
Perform motor circuit evaluation and motor quality test.
Installation of motor grounding brushes have been proven to retard the build up of the electrical field on the rotor, therefore eliminating at least 90% of the currents from passing through the bearing roller elements and thus the degradation of the motor bearings. IDSS has successfully achieved a longer bearing life at IBM World Headquarters and Foxwoods Resort through installation of grounding brushes on VFD applied motors. This corrective measure has proven effective for the last five years.
The new unfavorable condition of the motor having the better sealed bearings installed in the motors, being protected from moisture but not preventing the electrical discharge, allowed a cooking effect or drying of the lubricant due to the continual discharge of electricity. To compensate for this IDSS recommends drilling and tapping zerc fittings. This allowed for the purging of contaminated grease and replacement of fresh lubricant which will allow for a more reliable operation of the cooling towers. In order to facilitate this we had to drill and tap holes in the bearing caps to install 2 zerc fittings due to the TEC frame (total enclosure for wet environments.

The sealed motor bearings were being subjected to the Variable Frequency Drive producing an electrical discharge on the rotor causing a corona of electricity building up and trying to find a ground which occurs through the raceways and roller elements which was now drying out the lubricant actually carbonizing them.

The motors were also grounding out or shorting out due to the excessive moisture build up over the shut down periods on weekends, not having a cooling load.

IDSS recommends at least running the motors constantly to prevent this, also we have installed a electrically heating fiber glass tape on Foxwoods Resort’s cooling tower turbine pumps to avoid moisture build up.

Another solution may be to use air to evacuate tower motors of moisture build up after a prolonged shut down.

The cooling tower motor failures were found to be due to a continuous electrical discharge through the top motor bearing and compounding the problem is the sealed bearings which are actually baked and dried up by the electrical discharge.

To alleviate the problem IDSS recommends removing the seals and installing grease fittings to lubricate and purge old grease and any moisture from within the rolling elements.
Install grounding brushes to eliminate as much electrical discharging as possible.

We have removed the TEC type cooling tower motors and installed the rebuilt motors with grease fittings installed. Our machinist makes up grounding brushes with the brackets to mount on the motor.