Altitudes above 3000' seal level can start causing shortness of breath in people. The thin air at that altitude also has a negative effect on hoisting equipment derating motor capacity based upon altitude Most standard hoist motors are designed to operate below 3300 feet.
Some hoist motors are TENV and some are TEFC. TEFC motors are fan-cooled and rely on the fan to push air on the motor frame and housing to dissipate heat generated by the motor operation. TENV (non-ventilated) motors often have a heavier frame some with heat sinks or fins that rely on the ability of the ambient air to cool the frame. Since air is thinner and heat is not dissipated as quickly above 3300 feet. Most motors must be derated for altitude. In the case of a hoist, that derating results in a derating of the maximum load capacity at a given design duty that the hoist can operate or the number of minutes operating vs rest that the hoist can run. High heat also impacts this cooling as the motor will cool in a cold environment faster than one that is hot. High operating temperatures of motors are the leading cause of a shortened lifespan.
The following chart gives typical horsepower derating factors, but the derating factor should be checked for each motor. A 50 HP motor operated at 6000 feet, for example, would be derated to 47 HP, providing the 40°C ambient rating is still required. In the case of a 50 Ton hoist capacity, the hoist would be derated in capacity by the same 6%. With the new maximum capacity and duty cycle based off of 47 Ton capacity.
Altitude Derating factor
- 3300-5000 Feet - Derate to 97%
- 5001-6600 Feet - Derate to 94% 6601-8300 Feet - Derate to 90%
- 8301-9900 Feet - Derate to 86%
- 9901-11500 Feet - Derate to 82%
Variable frequency drives if installed as well as hoist motor and load brakes also generate heat and must be checked for proper heat dissipation at the operating elevation. This information is best provided by the hoist manufacturer.
CRANE 1 can assist you with special hoist and crane applications, including high altitude requirements. Give CRANE 1 a call, we are here to help!