THREE-PHASE INDUCTION MOTORS OF THE SERIES APPLICATION DESIGN PMH and PMT Three-phase low-speed induction motors of the series PMH are intended for direct drives of axial-flow fans for cooling towers without gears, for the environment with the ambient temperature up to + 40 °C (PMT up to +60°C). Due to a direct low speed the noise and vibration levels are reduced, life of the parts of the set is longer, the assembly costs are reduced and the requirements for maintenance are lower in comparison with a highspeed motor with a gearbox. Removal of a gearbox with oil filling is also beneficial for environment protection. The motors are designed for a possibility of the speed-changing ratio 1 : 2, enabling thus a more economical adjustment of the cooling power of a tower in different climatic conditions. They may be also delivered as singlespeed ones (without the designation D). The PMH motors are made for humid environment corresponding to the conditions of cooling towers - relative humidity up to 100 %, temperature of moist air being delivered (forming at the same time a cooling agent removing heat losses from the motor surface) up to + 40 °C (PMT up to +60°C) The frame is robust, made of grey cast iron, with ribs on the surface. The motor is cooled by external air flowing round the motor, inside the motor there is an auxiliary ventilation circuit. (PMT has its own fan) The rotor is mounted in antifriction bearings with grease lubrication, calculated service life is 110 000 ning hours. The relubrication interval is either 3 years or 15 000 running hours. The motor is mounted in a vertical position with the upward shaft extension. The motor withstands axial and radial loads from the axial-flow fan being driven. The shaft extension is provided with a work centre with a thread and with a thread angle 60°. The motor is provided with 2 heating elements 150 W/230 V to be heated during rest periods. The end windings are fitted with 6 pcs (in 2 sets) of posistors for thermal protection being embedded into them. run PMH PMT ® ELECTRIC MACHINES AND DRIVE
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