Cooling towers can use several power transmission technologies, including a gear drive, belt drive, direct drive, and electronically commutated (EC) drive. Each has advantages and disadvantages. The proper selection strikes an appropriate balance of initial cost versus operating costs.
Gear Drives: Moderate Initial Costs, Low Lifetime Operating Costs
The gear drive, which has been used to transmit power for decades, relies on internal gearing that meshes to transmit power.
In a cooling tower application, a gear drive reduces the high-speed power from the motor to the lower speed required to power the fan. The induction motor is relatively small because the gearbox multiplies torque.
Gear drives are effective at all cooling tower power levels. Their thick, casted shells housing the gear teeth and oil bath can withstand the high heat and humidity inside the cooling tower. Gearboxes require additional “no load” power to overcome the friction of internal components and oil viscosity. Net efficiency of the gearbox varies per application, but is generally near 96%.
The gear drive requires little maintenance. For example, some gearboxes using synthetic oil do not require an oil change for five years, but cooling tower owners and service contractors should be diligent about inspecting for potential leaks. Another positive feature of the gear drive is that it runs off direct online power. A variable frequency drive (VFD) is not required, but may be included for added motor speed control and energy use benefits.
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