Cooling Tower Direct Drive (CTDD) Technology in Geothermal Power Plant

CTDD technology has only one moving part – Direct Drive Motor (DDM). It replaces three cooling-tower-fan-drive components with multiple moving parts (induction motor, driveshaft, and gearbox as shown in the picture below). DDM is a slow speed, high torque, permanent magnet synchronous motor which is directly connected to the fan. It is designed and built for variable speed and is operated with a variable frequency drive (VFD)

CTDD benefits are:

  • Significantly improved reliability (5 year warranty, 20+ year rated life)
  • Reduced maintenance costs (eliminate oil changes, gearbox refurbishments, alignments, etc.)
  • Significant energy savings potential due to variable speed (typical 30-60% energy savings)
  • Improved safety (e.g., eliminates “windmilling” issues)
  • Eliminates oil contamination issues (leaking gearboxes)

Permanen Magnet Motor Technology

Synchronous PM motor uses laminated finned frame construction to provide a highly efficient powerdense package with flange mounting dimensions that can replace the right angle gearbox and jack shaft installation.

The TEAO (totally enclosed air over) RPM AC cooling tower motor is designed for minimal maintenance. Bearings require lubrication only once per year.

Water ingress along the shaft is prevented with the use of an Inpro/Seal® bearing isolator and a slinger. The electrical insulation system is manufactured using a VPI (vacuum pressure impregnation) process that ensures long motor life even in the most extreme environmental conditions. Condensation drains relieve any moisture that may collect inside the motor. No more changing gear oil, lubricating pillow block bearings or changing out belt

Figure 3. Baldor CTDD motor and VFD

PM motors have long been recognized as providing higher efficiencies than comparable induction motors. However, limitations in terms of motor control, as well as magnet material performance and cost, have severely restricted their use. Due to dramatic improvements in magnetic and thermal properties of PM materials over the past 20 years, synchronous PM motors now represent viable alternatives (figure 3).

Figure 3. Typical Partial Load Efficiencies of 75 HP, TEFC, 1800 RPM Motors

Project Review

Traditional technology of Cooling Tower Fan Drive System which consist of Induction Motor, Drive Shaft and Couplings, Gearbox, and Fan Assembly. As effort to ensure the project not interupt the plant operation detailed study and engineering review has been done such as:

  • Structural assessment of Cooling Tower Column.

The additional load due to replacement of gear reducer by new motor fan weight shall be analyzed for stability and capacity (strength) of centre column of cooling tower cell

  • Review mechanical aspect of retrofit

This review explore the specific site issues created by the mechanical retrofit of a Baldor/ABB FL5830 direct drive PMR fan motor. A major issue will include the increased height of the PMR motor as compared to the existing gearbox, since the existing concrete mounting pad must not be considered for alteration. All mechanical aspects will be addressed which include the new fan elevation, are commended adapter plate, the PMR motor cooling issues, fan torque and imbalance considerations.

  • Review Electrical and instrument System

This review explore the efect of harmonic from VFD to the existing system and mitigation, requirement of switchgear and space availability in the switchroom. For instrument and automation scope are review the compatibility communication with DCS and field instruments

After doing thorough review team confidence to implement this technology on of of the the existing cooling tower fans as pilot project.

 CTDD Operation

 Cooling Tower Direct Drive Demonstration Project including pre-commissioning, commissioning and start-up has been completed in June  2016.  As shown in figure below, CTDD is working well with operation around 75%-100% speed in daylight and around 25%-50% in the night.

The energy consumption:

New CTDD                    : 13 days = 16.330 MWh

1 year = 458.506 MWh

Existing CT Fan : 1 year = 1,299.685 MWh

Reduce Energy             : 841.179 MWh ≈ USD 52,994.28

                                                            Cooling Tower Direct Drive Performance monitoring

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